the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Climate transition over the past two centuries revealed by lake Ebinur in Xinjiang, northwest China
Abstract. Global climate has undergone dramatic changes over the past 200 years, accurately identifying the climate transition and its controlling factors will help to address the risks posed by global warming and predict future climate trends. To clarify climate change over the past 200 years, detailed analyses of chronology, grain size, color reflectance (L*, a*) and carbon content (TOC, TIC) were conducted on a 200-year high resolution (~ 2 a) sedimentary record from lake Ebinur in Xinjiang, northwest China. The results show that the median grain size (Md) of lake sediments ranges from 5.5 μm to 9.9 μm, with a mean value of 7.0 μm. Multi-parameter analysis of grain size suggests that the sediments in lake Ebinur are mainly transported by wind, and there are two kinds of different sources and transport processes: the fine-grained sediments (< 20 μm) are background dust that was transported by long distance high-altitude suspension, while the coarse-grained sediments (> 20 μm) are local and regional dusts that were transported from short distances at low altitudes. Comparative analysis of multi-proxies including grain size、color reflectance and carbon content reveals that 1920 AD is the time point of climate transition in the past 200 years. In the early period (1816–1876 AD), the high C values indicate strong transport dynamics; the high proportion of ultrafine component indicates strong pedogenesis, combined with high organic carbon content and high a* values, it is inferred that the water vapor content is relatively higher. Overall, this period corresponds to the cold and wet climate. In the later period (1920–2019 AD), the proxies show opposite changes, which may reveal a warm and dry climate. Based on a comprehensive analysis of multiple drivers (i.e., solar radiation, greenhouse gases and volcanic eruption), we propose that the increase of solar irradiance in 1920 AD played a dominant role in the Asian climate transition, and that the gradual rise in the concentrations of greenhouse gases (CO2 and CH4) may have a positive feedback effect on the climate transition.
- Preprint
(1813 KB) - Metadata XML
- BibTeX
- EndNote
Status: closed
-
RC1: 'Comment on cp-2022-92', Anonymous Referee #1, 23 Dec 2022
The manuscript by Wei et al. tries to use a sediment core from lake Ebinur in northwest China for paleoenvironmental reconstruction of the past ~200 years. For this purpose, the authors dated the record with 210Pb only, as 137Cs showed no activity. This was successful back to AD 1944 at 17.5 cm sediment depth while for the lower part a linear extrapolation was applied. Unfortunately, the authors do not provide any information how this was done. In my opinion this cannot be done as i) we usually have less compacted sediments in the upper part of sediment cores with a high sedimentation rate and ii) there is a change in lithology which the authors use for their environmental reconstruction. In addition to that, the authors give a basal age for the record of AD 1816. Such a precision seems to be impossible with a well dated record but for sure with such an approach. As there is still some Pb activity in the lower part of the dated record, the authors might want to continue measurements either to extent the chronology or to prove that there is no activity anymore.
For environmental reconstruction the authors used several methods. While some of the parameters might indeed be interpreted in the way it was done some can certainly not (especially the spectrophotometer data) and others miss explanation or evidence. I will try to explain that in the detailed comments below.
Although I am not a native speaker, I do have the feeling that the text also needs some language corrections, which might make it easier to read and understand.
Detailer comments:
- Line 29: 1819 --> This is an unrealistic age
- 73-74: tree-ring δD record from Kenya demonstrates that extreme drought in East Africa in the early 1920s --> What is the relation to China / this study?
- 138-139: The climate is generally characterized by warm-dry summers and cold wet winters --> If you can talk about wet conditions in this setting at all, this is not consistent with Fig. 2
- 195-197: The dry samples were weighed before and after carbonate removal, and the actual TOC values were obtained by converting the measured TOC values using the ratio of the mass before and after treatment. --> Why would you weigh them after carbonate removal? Is there some information missing?
- 220: using a linear extrapolation method --> I don’t know how this was done but I am sure that this cannot be done (see explanation above)
- 230-231: correlation coefficient (r2) --> This is not a correlation coefficient and needs more explanations
- 233: with over 60 % of the C value above 50 μm --> This needs more explanations
- 239: Thus, the sedimentary sequence can be divided into two units. --> How exactly did you determine the boundary of the units? This is very important as this is one of your major findings when this happened. According to some parameters the boundary could also be further downcore
- 240: Fig. 4b and c need more explanations
- 266-269: Correspondingly, the contents of TOC (0.25-0.34, mean 0.30) and TIC (1.91-2.95, mean 2.50) also showed strong fluctuations (Figs. 5m, 5n), which may have been influenced by strong wind activity during the cold period. --> How? What is the mechanism behind that?
- 270-271: In general, the ultrafine component (the grain size fraction of < 1 μm) is associated with pedogenesis and can be used as indicator of regional climate change --> this needs more explanation
- 272-274: In this unit, the proportion of ultrafine component is the highest in the whole sequence (1.7 %-10.2 %, mean 5.0 %), revealing the strongest pedogenesis in the study area --> This would imply that no soils have been present before modern soil formation and that soils formed are immediately removed. Have you considered soil erosion as one mechanism? This should be discussed
- 274-277: It is generally believed that pedogenesis is related to temperature and humidity (Sun et al., 2011). However, the temperature was lower and the wind speed was higher during 1816-1920 AD, so we considered that the strong pedogenesis during this period might be related to the high humidity. --> This is a lot of speculation. Especially if the comment above is considered
- 281-284: a* is usually affected by red minerals (e.g., hematite and goethite) and is thought to be associated with oxidation of sediments in arid region (Ji et al., 2005; Jiang et al., 2007). The high a* value (mean 0.76) in this unit indicates that more water vapor enhanced the oxidation during the cold period (Fig. 5l), thus providing more red minerals for the lake. --> Colors can react on various processes especially if you use dried samples. This is a lot of speculation and needs to be verified by further (mineralogical) analyses.
- 285-286: L* values within arid lakes are considered to reflect variations in the carbonate, and high L* values denote more carbonate content --> This can be the case – but it is certainly not the case here. In this case there should be a correlation between L* and TIC which is a much better carbonate indicator – which is not the case. In addition to that, why would you use an indirect indicator for carbonates if you have a direct one?
- 287-291: The L* value in this unit fluctuates between 73.2-76.1, with an average of 74.6 (Fig. 5k), which may be related to the changes of the lake water body. The cooling leads to weakening of evaporation and transpiration, and together with more water vapor from the westerlies (Guo et al., 2022), resulting in more water in the lake and more carbonate content. --> Wouldn’t you normally expect a higher carbonate content in more evaporative instead of less evaporative conditions? This needs more discussion
- 296: 816-1876 --> It is impossible to be this precise
- 305: a stable variation with slight fluctuations --> What is that?
- 308: EM2 --> Why are you putting so much emphasis on EM2? EM1 explains much more of the variation
- 310-311: This is probably duo to the decrease of the temperature gradient --> Between what?
- 313-314: the contents of TOC (0.25-0.32) and TIC (2.17-2.63) showed very slight fluctuations except for the top two points --> How do you interpret this?
- 316: revealing weaker pedogenesis --> Or transport?
- 316-319: The obvious decrease of a* value (mean 0.51) indicates the weakening of oxidation (Fig. 5l), which may be caused by reduced water vapor from westerly circulation and enhanced evaporation due to the increase in temperature. --> This is pure speculation as colors can be influenced by various factors
- 319-321: the relatively high L* value (mean 75.3) may be associated with an increase in summer glacial meltwater into the lake as a result of warming --> This needs to be explained
- However, the increase of L* value since 1955 AD may be related to the dramatic shrinkage of lake Ebinur by human activity --> How? This needs to be explained
- 324-326: unit 2 can be further divided into two sub-units according to the variation of all proxies: unit 2-a (24-16 cm, 1920-1955 AD) and unit 2-b (16-0 cm, 1955-2019 AD) (Figs. 5a-5n). --> Sorry, but I cannot see that. On what is it based?
- 330-334: The Y value of Sahu's formula is usually used to recognize the eolian environment, which is mainly determined by mean grain size, standard deviation, skewness, and kurtosis (Sahu, 1964). The Y values of all samples range from -19.5 to -7.6, lower than the threshold value of -2.74 (Fig. 7), supporting their windblown origin (Jiang et al., 2017b, 2022; Wei et al., 2021). --> This needs to go to the Results and Interpretation chapter
- 344-352: End-member simulations of all 96 grain size data show that there are two end member components in lake Ebinur sediments: 345 EM1 (~ 5.9 μm) and EM2 (~ 24.1 μm) (Fig. 4a). This is consistent with previous studies (Pye, 1987; Jiang et al., 2014; Wei et al., 2021), i.e., the fine particles (EM1) are transported by long distance high-altitude suspension and represent background deposition, while the coarse particles (EM2) are transported by short distance low-altitude and represent local and regional deposition. In addition, the EM2 component (~ 24.1 μm) shows a similar modal distribution with aeolian dust samples collected from the Ebinur drainage area (15-26 μm) (Ma et al., 2016), further supporting the possible transport mechanism model proposed by us. --> This also needs to go to the Results and Interpretation chapter
- 372-373: These two events (E1, E2) may be related to local strong wind events within the age error --> If you consider the error you should provide the error in your study. When did the local wins events occur? Can you integrate the wind data in Fig. 8?
- 389-391: These results are consistent with the cold-wet and warm-dry climate combinations revealed by Chen et al. (2010, 2015) in arid central Asia. --> No! There is an offset
- 391-393: Moreover, the lake Ebinur sedimentary record reveals that a climate transition around 1920 AD, the same as the reconstructed temperature records in China (Yang et al., 2002; Ge et al., 2013) --> No! This is a slow transition – not a shift as you are arguing
- 415-420: Fig. 9 --> If you want to compare this to your data, this should be included in Fig. 8
Considering all these weaknesses, which are sometimes not easy to overcome, I am afraid, but I have to recommend to reject this manuscript.
Citation: https://doi.org/10.5194/cp-2022-92-RC1 -
AC1: 'Reply on RC1', Xiaotong Wei, 10 Feb 2023
We are grateful to Reviewer 1 for giving us detailed comments to improve our manuscript. The responses to the comments from Reviewer 1 are addressed point by point as follows.
QI: The manuscript by Wei et al. tries to use a sediment core from lake Ebinur in northwest China for paleoenvironmental reconstruction of the past ~200 years. For this purpose, the authors dated the record with 210Pb only, as 137Cs showed no activity. This was successful back to AD 1944 at 17.5 cm sediment depth while for the lower part a linear extrapolation was applied. Unfortunately, the authors do not provide any information how this was done.
Thank you very much for your kind reminding. We established the chronology of core ABHHX mainly by the following methods:
1) For the upper part of the core, we calculated the ages of parallel cores ABH and ABHHX respectively based on the constant rate of supply (CRS) model of 210Pbex (formula (1)). The results show that the core ABH was dated at 16 cm to 1940 AD (Figure S1), and the bottom six data were discarded due to the abnormal deposition rate (Chen et al., 2006; Wei et al., 2021). Comparably, the core ABHHX calculated by the CRS model was dated at 18.5 cm to 1934 AD. The deposition rate of core ABHHX (2.18 mm yr-1) is closed to that of core ABH (2.03 mm yr-1) (Figure S1), so we consider it is reliable;
2) For the lower part of the core, we used a linear extrapolation method based on the following two reasons: a) the core ABHHX has a fine grain size (median grain size (Md): 5.4-9.9 μm, mean 7.0 μm) over the whole sequence; b) the core is only 48 cm long without distinct lithologic change. We performed a linear fit using the upper 210Pbex ages of the core ABHHX, and the correlation coefficient was as high as 0.95 (Figure S2). Based on the linear relationship, the age of the lower part of the core is extrapolated to establish the chronology of the whole sequence.
We have modified it, please see L.217-223, P.6.
Reference
Appleby, P.G. and Oldfield, F.: The calculation of lead-210 dates assuming a constant rate of supply of unsupported 210Pb to the sediment, Catena, 5, 1-8, https://doi.or g/10.1016/S0341-8162(78)80002-2, 1978.
Chen, F.H., Huang, X.Z., Zhang, J.W., Holmes, J.A., and Chen, J.H.: Humid Little Ice Age in arid central Asia documented by Bosten Lake, Xinjiang, China, Science in China Series D, 49(12): 1280-1290, https://doi.org/10.1007/s11430-006-2027-4, 2006.
Wei, X.T., Jiang, H.C., Xu, H.Y., Fan, J.W., Shi, W., Guo, Q.Q., and Zhang, S.Q.: Response of sedimentary and pollen records to the 1933 Diexi earthquake on the eastern Tibetan Plateau, Ecol. Indic., 129, 107887, https://doi.org/10.1016/j.ecoli nd.2021.107887, 2021.
Q2: In my opinion this cannot be done as i) we usually have less compacted sediments in the upper part of sediment cores with a high sedimentation rate and ii) there is a change in lithology which the authors use for their environmental reconstruction.
Thank you very much for your review. We believe that the method of establishing chronological sequence is feasible based on the following several points:
1) The core ABHHX is mainly composed of fine-grained sediments, and the median grain size (Md) varies from 5.4 μm to 9.9 μm with a mean value of 7.0 μm; and we think that the core deposition is near-continuous and homogeneous;
2) The core is very shallow, only 48 cm, and there is no distinct lithologic change; the core ABHHX shows homogeneous lithology, and the lower ages are derived by linear extrapolation from the upper 210Pb ages;
3) The dating of the upper core (~80 year) calculated by the 210Pb CRS model is reliable, for example, the events (E1 and E2) revealed by the sedimentary sequence can be compared with local strong wind events (Figure 8);
4) Based on downward extrapolation method, the climate changes over the past 200 years revealed by sedimentary sequence can be well contrasted regionally with previous climate records.
In addition, we did not use the change in lithology for environmental reconstruction.
Q3: In addition to that, the authors give a basal age for the record of AD 1816. Such a precision seems to be impossible with a well dated record but for sure with such an approach.
Thank you very much for your review. We believe that it is feasible to give a basal age of 1816 AD for the following points:
1) We think it's acceptable for most researchers to get a continuous record of age by linear extrapolation, and we're not the first to do it (Miao et al., 2003; Wang et al., 2006);
2) The age of upper core is controlled by 210Pb CRS model, and the results are reliable;
3) There is no obvious depositional discontinuity and distinct change in core lithology, so we believe that the deposition is continuous;
4) The climate changes and climate events revealed by our sedimentary sequence are well consistent with regional records (Figure 8);
5) Linear extrapolation requires a specific age in order to be plotted for comparative analysis.
Reference
Miao, Z., Mu, G.J., Yan, S., and Xie, H.Q.: Environmental Evolution of Aiby Lake Indicated by Ash core Sediment’s Information, Arid land Geography, 26, 5, 2003 (in Chinese).
Wang, R., Yang, X.D., and Zhu, L.P.: Environmental changes of Namu Co, Xizang during the past 200 years, 26(5): 791-798, 2006 (in Chinese).
Q4: As there is still some Pb activity in the lower part of the dated record, the authors might want to continue measurements either to extent the chronology or to prove that there is no activity anymore.
Thank you very much for your kind reminding. We tested 210Pb activity for the upper 20 cm of core ABH and core ABHHX, and the 210Pbex activity of core ABH is less than 0 at 19.5 cm (-5.26 Bq kg-1). Therefore, we believe that the core ABH has reached a stable state at 19 cm and is no activity anymore. According to the constant rate of supply (CRS) model, the core ABH was dated at 16 cm to 1940 AD, and the bottom six data were discarded (Figure S1) due to abnormal deposition rate (Chen et al., 2006; Wei et al, 2021). Comparably, the core ABHHX calculated by the CRS model was dated to at 18.5 cm 1934 AD. The deposition rate of core ABHHX (2.18 mm/yr) is close to that of core ABH (2.03 mm/yr) (Figure S1), so we consider the age of the upper core is reliable, and no further measurements are necessary.
Q5: For environmental reconstruction the authors used several methods. While some of the parameters might indeed be interpreted in the way it was done some can certainly not (especially the spectrophotometer data) and others miss explanation or evidence. I will try to explain that in the detailed comments below.
Thank you very much for your review. We will carefully respond to your detailed comments point by point as follows.
Q6: Although I am not a native speaker, I do have the feeling that the text also needs some language corrections, which might make it easier to read and understand.
Thank you very much for your kind reminding. We will make careful language corrections to the text.
Q7: Line 29: 1819 --> This is an unrealistic age
We believe that it is acceptable based on the following reasons:
1) The age of upper core is controlled by 210Pb CRS model, and the results are reliable;
2) The core ABHHX is mainly composed by fine-grained sediments (Md: 5.4-9.9 μm, mean 7.0 μm), and there is no obvious depositional discontinuity and distinct change in core lithology, indicating that the deposition is continuous and uniform. Therefore, we performed a linear extrapolation using the upper 210Pb ages, and the 48 cm core was dated back to 1816 AD;
3) The climate changes and climate events revealed by our sedimentary sequence are well consistent with regional records (Figure 8);
4) Linear extrapolation requires a specific age in order to be plotted for comparative analysis.
Q8: 73-74: tree-ring δD record from Kenya demonstrates that extreme drought in East Africa in the early 1920s --> What is the relation to China / this study?
We have modified it, please see L.71-74, P.2.
Q9: 138-139: The climate is generally characterized by warm-dry summers and cold wet winters --> If you can talk about wet conditions in this setting at all, this is not consistent with Fig. 2
We have modified it, please see L.136-137, P.4.
Q10: 195-197: The dry samples were weighed before and after carbonate removal, and the actual TOC values were obtained by converting the measured TOC values using the ratio of the mass before and after treatment. --> Why would you weigh them after carbonate removal? Is there some information missing?
According to the formula 2, the actual TOC values were calculated by multiplying the measured TOC values with the weight ratio of carbonate removed samples to unremoved samples (Fan et al., 2023). We have modified it, please see L.195-197, P.6.
Reference
Fan, J.W., Xu, H.Y., Jiang, H.C., Wei, X.T., Shi, W., Guo, Q.Q., Zhang, S.Q., Bai, X.Z., Liu, X.Q., and Xiao, J.L.:, Millennial- to centennial-scale anti-phase relationship between the Westerlies and the East Asian summer monsoon and its cultural response along the Silk Roads after a great earthquake in southern Altay ~ 3500 cal a BP, Journal of Quaternary Science, 38(1): 123-137, https://doi.org/10.1002/jqs.3468, 2023.
Q11: 220: using a linear extrapolation method --> I don’t know how this was done but I am sure that this cannot be done (see explanation above)
We believe that it is feasible to use a linear extrapolation method based on the following points:
1) We think it's acceptable for most researchers to get a continuous record of age by linear extrapolation, and we're not the first to do it (Miao et al., 2003; Wang et al., 2006);
2) The core ABHHX is mainly composed by fine-grained sediments (Md: 5.4-9.9 μm, mean 7.0 μm), and there is no obvious depositional discontinuity and distinct change in core lithology, indicating that the deposition is continuous and uniform;
3) The age of upper core is controlled by 210Pb CRS model, and the results are reliable;
4) Based on homogeneous lithology and uniform deposition of the core ABHHX, we performed a linear extrapolation using the upper 210Pbex ages, and the 48 cm core was dated back to 1816 AD.
Reference
Miao, Z., Mu, G.J., Yan, S., and Xie, H.Q.: Environmental Evolution of Aiby Lake Indicated by Ash core Sediment’s Information, Arid land Geography, 26, 5, 2003 (in Chinese).
Wang, R., Yang, X.D., and Zhu, L.P.: Environmental changes of Namu Co, Xizang during the past 200 years, 26(5): 791-798, 2006 (in Chinese).
Q12: 230-231: correlation coefficient (r2) --> This is not a correlation coefficient and needs more explanations
Done. Please see L.248-249, P.8.
Q13: 233: with over 60 % of the C value above 50 μm --> This needs more explanations
Here, we want to emphasize that ~ 60 % (29/48) of the samples have C values greater than 50 μm in the lower part of the sedimentary sequence. We have modified it, please see L.268, P.8.
Q14: 239: Thus, the sedimentary sequence can be divided into two units. --> How exactly did you determine the boundary of the units? This is very important as this is one of your major findings when this happened. According to some parameters the boundary could also be further downcore
We divided the whole sedimentary sequence into two units according to the following two points:
1) The grain size records show that the upper and lower parts of the sedimentary sequence have different characteristics of change with 1920 AD as the limit. The lower part is characterized by high-amplitude fluctuations and coarse grains (Md: 5.5-9.9 μm, mean 7.5 μm), and ~ 60 % of the samples have C values greater than 50 μm (Figures 6b, 6c), while the upper part has small fluctuations and finer grains (Md: 5.4-8.6 μm, mean 6.5 μm), and only ~ 20 % of the samples have C values exceeds 50 μm (Figures 6d, 6e);
2) Correspondingly, color reflectance (L*, a*) and carbon content (TOC, TIC) records also show different characteristics in the upper and lower parts with 1920 AD as the limit. For the lower part of the sequence, color reflectance (L*: 73.2-76.1, mean 74.6; a*: 0.4-1.0, mean 0.76) and carbon content (TOC: 0.22-0.43, mean 0.31; TIC: 1.91-2.95, mean 2.54) have large fluctuations (Figures 7k-7n). And for the upper part of the sequence, color reflectance (L*: 74.4-75.9., mean 75.3; a*: 0.2-0.7, mean 0.51) and carbon content (TOC: 0.25-0.32, mean 0.28; TIC: 2.17-2.63, mean 2.38) are characterized by small fluctuations except for the top two anomalies (Figures. 7k-7n).
We have modified it, please see L.265-278, P.8.
Q15: 240: Fig. 4b and c need more explanations
Done. Please see L.261-263, P.8.
Q16: 266-269: Correspondingly, the contents of TOC (0.25-0.34, mean 0.30) and TIC (1.91-2.95, mean 2.50) also showed strong fluctuations (Figs. 5m, 5n), which may have been influenced by strong wind activity during the cold period. --> How? What is the mechanism behind that?
Done. Please see L.317-319, P.10.
Q17: 270-271: In general, the ultrafine component (the grain size fraction of < 1 μm) is associated with pedogenesis and can be used as indicator of regional climate change --> this needs more explanation
The ultrafine component (the grain size fraction of < 1 μm) in aeolian sediments are formed during pedogenesis (Sun et al., 2006, 2011), which is usually influenced by chemical, biochemical and physical alterations closely connected with the local climate. For example, the pedogenesis in Chinese loess is closely connected with summer monsoonal precipitation (Sun et al., 2011). Sun et al (2011) has confirmed that the proportion of ultrafine components in loess strongly reflects the intensity of pedogenesis, and many researchers have used it as a proxy index to reveal climatic conditions in different periods (Wang et al., 2012; Jiang et al., 2023).
Reference
Jiang, H.C., Yin, Q.Z., Berger, A., Wei, L.H., Wu, Z.P., Wei, X.T., and Shi, W.: Orbitally and galactic cosmic forced abrupt climate events during the last glacial period, Quaternary Sci. Rev., 301, 107921, https://doi.org/10.1016/j.quascirev.2022.107921, 2023.
Sun, D.H.: Super-fine grain size components in Chinese loss and their palaeoclimatic implication, Quaternary Sciences, 26, 928-936, 2006 (in Chinese).
Sun, D.H., Su, R.X., Li, Z.J., and Lu, H.Y.: The ultrafine component in Chinese loess and its variation over the past 7-6 Ma: implications for the history of pedogenesis, Sedimentology, 58, 916-935, https://doi.org/10.1111/j.136 5-3091.2010.01189.x, 2011.
Wang, X., Sun, D.H., Wang, F., Li, B.F., and Wu, S.: The ultrafine component record from the late Cenozoic sequence in the central Tarim basin and its palaeoclimatic implications, Marine Geology and Quaternary Geology, 32(2): 143-151, https://doi.org/10.3724/SP.J.1140.2012.02143, 2012.
Q18: 272-274: In this unit, the proportion of ultrafine component is the highest in the whole sequence (1.7 %-10.2 %, mean 5.0 %), revealing the strongest pedogenesis in the study area --> This would imply that no soils have been present before modern soil formation and that soils formed are immediately removed. Have you considered soil erosion as one mechanism? This should be discussed
Ultrafine components in aeolian sediments are formed during pedogenesis and can be used to trace the history of regional pedogenesis (Sun et al., 2006, 2011). The ultrafine component exists not only in loess and paleosol, but also in some lake sediments in aeolian regions, which may be the product of pedogenesis on the surface in the catchment (Sun et al., 2006). The study area has strong wind conditions, and we cannot rule out that ultrafine component was transported to the lake within a short time after pedogenesis, which recorded the information of pedogenesis.
Reference
Sun, D.H.: Super-fine grain size components in Chinese loss and their palaeoclimatic implication, Quaternary Sciences, 26, 928-936, 2006 (in Chinese).
Sun, D.H., Su, R.X., Li, Z.J., and Lu, H.Y.: The ultrafine component in Chinese loess and its variation over the past 7-6 Ma: implications for the history of pedogenesis, Sedimentology, 58, 916-935, https://doi.org/10.1111/j.1 365-3091.2010.01189.x, 2011.
Q19: 274-277: It is generally believed that pedogenesis is related to temperature and humidity (Sun et al., 2011). However, the temperature was lower and the wind speed was higher during 1816-1920 AD, so we considered that the strong pedogenesis during this period might be related to the high humidity. --> This is a lot of speculation. Especially if the comment above is considered
We believe that the explanation given is acceptable based on the following several aspects:
1) The high proportion of ultrafine components reveals strong pedogenesis during the period of 1816-1920 AD, which is usually related to local temperature and humidity conditions;
2) During this period, the study area was in the cold Little Ice Age, which is supported by our multi-proxies records and previous climate records (Yang et al., 2002; Ge et al., 2013);
3) On this basis, we propose that the strong pedogenesis in this stage may be related to the high humidity condition (Wang et al., 2012), which is also supported by the previous research results: the westerlies brought more vapour to the arid central Asia during the cold LIA (Chen et al., 2010, 2015);
4) We acknowledge that this is speculation, but it is appropriate speculation based on data. So we think it is acceptable.
Reference
Chen, F.H., Chen, J.H., Holmes, J., Boomer, I., Austin, P., Gates, J.B., Wang, N.L., Brooks, S.J., and Zhang, J.W.: Moisture changes over the last millennium in arid central Asia: a review, synthesis and comparison with monsoon region, Quaternary Sci. Rev., 29, 1055-1068, https://doi.org/10.1016/j.quascirev.201 0.01.005, 2010.
