the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 23 May 2024
Perspective on ice age Terminations from absolute chronologies provided by global speleothem records
Abstract. Glacial Terminations represent the largest amplitude climate changes of the last several million years. Several possible orbital-insolation triggers have been described to initiate and sustain glacial Terminations. Because of the availability of radiocarbon dating, the most recent Termination (TI) has been extensively characterized. Yet, it is widely discussed whether the sequence of feedbacks, millennial events and rates of change seen in TI is recurrent over previous Terminations. Beyond the limit of radiocarbon dating, records from the speleothem archive provide absolute age control through uranium-thorium dating and high-resolution proxy measurements. The PAGES SISALv3 global speleothem database allows us to synthesize the available speleothem records covering Terminations. However, speleothem climate signals are encoded in a number of proxies, and unlike proxies in other archives like ice or marine cores, the climatic interpretation of a given proxy can vary quite significantly among different regions. In this study, we
- synthesize the available speleothem records providing climate information for Terminations: TII, TIIIA,TIII, TIV and TV,
- present the records based on the aspect of climate encoded in the available records,
- examine the effects of different ice volume corrections on the final climate proxy record,
- evaluate whether there are leads and lags in the manifestation of Terminations across different aspects of the climate systems and different regions,
- we suggest directions for future speleothem research covering Terminations, speculate on suitable tuning targets among marine and ice core proxies, and discuss what model outputs maybe most suitable for comparison.
We find that TII has the greatest number of globally distributed records followed by TIIA and TIII. The records covering TIV and TV are largely restricted to the East Asian and Southeast Asian monsoon regions. Modelling and data-model comparison studies have greatly increased our understanding of the interpretation of oxygen isotope records across Terminations. Ice volume corrections have the most significant impact on European speleothem records with moisture sourced directly from the North Atlantic region. Within each Termination, a sequence of events can be established between a sub-set of events and this sequence stays largely consistent across Terminations. However, improvements in dating and age-model uncertainties, higher resolution records and multi-proxy approaches are required to establish sequences within each sub-set of events. Beyond further research on targeted speleothem records, our recommendations for future directions include focusing on TII as a useful next target to understand climate dynamics, isotope-enabled transient simulations for better characterization of the other Terminations, and development of marine proxy records with signals common to speleothems to further improve the chronology of Terminations.
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RC1: 'Comment on cp-2024-37', Jasper Wassenburg, 23 Jun 2024
Review Kaushal et al. “Perspective on ice age Terminations from absolute chronologies provided by global speleothem records”.
General comments:
The presented manuscript compiles a global dataset of speleothem ice age Termination records for TII to TV with the purpose of describing chronological sequences of events, discuss differences and similarities between Terminations and the effects of different ice volume corrections. I believe this to be a very valuable contribution that clearly outlines future directions and targets for work on ice age Terminations. In particular, the tuning of other climate archives to speleothem proxies highlights the many purposes of speleothem records. In this regard the authors could, however, indicate some of the potential pitfalls more clearly. For example, correlating climate archives over large distances should be done with caution and only if proven that the different climate parameters respond to the same forcings without delay. The authors suggestion to use isotope enabled climate models for this purpose is indeed a critical one. Overall, the conclusions are well supported by the discussion. I’m looking forward to see this work published with a few revisions.
Specific comments:
My main comment only concerns the structure of the manuscript concerning seawater isotope corrections / ice volume corrections. Right now there is one subchapter (2.2.) devoted to “ice volume corrections”. Within this chapter also P-E changes and its effect on surface seawater d18O is discussed. I believe this subchapter should be named “sea surface d18O corrections” instead, because ice volume directly effects sea surface d18O as well.
Throughout the manuscript there is an ongoing discussion about sea surface d18O corrections. I think it would streamline the paper if everything concerning these corrections could be discussed in chapter 2.2, which ends with a clear conclusion on how every speleothem d18O record is corrected. This also means to move chapter 3.1. to chapter 2.
