the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Spring onset and seasonality patterns during the Lateglacial in the eastern Baltic region
- 1Department of Geology, Tallinn University of Technology, Tallinn, 19086, Estonia
- 2Department of Geosciences and Physical Geography, Utrecht University, Utrecht, 3584, The Netherlands
- 1Department of Geology, Tallinn University of Technology, Tallinn, 19086, Estonia
- 2Department of Geosciences and Physical Geography, Utrecht University, Utrecht, 3584, The Netherlands
Abstract. Spring onset is an important phenological observation that is sensitive to modern climate change and can be traced back in geological time. The Lateglacial (~14500–11700 cal yr BP) spring onset and growing season (growth-degree-days) dynamics in the eastern Baltic region were reconstructed using the micro-phenological approach based on the dwarf birch (Betula nana) subfossil leaf cuticles. The presented study sites, Lake Lielais Svetinu (eastern Latvia) and Lake Kosilase (central Estonia), are located ~200 km apart in the region affected by the south-eastern sector of the Scandinavian Ice Sheet. During the Lateglacial period the region and its biota were influenced by the retreating glacier and the different stages of the Baltic Ice Lake. The plant macrofossil data confirms that the study sites were located in different vegetation zones (arctic-to-boreal) during the Lateglacial period. The dynamics of the estimated length of the growing season and spring onset, combined with the regional collection of plant macrofossil records, suggest the importance of local settings to species migration. During the Lateglacial warming period (Bølling/Allerød), a notable spring warming and longer growing season was calculated based on micro-phenology, but the treeline did not extend beyond central Estonia. The comparison of pollen- and chironomid-inferred past temperature estimations with spring onset, growth-degree-days, and plant macrofossil data shows coherent patterns during the cooler Older Dryas and warmer Bølling/ Allerød periods while suggesting more complicated climate dynamics and possible warmer episodes during the Younger Dryas cold reversal.
Leeli Amon et al.
Status: final response (author comments only)
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RC1: 'Comment on cp-2021-133', Anonymous Referee #1, 14 Dec 2021
The article is a highly professional paper whose topic will be of interest to a wide range of specialists dealing with palaeoclimate. The results and methodology of the study expand the possibilities of reconstructing the climate of the past, paying attention to such an important aspect as the phenological season. The article is clearly written and does not need any improvements. It can be published without changes.
- AC1: 'Reply on RC1', Leeli Amon, 20 Dec 2021
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CC1: 'Comment on cp-2021-133', Irina Kurina, 26 Jan 2022
The manuscript “Spring onset and seasonality patterns during the Lateglacial in the eastern Baltic region” by Leeli Amon and co-authors draws the attention with an original proxy applied, which allows the reconstruction of the features of the spring season. This gives us new information about the palaeoenvironment, namely the spring onset, something that we cannot extract from other proxies (analysis of pollen and chironomid remains). Furthermore, this manuscript includes meaningful discussion in which the findings are compared with similar data obtained earlier for the nearby regions of Scandinavia. Thus the discussion shows the spatio-temporal variability of the spring onset during the Lateglacial period. I believe this manuscript deserves to be published in the journal Climate of the Past. Although I have a few critical comments that will help improve the structure of the manuscript and make it easier to read.
Lines 70-75 Description of the study area – I suggest to show modern climate conditions for the two coring lakes in a uniform way. I do not understand is it make sense to show mean temperature of the coldest and of the warmest month for the one coring site if you did not show these figures for the second coring site. Next, if you show snow cover duration in months and in days for the one coring site, then, I think, you should show snow cover duration in months and in days for the second coring site. But in the manuscript, for Latvia you marked snow cover duration in months only. Please, add also the number of days for Latvia. I understand that you took this information from the different literary sources that cited heterogeneous figures. But it is easy to calculate by yourself. As example, I calculated that snow cover duration from December 8th and 29th to March/April corresponds to 93-143 days (minimum-maximum) for Latvia. And now I can see that this number of days exceeds the number of days (75-130) that you pointed for Estonia.
Line 87-89 – you described what proxies were applied to the sediments from the L. Svetinu Lake. Please, add the information with what proxies the Lake Kosilase was investigated –uniformly as you did for the first one.
Line 114 – you used IntCal13 curve for calibration. Why did not you use IntCal20 curve, which is newer?
Line 137 – you wrote “During the Allerød, warming permitted the migration of various tree species to eastern Latvia…”. Please, clarify from where tree species migrated to Latvia.