Chen, J.H., Chen, F.H., Feng, S., Huang, W., Liu, J.B., and Zhou, A.F.: Hydroclimatic changes in China and surroundings during the Medieval Climate Anomaly and Little Ice Age: spatial patterns and possible mechanisms, Quaternary Sci. Rev., 107, 98-111, https://doi.org/10.1016/j.quascirev.2014.10.012, 2015.
Ge, Q., Hao, Z., Zheng, J., and Shao, X.: Temperature changes over the past 2000 yr in China and comparison with the Northern Hemisphere, Clim. Past, 9, 1153-1160, https://doi.org/10.5194/cp-9-1153-2013, 2013.
Wang, X., Sun, D.H., Wang, F., Li, B.F., and Wu, S.: The ultrafine component record from the late Cenozoic sequence in the central Tarim basin and its palaeoclimatic implications, Marine Geology and Quaternary Geology, 32(2): 143-151, https://doi.org/10.3724/SP.J.1140.2012.02143, 2012.
Yang, B., Braeuning, A., Johnson, K.R., and Shi, Y.F.: General characteristics of temperature variation in China during the last two millennia, Geophys. Res. Lett., 29, 38-1-38-4, https://doi.org/10.1029/2001GL014485, 2002.
Q20: 281-284: a* is usually affected by red minerals (e.g., hematite and goethite) and is thought to be associated with oxidation of sediments in arid region (Ji et al., 2005; Jiang et al., 2007). The high a* value (mean 0.76) in this unit indicates that more water vapor enhanced the oxidation during the cold period (Fig. 5l), thus providing more red minerals for the lake. --> Colors can react on various processes especially if you use dried samples. This is a lot of speculation and needs to be verified by further (mineralogical) analyses.
Thank you very much for your review. We believe that this explanation is credible based on the following several reasons:
1) We carried out color reflectance experiments on all samples, following the treatment method proposed by Jiang et al (2023). The results of such experiments can be successfully applied to reveal past climate change;
2) a* in sediment is related primarily to iron oxide mineral concentrations in arid region, especially hematite and goethite (Ji et al., 2002). The stronger the oxidation, the more red minerals are produced and the higher a* value;
3) Redness records from lake Qinghai show that increased precipitation enhances regional oxidation, producing more red minerals, and a* value increases (Ji et al., 2005).
In summary, we propose that the high a* value indicates that more water vapor enhanced the oxidation during the period 1816-1920 AD.
Reference
Ji, J.F., Balsam, W.L., Chen, J., and Liu, L.W.: Rapid and precise measurement of hematite and goethite concentrations in the Chinese loess sequences by diffuse reflectance spectroscopy, Clays and Clay Minerals, 50(2): 208-216, https://doi.org/10.1346/000986002760832801, 2002.
Ji, J.F., Shen, J., Balsam, W., Chen, J., Liu, L.W., and Liu, X.Q.: Asian monsoon oscillations in the northeastern Qinghai–Tibet Plateau since the late glacial as interpreted from visible reflectance of Qinghai Lake sediments, Earth Planet. Sc. Lett, 233, 61-70, https://doi.org/10.1016/j.epsl.2005.02.025, 2005.
Jiang, H.C., Yin, Q.Z., Berger, A., Wei, L.H., Wu, Z.P., Wei, X.T., and Shi, W.: Orbitally and galactic cosmic forced abrupt climate events during the last glacial period, Quaternary Sci. Rev., 301, 107921, https://doi.org/10.1016/j.quascirev.2022.107921, 2023.
Q21: 285-286: L* values within arid lakes are considered to reflect variations in the carbonate, and high L* values denote more carbonate content --> This can be the case – but it is certainly not the case here. In this case there should be a correlation between L* and TIC which is a much better carbonate indicator – which is not the case. In addition to that, why would you use an indirect indicator for carbonates if you have a direct one?
Thank you very much for your review. We believe that it is more reliable to reveal the environmental changes in arid areas by integrating the changes of multi-proxies. And it is not the first time that L* has been used to reveal carbonate changes (Xiao et al., 2006; Jiang et al., 2008). In our records, the L* and TIC show similar variations: they show large-amplitude fluctuations in the early period (1816-1920 AD) and more stable in the late period (1920-2019 AD).
Reference
Xiao, J.L., Wu, J.T., Si, B., Liang, W.D., Nakamura, T., Liu, B.L., and Inouchi, Y.: Holocene climate changes in the monsoon/arid transition reflected by carbon concentration in Daihai Lake of Inner Mongolia, The Holocene, 16, 551-560, https://doi.org/10.1191/0959683606hl950rp, 2006.
Jiang, H.C., Ji, J.L., Gao, L., Tang, Z.H., and Ding, Z.L.: Cooling-driven climate change at 12-11 Ma: Multiproxy records from a long fluviolacustrine sequence at Guyuan, Ningxia, China, Palaeogeogr. Palaeocl., 265, 148-158, https://doi.org/10.1016/j.palaeo.2008.05.006, 2008.
Q22: 287-291: The L* value in this unit fluctuates between 73.2-76.1, with an average of 74.6 (Fig. 5k), which may be related to the changes of the lake water body. The cooling leads to weakening of evaporation and transpiration, and together with more water vapor from the westerlies (Guo et al., 2022), resulting in more water in the lake and more carbonate content. --> Wouldn’t you normally expect a higher carbonate content in more evaporative instead of less evaporative conditions? This needs more discussion
Yes, in general, high carbonate content occurs under conditions of more evaporation. However, carbonates cannot be deposited without water in arid areas, because they are deposited in lakes. The cooling leads to weakening of evaporation and transpiration, and a relative increase in water vapor, which makes it possible to develop lakes that produce more carbonate (Guo et al., 2022). Evaporation and transpiration change with seasonal temperatures fluctuates.
Reference
Guo, Q.Q., Jiang, H.C., Fan, J.W., Li, Y.M., Shi, W., Zhang, S.Q., and Wei, X.T.: Strongest chemical weathering in response to the coldest period in Guyuan, Ningxia, China, during 14-11 Ma, Plos One, 17, e0268195, https://doi.org/10.137 1/journal.pone.0268195, 2022.
Q23: 296: 816-1876 --> It is impossible to be this precise
Sorry, we believe that this precise is acceptable according to the following four points:
1) The age of upper core is controlled by 210Pb CRS model, and the results are reliable;
2) The core ABHHX is mainly composed of fine-grained sediments (Md: 5.4-9.9 μm, mean 7.0 μm) and there is no obvious depositional discontinuity and distinct change in core lithology lithologic change, indicating that the deposition is continuous and uniform. Therefore, we performed a linear extrapolation using the upper 210Pb ages, and the 48 cm core was dated back to 1816 AD;
3) The climate changes and climate events revealed by our sedimentary sequence are well consistent with regional records (Figure 8);
4) Linear extrapolation requires a specific age in order to be plotted for comparative analysis.
Q24: 305: a stable variation with slight fluctuations --> What is that?
Done. Please see L.336, P.10.
Q25: 308: EM2 --> Why are you putting so much emphasis on EM2? EM1 explains much more of the variation
Here, we emphasize that EM2 changes are based on the following two reasons:
1) The whole sedimentary sequence is composed of two end-members (EM1 and EM2). EM1 (the fine particles) represents background deposition that transported by long distance high-altitude suspension, while EM2 (the coarse particles) represents local and regional deposition that transported by short distance low-altitude;
2) In the process of lake deposition, the coarse particles (EM2) are deposited first, followed by fine particles (EM1). In other words, the percentage content of EM1 is determined by the change of EM2. Therefore, EM2 has more important environmental information, reflecting the regional and local provenance supply.
Q26: 310-311: This is probably duo to the decrease of the temperature gradient --> Between what?
Thank you very much for your kind reminding. The temperature gradient here refers to the temperature gradient between March and August. The lake Ebinur area has the strongest wind transport conditions and the highest temperatures during March to August (Ge et al., 2016). The temperature gradient decreases with increasing temperatures since 1920 AD, resulting in the weakening of wind intensity and the decrease of coarse particles transported at low altitude and short distance.
We have modified it, please see L.342, P.10.
Reference
Ge, Y.X., Abuduwaili, J., Ma, L., Wu, N., and Liu, D.W.: Potential transport pathways of dust emanating from the playa of Ebinur Lake, Xinjiang, in arid northwest China, Atmos. Res., 178-179, 196-206, https://doi.org/10.1016/j.atmosres.2016.0 4.002, 2016.
Q27: 313-314: the contents of TOC (0.25-0.32) and TIC (2.17-2.63) showed very slight fluctuations except for the top two points --> How do you interpret this?
Done. Please see L.353-355, P.11.
Q28: 316: revealing weaker pedogenesis --> Or transport?
Done. Please see L.346, P.11.
Q29: 316-319: The obvious decrease of a* value (mean 0.51) indicates the weakening of oxidation (Fig. 5l), which may be caused by reduced water vapor from westerly circulation and enhanced evaporation due to the increase in temperature. --> This is pure speculation as colors can be influenced by various factors
Sorry, we think that this explanation is acceptable based on the following several reasons:
1) a* in sediment is related primarily to iron oxide mineral concentrations in arid region, especially hematite and goethite (Ji et al., 2002). The stronger the oxidation, the more red minerals are produced and the higher a* value, and vice versa;
2) Redness records from lake Qinghai show that high a* values indicate increased precipitation, while low a* values reflect more arid climatic conditions (Ji et al., 2005).
In summary, we give this explanation: as the temperatures rises, the water vapor brought by the westerly circulation decreases, and the evaporation is enhanced, resulting in the weakening of oxidation and the decrease of a* values.
Reference
Ji, J.F., Balsam, W.L., Chen, J., and Liu, L.W.: Rapid and precise measurement of hematite and goethite concentrations in the Chinese loess sequences by diffuse reflectance spectroscopy, Clays and Clay Minerals, 50(2): 208-216, https://doi.org/10.1346/000986002760832801, 2002.
Ji, J.F., Shen, J., Balsam, W., Chen, J., Liu, L.W., and Liu, X.Q.: Asian monsoon oscillations in the northeastern Qinghai–Tibet Plateau since the late glacial as interpreted from visible reflectance of Qinghai Lake sediments, Earth Planet. Sc. Lett, 233, 61-70, https://doi.org/10.1016/j.epsl.2005.02.025, 2005.
Q30: 319-321: the relatively high L* value (mean 75.3) may be associated with an increase in summer glacial meltwater into the lake as a result of warming --> This needs to be explained
Water is needed to deposit carbonate in arid areas, and in extremely arid lakes, high carbonate content occur in environments with more water. Higher L* values reflecting carbonate content indicate more water, which may be associated with an increase in summer glacial meltwater caused by warming into the lake. In summer, the lake Ebinur area has a stronger evaporation, the increased glacial meltwater provides favorable conditions for carbonates production.
Q31: However, the increase of L* value since 1955 AD may be related to the dramatic shrinkage of lake Ebinur by human activity --> How? This needs to be explained
Done. Please see L.351-352, P.11.
Q32: 324-326: unit 2 can be further divided into two sub-units according to the variation of all proxies: unit 2-a (24-16 cm, 1920-1955 AD) and unit 2-b (16-0 cm, 1955-2019 AD) (Figs. 5a-5n). --> Sorry, but I cannot see that. On what is it based?
Thank you very much for your review. We consider that unit 2 can be further divided into two sub-units mainly based on the following several aspects:
1) Bounded by 1955 AD, grain size records for the lower part of unit 2 show a trend to coarser trend (Md: 5.8-7.9 μm, mean 6.9 μm), while the upper part shows a trend to finer (Md: 5.4-8.6 μm, mean 6.4 μm) (Figures 7a-7g);
2) Correspondingly, the lower part of unit 2 has lower L* value (74.5-75.5, mean: 75.1) and higher a* value (0.4-0.7, mean 0.55), while the upper part has higher L* value (74.4-76.7, mean: 75.4) and lower a* value (0.2-0.8, mean: 0.49) (Figures 7k, 7l);
3) The total organic carbon (TOC) in the lower part of unit 2 shows a decreasing trend, while the upper part shows a fluctuation.
Q33: 330-334: The Y value of Sahu's formula is usually used to recognize the eolian environment, which is mainly determined by mean grain size, standard deviation, skewness, and kurtosis (Sahu, 1964). The Y values of all samples range from -19.5 to -7.6, lower than the threshold value of -2.74 (Fig. 7), supporting their windblown origin (Jiang et al., 2017b, 2022; Wei et al., 2021). --> This needs to go to the Results and Interpretation chapter
Done. Please see L.231-236, P.7.
Q34: 344-352: End-member simulations of all 96 grain size data show that there are two end member components in lake Ebinur sediments: 345 EM1 (~ 5.9 μm) and EM2 (~ 24.1 μm) (Fig. 4a). This is consistent with previous studies (Pye, 1987; Jiang et al., 2014; Wei et al., 2021), i.e., the fine particles (EM1) are transported by long distance high-altitude suspension and represent background deposition, while the coarse particles (EM2) are transported by short distance low-altitude and represent local and regional deposition. In addition, the EM2 component (~ 24.1 μm) shows a similar modal distribution with aeolian dust samples collected from the Ebinur drainage area (15-26 μm) (Ma et al., 2016), further supporting the possible transport mechanism model proposed by us. --> This also needs to go to the Results and Interpretation chapter
Done. Please see L.249-257, P.8.
Q35: 372-373: These two events (E1, E2) may be related to local strong wind events within the age error --> If you consider the error you should provide the error in your study. When did the local wins events occur? Can you integrate the wind data in Fig. 8?
Done. Please see Figure 8 and L.379-381, P.11.
Q36: 389-391: These results are consistent with the cold-wet and warm-dry climate combinations revealed by Chen et al. (2010, 2015) in arid central Asia. --> No! There is an offset
Our multi-proxies reveal a relatively cold and wet climate from 1816 AD to 1920 AD and a relatively warm and dry climate from 1920 AD to 2019 AD in the lake Ebinur region. This is consistent with the cold-wet and warm-dry climate combinations in arid central Asia revealed by Chen et al (2010, 2015), for example, the dry MCA and wet LIA. Although the humidity in Central Asia has been increasing with global warming in recent decades (Chen et al., 2010, 2015), as shown in figure 4 from Chen et al (2010): the early period (1816-1920 AD) had a wetter climate than the later period (1920-2019 AD).
Reference
Chen, F.H., Chen, J.H., Holmes, J., Boomer, I., Austin, P., Gates, J.B., Wang, N.L., Brooks, S.J., and Zhang, J.W.: Moisture changes over the last millennium in arid central Asia: a review, synthesis and comparison with monsoon region, Quaternary Sci. Rev., 29, 1055-1068, https://doi.org/10.1016/j.quascirev.201 0.01.005, 2010.
Chen, J.H., Chen, F.H., Feng, S., Huang, W., Liu, J.B., and Zhou, A.F.: Hydroclimatic changes in China and surroundings during the Medieval Climate Anomaly and Little Ice Age: spatial patterns and possible mechanisms, Quaternary Sci. Rev., 107, 98-111, https://doi.org/10.1016/j.quascirev.2014.10.012, 2015.
Q37: 391-393: Moreover, the lake Ebinur sedimentary record reveals that a climate transition around 1920 AD, the same as the reconstructed temperature records in China (Yang et al., 2002; Ge et al., 2013) --> No! This is a slow transition – not a shift as you are arguing
Our multi-proxies records show a clear transition in climate around 1920 AD: from a relatively cold and wet period (1816-1920 AD) to a relatively warm and dry period (1920-2019 AD). And Yang et al (2002) and Ge et al (2013) propose that China’s LIA ended in 1920 AD by synthesizing various paleoclimatic records, and since then the climate has entered a warm period. These two are consistent. The reason why the transition in our record occurred sharply may be due to the fact that lake Ebinur is located in the arid Central Asia, where extreme drought makes it sensitive to warming responses (Huang et al., 2017; Yao et al., 2022).
Reference
Ge, Q., Hao, Z., Zheng, J., and Shao, X.: Temperature changes over the past 2000 yr in China and comparison with the Northern Hemisphere, Clim. Past, 9, 1153-1160, https://doi.org/10.5194/cp-9-1153-2013, 2013.
Huang, W., Chang, S.Q., Xie, C.L., and Zhang, Z.P.: Moisture sources of extreme summer precipitation events in North Xinjiang and their relationship with atmospheric circulation, Advances in Climate Change Research, 8, 12-17, https:/ /doi.org/10.1016/j.accre.2017.02.001, 2017.
Yang, B., Braeuning, A., Johnson, K.R., and Shi, Y.F.: General characteristics of temperature variation in China during the last two millennia, Geophys. Res. Lett., 29, 38-1-38-4, https://doi.org/10.1029/2001GL014485, 2002.
Yao, J.Q., Chen, Y.N., Guan, X.F., Zhao, Y., Chen, J., and Mao, W.Y.: Recent climate and hydrological changes in a mountain–basin system in Xinjiang, China, Earth-Sci. Rev., 226, 103957, https://doi.org/10.1016/j.earscirev.2022.103957, 2022.
Q38: 415-420: Fig. 9 --> If you want to compare this to your data, this should be included in Fig. 8
Thank you very much for your review. In figure 8, we identified the time point of the climate transition over the past 200 years — 1920 AD, mainly through the multi-proxies records of lake Ebinur sedimentary sequence. In order to further discuss the main controlling factors of climate transition, we compare the changes of solar radiation, volcanic activity, and the concentrations of greenhouse gases in figure 9. If all the data in figure 9 were put into figure 8, it will be too crowded to properly represent the signal.
-
EC1: 'Comment on cp-2022-92', Pierre Francus, 11 Jan 2023
Dear authors,
I read your paper and the comments of Reviewer 1.
I find reviewer 1 comments very pertinent, and they should be addressed in a reply in the open discussion.I would like to raise some additional issues that you also should consider in another reply in the discussion.
The location of the cores, close to the shore and at a water depth of only 0.8 m, makes them sensitive to wave action and remobilization of sediment, especially in a region where wind is so strong. Moreover, since the lake is a closed system, it is sensitive to water level fluctuations that could completely change the sedimentary context and processes at the location of the cores. Actually, you mention in the paper that the lake experienced lake level fluctuation. Therefore, I’m not convinced that the sedimentation has been continuous, and is without a hiatus, or major perturbations. The fact that there is no 137 Cs peak is another clue that the sedimentary archive is not pristine.
In this context, retrieving complete cores (not sliced in the field) and looking at facies at the microscopic scale is mandatory to be able to decipher sedimentary processes and demonstrate the continuity of this archive.I also agree that the age model is weak, and not accurate enough to be able to claim that you can make a reconstruction with a 2-year resolution.
I agree with Reviewer 1 that interpretations of colour reflectance, carbon content are speculative. For instance, I doubt it is possibly derived transport condition from C-content (in reference to “In the early period (1816-1876 AD), the high C values indicate strong transport dynamics; the high proportion of ultrafine component indicates strong pedogenesis, combined with high organic carbon content and high a* values, it is inferred that the water vapor content is relatively higher.”
Reflectance values are also influenced by changes in oxygen content below the water/sediment interface (i.e., the redox front), and this is making your reflectance interpretation even weaker.Interpretation of grain-size data also remains speculative: “ultrafine components” can also be observed in permafrost lakes and peat as sources for higher TOC. The colour reflectance can neither tell us something about transport nor about water vapour even in combination with GSD and C.
I’m still waiting for a second review of your paper, but I encourage you to already tell in a reply if you will be able to address reviewer 1 and my comments, and if yes, how ?
Thank you in advance and best regards,
Pierre Francus,
Handling editorCitation: https://doi.org/10.5194/cp-2022-92-EC1 -
AC2: 'Reply on EC1', Xiaotong Wei, 10 Feb 2023
We are grateful to editor for giving us comments to improve our manuscript. And we have responded to reviewer 1's comments in AC1. The responses to the comments from editor are addressed point by point as follows.
Comments
QI: The location of the cores, close to the shore and at a water depth of only 0.8 m, makes them sensitive to wave action and remobilization of sediment, especially in a region where wind is so strong. Moreover, since the lake is a closed system, it is sensitive to water level fluctuations that could completely change the sedimentary context and processes at the location of the cores. Actually, you mention in the paper that the lake experienced lake level fluctuation. Therefore, I’m not convinced that the sedimentation has been continuous, and is without a hiatus, or major perturbations. The fact that there is no 137Cs peak is another clue that the sedimentary archive is not pristine.
Thank you very much for your kind reminding. We believe that the sedimentation has been continuous for the following reasons:
1) The core ABHHX is mainly composed of fine-grained sediments, and the median grain size (Md) only varies from 5.4 μm to 9.9 μm with a mean value of 7.0 μm; and we think of deposition as continuous and at a uniform rate;
2) The core is very shallow, only 48 cm, and there is no obvious depositional discontinuity and distinct change in core lithology, which is also supported by our multi-proxies records;
3) The 210Pb activity of the two cores shows obvious exponential decay and the dating results compare well, supporting the continuity of the sequence;
4) The 137Cs activity of both cores is 0, which may be related to the rapid decay and downward migration of 137Cs (Xiang, 1995; Gao et al., 2021).
Reference
Gao, S.P., Wang, J.B., Xu, B.Q., and Zhang, X.L.: Application and problems of 210Pb and 137Cs dating techniques in lake sediments, J. Lake Sci., 33, 622-631, http s://doi.org/10.18307/2021.0226, 2021 (in Chinese).
Xiang, L.: Limitations of the application of 137Cs limnochronology: A case study of 137Cs profile in Crawford lake sediment, J. Lake Sci., 7, 307-313, https://doi.org/10.18307/1995.0403, 1995 (in Chinese)
Q2: In this context, retrieving complete cores (not sliced in the field) and looking at facies at the microscopic scale is mandatory to be able to decipher sedimentary processes and demonstrate the continuity of this archive.
Yes, careful observation of sedimentary facies at the microscopic scale is very important to demonstrate the continuity of the archive. We have observed the lithofacies carefully during the process of field sampling, but no depositional discontinuity and distinct change of lithofacies have been found. In addition, the sediments of the whole sequence are fine and mainly composed of clayey silt (Md: 5.4-9.9 μm, mean 7.0 μm), which also supports the continuity of this archive.
Q3: I also agree that the age model is weak, and not accurate enough to be able to claim that you can make a reconstruction with a 2-year resolution.
Thank you very much for your review. We believe that it is acceptable based on the following reasons:
1) The age of the upper core was determined by 210Pb CRS model from two parallel cores and compares well. Furthermore, the events (E1 and E2) revealed by the sedimentary sequence can be compared with local strong wind events, and so we consider the results are reliable;
2) The core ABHHX is mainly composed by fine-grained sediments (Md: 5.4-9.9 μm, mean 7.0 μm), and there is no obvious depositional discontinuity and distinct change in core lithology, indicating that the deposition is continuous and uniform. Therefore, we performed a linear extrapolation using the upper 210Pb ages, and the 48 cm core was dated back to 1816 AD;
3) The climate changes revealed by our sedimentary sequence are well consistent with regional records (Figure 8).
Q4: I agree with Reviewer 1 that interpretations of colour reflectance, carbon content are speculative. For instance, I doubt it is possibly derived transport condition from C-content (in reference to “In the early period (1816-1876 AD), the high C values indicate strong transport dynamics; the high proportion of ultrafine component indicates strong pedogenesis, combined with high organic carbon content and high a* values, it is inferred that the water vapor content is relatively higher.”
We consider the explanation given is acceptable according to the following points:
1) The analysis of C-M diagrams is useful to interpret sediment transport dynamics, and C is the coarsest percentile of the grain-size distribution in samples (one percentile), representing the maximum transport capacity (Passega, 1957; Singh et al., 2007). The high C values indicate strong transport dynamics (Wei et al., 2021; Shi et al., 2022);
2) The ultrafine component (the grain size fraction of < 1 μm) in aeolian sediments are formed during pedogenesis (Sun et al., 2006, 2011), which is usually influenced by chemical, biochemical and physical alterations closely connected with the local climate. Sun et al (2011) has confirmed that the proportion of ultrafine component strongly reflects the intensity of pedogenesis, and the high proportion of ultrafine component indicates strong pedogenesis;
3) The total organic carbon (TOC) content in lake sediments in arid region can reflect the regional humidity, and more moisture is conducive to the formation of organic matter in lakes (Jiang et al., 2008). a* in sediment is related primarily to iron oxide mineral concentrations in arid region, especially hematite and goethite (Ji et al., 2002), and high a* values occur under strong oxidation conditions. Redness records from lake Qinghai show that high a* values indicate increased precipitation (Ji et al., 2005). Combined with high TOC content and high a* values, we think that the water vapor content is relatively higher.
Reference
Ji, J.F., Balsam, W.L., Chen, J., and Liu, L.W.: Rapid and precise measurement of hematite and goethite concentrations in the Chinese loess sequences by diffuse reflectance spectroscopy, Clays and Clay Minerals, 50(2): 208-216, https://doi.org/10.1346/000986002760832801, 2002.
Ji, J.F., Shen, J., Balsam, W., Chen, J., Liu, L.W., and Liu, X.Q.: Asian monsoon oscillations in the northeastern Qinghai–Tibet Plateau since the late glacial as interpreted from visible reflectance of Qinghai Lake sediments, Earth Planet. Sc. Lett, 233, 61-70, https://doi.org/10.1016/j.epsl.2005.02.025, 2005.
Jiang, H.C., Ji, J.L., Gao, L., Tang, Z.H., and Ding, Z.L.: Cooling-driven climate change at 12-11 Ma: Multiproxy records from a long fluviolacustrine sequence at Guyuan, Ningxia, China, Palaeogeogr. Palaeocl., 265, 148-158, https://doi.org/10.1016/ j.palaeo.2008.05.006, 2008.
Passega, R.: Texture as characteristic of clastic deposition, Bull. Amer. Assoc. Petrol. Geol., 41, 1952-1984, https://doi.org/10.1306/0BDA594E-16BD-11D7-8645000102C1865D, 1957.
Shi, W., Jiang, H.C., Xu, H.Y., Ma, S.Y., Fan, J.W., Zhang, S.Q., Guo, Q.Q., and Wei, X.T.: Response of modern fluvial sediments to regional tectonic activity along the upper Min River, eastern Tibet, Earth Surf. Dynam., 10, 1195-1209, https://doi.org/10.5194/esurf-10-1195-2022, 2022.