Lines 270 – 271: Considering the importance of the NISA d18O record for surface seawater isotope corrections I think it would be helpful to provide more background information why the NISA d18O can be used for this purpose as opposed to only referring to Stoll et al. (2022). Could you please comment on the potential temperature effect on the water to calcite isotope fractionation? A simple sentence that includes the effect of rainfall isotope d18O vs temperature and the cave air temperature water to calcite isotope fractionation would be sufficient. Then the reader who wonders why cave air temperature does not affect CaCO3 d18O will readily understand this interpretation as well.
Line 325 (and 343 – 345): Temperature is reconstructed with different proxies. Some may record cave air temperature, some record a vegetation - temperature driven d13C, and others record atmospheric air temperature with d2H or CaCO3 d18O. The seasons that are recorded by the different proxies may have a large impact on the reconstructed temperature amplitude, it would be good to mention and discuss this in more detail.
Chapter 5.3. Nice overview of how speleothem chronologies could potentially be used as tuning targets for climate archives that lack absolute chronologies. I do believe that this chapter could benefit if the potential pitfalls would be described. Please caution against tuning between records over long distances that are not necessarily part of the same systems.
Technical comments:
Line 12: should be “largest amplitude global climate”
Line 15: “a sequence of feedbacks” does not seem correct as a feedback is a consequence of an event that reinforces (positive) or buffers (negative) the effects of the event itself. Maybe rewrite to: “the sequence of millennial events, their climate feedbacks and rates of change”.
Line 19: “and unlike proxies in other archives like ice or marine cores,” I would delete this part. Ice cores over the world cannot be interpreted similar, for example if you compare a d18O ice from the Andes mountain range it may not be related to temperature as it is in the NGRIP ice core. Also marine sediments have proxies that may be interpreted differently around the world: In the Mediterranean d18O of surface dwelling foraminifera may be a P-E signal, whereas it might be dominated by temperature in regions where P-E is less dominant (polar regions?). I would rewrite it like this: “are encoded in a number of proxies, however, the climatic”
Line 28: “maybe” should be “may be”
Line 29: “IIA” should be “IIIA”
Line 42: see comment on line 12
Line 51: see comment on line 15
Line 68: add reference “Lisiecki and Stern (2016)” they also use the EA speleothem record to tune the older part of the record.
Line 143: “the timing temperature change,” should read “the timing of temperature changes”?
Line 143: temperature reconstruction can be provided by multiple proxies, such as fluid inclusions d2H (Affolter et al., 2019), calcite-water d18O with fluid inclusion and calcite d18O, TEX86 (Levy et al., 2023; Wassenburg et al., 2021) as well as (dual) clumped isotopes (Bajnai et al., 2020; Wassenburg et al., 2021).
Figure 1: To give the reader an idea of the total nr of Termination records, it would be good to include all available Termination speleothem records in Figure 1. This also gives the reader an idea of how many records have been excluded by using the author’s criteria and assess potential (if any) biases towards certain records or regions. The prioritized records could be indicated with different symbols or color as the ones that were left out.
Line 174: better reference is “Fohlmeister et al. (2018)” which is speleothem specific instead of “Kim et al., 2007” even though the difference between calcite and aragonite is similar, i.e. 0.8 permille.
Line 293: Provided that kinetic offsets from isotope equilibrium do not change.
Lines 303 - 304: See comment on lines 270 – 271.
Lines 307 - 309: Move to section 3.2. ice-volume corrections.
Line 325 (and 343 – 345): Temperature is reconstructed with different proxies. Some may record cave air temperature, some record a vegetation - temperature driven d13C, and others record atmospheric air temperature with d2H or CaCO3d18O. The seasons that are recorded by the different proxies may have a large impact on the reconstructed temperature amplitude, which needs to be discussed.