Singh, M., Singh, I. B., and Müller, G.: Sediment characteristics and transportation dynamics of the Ganga River, Geomorphology, 86, 144-175, https://doi.org/10.1016/j.geomorph.2006.08.011, 2007.
Sun, D.H.: Super-fine grain size components in Chinese loss and their palaeoclimatic implication, Quaternary Sciences, 26, 928-936, 2006 (in Chinese).
Sun, D.H., Su, R.X., Li, Z.J., and Lu, H.Y.: The ultrafine component in Chinese loess and its variation over the past 7-6 Ma: implications for the history of pedogenesis, Sedimentology, 58, 916-935, https://doi.org/10.1111/j.136 5-3091.2010.01189.x, 2011.
Wei, X.T., Jiang, H.C., Xu, H.Y., Fan, J.W., Shi, W., Guo, Q.Q., and Zhang, S.Q.: Response of sedimentary and pollen records to the 1933 Diexi earthquake on the eastern Tibetan Plateau, Ecol. Indic., 129, 107887, https://doi.org/10.1016/j.ecoli nd.2021.107887, 2021.
Q5: Reflectance values are also influenced by changes in oxygen content below the water/sediment interface (i.e., the redox front), and this is making your reflectance interpretation even weaker.
Yes, color reflectance values are also influenced by changes in oxygen content below the water/sediment interface. However, we consider that the main controlling factor is the change of regional water vapor, which strongly affects the redox reaction of the sediments and thus changes the color reflectance values. In addition, the increase in water vapor during 1816-1920 AD revealed by color reflectance values is also supported by a high TOC content, which is consistent with previous findings (Chen et al., 2010, 2015)。
Reference
Chen, F.H., Chen, J.H., Holmes, J., Boomer, I., Austin, P., Gates, J.B., Wang, N.L., Brooks, S.J., and Zhang, J.W.: Moisture changes over the last millennium in arid central Asia: a review, synthesis and comparison with monsoon region, Quaternary Sci. Rev., 29, 1055-1068, https://doi.org/10.1016/j.quascirev.201 0.01.005, 2010.
Chen, J.H., Chen, F.H., Feng, S., Huang, W., Liu, J.B., and Zhou, A.F.: Hydroclimatic changes in China and surroundings during the Medieval Climate Anomaly and Little Ice Age: spatial patterns and possible mechanisms, Quaternary Sci. Rev., 107, 98-111, https://doi.org/10.1016/j.quascirev.2014.10.012, 2015.
Q6: Interpretation of grain-size data also remains speculative: “ultrafine components” can also be observed in permafrost lakes and peat as sources for higher TOC. The colour reflectance can neither tell us something about transport nor about water vapour even in combination with GSD and C.
We believe that the interpretation of grain-size data is acceptable for several points:
1) Ultrafine components in aeolian sediments are formed during pedogenesis and can be used to trace the history of regional pedogenesis (Sun et al., 2006, 2011). The ultrafine component exists not only in loess and paleosol, but also in some lake sediments in aeolian regions, which may be the product of pedogenesis on the surface in the catchment (Sun et al., 2006);
2) There is no correlation between the proportion of ultrafine component and TOC content in our records, so we think that ultrafine component may only represent the pedogenesis in the catchment;
3) C-M diagrams can be used to interpret sediment transport dynamics, and C is the coarsest percentile of the grain-size distribution in samples (one percentile), representing the maximum transport capacity (Passega, 1957; Singh et al., 2007). The high C values indicate strong transport dynamics (Wei et al., 2021; Shi et al., 2022);
4) We combined the changes of color reflectance and TOC content to reveal the regional moisture, but not transport process. The high humidity revealed by our multi-proxies is consistent with regional records during 1816-1920 AD (Chen et al. 2006, 2010).
Reference
Chen, F.H., Huang, X.Z., Zhang, J.W., Holmes, J.A., and Chen, J.H.: Humid Little Ice Age in arid central Asia documented by Bosten Lake, Xinjiang, China, Sci. China Ser. D, 49, 1280-1290, https://doi.org/10.1007/s11430-006-2027-4, 2006.
Chen, F.H., Chen, J.H., Holmes, J., Boomer, I., Austin, P., Gates, J.B., Wang, N.L., Brooks, S.J., and Zhang, J.W.: Moisture changes over the last millennium in arid central Asia: a review, synthesis and comparison with monsoon region, Quaternary Sci. Rev., 29, 1055-1068, https://doi.org/10.1016/j.quascirev.2010.01.005, 2010.
Passega, R.: Texture as characteristic of clastic deposition, Bull. Amer. Assoc. Petrol. Geol., 41, 1952-1984, https://doi.org/10.1306/0BDA594E-16BD-11D7-8645000102C1865D, 1957.
Shi, W., Jiang, H.C., Xu, H.Y., Ma, S.Y., Fan, J.W., Zhang, S.Q., Guo, Q.Q., and Wei, X.T.: Response of modern fluvial sediments to regional tectonic activity along the upper Min River, eastern Tibet, Earth Surf. Dynam., 10, 1195-1209, https://doi.org/10.5194/esurf-10-1195-2022, 2022.
Singh, M., Singh, I. B., and Müller, G.: Sediment characteristics and transportation dynamics of the Ganga River, Geomorphology, 86, 144-175, https://doi.org/10.1016/j.geomorph.2006.08.011, 2007.
Sun, D.H.: Super-fine grain size components in Chinese loss and their palaeoclimatic implication, Quaternary Sciences, 26, 928-936, 2006 (in Chinese).
Sun, D.H., Su, R.X., Li, Z.J., and Lu, H.Y.: The ultrafine component in Chinese loess and its variation over the past 7-6 Ma: implications for the history of pedogenesis, Sedimentology, 58, 916-935, https://doi.org/10.1111/j.1 365-3091.2010.01189.x, 2011.
Wei, X.T., Jiang, H.C., Xu, H.Y., Fan, J.W., Shi, W., Guo, Q.Q., and Zhang, S.Q.: Response of sedimentary and pollen records to the 1933 Diexi earthquake on the eastern Tibetan Plateau, Ecol. Indic., 129, 107887, https://doi.org/10.1016/j.ecolind.2021.107887, 2021.
Citation: https://doi.org/10.5194/cp-2022-92-AC2
-
AC2: 'Reply on EC1', Xiaotong Wei, 10 Feb 2023
-
RC2: 'Comment on cp-2022-92', Anonymous Referee #2, 23 Feb 2023
Dear Editor and Authors of the manuscript "Climate transition over 1 the past two centuries revealed by lake Ebinur in Xinjiang, northwest China",
Thank you for considering me to read this article and to be part of the process. Below, I am sending the revisions of the manuscript.
Sincerely,
General comments
In this manuscript, the authors provide a multiproxy study of a short sediment core from a shallow terminal lake in a climate-sensitive arid area. This record includes a significant number of variables, mainly based on particle size parameters, that can be linked to recent paleoenvironmental changes.
I read carefully the manuscript, and I was also able to read the discussion, the comments and their responses. Based on this information, I agree with the comments of the Editor and Referee 1 concerning the problems in the chronological model (I provide more details in the comments below). Unfortunately, I do not see that the authors provided enough evidence in their relplies to support the model. This is a major obstacle to be addressed when the goal of the paper is to provide a high temporal resolution of the sequence in order to determine the exact year of a climate shift. As another related issue, it is difficult to understand the criteria for the separation of units and subunits, and thus, the exact point of the sedimentation changes. It also surprises me that the changes on the lake area and water discharges during the deposition of this sequence are completely ignored in the discussion in the shallow lake sedimentation processes. Finally, I suggest to revise the organization of the manuscript separating the data from interpretation, and discussions, following a clear and logical order, and to provide better explanation of the figures.
Considering that some of the mentioned points intefere with the goals and the precision proposed in this work, my suggestion is to reject the manuscript. I hope that the authors can think about a solution to the main problems (maybe adding marker layers to the model),or to consider a different approach, to send the new manuscript using this valuable data.
Specific comments
128-130. The climate of the study region is mainly dominated by westerlies and is a typical temperate continental climate, which is characterized by low rainfall and strong evaporation (Zhou et al., 2019, 2021).
138-139. The climate is generally characterized by warm-dry summers and cold wet winters (Fig. 2)
Along the manuscript and in the reconstruction, the authors mention wet climate in the area…I do not think this term is adequate for this site, there are relatively wetter and drier stages but within the analyzed time range, the climate seems mostly arid.
156-159...two parallel sediment cores (ABHHX and ABH, of 48 cm and 50 cm length, respectively) were retrieved from the northwest edge of lake Ebinur at a water depth of 0.8 m (45°04' N, 82°36' E, 193 m), using a 60-mm UWITEC gravity corer (Fig. 1)…
Considering the location of the coring site (if the coordinates provided in the manuscript of the coring site are correct, 45°04' N, 82°36'), the cores were taken close to the northwestern lake shore. The shallow water-depth and large area variations, immediately suggest that parts of lake bottom near the margins, such as the coring site, are susceptible to become air exposed. Moreover, historical satellite images from Google Earth show that the northern part of the lake was above the lake water level during images from the 80’s and 90’s. The same seems to be presented in maps of papers studying the lake area fluctuation (Wang et al. 2021. Simulation of Lake Water Volume in Ungauged Terminal Lake Basin Based on Multi-Source Remote Sensing. Remote Sensing. 13.10.3390/rs13040697; Zhang et al. 2015. Environ Monit Assess 187:4128DOI 10.1007/s10661-014-4128-4). The lake bottom exposure and wind action of part of the 20th century sediments may also explain the lack of the 137Cs signal in the Lake Ebinur sediments, which has been effectively detected in other lake sequences from the same region (Lan, Jianghu, et al. "Time marker of 137Cs fallout maximum in lake sediments of Northwest China." Quaternary Science Reviews 241 (2020): 106413), and in a different cores retrieved from the same lake at a greater water depth (Liu et al 2017 J. Limnol., 2017; 76(3): 534-545); Ma L, Wu J, Abuduwaili J, Liu W (2016) Geochemical Responses to Anthropogenic and Natural Influences in Ebinur Lake Sediments of Arid Northwest China. PLoS ONE 11(5): e0155819. doi:10.1371/journal.pone.0155819). This should be carefully considered by the authors since it challenges the assumed “continuous and uniform sedimentation”, and thus, questions the reliability of the age model (as pointed by RC1 and CE1), even when the mean particle size is similar along the sequence.
171-176. The activity of total 210Pb (210Pbtot) was determined via gamma emissions at 44.5 keV, and the activity of 226Ra was determined by measuring the activity of its daughter nuclide 214Pb at 295 keV and 352 keV. The activity of 137Cs was measured with the 662 keV photopeak. The supported 210Pb activity was assumed to be in equilibrium with in situ 226Ra activity, and the unsupported 210Pb activity (210Pbex) was calculated by subtracting the 226Ra activity from the 210Pbtot (Pratte et al., 2019).
In the Materials and methods section, the authors indicate the methodology for calculating the 210Pb activity. Nevertheless, they do not indicate how they constructed the age model from this data, this should be addressed in the methodology. Additionally, it is indicated that the model applied is the CRS, which assumes a constant rate of supply and a variable sedimentation rate. For the oldest part of the sequence a linear extrapolation is assumed. I find an inconsistency in this point when the authors argue "uniform rates" (reply to Q5). Finally, in the replies to the comments, they say that “six data were discarded due to abnormal deposition rate”. Where are these results? I think there is information missing from the manuscript.
177-186. In Materials and methods, the grain size distribution method is explained. However, the measured parameters are not mentioned. They should be mentioned in this section and explained in the Results and Interpretation section.
188-191. Each Sample of about 1.5 g was dried at 40 ℃ for 24 h, then crushed without damaging their grain-size (Jiang et al., 2008) and the color reflectance was measured by using a SPAD 503 handheld spectrophotometer.
The color reflectance methodology and the parameters’ meanings are not explained.
228-230. 4.2 Sedimentary Proxies record. All 96 grain-size data were analyzed by end-member analysis (EMA) using AnalySize software (Weltje, 1997; Paterson and Heslop, 2015; Jiang et al., 2022).
This is methodological aspect, please move these lines to the previous section.
231-239. Overall, the lower part of the sedimentary sequence is characterized by large fluctuations and coarse grains (Figs. 5a-5g), with over 60 % of the C value above 50 μm (Figs. 6b, 6c), reflecting strong transport dynamics (Passega, 1964; Jiang et al., 2017a; Wei et al., 2021). The particles in the upper part of the sequence are finer (Figs. 5a-5g), and only ~ 20 % the C value exceeds 50 μm (Figs. 6d, 6e), indicating smaller transport dynamics.
In addition, other proxies of lake Ebinur sequence (L*, a*, TOC and TIC) also show different variation characteristics in the corresponding upper and lower parts (Figs. 5k-5n). Thus, the sedimentary sequence can be divided into two units.
In this description, the "upper part" and the "lower part" of the sedimentary sequence are not well delimited. Furthermore, the criteria for the separation of the units and subunits should be clearly defined. This is important since the contact between unit 1 and unit 2 is established as the point where sedimentation and climate shifted.
Figure 5. This Figure includes some parameters that are not explained in the manuscript, or sometimes they are not explained, interpreted nor used along the manuscript (e.g. the Mode, EM1, <2 micrometers, etc.).
258-260. The variation of Md is clearly influenced by the coarse component: EM2 (0-37.6 %, mean 21.6 %) (Fig. 5g), i.e., the coarse particles are deposited first, and the fine particles are deposited later.
From the Figure 5, I cannot detect differences in excursions of the curves from EM1 and EM2, they seem quite similar. Please, explain them in the results.
260-263. Combined with the higher C value for this unit (22.6-86.5 μm, mean 54.5 μm) (Fig. 5i), it indicates that the wind is stronger at this stage, bringing more coarse-grained matter from local and regional dust (see Sect. 5.1 for the explanation of provenance).
Have the authors considered the role water inflow in sediment transport in any part of the sequence?
266-269. Correspondingly, the contents of TOC (0.25-0.34, mean 0.30) and TIC (1.91-2.95, mean 2.50) also showed strong fluctuations (Figs. 5m, 5n), which may have been influenced by strong wind activity during the cold period.
Please, provide an explanation of this relationship.
272-274. In this unit, the proportion of ultrafine component is the highest in the whole sequence (1.7 %-10.2 %, mean 5.0 %), revealing the strongest pedogenesis in the study area (Fig. 5h).
How do authors determine that the ultrafine component is local? Could it be part of the long-distance transport?
285-287. Related to humidity fluctuation, L* values within arid lakes are considered to reflect variations in the carbonate, and high L* values denote more carbonate content (Xiao et al., 2006; Jiang et al., 2008).
According to Figure 5, L* and TIC curves seem to fluctuate quite differently. Moreover, L* seems lower in unit 2 than in unit 1. Therefore, I think that the interpretation of the *L and TIC values needs further explanation.
294-298. Further, this unit can also be divided into two sub-units based on the changes of all proxies: unit 1-a and unit 1-b (Figs. 5a-5n). During the period of unit 1-a (48-34 cm, 1816-1876 AD), the study area has been under cold and wet climatic conditions, while unit 1-b (34-24 cm, 1876-1920 AD) was in a transition period from cold and warm.
This is not sustained by any explanation in this section, it seems an arbitrary division. The same is applicable to the following subunits. Please, provide more details.
Figure 6
This Figure is not mentioned or explained in the manuscript.
310-313. This is probably duo to the decrease of the temperature gradient as the temperature rise (Zhang et al., 2021), resulting in the weakening of wind intensity and the decrease of coarse particles transported at low altitude and short distance (Ge et al., 2016).
I saw that there was an explanation added in the response to a question about the meaning of the temperature gradient. I find that the relation of temperature changes and the grain size in this lake record is vague and should be better addressed in the discussion.
313-314. As well, the contents of TOC (0.25-0.32) and TIC (2.17-2.63) showed very slight fluctuations except for the top two points (Figs. 5m, 5n).
What does this mean?
329-334. 5.1 Provenance and transport mechanisms of lake Ebinur sediments. The Y value of Sahu's formula is usually used to recognize the eolian environment, which is mainly determined by mean grain size, standard deviation, skewness, and kurtosis (Sahu, 1964). The Y values of all samples range from -19.5 to -7.6, lower than the threshold value of -2.74 (Fig. 7), supporting their windblown origin (Jiang et al., 2017b, 2022; Wei et al., 2021).
The results of the end members and this interpretation should be in the Results and Interpretation section, before authors interpret the whole sequence. In my opinion, provenance is not analyzed in this section. In addition, please, provide further explanation about the formula and threshold value (is this number and formula used to recognize only the aeolian origin or to discriminate aeolian from beach transport, as in Sahu, 1964?).
- 5.2 Climatic events revealed by lake Ebinur sedimentary sequence
In this section, authors include also the human influence on the lake sediments, so it would be convenient to modify the title.
364-366. The L* value increased continuously after 1955 (Fig. 8f), indicating the increase of carbonate content, which may be caused by the rapid shrinkage of lake Ebinur.
This is contradictory with the rest of the interpretations of carbonate precipitation, since unlike in the underlying units, here, carbonate precipitation is interpreted as triggered by lake volume reduction. Please, explain the mechanisms of carbonate precipitation in this lake.
369-373. Notably, Md and EM2 show two abnormally high values since 1955 AD (Figs. 8a, 8b), and correspondingly, the C values also show high values (Fig. 8c), indicating strong transport dynamics (Jiang et al., 2017a; Shi et al., 2022). These two events (E1, E2) may be related to local strong wind events within the age error (Wang et al., 2003).
Please, indicate the ages and the errors of these two events. Are these events regional? Can they be tracked in different cores or in other records from the region? Could they be used as time markers?
426-429. The fine-grained sediments (< 20 μm) are background dust that was transported by long distance high-altitude suspension, while the coarse-grained sediments (> 20 μm) are local and regional dusts that were transported from short distances at low altitudes.
This is not analyzed in the results, in the interpretations or in the discussion.
- 5.3 Climate transition and possible forcing mechanism. Figure 9
In this comparative Figure, the main data obtained from of this work should be included.
-
AC3: 'Reply on RC2', Xiaotong Wei, 02 Mar 2023
We are grateful to Reviewer 2 for giving us detailed comments to improve our manuscript. The responses to the comments from Reviewer 2 are addressed point by point as follows.
General comments
Q1: In this manuscript, the authors provide a multiproxy study of a short sediment core from a shallow terminal lake in a climate-sensitive arid area. This record includes a significant number of variables, mainly based on particle size parameters, that can be linked to recent paleoenvironmental changes. I read carefully the manuscript, and I was also able to read the discussion, the comments and their responses. Based on this information, I agree with the comments of the Editor and Referee 1 concerning the problems in the chronological model (I provide more details in the comments below). Unfortunately, I do not see that the authors provided enough evidence in their relplies to support the model. This is a major obstacle to be addressed when the goal of the paper is to provide a high temporal resolution of the sequence in order to determine the exact year of a climate shift.
Thank you very much for your review. We believe that the chronological model is reliable according to the following points:
1) The dating of the upper core (~80 year) calculated by the 210Pb CRS model is reliable, for example, the events (E1 and E2) revealed by the sedimentary sequence can be compared with local strong wind events (Figure 8);
2) The whole core is mainly composed of fine-grained sediments (Md: 5.4-9.9 μm, mean 7.0 μm), and there is no distinct lithologic change. And we think that the core deposition is near-continuous and homogeneous;
3) Based on downward extrapolation method, the climate changes over the past 200 years revealed by sedimentary sequence can be well contrasted regionally with previous climate records.
Moreover, the climatic transition point (1920 AD) revealed by the lake Ebinur sedimentary sequence is supported by the reconstructed temperature records in China (Yang et al., 2002; Ge et al., 2013).
Reference
Ge, Q., Hao, Z., Zheng, J., and Shao, X.: Temperature changes over the past 2000 yr in China and comparison with the Northern Hemisphere, Clim. Past, 9, 1153-1160, https://doi.org/10.5194/cp-9-1153-2013, 2013.
Yang, B., Braeuning, A., Johnson, K.R., and Shi, Y.F.: General characteristics of temperature variation in China during the last two millennia, Geophys. Res. Lett., 29, 38-1-38-4, https://doi.org/10.1029/2001GL014485, 2002.
Q2: As another related issue, it is difficult to understand the criteria for the separation of units and subunits, and thus, the exact point of the sedimentation changes. It also surprises me that the changes on the lake area and water discharges during the deposition of this sequence are completely ignored in the discussion in the shallow lake sedimentation processes.
Thank you very much for your kind reminding. We have modified the criteria for the separation of units and subunits in detail. Please see L.266-279, P.8, L.326-334, P.10, and L.367-371, P.11.
The changes on the lake area and water discharges can seriously affect the sedimentation process of shallow lakes, for example, changes in L* value and TOC. However, our indicators are insufficient to explain the influence and further research is needed to reveal it.
Q3: Finally, I suggest to revise the organization of the manuscript separating the data from interpretation, and discussions, following a clear and logical order, and to provide better explanation of the figures. Considering that some of the mentioned points intefere with the goals and the precision proposed in this work, my suggestion is to reject the manuscript. I hope that the authors can think about a solution to the main problems (maybe adding marker layers to the model),or to consider a different approach, to send the new manuscript using this valuable data.
Thank you very much for your kind reminding. We have reorganized the results, interpretation, and discussions in the manuscript, and improved the explanation of the figures.
Specific comments
Q1: 128-130. The climate of the study region is mainly dominated by westerlies and is a typical temperate continental climate, which is characterized by low rainfall and strong evaporation (Zhou et al., 2019, 2021).
138-139. The climate is generally characterized by warm-dry summers and cold wet winters (Fig. 2)
Along the manuscript and in the reconstruction, the authors mention wet climate in the area…I do not think this term is adequate for this site, there are relatively wetter and drier stages but within the analyzed time range, the climate seems mostly arid.
Thank you very much for your kind reminding. We have modified it, please see L.136-137, P.4.
Q2: 156-159...two parallel sediment cores (ABHHX and ABH, of 48 cm and 50 cm length, respectively) were retrieved from the northwest edge of lake Ebinur at a water depth of 0.8 m (45°04' N, 82°36' E, 193 m), using a 60-mm UWITEC gravity corer (Fig. 1)…
Considering the location of the coring site (if the coordinates provided in the manuscript of the coring site are correct, 45°04' N, 82°36'), the cores were taken close to the northwestern lake shore. The shallow water-depth and large area variations, immediately suggest that parts of lake bottom near the margins, such as the coring site, are susceptible to become air exposed. Moreover, historical satellite images from Google Earth show that the northern part of the lake was above the lake water level during images from the 80’s and 90’s. The same seems to be presented in maps of papers studying the lake area fluctuation (Wang et al. 2021. Simulation of Lake Water Volume in Ungauged Terminal Lake Basin Based on Multi-Source Remote Sensing. Remote Sensing. 13.10.3390/rs13040697; Zhang et al. 2015. Environ Monit Assess 187: 4128DOI 10.1007/s10661-014-4128-4). The lake bottom exposure and wind action of part of the 20th century sediments may also explain the lack of the 137Cs signal in the Lake Ebinur sediments, which has been effectively detected in other lake sequences from the same region (Lan, Jianghu et al. "Time marker of 137Cs fallout maximum in lake sediments of Northwest China." Quaternary Science Reviews 241 (2020): 106413), and in a different cores retrieved from the same lake at a greater water depth (Liu et al 2017 J.Limnol., 2017; 76(3): 534-545); Ma L, Wu J, Abuduwaili J, Liu w (2016) Geochemical Responses to Anthropogenic and Natural Influences in Ebinur Lake Sediments of Arid Northwest China. PLoS ONE 11(5): E0155819. doi:10.1371/journal.pone.0155819). This should be carefully considered by the authors since it challenges the assumed “continuous and uniform sedimentation”, and thus, questions the reliability of the age model (as pointed by RC1 and CE1), even when the mean particle size is similar along the sequence. In my opinion this cannot be done as i) we usually have less compacted sediments in the upper part of sediment cores with a high sedimentation rate and ii) there is a change in lithology which the authors use for their environmental reconstruction.
Yes, the coring site is located on the northwest shore of Lake Ebinur, which may be exposed to air due to shallow water-depth and large area variations (Zhang et al., 2015; Wang et al., 2021). However, the northwest shore of the lake is dry during individual months of the year, and the variation is seasonal or even monthly, not interannual. In addition, 137Cs signals were detected in other lake sequences from the same region and in different cores retrieved from the same lake (Ma et al., 2016; Liu et al., 2017; Lan et al., 2020), which may explain the lack of the 137Cs signal in our core sediments. But we believe the deposition is continuous and uniform according to the following points:
1) The dating of the upper core (~80 year) calculated by the 210Pb CRS model of two parallel cores is reliable, and the events (E1 and E2) revealed by the sedimentary sequence can be compared with local strong wind events (Figure 8);
2) The core is very shallow, only 48 cm, and there is no distinct lithologic change. Combined with the fine particle size (Md: 5.4-9.9 μm, mean 7.0 μm), we think that the core deposition is near-continuous and homogeneous;
3) Based on downward extrapolation method, the climate changes over the past 200 years revealed by sedimentary sequence can be well contrasted regionally with previous climate records (Figure 8).
In addition, we did not use the change in lithology for environmental reconstruction.
Q3: 171-176. The activity of total 210Pb (210Pbtot) was determined via gamma emissions at 44.5 keV, and the activity of 226Ra was determined by measuring the activity of its daughter nuclide 214Pb at 295 keV and 352 keV. The activity of 137Cs was measured with the 662 keV photopeak. The supported 210Pb activity was assumed to be in equilibrium with in situ 226Ra activity, and the unsupported 210Pb activity (210Pbex) was calculated by subtracting the 226Ra activity from the 210Pbtot (Pratte et al., 2019).
In the Materials and methods section, the authors indicate the methodology for calculating the 210Pb activity. Nevertheless, they do not indicate how they constructed the age model from this data, this should be addressed in the methodology. Additionally, it is indicated that the model applied is the CRS, which assumes a constant rate of supply and a variable sedimentation rate. For the oldest part of the sequence a linear extrapolation is assumed. I find an inconsistency in this point when the authors argue "uniform rates" (reply to Q5). Finally, in the replies to the comments, they say that “six data were discarded due to abnormal deposition rate”. Where are these results? I think there is information missing from the manuscript.
Thank you very much for your review. We think that the description of the age method is sufficient (Xu et al., 2020; Fan et al., 2021), and we give a detailed explanation of the construction of the age model in the revised manuscript. Please see L.219-225, P.6-7.
Indeed, we reconstruct the age of the upper part by using the CRS model, which assumes a constant rate of supply and a variable sedimentation. For the lower part, we used a linear extrapolation. This may seem contradictory, but it is always necessary to give the age of the lower part in order to reconstruct the environment. Based on the following points, we believe that the result of linear extrapolation is acceptable:
1) Although the deposition rates calculated from 210Pbex activity are variable, they are all around 2mm/a;
2) The whole core is mainly composed of fine-grained sediments (Md: 5.4-9.9 μm, mean 7.0 μm), and there is no obvious depositional discontinuity and distinct change in core lithology, so we think that the core deposition is near-continuous and homogeneous;
3) The climate changes and climate events revealed by our sedimentary sequence are well consistent with regional records (Figure 8).
As shown in Figure S1, the bottom six data of core ABH were discarded due to the abnormal deposition rate, please see the Supplement material.
Reference
Fan, J.W., Jiang, H.C., Shi, W., Guo, Q.Q., Zhang, S.Q., Wei, X.T., Xu, H.Y., Zhong, N., Huang, S.T., Chang, X.D., and Xiao, J.L.: A 450-year lacustrine record of recurrent seismic activities around the Fuyun fault, Altay Mountains, Northwest China, Quatern. Int., 558, 75-88, https://doi.org/10.1016/j.quaint.2020.08.051, 2020.
Xu, H.Y., Jiang, H.C., Liu, K.B., Zhong, N.: Potential pollen evidence for the 1933 M 7.5 Diexi earthquake and implications for post-seismic landscape recovery, Environmental Research Letters, 15, 094043, https://doi.org/10.1088/1748-9326/ab9af6, 2020.
Q4: 177-186. In Materials and methods, the grain size distribution method is explained. However, the measured parameters are not mentioned. They should be mentioned in this section and explained in the Results and Interpretation section.
Thank you very much for your review. We believe that the measured parameters for grain size have been described. Please see L.176-185, P.5-6.
Q5: 188-191. Each Sample of about 1.5 g was dried at 40 ℃ for 24 h, then crushed without damaging their grain-size (Jiang et al., 2008) and the color reflectance was measured by using a SPAD 503 handheld spectrophotometer.
The color reflectance methodology and the parameters’ meanings are not explained.
Thank you very much for your review. We consider that the description of color reflectance methodology is sufficient, and the parameters’ meaning is explained in Section 4.2, please see L.308-309 and L.309-315, P.9-10.
Q6: 228-230. 4.2 Sedimentary Proxies record. All 96 grain-size data were analyzed by end-member analysis (EMA) using AnalySize software (Weltje, 1997; Paterson and Heslop, 2015; Jiang et al., 2022).
This is methodological aspect, please move these lines to the previous section.
Done. Please see L.185-187, P.6.
Q7: 231-239. Overall, the lower part of the sedimentary sequence is characterized by large fluctuations and coarse grains (Figs. 5a-5g), with over 60 % of the C value above 50 μm (Figs. 6b, 6c), reflecting strong transport dynamics (Passega, 1964; Jiang et al., 2017a; Wei et al., 2021). The particles in the upper part of the sequence are finer (Figs. 5a-5g), and only ~ 20 % the C value exceeds 50 μm (Figs. 6d, 6e), indicating smaller transport dynamics.
In addition, other proxies of lake Ebinur sequence (L*, a*, TOC and TIC) also show different variation characteristics in the corresponding upper and lower parts (Figs. 5k-5n). Thus, the sedimentary sequence can be divided into two units.
In this description, the "upper part" and the "lower part" of the sedimentary sequence are not well delimited. Furthermore, the criteria for the separation of the units and subunits should be clearly defined. This is important since the contact between unit 1 and unit 2 is established as the point where sedimentation and climate shifted.
Thank you very much for your kind reminding. We have modified it, please see L.266-279, P.8.
Q8: Figure 5. This Figure includes some parameters that are not explained in the manuscript, or sometimes they are not explained, interpreted nor used along the manuscript (e.g. the Mode, EM1, <2 micrometers, etc.).
Thank you very much for your kind reminding. We have modified it, please see L.292-293, P.9 and L.347-348, P.11. And we think EM1 and <2 μm fraction have less significance in the reconstructed sequences.
Q9: 258-260. The variation of Md is clearly influenced by the coarse component: EM2 (0-37.6 %, mean 21.6 %) (Fig. 5g), i.e., the coarse particles are deposited first, and the fine particles are deposited later.
From the Figure 5, I cannot detect differences in excursions of the curves from EM1 and EM2, they seem quite similar. Please, explain them in the results.
Yes, the whole sedimentary sequence is composed of two end-members: EM1 and EM2, which are negatively correlated. In the process of lake deposition, the coarse particles (EM2) are deposited first, followed by fine particles (EM1). In other words, the percentage content of EM1 is determined by the change of EM2. Therefore, EM2 has more important environmental information, reflecting the regional and local provenance supply.
Q10: 260-263. Combined with the higher C value for this unit (22.6-86.5 μm, mean 54.5 μm) (Fig. 5i), it indicates that the wind is stronger at this stage, bringing more coarse-grained matter from local and regional dust (see Sect. 5.1 for the explanation of provenance).
Have the authors considered the role water inflow in sediment transport in any part of the sequence?
Sorry, we think the sediments in lake Ebinur are aeolian for the following reasons:
1) The Y value of all samples range from -19.5- -7.6, lower than the threshold value of -2.74, supporting their windblown origin (Jiang et al., 2017, 2022; Wei et al., 2021);
2) The results of end-member simulation are also supported by modern observations: the EM2 component (~ 24.1 μm) shows a similar modal distribution with aeolian dust samples collected from the Ebinur drainage area (15-26 μm) (Ma et al., 2016);
3) The arid and windy climate in the lake Ebinur area provides favorable conditions for aeolian deposition.
In summary, we believe that the sediments in lake Ebinur were transported by wind rather than by water. Thus, the higher C value reflects stronger wind conditions.
Reference
Jiang, H.C., Zhong, N., Li, Y.H., Ma, X.L., Xu, H.Y., Shi, W., Zhang, S.Q., and Nie, G.Z.: A continuous 13.3-ka record of seismogenic dust events in lacustrine sediments in the eastern Tibetan Plateau, Sci. Rep., 7, 1-10, https://doi.org/10.10 38/s41598-017-16027-8, 2017.
Jiang, H.C., Zhang, J.Y., Zhang, S.Q., Zhong, N., Wan. S.M., Alsop, G.I., Xu, H.Y., Guo, Q.Q., and Yan, Z.: Tectonic and Climatic Impacts on Environmental Evolution in East Asia During the Palaeogene, Geophys. Res. Lett., 49, e2021GL096832, https://doi.org/10.1029/2021GL096832, 2022.
Ma, L., Wu, J.L., and Abuduwaili, J.: Variation in aeolian environments recorded by the particle size distribution of lacustrine sediments in Ebinur Lake, northwest China, SpringerPlus, 5, 1-8, https://doi.org/10.1186/s40064-016-2146-0, 2016.
Wei, X.T., Jiang, H.C., Xu, H.Y., Fan, J.W., Shi, W., Guo, Q.Q., and Zhang, S.Q.: Response of sedimentary and pollen records to the 1933 Diexi earthquake on the eastern Tibetan Plateau, Ecol. Indic., 129, 107887, https://doi.org/10.1016/j.ecoli nd.2021.107887, 2021.
Q11: 266-269. Correspondingly, the contents of TOC (0.25-0.34, mean 0.30) and TIC (1.91-2.95, mean 2.50) also showed strong fluctuations (Figs. 5m, 5n), which may have been influenced by strong wind activity during the cold period.
Please, provide an explanation of this relationship.
Thank you very much for your kind reminding. We have modified it, please see L.319-321, P.10.
Q12: 272-274. In this unit, the proportion of ultrafine component is the highest in the whole sequence (1.7 %-10.2 %, mean 5.0 %), revealing the strongest pedogenesis in the study area (Fig. 5h).
How do authors determine that the ultrafine component is local? Could it be part of the long-distance transport?
Thank you very much for your review. We consider the ultrafine component is local based on the following two aspects:
1) Ultrafine components in aeolian sediments are formed during pedogenesis and can be used to trace the history of regional pedogenesis (Sun et al., 2006, 2011). The ultrafine components of lake sediments in aeolian regions may be the products of pedogenesis on the surface in the catchment (Sun et al., 2006);
2) As shown in figure 8, the proportion of ultrafine components showed a consistent trend with the coarse particle fraction EM2 during 1816-1876 AD. This suggests that the ultrafine components produced by strong pedogenesis in the study area may be attached to the coarse-grained material from nearby sources and deposited by wind transport into the lake Ebinur.
Reference
Sun, D.H.: Super-fine grain size components in Chinese loss and their palaeoclimatic implication, Quaternary Sciences, 26, 928-936, 2006 (in Chinese).
Sun, D.H., Su, R.X., Li, Z.J., and Lu, H.Y.: The ultrafine component in Chinese loess and its variation over the past 7-6 Ma: implications for the history of pedogenesis, Sedimentology, 58, 916-935, https://doi.org/10.1111/j.1 365-3091.2010.01189.x, 2011.
Q13: 285-287. Related to humidity fluctuation, L* values within arid lakes are considered to reflect variations in the carbonate, and high L* values denote more carbonate content (Xiao et al., 2006; Jiang et al., 2008).
According to Figure 5, L* and TIC curves seem to fluctuate quite differently. Moreover, L* seems lower in unit 2 than in unit 1. Therefore, I think that the interpretation of the *L and TIC values needs further explanation.
The L* value in unit 2 (74.4-76.7, mean 75.3) is higher than in unit 1 (73.2-76.1, mean 74.6). And the L* and TIC show similar variations: they show large-amplitude fluctuations in the early period (1816-1920 AD) and more stable in the late period (1920-2019 AD).
Q14: 294-298. Further, this unit can also be divided into two sub-units based on the changes of all proxies: unit 1-a and unit 1-b (Figs. 5a-5n). During the period of unit 1-a (48-34 cm, 1816-1876 AD), the study area has been under cold and wet climatic conditions, while unit 1-b (34-24 cm, 1876-1920 AD) was in a transition period from cold and warm.
This is not sustained by any explanation in this section, it seems an arbitrary division. The same is applicable to the following subunits. Please, provide more details.
Done. Please see L.326-334 and L.367-371, P.10-11.
Q15: Figure 6
This Figure is not mentioned or explained in the manuscript.
Done. We have modified it, please see L.269 and L.275, P.8.
Q16: 310-313. This is probably duo to the decrease of the temperature gradient as the temperature rise (Zhang et al., 2021), resulting in the weakening of wind intensity and the decrease of coarse particles transported at low altitude and short distance (Ge et al., 2016).
I saw that there was an explanation added in the response to a question about the meaning of the temperature gradient. I find that the relation of temperature changes and the grain size in this lake record is vague and should be better addressed in the discussion.
Thank you very much for your kind reminding. The lake Ebinur area has the strongest wind transport conditions and the highest temperatures during March to August (Ge et al., 2016). In the cold period (1816-1920 AD), the temperature gradient between March and August is larger and there are stronger wind conditions, bringing more coarse particles (EM2, local and/or regional sources) to the lake. In the warm period (1920-2019 AD), the temperature gradient between March and August decreases as the temperature rise, resulting in the weakening of wind intensity and the decrease of coarse particles (EM2) transported at low altitude and short distance.
We have modified it, please see L.350, P.11.
Reference
Ge, Y.X., Abuduwaili, J., Ma, L., Wu, N., and Liu, D.W.: Potential transport pathways of dust emanating from the playa of Ebinur Lake, Xinjiang, in arid northwest China, Atmos. Res., 178-179, 196-206, https://doi.org/10.1016/j.atmosres.2016.0 4.002, 2016.
Q17: 313-314. As well, the contents of TOC (0.25-0.32) and TIC (2.17-2.63) showed very slight fluctuations except for the top two points (Figs. 5m, 5n).
What does this mean?
Thank you very much for your kind reminding. The contents of TOC (0.25-0.32) and TIC (2.17-2.63) showed small fluctuations except for the top two points (Figs. 7m, 7n), which may indicate that the lake water body at this stage was more stable than unit 1 stage.
We have modified it, please see L.361-363, P.11.
Q18: 329-334. 5.1 Provenance and transport mechanisms of lake Ebinur sediments. The Y value of Sahu's formula is usually used to recognize the eolian environment, which is mainly determined by mean grain size, standard deviation, skewness, and kurtosis (Sahu, 1964). The Y values of all samples range from -19.5 to -7.6, lower than the threshold value of -2.74 (Fig. 7), supporting their windblown origin (Jiang et al., 2017b, 2022; Wei et al., 2021).
The results of the end members and this interpretation should be in the Results and Interpretation section, before authors interpret the whole sequence. In my opinion, provenance is not analyzed in this section. In addition, please, provide further explanation about the formula and threshold value (is this number and formula used to recognize only the aeolian origin or to discriminate aeolian from beach transport, as in Sahu, 1964?)
Done. Please see L.233-243, P.7.
The Sahu’s formula is mainly used to distinguish aeolian sediments and beach sediments. Sahu (1964) proposed that the Y value of eolian sediments should be less than -2.7411, and Y values of typical aeolian sediments are negative, while Y values of hydrogenic sediments are positive, which has been confirmed by Lu et al (1999) and Wu et al (2017).
Reference
Lu, H.Y., An, Z.S.: Comparison of grain-size distribution of red clay and loess-paleosol deposits in Chinese Loess Plateau, Acta Sedimentologica Sinica, 17(2), 7, 1999 (in Chinese),.
Sahu, B.K.: Depositional mechanisms from the size analysis of clastic sediments, J. Sediment. Res., 34, 73-83, https://doi.org/10.1306/74d70fce-2b21-11d7-8648000 102c1865d, 1964.
Wu, H.B., Liu, X.M., lv, B., Ma, M.M., Ji, J.P., Wang, W.Y., Zhang, Y.Y, Hou, J.L.: Aeolian origin of the Twelve Apostles section, in Australia, Quaternary Science, 37(1), 82-96, https://doi.org//10.11928/j.issn.1001-7410.2017.01.08, 2017.
Q19: 5.2 Climatic events revealed by lake Ebinur sedimentary sequence
In this section, authors include also the human influence on the lake sediments, so it would be convenient to modify the title.
Done. Please see L.374-375, P.11.
Q20: 364-366. The L* value increased continuously after 1955 (Fig. 8f), indicating the increase of carbonate content, which may be caused by the rapid shrinkage of lake Ebinur.
This is contradictory with the rest of the interpretations of carbonate precipitation, since unlike in the underlying units, here, carbonate precipitation is interpreted as triggered by lake volume reduction. Please, explain the mechanisms of carbonate precipitation in this lake.
Thank you very much for your kind reminding. We have modified it, please see L.387-389, P.11. Water is needed to deposit carbonate in arid areas, and in extremely arid lakes, high carbonate content occurs in environments with more water. Higher L* values reflecting carbonate content indicate more water, which may be associated with an increase in summer glacial meltwater caused by warming into the lake. In summer, the lake Ebinur area has a stronger evaporation, the increased glacial meltwater provides favorable conditions for carbonates production.
Q21: 369-373. Notably, Md and EM2 show two abnormally high values since 1955 AD (Figs. 8a, 8b), and correspondingly, the C values also show high values (Fig. 8c), indicating strong transport dynamics (Jiang et al., 2017a; Shi et al., 2022). These two events (E1, E2) may be related to local strong wind events within the age error (Wang et al., 2003).
Please, indicate the ages and the errors of these two events. Are these events regional? Can they be tracked in different cores or in other records from the region? Could they be used as time markers?
Done. Please see L.392-394, P.12.
These two strong wind events were regional and reported by Overview of Disaster Prevention (Wang et al., 2003). Strong winds at Alashankou in 1986 AD and 2002 AD killed more than 1000 ducks in the lake Ebinur area and could be used as time markers. Unfortunately, these two strong wind events have not yet been found in different cores or in other records, which may be related to the location of coring site (near the Ala Mountain Pass).
Reference
Wang, K.P., Zhao, Y.Z., and Ma, J.L.: Strong wind-more than 1000 ducks killed or injured in the lake Ebinur wetland, Overview of Disaster Prevention, 1, 32, 2003 (in Chinese).
Q22: 426-429. The fine-grained sediments (< 20 μm) are background dust that was transported by long distance high-altitude suspension, while the coarse-grained sediments (> 20 μm) are local and regional dusts that were transported from short distances at low altitudes.
This is not analyzed in the results, in the interpretations or in the discussion.
Thank you very much for your kind reminding. The EM1 fraction of lake Ebinur sediments has a modal grain size of 5.9 μm, and the content ranges from 62.1% to 100%, with a mean of 83.6%, which corresponds well to the < 20 μm grain size fraction (70.2%-97.0%, mean 84.7%). And the modal grain size of EM2 fraction is 24.1 μm (0-37.9 %, mean 16.4%), which corresponds well to the > 20 μm grain size fraction (3.0%-29.8%, mean 15.3%). This is consistent with the finding of previous studies that the fine-grained sediments (< 20 μm) are background dust that was transported by long distance high-altitude suspension, while the coarse-grained sediments (> 20 μm) are local and regional dusts that were transported from short distances at low altitudes. (Pye, 1987; Jiang et al., 2014; Wei et al., 2021). In addition, the EM2 fraction (~ 24.1 μm) shows a similar modal distribution with aeolian dust samples collected from the Ebinur drainage area (15-26 μm) (Ma et al., 2016), further supporting the possible transport mechanism model.
Reference
Jiang, H.C., Mao, X., Xu, H.Y., Yang, H.L., Ma, X.L., Zhong, N., and Li, Y.H.: Provenance and earthquake signature of the last deglacial Xinmocun lacustrine sediments at Diexi, East Tibet, Geomorphology, 204, 518-531, https://doi.org/10. 1016/j.geomorph.2013.08.032, 2014.
Ma, L., Wu, J.L., and Abuduwaili, J.: Variation in aeolian environments recorded by the particle size distribution of lacustrine sediments in Ebinur Lake, northwest China, SpringerPlus, 5, 1-8, https://doi.org/10.1186/s40064-016-2146-0, 2016.
Pye, K.: Eolian Dust and Dust Deposits, Academic Press, London, 1987.
Wei, X.T., Jiang, H.C., Xu, H.Y., Fan, J.W., Shi, W., Guo, Q.Q., and Zhang, S.Q.: Response of sedimentary and pollen records to the 1933 Diexi earthquake on the eastern Tibetan Plateau, Ecol. Indic., 129, 107887, https://doi.org/10.1016/j.ecoli nd.2021.107887, 2021.
Q23: 5.3 Climate transition and possible forcing mechanism. Figure 9
In this comparative Figure, the main data obtained from of this work should be included.
Thank you very much for your review. In figure 8, we identified the time point of the climate transition over the past 200 years-1920 AD, mainly through the multi-proxies of lake Ebinur sedimentary sequence. If our multi-proxies were put into figure 9, it will be too crowded to properly represent the signal.
-
RC3: 'Comment on cp-2022-92', Anonymous Referee #3, 03 Mar 2023
Xiaotong Wei and co-authors present a multi-proxy study on short sediment core from a closed lake system (Lake Ebinur) in northwestern China. They measured grain size, color reflectance and carbon content on discrete samples. So far, I have not looked at the other reviews and the replays by the authors on the discussion website of Climate of the Past in order to provide an unbiased report on the manuscript as possible.
About grain size:
The authors relay their story mostly on the grain size data. They relate the grain size to the wind strength and argue that the wind activity was stronger in the first half of their record. As the core comes from a closed lake basin, the lake level could have a strong influence on the sediment composition. The water depth at the coring site is only 0.8 m and so lake level fluctuations must have a huge influence. Fig. 8k shows the fluctuations of the lake surface since 1955, which are mainly due to anthropogenic changes. However, there must also have been fluctuations in the lake level before that, caused by climate fluctuations.
The grain size fluctuates considerably larger in the older part of the record. Key here would be the sedimentology of the courser grain size intervals. Are these discrete layers? Are they graded? Unfortunately, the core was sampled in the field and no core photographs are available to study the sedimentology in detail. The similar evolution of the mean grain size and the lake area (Fig. 8a, 8k) indicates, in my opinion, a strong influence of lake level on sediment composition.
Other open questions concerning the grain size:
- The authors mention in line 320 glacial meltwater and relate the increase in the L* value to the glacial melting in last decades. Here the question would be how strong this influence was in the older part of the record.
- The authors relate the ultrafine components to be associated with pedogenesis. Here the question would be how fast pedogenesis would react to climate change and how large would be the time lag with the production of ultrafine particles.
External forcing factors:
The authors try to relate the observed changes in the Lake Ebinur sedimentary record to external climate forcings like greenhouse gases or total solar irradiance (TSI). They propose that the climate transition around 1920 AD was manly controlled by TSI. However, they do not provide any mechanistical model how TSI would influence the sediment deposition in Lake Ebinur. The identification of the TSI as the most important external factor is therefore based on weak scientific grounds.
Citation: https://doi.org/10.5194/cp-2022-92-RC3 -
AC4: 'Reply on RC3', Xiaotong Wei, 06 Mar 2023
We are grateful to Reviewer 3 for giving us detailed comments to improve our manuscript. The responses to the comments from Reviewer 3 are addressed point by point as follows.
General Comments
Xiaotong Wei and co-authors present a multi-proxy study on short sediment core from a closed lake system (Lake Ebinur) in northwestern China. They measured grain size, color reflectance and carbon content on discrete samples. So far, I have not looked at the other reviews and the replays by the authors on the discussion website of Climate of the Past in order to provide an unbiased report on the manuscript as possible.
Thank you very much for your review. We have responded to the reviewer's comments point by point. Please see “Reply on RC1 (2)” and “Reply on EC1” on the website discussion of Climate of the Past.
About grain size:
Q1: The authors relay their story mostly on the grain size data. They relate the grain size to the wind strength and argue that the wind activity was stronger in the first half of their record. As the core comes from a closed lake basin, the lake level could have a strong influence on the sediment composition. The water depth at the coring site is only 0.8 m and so lake level fluctuations must have a huge influence. Fig. 8k shows the fluctuations of the lake surface since 1955, which are mainly due to anthropogenic changes. However, there must also have been fluctuations in the lake level before that, caused by climate fluctuations.
The grain size fluctuates considerably larger in the older part of the record. Key here would be the sedimentology of the courser grain size intervals. Are these discrete layers? Are they graded? Unfortunately, the core was sampled in the field and no core photographs are available to study the sedimentology in detail. The similar evolution of the mean grain size and the lake area (Fig. 8a, 8k) indicates, in my opinion, a strong influence of lake level on sediment composition.
Yes, the fluctuations of the lake level could have some effects on the sediment composition. However, we consider the grain size changes reflect the wind strength based on the following three points:
1) In the field sampling process, the coarse-grained layer in the lower part did not show obvious depositional discontinuity and lithology change, so we believe that the deposition is continuous;
2) The whole core is mainly composed of fine-grained sediments with a maximum median grain size of 9.9 μm, and we think
3) The Y values of all samples (-19.5 to -7.6) are lower than -2.74, supporting their windblown origin (Jiang et al., 2017, 2022; Wei et al., 2021);
4) The EM2 component (~ 24.1 μm) shows a similar modal distribution with aeolian dust samples collected from the Ebinur drainage area (15-26 μm) (Ma et al., 2016), further supporting the windblown origin.
Reference
Jiang, H.C., Zhong, N., Li, Y.H., Ma, X.L., Xu, H.Y., Shi, W., Zhang, S.Q., and Nie, G.Z.: A continuous 13.3-ka record of seismogenic dust events in lacustrine sediments in the eastern Tibetan Plateau, Sci. Rep., 7, 1-10, https://doi.org/10.10 38/s41598-017-16027-8, 2017.
Jiang, H.C., Zhang, J.Y., Zhang, S.Q., Zhong, N., Wan. S.M., Alsop, G.I., Xu, H.Y., Guo, Q.Q., and Yan, Z.: Tectonic and Climatic Impacts on Environmental Evolution in East Asia During the Palaeogene, Geophys. Res. Lett., 49, e2021GL096832, https://doi.org/10.1029/2021GL096832, 2022.
Ma, L., Wu, J.L., and Abuduwaili, J.: Variation in aeolian environments recorded by the particle size distribution of lacustrine sediments in Ebinur Lake, northwest China, SpringerPlus, 5, 1-8, https://doi.org/10.1186/s40064-016-2146-0, 2016.
Wei, X.T., Jiang, H.C., Xu, H.Y., Fan, J.W., Shi, W., Guo, Q.Q., and Zhang, S.Q.: Response of sedimentary and pollen records to the 1933 Diexi earthquake on the eastern Tibetan Plateau, Ecol. Indic., 129, 107887, https://doi.org/10.1016/j.ecoli nd.2021.107887, 2021.
Other open questions concerning the grain size:
Q2: The authors mention in line 320 glacial meltwater and relate the increase in the L* value to the glacial melting in last decades. Here the question would be how strong this influence was in the older part of the record.
Thank you very much for your kind reminding. In the older part of the record, L* values show large-amplitude fluctuations, which may be mainly related to more water vapor brought by the westerlies in the cold period. In this study, we were unable to quantify the contribution of glacier melting to L* value in the older part of the record, which may require more research.
Q3: The authors relate the ultrafine components to be associated with pedogenesis. Here the question would be how fast pedogenesis would react to climate change and how large would be the time lag with the production of ultrafine particles.
Thank you very much for your review. It is true that pedogenesis has a time lag in response to climate change. However, our data are insufficient to tell how long the time lag is, which requires more specific research.
External forcing factors:
Q4: The authors try to relate the observed changes in the Lake Ebinur sedimentary record to external climate forcings like greenhouse gases or total solar irradiance (TSI). They propose that the climate transition around 1920 AD was manly controlled by TSI. However, they do not provide any mechanistical model how TSI would influence the sediment deposition in Lake Ebinur. The identification of the TSI as the most important external factor is therefore based on weak scientific grounds.