Line 394: At the Jiangjun cave site the amplitude was about 4-5 degrees C, which would correspond to max. 1 permille in calcite d18O. The 2 permille indicated in line 394 as a “temperature effect” is thus not correct. Instead, the additional 1 permille change was explained by a potential bias of the fluid inclusion d18O towards high intensity monsoon rainfall that affected the fabric and incorporation of the fluid inclusions through drip rates.
Lines 472 – 473: Would it be an idea to use a linear interpolation for the ice volume correction curves, such that you can maintain the original resolution of the speleothem isotope records, but still use an ice-volume correction?
I wonder if ordering the figures top down according to the timing of the “first response” to the glacial termination would be a better representation of the results. I do believe that it will be easier to read the figure as it would follow the same order as the records are mentioned in the manuscript.
Line 477: It already starts increasing around 140,000 yrs BP? What is the “starting point” of increasing insolation based on?
Line 485: This should be coincident with the TII interstadial event, that is actually visible in quite a few EAM records as well as increased runoff in the bay of Bengal (Nilsson-Kerr et al., 2019).
5.2. Excellent chapter. The only discussion point you might want to add is that north Europe may be expected to show a cooling in response to freshening and AMOC shutdown, but this is not clear in the northern Europe d18O records.
5.4. well done.
Chapter 6. Good future directions, well supported by the compiled speleothem Termination records.
Best wishes,
Jasper Wassenburg
Affolter, S., Häuselmann, A., Fleitmann, D., Edwards, R.L., Cheng, H., Leuenberger, M., 2019. Central Europe temperature constrained by speleothem fluid inclusion water isotopes over the past 14,000 years. Science Advances 5(6), eaav3809. doi.org/10.1126/sciadv.aav3809.
Bajnai, D., Guo, W., Spötl, C., Coplen, T.B., Methner, K., Löffler, N., Krsnik, E., Gischler, E., Hansen, M., Henkel, D., Price, G.D., Raddatz, J., Scholz, D., Fiebig, J., 2020. Dual clumped isotope thermometry resolves kinetic biases in carbonate formation temperatures. Nat. Commun. 11(1), 4005. doi.org/10.1038/s41467-020-17501-0.
Levy, E.J., Vonhof, H.B., Bar-Matthews, M., Martínez-García, A., Ayalon, A., Matthews, A., Silverman, V., Raveh-Rubin, S., Zilberman, T., Yasur, G., Schmitt, M., Haug, G.H., 2023. Weakened AMOC related to cooling and atmospheric circulation shifts in the last interglacial Eastern Mediterranean. Nat. Commun. 14(1), 5180. doi.org/10.1038/s41467-023-40880-z.
Nilsson-Kerr, K., Anand, P., Sexton, P.F., Leng, M.J., Misra, S., Clemens, S.C., Hammond, S.J., 2019. Role of Asian summer monsoon subsystems in the inter-hemispheric progression of deglaciation. Nat. Geosci. 12(4), 290-295. doi.org/10.1038/s41561-019-0319-5.
Wassenburg, J.A., Vonhof, H.B., Cheng, H., Martínez-García, A., Ebner, P.-R., Li, X., Zhang, H., Sha, L., Tian, Y., Edwards, R.L., Fiebig, J., Haug, G.H., 2021. Penultimate deglaciation Asian monsoon response to North Atlantic circulation collapse. Nat. Geosci.(14), 937-941. doi.org/10.1038/s41561-021-00851-9.
Citation: https://doi.org/10.5194/cp-2024-37-RC1 -
AC1: 'Reply on RC1', Nikita Kaushal, 29 Sep 2024
Dear Prof. Wassenburg,
Thank you for reviewing the article. And thank you for your kind and articulate comments valuing the work presented in this publication. We greatly appreciate your suggestions. We have addressed your comments in the attached document. These suggestions will certainly improve the quality of this manuscript.