Thank you very much for your kind reminding. In this study, the most important achievement is that we reveal the 1920 AD climate transition point through the multi-proxies record of the lake Ebinur sedimentary sequence. Then, we try to explore the main controlling factors of climate transition by comparing the external drivers (total solar irradiance, greenhouse gases, and volcanic eruption). The results show that the large increase of TSI in 1920 AD may be the main controlling factor of the climate transition. More simulation studies are needed to develop a mechanism model of how TSI would influence the sediment deposition in lake Ebinur.
Citation: https://doi.org/10.5194/cp-2022-92-AC4
-
AC4: 'Reply on RC3', Xiaotong Wei, 06 Mar 2023
Status: closed
-
RC1: 'Comment on cp-2022-92', Anonymous Referee #1, 23 Dec 2022
The manuscript by Wei et al. tries to use a sediment core from lake Ebinur in northwest China for paleoenvironmental reconstruction of the past ~200 years. For this purpose, the authors dated the record with 210Pb only, as 137Cs showed no activity. This was successful back to AD 1944 at 17.5 cm sediment depth while for the lower part a linear extrapolation was applied. Unfortunately, the authors do not provide any information how this was done. In my opinion this cannot be done as i) we usually have less compacted sediments in the upper part of sediment cores with a high sedimentation rate and ii) there is a change in lithology which the authors use for their environmental reconstruction. In addition to that, the authors give a basal age for the record of AD 1816. Such a precision seems to be impossible with a well dated record but for sure with such an approach. As there is still some Pb activity in the lower part of the dated record, the authors might want to continue measurements either to extent the chronology or to prove that there is no activity anymore.
For environmental reconstruction the authors used several methods. While some of the parameters might indeed be interpreted in the way it was done some can certainly not (especially the spectrophotometer data) and others miss explanation or evidence. I will try to explain that in the detailed comments below.
Although I am not a native speaker, I do have the feeling that the text also needs some language corrections, which might make it easier to read and understand.
Detailer comments:
- Line 29: 1819 --> This is an unrealistic age
- 73-74: tree-ring δD record from Kenya demonstrates that extreme drought in East Africa in the early 1920s --> What is the relation to China / this study?
- 138-139: The climate is generally characterized by warm-dry summers and cold wet winters --> If you can talk about wet conditions in this setting at all, this is not consistent with Fig. 2
- 195-197: The dry samples were weighed before and after carbonate removal, and the actual TOC values were obtained by converting the measured TOC values using the ratio of the mass before and after treatment. --> Why would you weigh them after carbonate removal? Is there some information missing?
- 220: using a linear extrapolation method --> I don’t know how this was done but I am sure that this cannot be done (see explanation above)
- 230-231: correlation coefficient (r2) --> This is not a correlation coefficient and needs more explanations
- 233: with over 60 % of the C value above 50 μm --> This needs more explanations
- 239: Thus, the sedimentary sequence can be divided into two units. --> How exactly did you determine the boundary of the units? This is very important as this is one of your major findings when this happened. According to some parameters the boundary could also be further downcore
- 240: Fig. 4b and c need more explanations
- 266-269: Correspondingly, the contents of TOC (0.25-0.34, mean 0.30) and TIC (1.91-2.95, mean 2.50) also showed strong fluctuations (Figs. 5m, 5n), which may have been influenced by strong wind activity during the cold period. --> How? What is the mechanism behind that?
- 270-271: In general, the ultrafine component (the grain size fraction of < 1 μm) is associated with pedogenesis and can be used as indicator of regional climate change --> this needs more explanation
- 272-274: In this unit, the proportion of ultrafine component is the highest in the whole sequence (1.7 %-10.2 %, mean 5.0 %), revealing the strongest pedogenesis in the study area --> This would imply that no soils have been present before modern soil formation and that soils formed are immediately removed. Have you considered soil erosion as one mechanism? This should be discussed
- 274-277: It is generally believed that pedogenesis is related to temperature and humidity (Sun et al., 2011). However, the temperature was lower and the wind speed was higher during 1816-1920 AD, so we considered that the strong pedogenesis during this period might be related to the high humidity. --> This is a lot of speculation. Especially if the comment above is considered
- 281-284: a* is usually affected by red minerals (e.g., hematite and goethite) and is thought to be associated with oxidation of sediments in arid region (Ji et al., 2005; Jiang et al., 2007). The high a* value (mean 0.76) in this unit indicates that more water vapor enhanced the oxidation during the cold period (Fig. 5l), thus providing more red minerals for the lake. --> Colors can react on various processes especially if you use dried samples. This is a lot of speculation and needs to be verified by further (mineralogical) analyses.
- 285-286: L* values within arid lakes are considered to reflect variations in the carbonate, and high L* values denote more carbonate content --> This can be the case – but it is certainly not the case here. In this case there should be a correlation between L* and TIC which is a much better carbonate indicator – which is not the case. In addition to that, why would you use an indirect indicator for carbonates if you have a direct one?
- 287-291: The L* value in this unit fluctuates between 73.2-76.1, with an average of 74.6 (Fig. 5k), which may be related to the changes of the lake water body. The cooling leads to weakening of evaporation and transpiration, and together with more water vapor from the westerlies (Guo et al., 2022), resulting in more water in the lake and more carbonate content. --> Wouldn’t you normally expect a higher carbonate content in more evaporative instead of less evaporative conditions? This needs more discussion
- 296: 816-1876 --> It is impossible to be this precise
- 305: a stable variation with slight fluctuations --> What is that?
- 308: EM2 --> Why are you putting so much emphasis on EM2? EM1 explains much more of the variation
- 310-311: This is probably duo to the decrease of the temperature gradient --> Between what?
- 313-314: the contents of TOC (0.25-0.32) and TIC (2.17-2.63) showed very slight fluctuations except for the top two points --> How do you interpret this?
- 316: revealing weaker pedogenesis --> Or transport?
- 316-319: The obvious decrease of a* value (mean 0.51) indicates the weakening of oxidation (Fig. 5l), which may be caused by reduced water vapor from westerly circulation and enhanced evaporation due to the increase in temperature. --> This is pure speculation as colors can be influenced by various factors
- 319-321: the relatively high L* value (mean 75.3) may be associated with an increase in summer glacial meltwater into the lake as a result of warming --> This needs to be explained
- However, the increase of L* value since 1955 AD may be related to the dramatic shrinkage of lake Ebinur by human activity --> How? This needs to be explained
- 324-326: unit 2 can be further divided into two sub-units according to the variation of all proxies: unit 2-a (24-16 cm, 1920-1955 AD) and unit 2-b (16-0 cm, 1955-2019 AD) (Figs. 5a-5n). --> Sorry, but I cannot see that. On what is it based?
- 330-334: The Y value of Sahu's formula is usually used to recognize the eolian environment, which is mainly determined by mean grain size, standard deviation, skewness, and kurtosis (Sahu, 1964). The Y values of all samples range from -19.5 to -7.6, lower than the threshold value of -2.74 (Fig. 7), supporting their windblown origin (Jiang et al., 2017b, 2022; Wei et al., 2021). --> This needs to go to the Results and Interpretation chapter
- 344-352: End-member simulations of all 96 grain size data show that there are two end member components in lake Ebinur sediments: 345 EM1 (~ 5.9 μm) and EM2 (~ 24.1 μm) (Fig. 4a). This is consistent with previous studies (Pye, 1987; Jiang et al., 2014; Wei et al., 2021), i.e., the fine particles (EM1) are transported by long distance high-altitude suspension and represent background deposition, while the coarse particles (EM2) are transported by short distance low-altitude and represent local and regional deposition. In addition, the EM2 component (~ 24.1 μm) shows a similar modal distribution with aeolian dust samples collected from the Ebinur drainage area (15-26 μm) (Ma et al., 2016), further supporting the possible transport mechanism model proposed by us. --> This also needs to go to the Results and Interpretation chapter
- 372-373: These two events (E1, E2) may be related to local strong wind events within the age error --> If you consider the error you should provide the error in your study. When did the local wins events occur? Can you integrate the wind data in Fig. 8?
- 389-391: These results are consistent with the cold-wet and warm-dry climate combinations revealed by Chen et al. (2010, 2015) in arid central Asia. --> No! There is an offset
- 391-393: Moreover, the lake Ebinur sedimentary record reveals that a climate transition around 1920 AD, the same as the reconstructed temperature records in China (Yang et al., 2002; Ge et al., 2013) --> No! This is a slow transition – not a shift as you are arguing
- 415-420: Fig. 9 --> If you want to compare this to your data, this should be included in Fig. 8
Considering all these weaknesses, which are sometimes not easy to overcome, I am afraid, but I have to recommend to reject this manuscript.
Citation: https://doi.org/10.5194/cp-2022-92-RC1 -
AC1: 'Reply on RC1', Xiaotong Wei, 10 Feb 2023
We are grateful to Reviewer 1 for giving us detailed comments to improve our manuscript. The responses to the comments from Reviewer 1 are addressed point by point as follows.
QI: The manuscript by Wei et al. tries to use a sediment core from lake Ebinur in northwest China for paleoenvironmental reconstruction of the past ~200 years. For this purpose, the authors dated the record with 210Pb only, as 137Cs showed no activity. This was successful back to AD 1944 at 17.5 cm sediment depth while for the lower part a linear extrapolation was applied. Unfortunately, the authors do not provide any information how this was done.
Thank you very much for your kind reminding. We established the chronology of core ABHHX mainly by the following methods:
1) For the upper part of the core, we calculated the ages of parallel cores ABH and ABHHX respectively based on the constant rate of supply (CRS) model of 210Pbex (formula (1)). The results show that the core ABH was dated at 16 cm to 1940 AD (Figure S1), and the bottom six data were discarded due to the abnormal deposition rate (Chen et al., 2006; Wei et al., 2021). Comparably, the core ABHHX calculated by the CRS model was dated at 18.5 cm to 1934 AD. The deposition rate of core ABHHX (2.18 mm yr-1) is closed to that of core ABH (2.03 mm yr-1) (Figure S1), so we consider it is reliable;
2) For the lower part of the core, we used a linear extrapolation method based on the following two reasons: a) the core ABHHX has a fine grain size (median grain size (Md): 5.4-9.9 μm, mean 7.0 μm) over the whole sequence; b) the core is only 48 cm long without distinct lithologic change. We performed a linear fit using the upper 210Pbex ages of the core ABHHX, and the correlation coefficient was as high as 0.95 (Figure S2). Based on the linear relationship, the age of the lower part of the core is extrapolated to establish the chronology of the whole sequence.
We have modified it, please see L.217-223, P.6.
Reference
Appleby, P.G. and Oldfield, F.: The calculation of lead-210 dates assuming a constant rate of supply of unsupported 210Pb to the sediment, Catena, 5, 1-8, https://doi.or g/10.1016/S0341-8162(78)80002-2, 1978.
Chen, F.H., Huang, X.Z., Zhang, J.W., Holmes, J.A., and Chen, J.H.: Humid Little Ice Age in arid central Asia documented by Bosten Lake, Xinjiang, China, Science in China Series D, 49(12): 1280-1290, https://doi.org/10.1007/s11430-006-2027-4, 2006.
Wei, X.T., Jiang, H.C., Xu, H.Y., Fan, J.W., Shi, W., Guo, Q.Q., and Zhang, S.Q.: Response of sedimentary and pollen records to the 1933 Diexi earthquake on the eastern Tibetan Plateau, Ecol. Indic., 129, 107887, https://doi.org/10.1016/j.ecoli nd.2021.107887, 2021.
Q2: In my opinion this cannot be done as i) we usually have less compacted sediments in the upper part of sediment cores with a high sedimentation rate and ii) there is a change in lithology which the authors use for their environmental reconstruction.
Thank you very much for your review. We believe that the method of establishing chronological sequence is feasible based on the following several points:
1) The core ABHHX is mainly composed of fine-grained sediments, and the median grain size (Md) varies from 5.4 μm to 9.9 μm with a mean value of 7.0 μm; and we think that the core deposition is near-continuous and homogeneous;
2) The core is very shallow, only 48 cm, and there is no distinct lithologic change; the core ABHHX shows homogeneous lithology, and the lower ages are derived by linear extrapolation from the upper 210Pb ages;
3) The dating of the upper core (~80 year) calculated by the 210Pb CRS model is reliable, for example, the events (E1 and E2) revealed by the sedimentary sequence can be compared with local strong wind events (Figure 8);
4) Based on downward extrapolation method, the climate changes over the past 200 years revealed by sedimentary sequence can be well contrasted regionally with previous climate records.
In addition, we did not use the change in lithology for environmental reconstruction.
Q3: In addition to that, the authors give a basal age for the record of AD 1816. Such a precision seems to be impossible with a well dated record but for sure with such an approach.
Thank you very much for your review. We believe that it is feasible to give a basal age of 1816 AD for the following points:
1) We think it's acceptable for most researchers to get a continuous record of age by linear extrapolation, and we're not the first to do it (Miao et al., 2003; Wang et al., 2006);
2) The age of upper core is controlled by 210Pb CRS model, and the results are reliable;
3) There is no obvious depositional discontinuity and distinct change in core lithology, so we believe that the deposition is continuous;
4) The climate changes and climate events revealed by our sedimentary sequence are well consistent with regional records (Figure 8);
5) Linear extrapolation requires a specific age in order to be plotted for comparative analysis.
Reference
Miao, Z., Mu, G.J., Yan, S., and Xie, H.Q.: Environmental Evolution of Aiby Lake Indicated by Ash core Sediment’s Information, Arid land Geography, 26, 5, 2003 (in Chinese).
Wang, R., Yang, X.D., and Zhu, L.P.: Environmental changes of Namu Co, Xizang during the past 200 years, 26(5): 791-798, 2006 (in Chinese).
Q4: As there is still some Pb activity in the lower part of the dated record, the authors might want to continue measurements either to extent the chronology or to prove that there is no activity anymore.
Thank you very much for your kind reminding. We tested 210Pb activity for the upper 20 cm of core ABH and core ABHHX, and the 210Pbex activity of core ABH is less than 0 at 19.5 cm (-5.26 Bq kg-1). Therefore, we believe that the core ABH has reached a stable state at 19 cm and is no activity anymore. According to the constant rate of supply (CRS) model, the core ABH was dated at 16 cm to 1940 AD, and the bottom six data were discarded (Figure S1) due to abnormal deposition rate (Chen et al., 2006; Wei et al, 2021). Comparably, the core ABHHX calculated by the CRS model was dated to at 18.5 cm 1934 AD. The deposition rate of core ABHHX (2.18 mm/yr) is close to that of core ABH (2.03 mm/yr) (Figure S1), so we consider the age of the upper core is reliable, and no further measurements are necessary.
Q5: For environmental reconstruction the authors used several methods. While some of the parameters might indeed be interpreted in the way it was done some can certainly not (especially the spectrophotometer data) and others miss explanation or evidence. I will try to explain that in the detailed comments below.
Thank you very much for your review. We will carefully respond to your detailed comments point by point as follows.
Q6: Although I am not a native speaker, I do have the feeling that the text also needs some language corrections, which might make it easier to read and understand.
Thank you very much for your kind reminding. We will make careful language corrections to the text.
Q7: Line 29: 1819 --> This is an unrealistic age
We believe that it is acceptable based on the following reasons:
1) The age of upper core is controlled by 210Pb CRS model, and the results are reliable;
2) The core ABHHX is mainly composed by fine-grained sediments (Md: 5.4-9.9 μm, mean 7.0 μm), and there is no obvious depositional discontinuity and distinct change in core lithology, indicating that the deposition is continuous and uniform. Therefore, we performed a linear extrapolation using the upper 210Pb ages, and the 48 cm core was dated back to 1816 AD;
3) The climate changes and climate events revealed by our sedimentary sequence are well consistent with regional records (Figure 8);
4) Linear extrapolation requires a specific age in order to be plotted for comparative analysis.
Q8: 73-74: tree-ring δD record from Kenya demonstrates that extreme drought in East Africa in the early 1920s --> What is the relation to China / this study?
We have modified it, please see L.71-74, P.2.
Q9: 138-139: The climate is generally characterized by warm-dry summers and cold wet winters --> If you can talk about wet conditions in this setting at all, this is not consistent with Fig. 2
We have modified it, please see L.136-137, P.4.
Q10: 195-197: The dry samples were weighed before and after carbonate removal, and the actual TOC values were obtained by converting the measured TOC values using the ratio of the mass before and after treatment. --> Why would you weigh them after carbonate removal? Is there some information missing?
According to the formula 2, the actual TOC values were calculated by multiplying the measured TOC values with the weight ratio of carbonate removed samples to unremoved samples (Fan et al., 2023). We have modified it, please see L.195-197, P.6.
Reference
Fan, J.W., Xu, H.Y., Jiang, H.C., Wei, X.T., Shi, W., Guo, Q.Q., Zhang, S.Q., Bai, X.Z., Liu, X.Q., and Xiao, J.L.:, Millennial- to centennial-scale anti-phase relationship between the Westerlies and the East Asian summer monsoon and its cultural response along the Silk Roads after a great earthquake in southern Altay ~ 3500 cal a BP, Journal of Quaternary Science, 38(1): 123-137, https://doi.org/10.1002/jqs.3468, 2023.
Q11: 220: using a linear extrapolation method --> I don’t know how this was done but I am sure that this cannot be done (see explanation above)
We believe that it is feasible to use a linear extrapolation method based on the following points:
1) We think it's acceptable for most researchers to get a continuous record of age by linear extrapolation, and we're not the first to do it (Miao et al., 2003; Wang et al., 2006);
2) The core ABHHX is mainly composed by fine-grained sediments (Md: 5.4-9.9 μm, mean 7.0 μm), and there is no obvious depositional discontinuity and distinct change in core lithology, indicating that the deposition is continuous and uniform;
3) The age of upper core is controlled by 210Pb CRS model, and the results are reliable;
4) Based on homogeneous lithology and uniform deposition of the core ABHHX, we performed a linear extrapolation using the upper 210Pbex ages, and the 48 cm core was dated back to 1816 AD.
Reference
Miao, Z., Mu, G.J., Yan, S., and Xie, H.Q.: Environmental Evolution of Aiby Lake Indicated by Ash core Sediment’s Information, Arid land Geography, 26, 5, 2003 (in Chinese).
Wang, R., Yang, X.D., and Zhu, L.P.: Environmental changes of Namu Co, Xizang during the past 200 years, 26(5): 791-798, 2006 (in Chinese).
Q12: 230-231: correlation coefficient (r2) --> This is not a correlation coefficient and needs more explanations
Done. Please see L.248-249, P.8.
Q13: 233: with over 60 % of the C value above 50 μm --> This needs more explanations
Here, we want to emphasize that ~ 60 % (29/48) of the samples have C values greater than 50 μm in the lower part of the sedimentary sequence. We have modified it, please see L.268, P.8.
Q14: 239: Thus, the sedimentary sequence can be divided into two units. --> How exactly did you determine the boundary of the units? This is very important as this is one of your major findings when this happened. According to some parameters the boundary could also be further downcore
We divided the whole sedimentary sequence into two units according to the following two points:
1) The grain size records show that the upper and lower parts of the sedimentary sequence have different characteristics of change with 1920 AD as the limit. The lower part is characterized by high-amplitude fluctuations and coarse grains (Md: 5.5-9.9 μm, mean 7.5 μm), and ~ 60 % of the samples have C values greater than 50 μm (Figures 6b, 6c), while the upper part has small fluctuations and finer grains (Md: 5.4-8.6 μm, mean 6.5 μm), and only ~ 20 % of the samples have C values exceeds 50 μm (Figures 6d, 6e);
2) Correspondingly, color reflectance (L*, a*) and carbon content (TOC, TIC) records also show different characteristics in the upper and lower parts with 1920 AD as the limit. For the lower part of the sequence, color reflectance (L*: 73.2-76.1, mean 74.6; a*: 0.4-1.0, mean 0.76) and carbon content (TOC: 0.22-0.43, mean 0.31; TIC: 1.91-2.95, mean 2.54) have large fluctuations (Figures 7k-7n). And for the upper part of the sequence, color reflectance (L*: 74.4-75.9., mean 75.3; a*: 0.2-0.7, mean 0.51) and carbon content (TOC: 0.25-0.32, mean 0.28; TIC: 2.17-2.63, mean 2.38) are characterized by small fluctuations except for the top two anomalies (Figures. 7k-7n).
We have modified it, please see L.265-278, P.8.
Q15: 240: Fig. 4b and c need more explanations
Done. Please see L.261-263, P.8.
Q16: 266-269: Correspondingly, the contents of TOC (0.25-0.34, mean 0.30) and TIC (1.91-2.95, mean 2.50) also showed strong fluctuations (Figs. 5m, 5n), which may have been influenced by strong wind activity during the cold period. --> How? What is the mechanism behind that?
Done. Please see L.317-319, P.10.
Q17: 270-271: In general, the ultrafine component (the grain size fraction of < 1 μm) is associated with pedogenesis and can be used as indicator of regional climate change --> this needs more explanation
The ultrafine component (the grain size fraction of < 1 μm) in aeolian sediments are formed during pedogenesis (Sun et al., 2006, 2011), which is usually influenced by chemical, biochemical and physical alterations closely connected with the local climate. For example, the pedogenesis in Chinese loess is closely connected with summer monsoonal precipitation (Sun et al., 2011). Sun et al (2011) has confirmed that the proportion of ultrafine components in loess strongly reflects the intensity of pedogenesis, and many researchers have used it as a proxy index to reveal climatic conditions in different periods (Wang et al., 2012; Jiang et al., 2023).
Reference
Jiang, H.C., Yin, Q.Z., Berger, A., Wei, L.H., Wu, Z.P., Wei, X.T., and Shi, W.: Orbitally and galactic cosmic forced abrupt climate events during the last glacial period, Quaternary Sci. Rev., 301, 107921, https://doi.org/10.1016/j.quascirev.2022.107921, 2023.
Sun, D.H.: Super-fine grain size components in Chinese loss and their palaeoclimatic implication, Quaternary Sciences, 26, 928-936, 2006 (in Chinese).
Sun, D.H., Su, R.X., Li, Z.J., and Lu, H.Y.: The ultrafine component in Chinese loess and its variation over the past 7-6 Ma: implications for the history of pedogenesis, Sedimentology, 58, 916-935, https://doi.org/10.1111/j.136 5-3091.2010.01189.x, 2011.
Wang, X., Sun, D.H., Wang, F., Li, B.F., and Wu, S.: The ultrafine component record from the late Cenozoic sequence in the central Tarim basin and its palaeoclimatic implications, Marine Geology and Quaternary Geology, 32(2): 143-151, https://doi.org/10.3724/SP.J.1140.2012.02143, 2012.
Q18: 272-274: In this unit, the proportion of ultrafine component is the highest in the whole sequence (1.7 %-10.2 %, mean 5.0 %), revealing the strongest pedogenesis in the study area --> This would imply that no soils have been present before modern soil formation and that soils formed are immediately removed. Have you considered soil erosion as one mechanism? This should be discussed
Ultrafine components in aeolian sediments are formed during pedogenesis and can be used to trace the history of regional pedogenesis (Sun et al., 2006, 2011). The ultrafine component exists not only in loess and paleosol, but also in some lake sediments in aeolian regions, which may be the product of pedogenesis on the surface in the catchment (Sun et al., 2006). The study area has strong wind conditions, and we cannot rule out that ultrafine component was transported to the lake within a short time after pedogenesis, which recorded the information of pedogenesis.
Reference
Sun, D.H.: Super-fine grain size components in Chinese loss and their palaeoclimatic implication, Quaternary Sciences, 26, 928-936, 2006 (in Chinese).
Sun, D.H., Su, R.X., Li, Z.J., and Lu, H.Y.: The ultrafine component in Chinese loess and its variation over the past 7-6 Ma: implications for the history of pedogenesis, Sedimentology, 58, 916-935, https://doi.org/10.1111/j.1 365-3091.2010.01189.x, 2011.
Q19: 274-277: It is generally believed that pedogenesis is related to temperature and humidity (Sun et al., 2011). However, the temperature was lower and the wind speed was higher during 1816-1920 AD, so we considered that the strong pedogenesis during this period might be related to the high humidity. --> This is a lot of speculation. Especially if the comment above is considered
We believe that the explanation given is acceptable based on the following several aspects:
1) The high proportion of ultrafine components reveals strong pedogenesis during the period of 1816-1920 AD, which is usually related to local temperature and humidity conditions;
2) During this period, the study area was in the cold Little Ice Age, which is supported by our multi-proxies records and previous climate records (Yang et al., 2002; Ge et al., 2013);
3) On this basis, we propose that the strong pedogenesis in this stage may be related to the high humidity condition (Wang et al., 2012), which is also supported by the previous research results: the westerlies brought more vapour to the arid central Asia during the cold LIA (Chen et al., 2010, 2015);
4) We acknowledge that this is speculation, but it is appropriate speculation based on data. So we think it is acceptable.
Reference
Chen, F.H., Chen, J.H., Holmes, J., Boomer, I., Austin, P., Gates, J.B., Wang, N.L., Brooks, S.J., and Zhang, J.W.: Moisture changes over the last millennium in arid central Asia: a review, synthesis and comparison with monsoon region, Quaternary Sci. Rev., 29, 1055-1068, https://doi.org/10.1016/j.quascirev.201 0.01.005, 2010.
Chen, J.H., Chen, F.H., Feng, S., Huang, W., Liu, J.B., and Zhou, A.F.: Hydroclimatic changes in China and surroundings during the Medieval Climate Anomaly and Little Ice Age: spatial patterns and possible mechanisms, Quaternary Sci. Rev., 107, 98-111, https://doi.org/10.1016/j.quascirev.2014.10.012, 2015.
Ge, Q., Hao, Z., Zheng, J., and Shao, X.: Temperature changes over the past 2000 yr in China and comparison with the Northern Hemisphere, Clim. Past, 9, 1153-1160, https://doi.org/10.5194/cp-9-1153-2013, 2013.
Wang, X., Sun, D.H., Wang, F., Li, B.F., and Wu, S.: The ultrafine component record from the late Cenozoic sequence in the central Tarim basin and its palaeoclimatic implications, Marine Geology and Quaternary Geology, 32(2): 143-151, https://doi.org/10.3724/SP.J.1140.2012.02143, 2012.
Yang, B., Braeuning, A., Johnson, K.R., and Shi, Y.F.: General characteristics of temperature variation in China during the last two millennia, Geophys. Res. Lett., 29, 38-1-38-4, https://doi.org/10.1029/2001GL014485, 2002.
Q20: 281-284: a* is usually affected by red minerals (e.g., hematite and goethite) and is thought to be associated with oxidation of sediments in arid region (Ji et al., 2005; Jiang et al., 2007). The high a* value (mean 0.76) in this unit indicates that more water vapor enhanced the oxidation during the cold period (Fig. 5l), thus providing more red minerals for the lake. --> Colors can react on various processes especially if you use dried samples. This is a lot of speculation and needs to be verified by further (mineralogical) analyses.
Thank you very much for your review. We believe that this explanation is credible based on the following several reasons:
1) We carried out color reflectance experiments on all samples, following the treatment method proposed by Jiang et al (2023). The results of such experiments can be successfully applied to reveal past climate change;
2) a* in sediment is related primarily to iron oxide mineral concentrations in arid region, especially hematite and goethite (Ji et al., 2002). The stronger the oxidation, the more red minerals are produced and the higher a* value;
3) Redness records from lake Qinghai show that increased precipitation enhances regional oxidation, producing more red minerals, and a* value increases (Ji et al., 2005).
In summary, we propose that the high a* value indicates that more water vapor enhanced the oxidation during the period 1816-1920 AD.
Reference
Ji, J.F., Balsam, W.L., Chen, J., and Liu, L.W.: Rapid and precise measurement of hematite and goethite concentrations in the Chinese loess sequences by diffuse reflectance spectroscopy, Clays and Clay Minerals, 50(2): 208-216, https://doi.org/10.1346/000986002760832801, 2002.
Ji, J.F., Shen, J., Balsam, W., Chen, J., Liu, L.W., and Liu, X.Q.: Asian monsoon oscillations in the northeastern Qinghai–Tibet Plateau since the late glacial as interpreted from visible reflectance of Qinghai Lake sediments, Earth Planet. Sc. Lett, 233, 61-70, https://doi.org/10.1016/j.epsl.2005.02.025, 2005.
Jiang, H.C., Yin, Q.Z., Berger, A., Wei, L.H., Wu, Z.P., Wei, X.T., and Shi, W.: Orbitally and galactic cosmic forced abrupt climate events during the last glacial period, Quaternary Sci. Rev., 301, 107921, https://doi.org/10.1016/j.quascirev.2022.107921, 2023.
Q21: 285-286: L* values within arid lakes are considered to reflect variations in the carbonate, and high L* values denote more carbonate content --> This can be the case – but it is certainly not the case here. In this case there should be a correlation between L* and TIC which is a much better carbonate indicator – which is not the case. In addition to that, why would you use an indirect indicator for carbonates if you have a direct one?
Thank you very much for your review. We believe that it is more reliable to reveal the environmental changes in arid areas by integrating the changes of multi-proxies. And it is not the first time that L* has been used to reveal carbonate changes (Xiao et al., 2006; Jiang et al., 2008). In our records, the L* and TIC show similar variations: they show large-amplitude fluctuations in the early period (1816-1920 AD) and more stable in the late period (1920-2019 AD).
Reference
Xiao, J.L., Wu, J.T., Si, B., Liang, W.D., Nakamura, T., Liu, B.L., and Inouchi, Y.: Holocene climate changes in the monsoon/arid transition reflected by carbon concentration in Daihai Lake of Inner Mongolia, The Holocene, 16, 551-560, https://doi.org/10.1191/0959683606hl950rp, 2006.
Jiang, H.C., Ji, J.L., Gao, L., Tang, Z.H., and Ding, Z.L.: Cooling-driven climate change at 12-11 Ma: Multiproxy records from a long fluviolacustrine sequence at Guyuan, Ningxia, China, Palaeogeogr. Palaeocl., 265, 148-158, https://doi.org/10.1016/j.palaeo.2008.05.006, 2008.
Q22: 287-291: The L* value in this unit fluctuates between 73.2-76.1, with an average of 74.6 (Fig. 5k), which may be related to the changes of the lake water body. The cooling leads to weakening of evaporation and transpiration, and together with more water vapor from the westerlies (Guo et al., 2022), resulting in more water in the lake and more carbonate content. --> Wouldn’t you normally expect a higher carbonate content in more evaporative instead of less evaporative conditions? This needs more discussion
Yes, in general, high carbonate content occurs under conditions of more evaporation. However, carbonates cannot be deposited without water in arid areas, because they are deposited in lakes. The cooling leads to weakening of evaporation and transpiration, and a relative increase in water vapor, which makes it possible to develop lakes that produce more carbonate (Guo et al., 2022). Evaporation and transpiration change with seasonal temperatures fluctuates.
Reference
Guo, Q.Q., Jiang, H.C., Fan, J.W., Li, Y.M., Shi, W., Zhang, S.Q., and Wei, X.T.: Strongest chemical weathering in response to the coldest period in Guyuan, Ningxia, China, during 14-11 Ma, Plos One, 17, e0268195, https://doi.org/10.137 1/journal.pone.0268195, 2022.
Q23: 296: 816-1876 --> It is impossible to be this precise
Sorry, we believe that this precise is acceptable according to the following four points:
1) The age of upper core is controlled by 210Pb CRS model, and the results are reliable;
2) The core ABHHX is mainly composed of fine-grained sediments (Md: 5.4-9.9 μm, mean 7.0 μm) and there is no obvious depositional discontinuity and distinct change in core lithology lithologic change, indicating that the deposition is continuous and uniform. Therefore, we performed a linear extrapolation using the upper 210Pb ages, and the 48 cm core was dated back to 1816 AD;
3) The climate changes and climate events revealed by our sedimentary sequence are well consistent with regional records (Figure 8);
4) Linear extrapolation requires a specific age in order to be plotted for comparative analysis.
Q24: 305: a stable variation with slight fluctuations --> What is that?
Done. Please see L.336, P.10.
Q25: 308: EM2 --> Why are you putting so much emphasis on EM2? EM1 explains much more of the variation
Here, we emphasize that EM2 changes are based on the following two reasons:
1) The whole sedimentary sequence is composed of two end-members (EM1 and EM2). EM1 (the fine particles) represents background deposition that transported by long distance high-altitude suspension, while EM2 (the coarse particles) represents local and regional deposition that transported by short distance low-altitude;
2) In the process of lake deposition, the coarse particles (EM2) are deposited first, followed by fine particles (EM1). In other words, the percentage content of EM1 is determined by the change of EM2. Therefore, EM2 has more important environmental information, reflecting the regional and local provenance supply.
Q26: 310-311: This is probably duo to the decrease of the temperature gradient --> Between what?
Thank you very much for your kind reminding. The temperature gradient here refers to the temperature gradient between March and August. The lake Ebinur area has the strongest wind transport conditions and the highest temperatures during March to August (Ge et al., 2016). The temperature gradient decreases with increasing temperatures since 1920 AD, resulting in the weakening of wind intensity and the decrease of coarse particles transported at low altitude and short distance.
We have modified it, please see L.342, P.10.
Reference
Ge, Y.X., Abuduwaili, J., Ma, L., Wu, N., and Liu, D.W.: Potential transport pathways of dust emanating from the playa of Ebinur Lake, Xinjiang, in arid northwest China, Atmos. Res., 178-179, 196-206, https://doi.org/10.1016/j.atmosres.2016.0 4.002, 2016.
Q27: 313-314: the contents of TOC (0.25-0.32) and TIC (2.17-2.63) showed very slight fluctuations except for the top two points --> How do you interpret this?
Done. Please see L.353-355, P.11.
Q28: 316: revealing weaker pedogenesis --> Or transport?
Done. Please see L.346, P.11.
Q29: 316-319: The obvious decrease of a* value (mean 0.51) indicates the weakening of oxidation (Fig. 5l), which may be caused by reduced water vapor from westerly circulation and enhanced evaporation due to the increase in temperature. --> This is pure speculation as colors can be influenced by various factors
Sorry, we think that this explanation is acceptable based on the following several reasons:
1) a* in sediment is related primarily to iron oxide mineral concentrations in arid region, especially hematite and goethite (Ji et al., 2002). The stronger the oxidation, the more red minerals are produced and the higher a* value, and vice versa;
2) Redness records from lake Qinghai show that high a* values indicate increased precipitation, while low a* values reflect more arid climatic conditions (Ji et al., 2005).
In summary, we give this explanation: as the temperatures rises, the water vapor brought by the westerly circulation decreases, and the evaporation is enhanced, resulting in the weakening of oxidation and the decrease of a* values.
Reference
Ji, J.F., Balsam, W.L., Chen, J., and Liu, L.W.: Rapid and precise measurement of hematite and goethite concentrations in the Chinese loess sequences by diffuse reflectance spectroscopy, Clays and Clay Minerals, 50(2): 208-216, https://doi.org/10.1346/000986002760832801, 2002.
Ji, J.F., Shen, J., Balsam, W., Chen, J., Liu, L.W., and Liu, X.Q.: Asian monsoon oscillations in the northeastern Qinghai–Tibet Plateau since the late glacial as interpreted from visible reflectance of Qinghai Lake sediments, Earth Planet. Sc. Lett, 233, 61-70, https://doi.org/10.1016/j.epsl.2005.02.025, 2005.
Q30: 319-321: the relatively high L* value (mean 75.3) may be associated with an increase in summer glacial meltwater into the lake as a result of warming --> This needs to be explained
Water is needed to deposit carbonate in arid areas, and in extremely arid lakes, high carbonate content occur in environments with more water. Higher L* values reflecting carbonate content indicate more water, which may be associated with an increase in summer glacial meltwater caused by warming into the lake. In summer, the lake Ebinur area has a stronger evaporation, the increased glacial meltwater provides favorable conditions for carbonates production.
Q31: However, the increase of L* value since 1955 AD may be related to the dramatic shrinkage of lake Ebinur by human activity --> How? This needs to be explained
Done. Please see L.351-352, P.11.
Q32: 324-326: unit 2 can be further divided into two sub-units according to the variation of all proxies: unit 2-a (24-16 cm, 1920-1955 AD) and unit 2-b (16-0 cm, 1955-2019 AD) (Figs. 5a-5n). --> Sorry, but I cannot see that. On what is it based?
Thank you very much for your review. We consider that unit 2 can be further divided into two sub-units mainly based on the following several aspects:
1) Bounded by 1955 AD, grain size records for the lower part of unit 2 show a trend to coarser trend (Md: 5.8-7.9 μm, mean 6.9 μm), while the upper part shows a trend to finer (Md: 5.4-8.6 μm, mean 6.4 μm) (Figures 7a-7g);
2) Correspondingly, the lower part of unit 2 has lower L* value (74.5-75.5, mean: 75.1) and higher a* value (0.4-0.7, mean 0.55), while the upper part has higher L* value (74.4-76.7, mean: 75.4) and lower a* value (0.2-0.8, mean: 0.49) (Figures 7k, 7l);
3) The total organic carbon (TOC) in the lower part of unit 2 shows a decreasing trend, while the upper part shows a fluctuation.
Q33: 330-334: The Y value of Sahu's formula is usually used to recognize the eolian environment, which is mainly determined by mean grain size, standard deviation, skewness, and kurtosis (Sahu, 1964). The Y values of all samples range from -19.5 to -7.6, lower than the threshold value of -2.74 (Fig. 7), supporting their windblown origin (Jiang et al., 2017b, 2022; Wei et al., 2021). --> This needs to go to the Results and Interpretation chapter
Done. Please see L.231-236, P.7.
Q34: 344-352: End-member simulations of all 96 grain size data show that there are two end member components in lake Ebinur sediments: 345 EM1 (~ 5.9 μm) and EM2 (~ 24.1 μm) (Fig. 4a). This is consistent with previous studies (Pye, 1987; Jiang et al., 2014; Wei et al., 2021), i.e., the fine particles (EM1) are transported by long distance high-altitude suspension and represent background deposition, while the coarse particles (EM2) are transported by short distance low-altitude and represent local and regional deposition. In addition, the EM2 component (~ 24.1 μm) shows a similar modal distribution with aeolian dust samples collected from the Ebinur drainage area (15-26 μm) (Ma et al., 2016), further supporting the possible transport mechanism model proposed by us. --> This also needs to go to the Results and Interpretation chapter
Done. Please see L.249-257, P.8.
Q35: 372-373: These two events (E1, E2) may be related to local strong wind events within the age error --> If you consider the error you should provide the error in your study. When did the local wins events occur? Can you integrate the wind data in Fig. 8?
Done. Please see Figure 8 and L.379-381, P.11.
Q36: 389-391: These results are consistent with the cold-wet and warm-dry climate combinations revealed by Chen et al. (2010, 2015) in arid central Asia. --> No! There is an offset
Our multi-proxies reveal a relatively cold and wet climate from 1816 AD to 1920 AD and a relatively warm and dry climate from 1920 AD to 2019 AD in the lake Ebinur region. This is consistent with the cold-wet and warm-dry climate combinations in arid central Asia revealed by Chen et al (2010, 2015), for example, the dry MCA and wet LIA. Although the humidity in Central Asia has been increasing with global warming in recent decades (Chen et al., 2010, 2015), as shown in figure 4 from Chen et al (2010): the early period (1816-1920 AD) had a wetter climate than the later period (1920-2019 AD).
Reference
Chen, F.H., Chen, J.H., Holmes, J., Boomer, I., Austin, P., Gates, J.B., Wang, N.L., Brooks, S.J., and Zhang, J.W.: Moisture changes over the last millennium in arid central Asia: a review, synthesis and comparison with monsoon region, Quaternary Sci. Rev., 29, 1055-1068, https://doi.org/10.1016/j.quascirev.201 0.01.005, 2010.
Chen, J.H., Chen, F.H., Feng, S., Huang, W., Liu, J.B., and Zhou, A.F.: Hydroclimatic changes in China and surroundings during the Medieval Climate Anomaly and Little Ice Age: spatial patterns and possible mechanisms, Quaternary Sci. Rev., 107, 98-111, https://doi.org/10.1016/j.quascirev.2014.10.012, 2015.
Q37: 391-393: Moreover, the lake Ebinur sedimentary record reveals that a climate transition around 1920 AD, the same as the reconstructed temperature records in China (Yang et al., 2002; Ge et al., 2013) --> No! This is a slow transition – not a shift as you are arguing
Our multi-proxies records show a clear transition in climate around 1920 AD: from a relatively cold and wet period (1816-1920 AD) to a relatively warm and dry period (1920-2019 AD). And Yang et al (2002) and Ge et al (2013) propose that China’s LIA ended in 1920 AD by synthesizing various paleoclimatic records, and since then the climate has entered a warm period. These two are consistent. The reason why the transition in our record occurred sharply may be due to the fact that lake Ebinur is located in the arid Central Asia, where extreme drought makes it sensitive to warming responses (Huang et al., 2017; Yao et al., 2022).
Reference
Ge, Q., Hao, Z., Zheng, J., and Shao, X.: Temperature changes over the past 2000 yr in China and comparison with the Northern Hemisphere, Clim. Past, 9, 1153-1160, https://doi.org/10.5194/cp-9-1153-2013, 2013.
Huang, W., Chang, S.Q., Xie, C.L., and Zhang, Z.P.: Moisture sources of extreme summer precipitation events in North Xinjiang and their relationship with atmospheric circulation, Advances in Climate Change Research, 8, 12-17, https:/ /doi.org/10.1016/j.accre.2017.02.001, 2017.
Yang, B., Braeuning, A., Johnson, K.R., and Shi, Y.F.: General characteristics of temperature variation in China during the last two millennia, Geophys. Res. Lett., 29, 38-1-38-4, https://doi.org/10.1029/2001GL014485, 2002.
Yao, J.Q., Chen, Y.N., Guan, X.F., Zhao, Y., Chen, J., and Mao, W.Y.: Recent climate and hydrological changes in a mountain–basin system in Xinjiang, China, Earth-Sci. Rev., 226, 103957, https://doi.org/10.1016/j.earscirev.2022.103957, 2022.
Q38: 415-420: Fig. 9 --> If you want to compare this to your data, this should be included in Fig. 8
Thank you very much for your review. In figure 8, we identified the time point of the climate transition over the past 200 years — 1920 AD, mainly through the multi-proxies records of lake Ebinur sedimentary sequence. In order to further discuss the main controlling factors of climate transition, we compare the changes of solar radiation, volcanic activity, and the concentrations of greenhouse gases in figure 9. If all the data in figure 9 were put into figure 8, it will be too crowded to properly represent the signal.
-
EC1: 'Comment on cp-2022-92', Pierre Francus, 11 Jan 2023
Dear authors,
I read your paper and the comments of Reviewer 1.
I find reviewer 1 comments very pertinent, and they should be addressed in a reply in the open discussion.I would like to raise some additional issues that you also should consider in another reply in the discussion.
The location of the cores, close to the shore and at a water depth of only 0.8 m, makes them sensitive to wave action and remobilization of sediment, especially in a region where wind is so strong. Moreover, since the lake is a closed system, it is sensitive to water level fluctuations that could completely change the sedimentary context and processes at the location of the cores. Actually, you mention in the paper that the lake experienced lake level fluctuation. Therefore, I’m not convinced that the sedimentation has been continuous, and is without a hiatus, or major perturbations. The fact that there is no 137 Cs peak is another clue that the sedimentary archive is not pristine.
In this context, retrieving complete cores (not sliced in the field) and looking at facies at the microscopic scale is mandatory to be able to decipher sedimentary processes and demonstrate the continuity of this archive.I also agree that the age model is weak, and not accurate enough to be able to claim that you can make a reconstruction with a 2-year resolution.
I agree with Reviewer 1 that interpretations of colour reflectance, carbon content are speculative. For instance, I doubt it is possibly derived transport condition from C-content (in reference to “In the early period (1816-1876 AD), the high C values indicate strong transport dynamics; the high proportion of ultrafine component indicates strong pedogenesis, combined with high organic carbon content and high a* values, it is inferred that the water vapor content is relatively higher.”
Reflectance values are also influenced by changes in oxygen content below the water/sediment interface (i.e., the redox front), and this is making your reflectance interpretation even weaker.Interpretation of grain-size data also remains speculative: “ultrafine components” can also be observed in permafrost lakes and peat as sources for higher TOC. The colour reflectance can neither tell us something about transport nor about water vapour even in combination with GSD and C.
I’m still waiting for a second review of your paper, but I encourage you to already tell in a reply if you will be able to address reviewer 1 and my comments, and if yes, how ?
Thank you in advance and best regards,
Pierre Francus,
Handling editorCitation: https://doi.org/10.5194/cp-2022-92-EC1 -
AC2: 'Reply on EC1', Xiaotong Wei, 10 Feb 2023
We are grateful to editor for giving us comments to improve our manuscript. And we have responded to reviewer 1's comments in AC1. The responses to the comments from editor are addressed point by point as follows.
Comments
QI: The location of the cores, close to the shore and at a water depth of only 0.8 m, makes them sensitive to wave action and remobilization of sediment, especially in a region where wind is so strong. Moreover, since the lake is a closed system, it is sensitive to water level fluctuations that could completely change the sedimentary context and processes at the location of the cores. Actually, you mention in the paper that the lake experienced lake level fluctuation. Therefore, I’m not convinced that the sedimentation has been continuous, and is without a hiatus, or major perturbations. The fact that there is no 137Cs peak is another clue that the sedimentary archive is not pristine.
Thank you very much for your kind reminding. We believe that the sedimentation has been continuous for the following reasons:
1) The core ABHHX is mainly composed of fine-grained sediments, and the median grain size (Md) only varies from 5.4 μm to 9.9 μm with a mean value of 7.0 μm; and we think of deposition as continuous and at a uniform rate;
2) The core is very shallow, only 48 cm, and there is no obvious depositional discontinuity and distinct change in core lithology, which is also supported by our multi-proxies records;
3) The 210Pb activity of the two cores shows obvious exponential decay and the dating results compare well, supporting the continuity of the sequence;
4) The 137Cs activity of both cores is 0, which may be related to the rapid decay and downward migration of 137Cs (Xiang, 1995; Gao et al., 2021).
Reference
Gao, S.P., Wang, J.B., Xu, B.Q., and Zhang, X.L.: Application and problems of 210Pb and 137Cs dating techniques in lake sediments, J. Lake Sci., 33, 622-631, http s://doi.org/10.18307/2021.0226, 2021 (in Chinese).
Xiang, L.: Limitations of the application of 137Cs limnochronology: A case study of 137Cs profile in Crawford lake sediment, J. Lake Sci., 7, 307-313, https://doi.org/10.18307/1995.0403, 1995 (in Chinese)
Q2: In this context, retrieving complete cores (not sliced in the field) and looking at facies at the microscopic scale is mandatory to be able to decipher sedimentary processes and demonstrate the continuity of this archive.
Yes, careful observation of sedimentary facies at the microscopic scale is very important to demonstrate the continuity of the archive. We have observed the lithofacies carefully during the process of field sampling, but no depositional discontinuity and distinct change of lithofacies have been found. In addition, the sediments of the whole sequence are fine and mainly composed of clayey silt (Md: 5.4-9.9 μm, mean 7.0 μm), which also supports the continuity of this archive.
Q3: I also agree that the age model is weak, and not accurate enough to be able to claim that you can make a reconstruction with a 2-year resolution.
Thank you very much for your review. We believe that it is acceptable based on the following reasons:
1) The age of the upper core was determined by 210Pb CRS model from two parallel cores and compares well. Furthermore, the events (E1 and E2) revealed by the sedimentary sequence can be compared with local strong wind events, and so we consider the results are reliable;
2) The core ABHHX is mainly composed by fine-grained sediments (Md: 5.4-9.9 μm, mean 7.0 μm), and there is no obvious depositional discontinuity and distinct change in core lithology, indicating that the deposition is continuous and uniform. Therefore, we performed a linear extrapolation using the upper 210Pb ages, and the 48 cm core was dated back to 1816 AD;
3) The climate changes revealed by our sedimentary sequence are well consistent with regional records (Figure 8).
Q4: I agree with Reviewer 1 that interpretations of colour reflectance, carbon content are speculative. For instance, I doubt it is possibly derived transport condition from C-content (in reference to “In the early period (1816-1876 AD), the high C values indicate strong transport dynamics; the high proportion of ultrafine component indicates strong pedogenesis, combined with high organic carbon content and high a* values, it is inferred that the water vapor content is relatively higher.”
We consider the explanation given is acceptable according to the following points:
1) The analysis of C-M diagrams is useful to interpret sediment transport dynamics, and C is the coarsest percentile of the grain-size distribution in samples (one percentile), representing the maximum transport capacity (Passega, 1957; Singh et al., 2007). The high C values indicate strong transport dynamics (Wei et al., 2021; Shi et al., 2022);
2) The ultrafine component (the grain size fraction of < 1 μm) in aeolian sediments are formed during pedogenesis (Sun et al., 2006, 2011), which is usually influenced by chemical, biochemical and physical alterations closely connected with the local climate. Sun et al (2011) has confirmed that the proportion of ultrafine component strongly reflects the intensity of pedogenesis, and the high proportion of ultrafine component indicates strong pedogenesis;
3) The total organic carbon (TOC) content in lake sediments in arid region can reflect the regional humidity, and more moisture is conducive to the formation of organic matter in lakes (Jiang et al., 2008). a* in sediment is related primarily to iron oxide mineral concentrations in arid region, especially hematite and goethite (Ji et al., 2002), and high a* values occur under strong oxidation conditions. Redness records from lake Qinghai show that high a* values indicate increased precipitation (Ji et al., 2005). Combined with high TOC content and high a* values, we think that the water vapor content is relatively higher.
Reference
Ji, J.F., Balsam, W.L., Chen, J., and Liu, L.W.: Rapid and precise measurement of hematite and goethite concentrations in the Chinese loess sequences by diffuse reflectance spectroscopy, Clays and Clay Minerals, 50(2): 208-216, https://doi.org/10.1346/000986002760832801, 2002.
Ji, J.F., Shen, J., Balsam, W., Chen, J., Liu, L.W., and Liu, X.Q.: Asian monsoon oscillations in the northeastern Qinghai–Tibet Plateau since the late glacial as interpreted from visible reflectance of Qinghai Lake sediments, Earth Planet. Sc. Lett, 233, 61-70, https://doi.org/10.1016/j.epsl.2005.02.025, 2005.
Jiang, H.C., Ji, J.L., Gao, L., Tang, Z.H., and Ding, Z.L.: Cooling-driven climate change at 12-11 Ma: Multiproxy records from a long fluviolacustrine sequence at Guyuan, Ningxia, China, Palaeogeogr. Palaeocl., 265, 148-158, https://doi.org/10.1016/ j.palaeo.2008.05.006, 2008.
Passega, R.: Texture as characteristic of clastic deposition, Bull. Amer. Assoc. Petrol. Geol., 41, 1952-1984, https://doi.org/10.1306/0BDA594E-16BD-11D7-8645000102C1865D, 1957.
Shi, W., Jiang, H.C., Xu, H.Y., Ma, S.Y., Fan, J.W., Zhang, S.Q., Guo, Q.Q., and Wei, X.T.: Response of modern fluvial sediments to regional tectonic activity along the upper Min River, eastern Tibet, Earth Surf. Dynam., 10, 1195-1209, https://doi.org/10.5194/esurf-10-1195-2022, 2022.
Singh, M., Singh, I. B., and Müller, G.: Sediment characteristics and transportation dynamics of the Ganga River, Geomorphology, 86, 144-175, https://doi.org/10.1016/j.geomorph.2006.08.011, 2007.
Sun, D.H.: Super-fine grain size components in Chinese loss and their palaeoclimatic implication, Quaternary Sciences, 26, 928-936, 2006 (in Chinese).
Sun, D.H., Su, R.X., Li, Z.J., and Lu, H.Y.: The ultrafine component in Chinese loess and its variation over the past 7-6 Ma: implications for the history of pedogenesis, Sedimentology, 58, 916-935, https://doi.org/10.1111/j.136 5-3091.2010.01189.x, 2011.
Wei, X.T., Jiang, H.C., Xu, H.Y., Fan, J.W., Shi, W., Guo, Q.Q., and Zhang, S.Q.: Response of sedimentary and pollen records to the 1933 Diexi earthquake on the eastern Tibetan Plateau, Ecol. Indic., 129, 107887, https://doi.org/10.1016/j.ecoli nd.2021.107887, 2021.