Best wishes
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AC1: 'Reply on RC1', Nikita Kaushal, 29 Sep 2024
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RC2: 'Comment on cp-2024-37', Anonymous Referee #2, 09 Aug 2024
This is an interesting manuscript and a good start to stimulate further research on the timing and nature of Terminations. There is no doubt that speleothems have a great potential as they can be dated accurately and precisely with low age uncertainties. The manuscript tries to gather existing speleothem records in order to examine Terminations II, IIIA, III, IV and V in closer detail, with a focus on the sequence of events. I agree with the authors that a comprehensive overview on Terminations in speleothem is currently missing and this overdue. However, I have the feeling that the manuscript was put together quite hastily as the general structure is quite complex and many highly relevant figures are only provided as supplemental information and not in the main text (see comments below). I have the feeling that the authors should try to develop a more concise structure and to present their selection criteria for records more clearly. Furthermore, a more rigid statistical approach is required (see comments below).
Some parts on the interpretation of oxygen isotope values in section 2.1 should be moved to section 3. Furthermore, stronger emphasis should be given to the number of dates and sampling resolution of the selected key-records.
Many other speleothem records were not really considered in this overview, despite the fact that they could contribute some important additional information on the timing and nature of certain terminations. For instance the timing of the onset of stalagmite growth, e.g. the Sieben Hengste (Switzerland) record covering TII (Luetscher, M., Moseley, G.E., Festi, D., Hof, F., Edwards, R.L., Spötl, C., 2021. A Last Interglacial speleothem record from the Sieben Hengste cave system (Switzerland): Implications for alpine paleovegetation. Quaternary Science Reviews 262.) This record is very well dated and covers Termination II. Within the Alps, the Schafsloch record (Hauselmann et al., QSR, 2016) from Switzerland covering TII is not even mentioned in the text. There are also other speleothem records which could be useful and suited for this review, even if they cover only parts of a Termination. I think the authors should have done a more comprehensive review of the existing literature. Though some of the records are shown as supplemental figures, it appears that the selection of records in the main text is somewhat arbitrary. Furthermore, the fact that many important figures are shown in the supplemental information doesn’t really increase the readability.
It remains unclear to what extent different age models (COPRA/Bchron/Stalage etc.) have an effect on the timing of Terminations and it would be useful to show the effects on 2-3 records in the main text. If the effects are minimal, then one can exclude at least on potential source of uncertainty.
A stronger consideration of carbon isotope records would be also useful, particularly for speleothem records from temperate regions where vegetation and soil microbial activity are highly dependent on temperature and rainfall. The full potential of the speleothem isotope records is not exploited
Is section 2.3 really necessary as no 13C record is shown in the current version of the manuscript.
The Figure 7 is not always correct. For instance, for TII, there is only one temperature increase in Europe, whereas the text states “final step of temperature increase in Europe and North America” (lines 644-645. Please make sure that Figure 7 is indeed conform with the main text. Furthermore, please make clear how the amplitude of the change was calculated. Ice volume correction applied. In this figure, one could also display insolation forcing to reveal the phasing more clearly.
The effects of the “ice volume-correction” should be also shown more clearly as this is an important aspect as ice-volume corrections can affect the overall structure of Terminations.
Specific Comments:
Section 3.1 Records of surface ocean freshening: In this section, the Corchia Cave record should be also mentioned.
Lines 120-121: What is the specific rationale behind the use of single records and not composite records? Composite records are considered to be more robust than individual records.
Citation: https://doi.org/10.5194/cp-2024-37-RC2 -
AC2: 'Reply on RC2', Nikita Kaushal, 29 Sep 2024
Dear Referee 2,
Thank you for your comments on the relevance of such a study though we are sorry that you find the
structure to be complex, that many figures are in the supplemental material, and that the selection
criteria are not quite clear. We understand also that you would like to see a more rigid statistical
approach. We will address your comments in the attached document and this will hopefully address these concerns.
Best wishes
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AC2: 'Reply on RC2', Nikita Kaushal, 29 Sep 2024
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