Q5: Reflectance values are also influenced by changes in oxygen content below the water/sediment interface (i.e., the redox front), and this is making your reflectance interpretation even weaker.
Yes, color reflectance values are also influenced by changes in oxygen content below the water/sediment interface. However, we consider that the main controlling factor is the change of regional water vapor, which strongly affects the redox reaction of the sediments and thus changes the color reflectance values. In addition, the increase in water vapor during 1816-1920 AD revealed by color reflectance values is also supported by a high TOC content, which is consistent with previous findings (Chen et al., 2010, 2015)。
Reference
Chen, F.H., Chen, J.H., Holmes, J., Boomer, I., Austin, P., Gates, J.B., Wang, N.L., Brooks, S.J., and Zhang, J.W.: Moisture changes over the last millennium in arid central Asia: a review, synthesis and comparison with monsoon region, Quaternary Sci. Rev., 29, 1055-1068, https://doi.org/10.1016/j.quascirev.201 0.01.005, 2010.
Chen, J.H., Chen, F.H., Feng, S., Huang, W., Liu, J.B., and Zhou, A.F.: Hydroclimatic changes in China and surroundings during the Medieval Climate Anomaly and Little Ice Age: spatial patterns and possible mechanisms, Quaternary Sci. Rev., 107, 98-111, https://doi.org/10.1016/j.quascirev.2014.10.012, 2015.
Q6: Interpretation of grain-size data also remains speculative: “ultrafine components” can also be observed in permafrost lakes and peat as sources for higher TOC. The colour reflectance can neither tell us something about transport nor about water vapour even in combination with GSD and C.
We believe that the interpretation of grain-size data is acceptable for several points:
1) Ultrafine components in aeolian sediments are formed during pedogenesis and can be used to trace the history of regional pedogenesis (Sun et al., 2006, 2011). The ultrafine component exists not only in loess and paleosol, but also in some lake sediments in aeolian regions, which may be the product of pedogenesis on the surface in the catchment (Sun et al., 2006);
2) There is no correlation between the proportion of ultrafine component and TOC content in our records, so we think that ultrafine component may only represent the pedogenesis in the catchment;
3) C-M diagrams can be used to interpret sediment transport dynamics, and C is the coarsest percentile of the grain-size distribution in samples (one percentile), representing the maximum transport capacity (Passega, 1957; Singh et al., 2007). The high C values indicate strong transport dynamics (Wei et al., 2021; Shi et al., 2022);
4) We combined the changes of color reflectance and TOC content to reveal the regional moisture, but not transport process. The high humidity revealed by our multi-proxies is consistent with regional records during 1816-1920 AD (Chen et al. 2006, 2010).
Reference
Chen, F.H., Huang, X.Z., Zhang, J.W., Holmes, J.A., and Chen, J.H.: Humid Little Ice Age in arid central Asia documented by Bosten Lake, Xinjiang, China, Sci. China Ser. D, 49, 1280-1290, https://doi.org/10.1007/s11430-006-2027-4, 2006.
Chen, F.H., Chen, J.H., Holmes, J., Boomer, I., Austin, P., Gates, J.B., Wang, N.L., Brooks, S.J., and Zhang, J.W.: Moisture changes over the last millennium in arid central Asia: a review, synthesis and comparison with monsoon region, Quaternary Sci. Rev., 29, 1055-1068, https://doi.org/10.1016/j.quascirev.2010.01.005, 2010.
Passega, R.: Texture as characteristic of clastic deposition, Bull. Amer. Assoc. Petrol. Geol., 41, 1952-1984, https://doi.org/10.1306/0BDA594E-16BD-11D7-8645000102C1865D, 1957.
Shi, W., Jiang, H.C., Xu, H.Y., Ma, S.Y., Fan, J.W., Zhang, S.Q., Guo, Q.Q., and Wei, X.T.: Response of modern fluvial sediments to regional tectonic activity along the upper Min River, eastern Tibet, Earth Surf. Dynam., 10, 1195-1209, https://doi.org/10.5194/esurf-10-1195-2022, 2022.
Singh, M., Singh, I. B., and Müller, G.: Sediment characteristics and transportation dynamics of the Ganga River, Geomorphology, 86, 144-175, https://doi.org/10.1016/j.geomorph.2006.08.011, 2007.
Sun, D.H.: Super-fine grain size components in Chinese loss and their palaeoclimatic implication, Quaternary Sciences, 26, 928-936, 2006 (in Chinese).
Sun, D.H., Su, R.X., Li, Z.J., and Lu, H.Y.: The ultrafine component in Chinese loess and its variation over the past 7-6 Ma: implications for the history of pedogenesis, Sedimentology, 58, 916-935, https://doi.org/10.1111/j.1 365-3091.2010.01189.x, 2011.
Wei, X.T., Jiang, H.C., Xu, H.Y., Fan, J.W., Shi, W., Guo, Q.Q., and Zhang, S.Q.: Response of sedimentary and pollen records to the 1933 Diexi earthquake on the eastern Tibetan Plateau, Ecol. Indic., 129, 107887, https://doi.org/10.1016/j.ecolind.2021.107887, 2021.
Citation: https://doi.org/10.5194/cp-2022-92-AC2
-
AC2: 'Reply on EC1', Xiaotong Wei, 10 Feb 2023
-
RC2: 'Comment on cp-2022-92', Anonymous Referee #2, 23 Feb 2023
Dear Editor and Authors of the manuscript "Climate transition over 1 the past two centuries revealed by lake Ebinur in Xinjiang, northwest China",
Thank you for considering me to read this article and to be part of the process. Below, I am sending the revisions of the manuscript.
Sincerely,
General comments
In this manuscript, the authors provide a multiproxy study of a short sediment core from a shallow terminal lake in a climate-sensitive arid area. This record includes a significant number of variables, mainly based on particle size parameters, that can be linked to recent paleoenvironmental changes.
I read carefully the manuscript, and I was also able to read the discussion, the comments and their responses. Based on this information, I agree with the comments of the Editor and Referee 1 concerning the problems in the chronological model (I provide more details in the comments below). Unfortunately, I do not see that the authors provided enough evidence in their relplies to support the model. This is a major obstacle to be addressed when the goal of the paper is to provide a high temporal resolution of the sequence in order to determine the exact year of a climate shift. As another related issue, it is difficult to understand the criteria for the separation of units and subunits, and thus, the exact point of the sedimentation changes. It also surprises me that the changes on the lake area and water discharges during the deposition of this sequence are completely ignored in the discussion in the shallow lake sedimentation processes. Finally, I suggest to revise the organization of the manuscript separating the data from interpretation, and discussions, following a clear and logical order, and to provide better explanation of the figures.
Considering that some of the mentioned points intefere with the goals and the precision proposed in this work, my suggestion is to reject the manuscript. I hope that the authors can think about a solution to the main problems (maybe adding marker layers to the model),or to consider a different approach, to send the new manuscript using this valuable data.
Specific comments
128-130. The climate of the study region is mainly dominated by westerlies and is a typical temperate continental climate, which is characterized by low rainfall and strong evaporation (Zhou et al., 2019, 2021).
138-139. The climate is generally characterized by warm-dry summers and cold wet winters (Fig. 2)
Along the manuscript and in the reconstruction, the authors mention wet climate in the area…I do not think this term is adequate for this site, there are relatively wetter and drier stages but within the analyzed time range, the climate seems mostly arid.
156-159...two parallel sediment cores (ABHHX and ABH, of 48 cm and 50 cm length, respectively) were retrieved from the northwest edge of lake Ebinur at a water depth of 0.8 m (45°04' N, 82°36' E, 193 m), using a 60-mm UWITEC gravity corer (Fig. 1)…
Considering the location of the coring site (if the coordinates provided in the manuscript of the coring site are correct, 45°04' N, 82°36'), the cores were taken close to the northwestern lake shore. The shallow water-depth and large area variations, immediately suggest that parts of lake bottom near the margins, such as the coring site, are susceptible to become air exposed. Moreover, historical satellite images from Google Earth show that the northern part of the lake was above the lake water level during images from the 80’s and 90’s. The same seems to be presented in maps of papers studying the lake area fluctuation (Wang et al. 2021. Simulation of Lake Water Volume in Ungauged Terminal Lake Basin Based on Multi-Source Remote Sensing. Remote Sensing. 13.10.3390/rs13040697; Zhang et al. 2015. Environ Monit Assess 187:4128DOI 10.1007/s10661-014-4128-4). The lake bottom exposure and wind action of part of the 20th century sediments may also explain the lack of the 137Cs signal in the Lake Ebinur sediments, which has been effectively detected in other lake sequences from the same region (Lan, Jianghu, et al. "Time marker of 137Cs fallout maximum in lake sediments of Northwest China." Quaternary Science Reviews 241 (2020): 106413), and in a different cores retrieved from the same lake at a greater water depth (Liu et al 2017 J. Limnol., 2017; 76(3): 534-545); Ma L, Wu J, Abuduwaili J, Liu W (2016) Geochemical Responses to Anthropogenic and Natural Influences in Ebinur Lake Sediments of Arid Northwest China. PLoS ONE 11(5): e0155819. doi:10.1371/journal.pone.0155819). This should be carefully considered by the authors since it challenges the assumed “continuous and uniform sedimentation”, and thus, questions the reliability of the age model (as pointed by RC1 and CE1), even when the mean particle size is similar along the sequence.
171-176. The activity of total 210Pb (210Pbtot) was determined via gamma emissions at 44.5 keV, and the activity of 226Ra was determined by measuring the activity of its daughter nuclide 214Pb at 295 keV and 352 keV. The activity of 137Cs was measured with the 662 keV photopeak. The supported 210Pb activity was assumed to be in equilibrium with in situ 226Ra activity, and the unsupported 210Pb activity (210Pbex) was calculated by subtracting the 226Ra activity from the 210Pbtot (Pratte et al., 2019).
In the Materials and methods section, the authors indicate the methodology for calculating the 210Pb activity. Nevertheless, they do not indicate how they constructed the age model from this data, this should be addressed in the methodology. Additionally, it is indicated that the model applied is the CRS, which assumes a constant rate of supply and a variable sedimentation rate. For the oldest part of the sequence a linear extrapolation is assumed. I find an inconsistency in this point when the authors argue "uniform rates" (reply to Q5). Finally, in the replies to the comments, they say that “six data were discarded due to abnormal deposition rate”. Where are these results? I think there is information missing from the manuscript.
177-186. In Materials and methods, the grain size distribution method is explained. However, the measured parameters are not mentioned. They should be mentioned in this section and explained in the Results and Interpretation section.
188-191. Each Sample of about 1.5 g was dried at 40 ℃ for 24 h, then crushed without damaging their grain-size (Jiang et al., 2008) and the color reflectance was measured by using a SPAD 503 handheld spectrophotometer.
The color reflectance methodology and the parameters’ meanings are not explained.
228-230. 4.2 Sedimentary Proxies record. All 96 grain-size data were analyzed by end-member analysis (EMA) using AnalySize software (Weltje, 1997; Paterson and Heslop, 2015; Jiang et al., 2022).
This is methodological aspect, please move these lines to the previous section.
231-239. Overall, the lower part of the sedimentary sequence is characterized by large fluctuations and coarse grains (Figs. 5a-5g), with over 60 % of the C value above 50 μm (Figs. 6b, 6c), reflecting strong transport dynamics (Passega, 1964; Jiang et al., 2017a; Wei et al., 2021). The particles in the upper part of the sequence are finer (Figs. 5a-5g), and only ~ 20 % the C value exceeds 50 μm (Figs. 6d, 6e), indicating smaller transport dynamics.
In addition, other proxies of lake Ebinur sequence (L*, a*, TOC and TIC) also show different variation characteristics in the corresponding upper and lower parts (Figs. 5k-5n). Thus, the sedimentary sequence can be divided into two units.
In this description, the "upper part" and the "lower part" of the sedimentary sequence are not well delimited. Furthermore, the criteria for the separation of the units and subunits should be clearly defined. This is important since the contact between unit 1 and unit 2 is established as the point where sedimentation and climate shifted.
Figure 5. This Figure includes some parameters that are not explained in the manuscript, or sometimes they are not explained, interpreted nor used along the manuscript (e.g. the Mode, EM1, <2 micrometers, etc.).
258-260. The variation of Md is clearly influenced by the coarse component: EM2 (0-37.6 %, mean 21.6 %) (Fig. 5g), i.e., the coarse particles are deposited first, and the fine particles are deposited later.
From the Figure 5, I cannot detect differences in excursions of the curves from EM1 and EM2, they seem quite similar. Please, explain them in the results.
260-263. Combined with the higher C value for this unit (22.6-86.5 μm, mean 54.5 μm) (Fig. 5i), it indicates that the wind is stronger at this stage, bringing more coarse-grained matter from local and regional dust (see Sect. 5.1 for the explanation of provenance).
Have the authors considered the role water inflow in sediment transport in any part of the sequence?
266-269. Correspondingly, the contents of TOC (0.25-0.34, mean 0.30) and TIC (1.91-2.95, mean 2.50) also showed strong fluctuations (Figs. 5m, 5n), which may have been influenced by strong wind activity during the cold period.
Please, provide an explanation of this relationship.
272-274. In this unit, the proportion of ultrafine component is the highest in the whole sequence (1.7 %-10.2 %, mean 5.0 %), revealing the strongest pedogenesis in the study area (Fig. 5h).
How do authors determine that the ultrafine component is local? Could it be part of the long-distance transport?
285-287. Related to humidity fluctuation, L* values within arid lakes are considered to reflect variations in the carbonate, and high L* values denote more carbonate content (Xiao et al., 2006; Jiang et al., 2008).
According to Figure 5, L* and TIC curves seem to fluctuate quite differently. Moreover, L* seems lower in unit 2 than in unit 1. Therefore, I think that the interpretation of the *L and TIC values needs further explanation.
294-298. Further, this unit can also be divided into two sub-units based on the changes of all proxies: unit 1-a and unit 1-b (Figs. 5a-5n). During the period of unit 1-a (48-34 cm, 1816-1876 AD), the study area has been under cold and wet climatic conditions, while unit 1-b (34-24 cm, 1876-1920 AD) was in a transition period from cold and warm.
This is not sustained by any explanation in this section, it seems an arbitrary division. The same is applicable to the following subunits. Please, provide more details.
Figure 6
This Figure is not mentioned or explained in the manuscript.
310-313. This is probably duo to the decrease of the temperature gradient as the temperature rise (Zhang et al., 2021), resulting in the weakening of wind intensity and the decrease of coarse particles transported at low altitude and short distance (Ge et al., 2016).
I saw that there was an explanation added in the response to a question about the meaning of the temperature gradient. I find that the relation of temperature changes and the grain size in this lake record is vague and should be better addressed in the discussion.
313-314. As well, the contents of TOC (0.25-0.32) and TIC (2.17-2.63) showed very slight fluctuations except for the top two points (Figs. 5m, 5n).
What does this mean?
329-334. 5.1 Provenance and transport mechanisms of lake Ebinur sediments. The Y value of Sahu's formula is usually used to recognize the eolian environment, which is mainly determined by mean grain size, standard deviation, skewness, and kurtosis (Sahu, 1964). The Y values of all samples range from -19.5 to -7.6, lower than the threshold value of -2.74 (Fig. 7), supporting their windblown origin (Jiang et al., 2017b, 2022; Wei et al., 2021).
The results of the end members and this interpretation should be in the Results and Interpretation section, before authors interpret the whole sequence. In my opinion, provenance is not analyzed in this section. In addition, please, provide further explanation about the formula and threshold value (is this number and formula used to recognize only the aeolian origin or to discriminate aeolian from beach transport, as in Sahu, 1964?).
- 5.2 Climatic events revealed by lake Ebinur sedimentary sequence
In this section, authors include also the human influence on the lake sediments, so it would be convenient to modify the title.
364-366. The L* value increased continuously after 1955 (Fig. 8f), indicating the increase of carbonate content, which may be caused by the rapid shrinkage of lake Ebinur.
This is contradictory with the rest of the interpretations of carbonate precipitation, since unlike in the underlying units, here, carbonate precipitation is interpreted as triggered by lake volume reduction. Please, explain the mechanisms of carbonate precipitation in this lake.
369-373. Notably, Md and EM2 show two abnormally high values since 1955 AD (Figs. 8a, 8b), and correspondingly, the C values also show high values (Fig. 8c), indicating strong transport dynamics (Jiang et al., 2017a; Shi et al., 2022). These two events (E1, E2) may be related to local strong wind events within the age error (Wang et al., 2003).
Please, indicate the ages and the errors of these two events. Are these events regional? Can they be tracked in different cores or in other records from the region? Could they be used as time markers?
426-429. The fine-grained sediments (< 20 μm) are background dust that was transported by long distance high-altitude suspension, while the coarse-grained sediments (> 20 μm) are local and regional dusts that were transported from short distances at low altitudes.
This is not analyzed in the results, in the interpretations or in the discussion.
- 5.3 Climate transition and possible forcing mechanism. Figure 9
In this comparative Figure, the main data obtained from of this work should be included.
-
AC3: 'Reply on RC2', Xiaotong Wei, 02 Mar 2023
We are grateful to Reviewer 2 for giving us detailed comments to improve our manuscript. The responses to the comments from Reviewer 2 are addressed point by point as follows.
General comments
Q1: In this manuscript, the authors provide a multiproxy study of a short sediment core from a shallow terminal lake in a climate-sensitive arid area. This record includes a significant number of variables, mainly based on particle size parameters, that can be linked to recent paleoenvironmental changes. I read carefully the manuscript, and I was also able to read the discussion, the comments and their responses. Based on this information, I agree with the comments of the Editor and Referee 1 concerning the problems in the chronological model (I provide more details in the comments below). Unfortunately, I do not see that the authors provided enough evidence in their relplies to support the model. This is a major obstacle to be addressed when the goal of the paper is to provide a high temporal resolution of the sequence in order to determine the exact year of a climate shift.
Thank you very much for your review. We believe that the chronological model is reliable according to the following points:
1) The dating of the upper core (~80 year) calculated by the 210Pb CRS model is reliable, for example, the events (E1 and E2) revealed by the sedimentary sequence can be compared with local strong wind events (Figure 8);
2) The whole core is mainly composed of fine-grained sediments (Md: 5.4-9.9 μm, mean 7.0 μm), and there is no distinct lithologic change. And we think that the core deposition is near-continuous and homogeneous;
3) Based on downward extrapolation method, the climate changes over the past 200 years revealed by sedimentary sequence can be well contrasted regionally with previous climate records.
Moreover, the climatic transition point (1920 AD) revealed by the lake Ebinur sedimentary sequence is supported by the reconstructed temperature records in China (Yang et al., 2002; Ge et al., 2013).
Reference
Ge, Q., Hao, Z., Zheng, J., and Shao, X.: Temperature changes over the past 2000 yr in China and comparison with the Northern Hemisphere, Clim. Past, 9, 1153-1160, https://doi.org/10.5194/cp-9-1153-2013, 2013.
Yang, B., Braeuning, A., Johnson, K.R., and Shi, Y.F.: General characteristics of temperature variation in China during the last two millennia, Geophys. Res. Lett., 29, 38-1-38-4, https://doi.org/10.1029/2001GL014485, 2002.
Q2: As another related issue, it is difficult to understand the criteria for the separation of units and subunits, and thus, the exact point of the sedimentation changes. It also surprises me that the changes on the lake area and water discharges during the deposition of this sequence are completely ignored in the discussion in the shallow lake sedimentation processes.
Thank you very much for your kind reminding. We have modified the criteria for the separation of units and subunits in detail. Please see L.266-279, P.8, L.326-334, P.10, and L.367-371, P.11.
The changes on the lake area and water discharges can seriously affect the sedimentation process of shallow lakes, for example, changes in L* value and TOC. However, our indicators are insufficient to explain the influence and further research is needed to reveal it.
Q3: Finally, I suggest to revise the organization of the manuscript separating the data from interpretation, and discussions, following a clear and logical order, and to provide better explanation of the figures. Considering that some of the mentioned points intefere with the goals and the precision proposed in this work, my suggestion is to reject the manuscript. I hope that the authors can think about a solution to the main problems (maybe adding marker layers to the model),or to consider a different approach, to send the new manuscript using this valuable data.
Thank you very much for your kind reminding. We have reorganized the results, interpretation, and discussions in the manuscript, and improved the explanation of the figures.
Specific comments
Q1: 128-130. The climate of the study region is mainly dominated by westerlies and is a typical temperate continental climate, which is characterized by low rainfall and strong evaporation (Zhou et al., 2019, 2021).
138-139. The climate is generally characterized by warm-dry summers and cold wet winters (Fig. 2)
Along the manuscript and in the reconstruction, the authors mention wet climate in the area…I do not think this term is adequate for this site, there are relatively wetter and drier stages but within the analyzed time range, the climate seems mostly arid.
Thank you very much for your kind reminding. We have modified it, please see L.136-137, P.4.
Q2: 156-159...two parallel sediment cores (ABHHX and ABH, of 48 cm and 50 cm length, respectively) were retrieved from the northwest edge of lake Ebinur at a water depth of 0.8 m (45°04' N, 82°36' E, 193 m), using a 60-mm UWITEC gravity corer (Fig. 1)…
Considering the location of the coring site (if the coordinates provided in the manuscript of the coring site are correct, 45°04' N, 82°36'), the cores were taken close to the northwestern lake shore. The shallow water-depth and large area variations, immediately suggest that parts of lake bottom near the margins, such as the coring site, are susceptible to become air exposed. Moreover, historical satellite images from Google Earth show that the northern part of the lake was above the lake water level during images from the 80’s and 90’s. The same seems to be presented in maps of papers studying the lake area fluctuation (Wang et al. 2021. Simulation of Lake Water Volume in Ungauged Terminal Lake Basin Based on Multi-Source Remote Sensing. Remote Sensing. 13.10.3390/rs13040697; Zhang et al. 2015. Environ Monit Assess 187: 4128DOI 10.1007/s10661-014-4128-4). The lake bottom exposure and wind action of part of the 20th century sediments may also explain the lack of the 137Cs signal in the Lake Ebinur sediments, which has been effectively detected in other lake sequences from the same region (Lan, Jianghu et al. "Time marker of 137Cs fallout maximum in lake sediments of Northwest China." Quaternary Science Reviews 241 (2020): 106413), and in a different cores retrieved from the same lake at a greater water depth (Liu et al 2017 J.Limnol., 2017; 76(3): 534-545); Ma L, Wu J, Abuduwaili J, Liu w (2016) Geochemical Responses to Anthropogenic and Natural Influences in Ebinur Lake Sediments of Arid Northwest China. PLoS ONE 11(5): E0155819. doi:10.1371/journal.pone.0155819). This should be carefully considered by the authors since it challenges the assumed “continuous and uniform sedimentation”, and thus, questions the reliability of the age model (as pointed by RC1 and CE1), even when the mean particle size is similar along the sequence. In my opinion this cannot be done as i) we usually have less compacted sediments in the upper part of sediment cores with a high sedimentation rate and ii) there is a change in lithology which the authors use for their environmental reconstruction.
Yes, the coring site is located on the northwest shore of Lake Ebinur, which may be exposed to air due to shallow water-depth and large area variations (Zhang et al., 2015; Wang et al., 2021). However, the northwest shore of the lake is dry during individual months of the year, and the variation is seasonal or even monthly, not interannual. In addition, 137Cs signals were detected in other lake sequences from the same region and in different cores retrieved from the same lake (Ma et al., 2016; Liu et al., 2017; Lan et al., 2020), which may explain the lack of the 137Cs signal in our core sediments. But we believe the deposition is continuous and uniform according to the following points:
1) The dating of the upper core (~80 year) calculated by the 210Pb CRS model of two parallel cores is reliable, and the events (E1 and E2) revealed by the sedimentary sequence can be compared with local strong wind events (Figure 8);
2) The core is very shallow, only 48 cm, and there is no distinct lithologic change. Combined with the fine particle size (Md: 5.4-9.9 μm, mean 7.0 μm), we think that the core deposition is near-continuous and homogeneous;
3) Based on downward extrapolation method, the climate changes over the past 200 years revealed by sedimentary sequence can be well contrasted regionally with previous climate records (Figure 8).
In addition, we did not use the change in lithology for environmental reconstruction.
Q3: 171-176. The activity of total 210Pb (210Pbtot) was determined via gamma emissions at 44.5 keV, and the activity of 226Ra was determined by measuring the activity of its daughter nuclide 214Pb at 295 keV and 352 keV. The activity of 137Cs was measured with the 662 keV photopeak. The supported 210Pb activity was assumed to be in equilibrium with in situ 226Ra activity, and the unsupported 210Pb activity (210Pbex) was calculated by subtracting the 226Ra activity from the 210Pbtot (Pratte et al., 2019).
In the Materials and methods section, the authors indicate the methodology for calculating the 210Pb activity. Nevertheless, they do not indicate how they constructed the age model from this data, this should be addressed in the methodology. Additionally, it is indicated that the model applied is the CRS, which assumes a constant rate of supply and a variable sedimentation rate. For the oldest part of the sequence a linear extrapolation is assumed. I find an inconsistency in this point when the authors argue "uniform rates" (reply to Q5). Finally, in the replies to the comments, they say that “six data were discarded due to abnormal deposition rate”. Where are these results? I think there is information missing from the manuscript.
Thank you very much for your review. We think that the description of the age method is sufficient (Xu et al., 2020; Fan et al., 2021), and we give a detailed explanation of the construction of the age model in the revised manuscript. Please see L.219-225, P.6-7.
Indeed, we reconstruct the age of the upper part by using the CRS model, which assumes a constant rate of supply and a variable sedimentation. For the lower part, we used a linear extrapolation. This may seem contradictory, but it is always necessary to give the age of the lower part in order to reconstruct the environment. Based on the following points, we believe that the result of linear extrapolation is acceptable:
1) Although the deposition rates calculated from 210Pbex activity are variable, they are all around 2mm/a;
2) The whole core is mainly composed of fine-grained sediments (Md: 5.4-9.9 μm, mean 7.0 μm), and there is no obvious depositional discontinuity and distinct change in core lithology, so we think that the core deposition is near-continuous and homogeneous;
3) The climate changes and climate events revealed by our sedimentary sequence are well consistent with regional records (Figure 8).
As shown in Figure S1, the bottom six data of core ABH were discarded due to the abnormal deposition rate, please see the Supplement material.
Reference
Fan, J.W., Jiang, H.C., Shi, W., Guo, Q.Q., Zhang, S.Q., Wei, X.T., Xu, H.Y., Zhong, N., Huang, S.T., Chang, X.D., and Xiao, J.L.: A 450-year lacustrine record of recurrent seismic activities around the Fuyun fault, Altay Mountains, Northwest China, Quatern. Int., 558, 75-88, https://doi.org/10.1016/j.quaint.2020.08.051, 2020.
Xu, H.Y., Jiang, H.C., Liu, K.B., Zhong, N.: Potential pollen evidence for the 1933 M 7.5 Diexi earthquake and implications for post-seismic landscape recovery, Environmental Research Letters, 15, 094043, https://doi.org/10.1088/1748-9326/ab9af6, 2020.
Q4: 177-186. In Materials and methods, the grain size distribution method is explained. However, the measured parameters are not mentioned. They should be mentioned in this section and explained in the Results and Interpretation section.
Thank you very much for your review. We believe that the measured parameters for grain size have been described. Please see L.176-185, P.5-6.
Q5: 188-191. Each Sample of about 1.5 g was dried at 40 ℃ for 24 h, then crushed without damaging their grain-size (Jiang et al., 2008) and the color reflectance was measured by using a SPAD 503 handheld spectrophotometer.
The color reflectance methodology and the parameters’ meanings are not explained.
Thank you very much for your review. We consider that the description of color reflectance methodology is sufficient, and the parameters’ meaning is explained in Section 4.2, please see L.308-309 and L.309-315, P.9-10.
Q6: 228-230. 4.2 Sedimentary Proxies record. All 96 grain-size data were analyzed by end-member analysis (EMA) using AnalySize software (Weltje, 1997; Paterson and Heslop, 2015; Jiang et al., 2022).
This is methodological aspect, please move these lines to the previous section.
Done. Please see L.185-187, P.6.
Q7: 231-239. Overall, the lower part of the sedimentary sequence is characterized by large fluctuations and coarse grains (Figs. 5a-5g), with over 60 % of the C value above 50 μm (Figs. 6b, 6c), reflecting strong transport dynamics (Passega, 1964; Jiang et al., 2017a; Wei et al., 2021). The particles in the upper part of the sequence are finer (Figs. 5a-5g), and only ~ 20 % the C value exceeds 50 μm (Figs. 6d, 6e), indicating smaller transport dynamics.
In addition, other proxies of lake Ebinur sequence (L*, a*, TOC and TIC) also show different variation characteristics in the corresponding upper and lower parts (Figs. 5k-5n). Thus, the sedimentary sequence can be divided into two units.
In this description, the "upper part" and the "lower part" of the sedimentary sequence are not well delimited. Furthermore, the criteria for the separation of the units and subunits should be clearly defined. This is important since the contact between unit 1 and unit 2 is established as the point where sedimentation and climate shifted.
Thank you very much for your kind reminding. We have modified it, please see L.266-279, P.8.
Q8: Figure 5. This Figure includes some parameters that are not explained in the manuscript, or sometimes they are not explained, interpreted nor used along the manuscript (e.g. the Mode, EM1, <2 micrometers, etc.).
Thank you very much for your kind reminding. We have modified it, please see L.292-293, P.9 and L.347-348, P.11. And we think EM1 and <2 μm fraction have less significance in the reconstructed sequences.
Q9: 258-260. The variation of Md is clearly influenced by the coarse component: EM2 (0-37.6 %, mean 21.6 %) (Fig. 5g), i.e., the coarse particles are deposited first, and the fine particles are deposited later.
From the Figure 5, I cannot detect differences in excursions of the curves from EM1 and EM2, they seem quite similar. Please, explain them in the results.
Yes, the whole sedimentary sequence is composed of two end-members: EM1 and EM2, which are negatively correlated. In the process of lake deposition, the coarse particles (EM2) are deposited first, followed by fine particles (EM1). In other words, the percentage content of EM1 is determined by the change of EM2. Therefore, EM2 has more important environmental information, reflecting the regional and local provenance supply.
Q10: 260-263. Combined with the higher C value for this unit (22.6-86.5 μm, mean 54.5 μm) (Fig. 5i), it indicates that the wind is stronger at this stage, bringing more coarse-grained matter from local and regional dust (see Sect. 5.1 for the explanation of provenance).
Have the authors considered the role water inflow in sediment transport in any part of the sequence?
Sorry, we think the sediments in lake Ebinur are aeolian for the following reasons:
1) The Y value of all samples range from -19.5- -7.6, lower than the threshold value of -2.74, supporting their windblown origin (Jiang et al., 2017, 2022; Wei et al., 2021);
2) The results of end-member simulation are also supported by modern observations: the EM2 component (~ 24.1 μm) shows a similar modal distribution with aeolian dust samples collected from the Ebinur drainage area (15-26 μm) (Ma et al., 2016);
3) The arid and windy climate in the lake Ebinur area provides favorable conditions for aeolian deposition.
In summary, we believe that the sediments in lake Ebinur were transported by wind rather than by water. Thus, the higher C value reflects stronger wind conditions.
Reference
Jiang, H.C., Zhong, N., Li, Y.H., Ma, X.L., Xu, H.Y., Shi, W., Zhang, S.Q., and Nie, G.Z.: A continuous 13.3-ka record of seismogenic dust events in lacustrine sediments in the eastern Tibetan Plateau, Sci. Rep., 7, 1-10, https://doi.org/10.10 38/s41598-017-16027-8, 2017.
Jiang, H.C., Zhang, J.Y., Zhang, S.Q., Zhong, N., Wan. S.M., Alsop, G.I., Xu, H.Y., Guo, Q.Q., and Yan, Z.: Tectonic and Climatic Impacts on Environmental Evolution in East Asia During the Palaeogene, Geophys. Res. Lett., 49, e2021GL096832, https://doi.org/10.1029/2021GL096832, 2022.
Ma, L., Wu, J.L., and Abuduwaili, J.: Variation in aeolian environments recorded by the particle size distribution of lacustrine sediments in Ebinur Lake, northwest China, SpringerPlus, 5, 1-8, https://doi.org/10.1186/s40064-016-2146-0, 2016.
Wei, X.T., Jiang, H.C., Xu, H.Y., Fan, J.W., Shi, W., Guo, Q.Q., and Zhang, S.Q.: Response of sedimentary and pollen records to the 1933 Diexi earthquake on the eastern Tibetan Plateau, Ecol. Indic., 129, 107887, https://doi.org/10.1016/j.ecoli nd.2021.107887, 2021.
Q11: 266-269. Correspondingly, the contents of TOC (0.25-0.34, mean 0.30) and TIC (1.91-2.95, mean 2.50) also showed strong fluctuations (Figs. 5m, 5n), which may have been influenced by strong wind activity during the cold period.
Please, provide an explanation of this relationship.
Thank you very much for your kind reminding. We have modified it, please see L.319-321, P.10.
Q12: 272-274. In this unit, the proportion of ultrafine component is the highest in the whole sequence (1.7 %-10.2 %, mean 5.0 %), revealing the strongest pedogenesis in the study area (Fig. 5h).
How do authors determine that the ultrafine component is local? Could it be part of the long-distance transport?
Thank you very much for your review. We consider the ultrafine component is local based on the following two aspects:
1) Ultrafine components in aeolian sediments are formed during pedogenesis and can be used to trace the history of regional pedogenesis (Sun et al., 2006, 2011). The ultrafine components of lake sediments in aeolian regions may be the products of pedogenesis on the surface in the catchment (Sun et al., 2006);
2) As shown in figure 8, the proportion of ultrafine components showed a consistent trend with the coarse particle fraction EM2 during 1816-1876 AD. This suggests that the ultrafine components produced by strong pedogenesis in the study area may be attached to the coarse-grained material from nearby sources and deposited by wind transport into the lake Ebinur.
Reference
Sun, D.H.: Super-fine grain size components in Chinese loss and their palaeoclimatic implication, Quaternary Sciences, 26, 928-936, 2006 (in Chinese).
Sun, D.H., Su, R.X., Li, Z.J., and Lu, H.Y.: The ultrafine component in Chinese loess and its variation over the past 7-6 Ma: implications for the history of pedogenesis, Sedimentology, 58, 916-935, https://doi.org/10.1111/j.1 365-3091.2010.01189.x, 2011.
Q13: 285-287. Related to humidity fluctuation, L* values within arid lakes are considered to reflect variations in the carbonate, and high L* values denote more carbonate content (Xiao et al., 2006; Jiang et al., 2008).
According to Figure 5, L* and TIC curves seem to fluctuate quite differently. Moreover, L* seems lower in unit 2 than in unit 1. Therefore, I think that the interpretation of the *L and TIC values needs further explanation.
The L* value in unit 2 (74.4-76.7, mean 75.3) is higher than in unit 1 (73.2-76.1, mean 74.6). And the L* and TIC show similar variations: they show large-amplitude fluctuations in the early period (1816-1920 AD) and more stable in the late period (1920-2019 AD).
Q14: 294-298. Further, this unit can also be divided into two sub-units based on the changes of all proxies: unit 1-a and unit 1-b (Figs. 5a-5n). During the period of unit 1-a (48-34 cm, 1816-1876 AD), the study area has been under cold and wet climatic conditions, while unit 1-b (34-24 cm, 1876-1920 AD) was in a transition period from cold and warm.
This is not sustained by any explanation in this section, it seems an arbitrary division. The same is applicable to the following subunits. Please, provide more details.
Done. Please see L.326-334 and L.367-371, P.10-11.
Q15: Figure 6
This Figure is not mentioned or explained in the manuscript.
Done. We have modified it, please see L.269 and L.275, P.8.
Q16: 310-313. This is probably duo to the decrease of the temperature gradient as the temperature rise (Zhang et al., 2021), resulting in the weakening of wind intensity and the decrease of coarse particles transported at low altitude and short distance (Ge et al., 2016).
I saw that there was an explanation added in the response to a question about the meaning of the temperature gradient. I find that the relation of temperature changes and the grain size in this lake record is vague and should be better addressed in the discussion.
Thank you very much for your kind reminding. The lake Ebinur area has the strongest wind transport conditions and the highest temperatures during March to August (Ge et al., 2016). In the cold period (1816-1920 AD), the temperature gradient between March and August is larger and there are stronger wind conditions, bringing more coarse particles (EM2, local and/or regional sources) to the lake. In the warm period (1920-2019 AD), the temperature gradient between March and August decreases as the temperature rise, resulting in the weakening of wind intensity and the decrease of coarse particles (EM2) transported at low altitude and short distance.
We have modified it, please see L.350, P.11.
Reference
Ge, Y.X., Abuduwaili, J., Ma, L., Wu, N., and Liu, D.W.: Potential transport pathways of dust emanating from the playa of Ebinur Lake, Xinjiang, in arid northwest China, Atmos. Res., 178-179, 196-206, https://doi.org/10.1016/j.atmosres.2016.0 4.002, 2016.
Q17: 313-314. As well, the contents of TOC (0.25-0.32) and TIC (2.17-2.63) showed very slight fluctuations except for the top two points (Figs. 5m, 5n).
What does this mean?
Thank you very much for your kind reminding. The contents of TOC (0.25-0.32) and TIC (2.17-2.63) showed small fluctuations except for the top two points (Figs. 7m, 7n), which may indicate that the lake water body at this stage was more stable than unit 1 stage.
We have modified it, please see L.361-363, P.11.
Q18: 329-334. 5.1 Provenance and transport mechanisms of lake Ebinur sediments. The Y value of Sahu's formula is usually used to recognize the eolian environment, which is mainly determined by mean grain size, standard deviation, skewness, and kurtosis (Sahu, 1964). The Y values of all samples range from -19.5 to -7.6, lower than the threshold value of -2.74 (Fig. 7), supporting their windblown origin (Jiang et al., 2017b, 2022; Wei et al., 2021).
The results of the end members and this interpretation should be in the Results and Interpretation section, before authors interpret the whole sequence. In my opinion, provenance is not analyzed in this section. In addition, please, provide further explanation about the formula and threshold value (is this number and formula used to recognize only the aeolian origin or to discriminate aeolian from beach transport, as in Sahu, 1964?)
Done. Please see L.233-243, P.7.
The Sahu’s formula is mainly used to distinguish aeolian sediments and beach sediments. Sahu (1964) proposed that the Y value of eolian sediments should be less than -2.7411, and Y values of typical aeolian sediments are negative, while Y values of hydrogenic sediments are positive, which has been confirmed by Lu et al (1999) and Wu et al (2017).
Reference
Lu, H.Y., An, Z.S.: Comparison of grain-size distribution of red clay and loess-paleosol deposits in Chinese Loess Plateau, Acta Sedimentologica Sinica, 17(2), 7, 1999 (in Chinese),.
Sahu, B.K.: Depositional mechanisms from the size analysis of clastic sediments, J. Sediment. Res., 34, 73-83, https://doi.org/10.1306/74d70fce-2b21-11d7-8648000 102c1865d, 1964.
Wu, H.B., Liu, X.M., lv, B., Ma, M.M., Ji, J.P., Wang, W.Y., Zhang, Y.Y, Hou, J.L.: Aeolian origin of the Twelve Apostles section, in Australia, Quaternary Science, 37(1), 82-96, https://doi.org//10.11928/j.issn.1001-7410.2017.01.08, 2017.
Q19: 5.2 Climatic events revealed by lake Ebinur sedimentary sequence
In this section, authors include also the human influence on the lake sediments, so it would be convenient to modify the title.
Done. Please see L.374-375, P.11.
Q20: 364-366. The L* value increased continuously after 1955 (Fig. 8f), indicating the increase of carbonate content, which may be caused by the rapid shrinkage of lake Ebinur.
This is contradictory with the rest of the interpretations of carbonate precipitation, since unlike in the underlying units, here, carbonate precipitation is interpreted as triggered by lake volume reduction. Please, explain the mechanisms of carbonate precipitation in this lake.
Thank you very much for your kind reminding. We have modified it, please see L.387-389, P.11. Water is needed to deposit carbonate in arid areas, and in extremely arid lakes, high carbonate content occurs in environments with more water. Higher L* values reflecting carbonate content indicate more water, which may be associated with an increase in summer glacial meltwater caused by warming into the lake. In summer, the lake Ebinur area has a stronger evaporation, the increased glacial meltwater provides favorable conditions for carbonates production.
Q21: 369-373. Notably, Md and EM2 show two abnormally high values since 1955 AD (Figs. 8a, 8b), and correspondingly, the C values also show high values (Fig. 8c), indicating strong transport dynamics (Jiang et al., 2017a; Shi et al., 2022). These two events (E1, E2) may be related to local strong wind events within the age error (Wang et al., 2003).
Please, indicate the ages and the errors of these two events. Are these events regional? Can they be tracked in different cores or in other records from the region? Could they be used as time markers?
Done. Please see L.392-394, P.12.
These two strong wind events were regional and reported by Overview of Disaster Prevention (Wang et al., 2003). Strong winds at Alashankou in 1986 AD and 2002 AD killed more than 1000 ducks in the lake Ebinur area and could be used as time markers. Unfortunately, these two strong wind events have not yet been found in different cores or in other records, which may be related to the location of coring site (near the Ala Mountain Pass).
Reference
Wang, K.P., Zhao, Y.Z., and Ma, J.L.: Strong wind-more than 1000 ducks killed or injured in the lake Ebinur wetland, Overview of Disaster Prevention, 1, 32, 2003 (in Chinese).
Q22: 426-429. The fine-grained sediments (< 20 μm) are background dust that was transported by long distance high-altitude suspension, while the coarse-grained sediments (> 20 μm) are local and regional dusts that were transported from short distances at low altitudes.
This is not analyzed in the results, in the interpretations or in the discussion.
Thank you very much for your kind reminding. The EM1 fraction of lake Ebinur sediments has a modal grain size of 5.9 μm, and the content ranges from 62.1% to 100%, with a mean of 83.6%, which corresponds well to the < 20 μm grain size fraction (70.2%-97.0%, mean 84.7%). And the modal grain size of EM2 fraction is 24.1 μm (0-37.9 %, mean 16.4%), which corresponds well to the > 20 μm grain size fraction (3.0%-29.8%, mean 15.3%). This is consistent with the finding of previous studies that the fine-grained sediments (< 20 μm) are background dust that was transported by long distance high-altitude suspension, while the coarse-grained sediments (> 20 μm) are local and regional dusts that were transported from short distances at low altitudes. (Pye, 1987; Jiang et al., 2014; Wei et al., 2021). In addition, the EM2 fraction (~ 24.1 μm) shows a similar modal distribution with aeolian dust samples collected from the Ebinur drainage area (15-26 μm) (Ma et al., 2016), further supporting the possible transport mechanism model.
Reference
Jiang, H.C., Mao, X., Xu, H.Y., Yang, H.L., Ma, X.L., Zhong, N., and Li, Y.H.: Provenance and earthquake signature of the last deglacial Xinmocun lacustrine sediments at Diexi, East Tibet, Geomorphology, 204, 518-531, https://doi.org/10. 1016/j.geomorph.2013.08.032, 2014.
Ma, L., Wu, J.L., and Abuduwaili, J.: Variation in aeolian environments recorded by the particle size distribution of lacustrine sediments in Ebinur Lake, northwest China, SpringerPlus, 5, 1-8, https://doi.org/10.1186/s40064-016-2146-0, 2016.
Pye, K.: Eolian Dust and Dust Deposits, Academic Press, London, 1987.
Wei, X.T., Jiang, H.C., Xu, H.Y., Fan, J.W., Shi, W., Guo, Q.Q., and Zhang, S.Q.: Response of sedimentary and pollen records to the 1933 Diexi earthquake on the eastern Tibetan Plateau, Ecol. Indic., 129, 107887, https://doi.org/10.1016/j.ecoli nd.2021.107887, 2021.
Q23: 5.3 Climate transition and possible forcing mechanism. Figure 9
In this comparative Figure, the main data obtained from of this work should be included.
Thank you very much for your review. In figure 8, we identified the time point of the climate transition over the past 200 years-1920 AD, mainly through the multi-proxies of lake Ebinur sedimentary sequence. If our multi-proxies were put into figure 9, it will be too crowded to properly represent the signal.
-
RC3: 'Comment on cp-2022-92', Anonymous Referee #3, 03 Mar 2023
Xiaotong Wei and co-authors present a multi-proxy study on short sediment core from a closed lake system (Lake Ebinur) in northwestern China. They measured grain size, color reflectance and carbon content on discrete samples. So far, I have not looked at the other reviews and the replays by the authors on the discussion website of Climate of the Past in order to provide an unbiased report on the manuscript as possible.
About grain size:
The authors relay their story mostly on the grain size data. They relate the grain size to the wind strength and argue that the wind activity was stronger in the first half of their record. As the core comes from a closed lake basin, the lake level could have a strong influence on the sediment composition. The water depth at the coring site is only 0.8 m and so lake level fluctuations must have a huge influence. Fig. 8k shows the fluctuations of the lake surface since 1955, which are mainly due to anthropogenic changes. However, there must also have been fluctuations in the lake level before that, caused by climate fluctuations.
The grain size fluctuates considerably larger in the older part of the record. Key here would be the sedimentology of the courser grain size intervals. Are these discrete layers? Are they graded? Unfortunately, the core was sampled in the field and no core photographs are available to study the sedimentology in detail. The similar evolution of the mean grain size and the lake area (Fig. 8a, 8k) indicates, in my opinion, a strong influence of lake level on sediment composition.
Other open questions concerning the grain size:
- The authors mention in line 320 glacial meltwater and relate the increase in the L* value to the glacial melting in last decades. Here the question would be how strong this influence was in the older part of the record.
- The authors relate the ultrafine components to be associated with pedogenesis. Here the question would be how fast pedogenesis would react to climate change and how large would be the time lag with the production of ultrafine particles.
External forcing factors:
The authors try to relate the observed changes in the Lake Ebinur sedimentary record to external climate forcings like greenhouse gases or total solar irradiance (TSI). They propose that the climate transition around 1920 AD was manly controlled by TSI. However, they do not provide any mechanistical model how TSI would influence the sediment deposition in Lake Ebinur. The identification of the TSI as the most important external factor is therefore based on weak scientific grounds.
Citation: https://doi.org/10.5194/cp-2022-92-RC3 -
AC4: 'Reply on RC3', Xiaotong Wei, 06 Mar 2023
We are grateful to Reviewer 3 for giving us detailed comments to improve our manuscript. The responses to the comments from Reviewer 3 are addressed point by point as follows.
General Comments
Xiaotong Wei and co-authors present a multi-proxy study on short sediment core from a closed lake system (Lake Ebinur) in northwestern China. They measured grain size, color reflectance and carbon content on discrete samples. So far, I have not looked at the other reviews and the replays by the authors on the discussion website of Climate of the Past in order to provide an unbiased report on the manuscript as possible.
Thank you very much for your review. We have responded to the reviewer's comments point by point. Please see “Reply on RC1 (2)” and “Reply on EC1” on the website discussion of Climate of the Past.
About grain size:
Q1: The authors relay their story mostly on the grain size data. They relate the grain size to the wind strength and argue that the wind activity was stronger in the first half of their record. As the core comes from a closed lake basin, the lake level could have a strong influence on the sediment composition. The water depth at the coring site is only 0.8 m and so lake level fluctuations must have a huge influence. Fig. 8k shows the fluctuations of the lake surface since 1955, which are mainly due to anthropogenic changes. However, there must also have been fluctuations in the lake level before that, caused by climate fluctuations.
The grain size fluctuates considerably larger in the older part of the record. Key here would be the sedimentology of the courser grain size intervals. Are these discrete layers? Are they graded? Unfortunately, the core was sampled in the field and no core photographs are available to study the sedimentology in detail. The similar evolution of the mean grain size and the lake area (Fig. 8a, 8k) indicates, in my opinion, a strong influence of lake level on sediment composition.
Yes, the fluctuations of the lake level could have some effects on the sediment composition. However, we consider the grain size changes reflect the wind strength based on the following three points:
1) In the field sampling process, the coarse-grained layer in the lower part did not show obvious depositional discontinuity and lithology change, so we believe that the deposition is continuous;
2) The whole core is mainly composed of fine-grained sediments with a maximum median grain size of 9.9 μm, and we think
3) The Y values of all samples (-19.5 to -7.6) are lower than -2.74, supporting their windblown origin (Jiang et al., 2017, 2022; Wei et al., 2021);
4) The EM2 component (~ 24.1 μm) shows a similar modal distribution with aeolian dust samples collected from the Ebinur drainage area (15-26 μm) (Ma et al., 2016), further supporting the windblown origin.
Reference
Jiang, H.C., Zhong, N., Li, Y.H., Ma, X.L., Xu, H.Y., Shi, W., Zhang, S.Q., and Nie, G.Z.: A continuous 13.3-ka record of seismogenic dust events in lacustrine sediments in the eastern Tibetan Plateau, Sci. Rep., 7, 1-10, https://doi.org/10.10 38/s41598-017-16027-8, 2017.
Jiang, H.C., Zhang, J.Y., Zhang, S.Q., Zhong, N., Wan. S.M., Alsop, G.I., Xu, H.Y., Guo, Q.Q., and Yan, Z.: Tectonic and Climatic Impacts on Environmental Evolution in East Asia During the Palaeogene, Geophys. Res. Lett., 49, e2021GL096832, https://doi.org/10.1029/2021GL096832, 2022.
Ma, L., Wu, J.L., and Abuduwaili, J.: Variation in aeolian environments recorded by the particle size distribution of lacustrine sediments in Ebinur Lake, northwest China, SpringerPlus, 5, 1-8, https://doi.org/10.1186/s40064-016-2146-0, 2016.
Wei, X.T., Jiang, H.C., Xu, H.Y., Fan, J.W., Shi, W., Guo, Q.Q., and Zhang, S.Q.: Response of sedimentary and pollen records to the 1933 Diexi earthquake on the eastern Tibetan Plateau, Ecol. Indic., 129, 107887, https://doi.org/10.1016/j.ecoli nd.2021.107887, 2021.
Other open questions concerning the grain size:
Q2: The authors mention in line 320 glacial meltwater and relate the increase in the L* value to the glacial melting in last decades. Here the question would be how strong this influence was in the older part of the record.
Thank you very much for your kind reminding. In the older part of the record, L* values show large-amplitude fluctuations, which may be mainly related to more water vapor brought by the westerlies in the cold period. In this study, we were unable to quantify the contribution of glacier melting to L* value in the older part of the record, which may require more research.
Q3: The authors relate the ultrafine components to be associated with pedogenesis. Here the question would be how fast pedogenesis would react to climate change and how large would be the time lag with the production of ultrafine particles.
Thank you very much for your review. It is true that pedogenesis has a time lag in response to climate change. However, our data are insufficient to tell how long the time lag is, which requires more specific research.
External forcing factors:
Q4: The authors try to relate the observed changes in the Lake Ebinur sedimentary record to external climate forcings like greenhouse gases or total solar irradiance (TSI). They propose that the climate transition around 1920 AD was manly controlled by TSI. However, they do not provide any mechanistical model how TSI would influence the sediment deposition in Lake Ebinur. The identification of the TSI as the most important external factor is therefore based on weak scientific grounds.
Thank you very much for your kind reminding. In this study, the most important achievement is that we reveal the 1920 AD climate transition point through the multi-proxies record of the lake Ebinur sedimentary sequence. Then, we try to explore the main controlling factors of climate transition by comparing the external drivers (total solar irradiance, greenhouse gases, and volcanic eruption). The results show that the large increase of TSI in 1920 AD may be the main controlling factor of the climate transition. More simulation studies are needed to develop a mechanism model of how TSI would influence the sediment deposition in lake Ebinur.
Citation: https://doi.org/10.5194/cp-2022-92-AC4
-
AC4: 'Reply on RC3', Xiaotong Wei, 06 Mar 2023
Viewed
HTML | XML | Total | BibTeX | EndNote | |
---|---|---|---|---|---|
645 | 203 | 63 | 911 | 33 | 37 |
- HTML: 645
- PDF: 203
- XML: 63
- Total: 911
- BibTeX: 33
- EndNote: 37
Viewed (geographical distribution)
Country | # | Views | % |
---|
Total: | 0 |
HTML: | 0 |
PDF: | 0 |
XML: | 0 |
- 1