Lines 177-178 – you wrote “similar to the modern tundra greening process and earlier spring dates reported by modern phenological observations”. Could you add reference to these modern phenological observations? Next, in the Introduction section (Lines 26-28) you mentioned “The earlier unfolding of leaves has been observed since the mid-20th century all over the Northern Hemisphere (links), although the rate of change has decelerated during the last few decades (link)”. I consider, that this phrase (Lines 26-28) contradicts to the phrase from Lines 177-178. Could you explain why the rate of leaf unfolding has decelerated during the last decades? And, next, how does this fact compare to “earlier spring dates”, which you wrote in Lines 177-178?
Lines 137, 142 and further – in the Discussion you mentioned the names of the known phases (Younger Dryas, Allerød) of the Lateglacial period. Please add to them the age range in brackets. It would be easier to read.
Figures 2 and 3 – it would be easier to read if you also point the boundaries of the known phases (as example, Younger Dryas, Bølling, Allerød) of the Lateglacial period in these figures.
Figure 2 – please, could you add scale to the photo of B. nana leaves?
Caption to the Figure 1 – why did you select the time slice of 13300 cal yr BP to show the vegetation zones? Probably you should add a short explanation (as example, it was the warmest phase in the Lateglacial or something like that).
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AC2: 'Reply on CC1', Leeli Amon, 19 Apr 2022
We thank Dr Kurina for the support, careful reading, and helpful comments.
Q: Lines 70-75 Description of the study area – I suggest to show modern climate conditions for the two coring lakes in a uniform way.
A: The modern climate data around the two study sites (Estonia: Lake Kosilase and Latvia: Lake Lielais Svetinu) are now presented in more uniform way. We discussed the days of snow cover and decided that we would go with months only: as You noted the variability between the modern observed years may be high. In case of present paleodataset from sediments we are working with much lower resolution, averaged over years.
Q: Line 87-89 – you described what proxies were applied to the sediments from the L. Svetinu Lake. Please, add the information with what proxies the Lake Kosilase was investigated –uniformly as you did for the first one.
A: Lake Kosilase is under study currently – only an unpublished plant macrofossil dataset and two radiocarbon dates, published in the present article are available.
Q: Line 114 – you used IntCal13 curve for calibration. Why did not you use IntCal20 curve, which is newer?
A: We used IntCal13 for both Lake Kosilase and Lake Lielais Svetinu, because Lielais Svetinu age model was already published using IntCal13. We re-calibrated both chronologies with IntCal20. Recalibrated ages with IntCal20 for Lake Lielais Svetinu differed from IntCal13 results about 0 to max. 50 years. Kosilase recalibrated age ranges at 95.4% probability changed slightly (Table 1), however median age values of the chronology did not change, a revision of the figures was not necessary.
Q: Line 137 – you wrote “During the Allerød, warming permitted the migration of various tree species to eastern Latvia…”. Please, clarify from where tree species migrated to Latvia.
A: The studies of Lateglacial treeline advancements in the region (Amon et al. 2014) suggest that the trees came from the southern, south-eastern regions (e.g. Lithuania and Belarus (in case of spruce) where more favorable conditions supported the trees and formation of forests before the environmental conditions allowed the migration of trees to Latvia.
Q: Lines 177-178 – you wrote “similar to the modern tundra greening process and earlier spring dates reported by modern phenological observations”. Could you add reference to these modern phenological observations? Next, in the Introduction section (Lines 26-28) you mentioned “The earlier unfolding of leaves has been observed since the mid-20th century all over the Northern Hemisphere (links), although the rate of change has decelerated during the last few decades (link)”. I consider, that this phrase (Lines 26-28) contradicts to the phrase from Lines 177-178. Could you explain why the rate of leaf unfolding has decelerated during the last decades? And, next, how does this fact compare to “earlier spring dates”, which you wrote in Lines 177-178?
A: The hypothesis of a slowdown in responsiveness raised by Fu et al (2015) has in the meanwhile been shown to be an artifact of analysis strategy (Wolkovich et al., Global Change Biology, 2021;27:4947-4949 doi: 10.1111/gcb.15746). We would like to remove “although the rate of change has decelerated during the last few decades (Fu et al., 2015).”. We rephrased the sentences, and added the relevant new references.
Q: Lines 137, 142 and further – in the Discussion you mentioned the names of the known phases (Younger Dryas, Allerød) of the Lateglacial period. Please add to them the age range in brackets.
A: The age range is added at the first mention of the climatic phase in the Discussion.
Q: Figures 2 and 3 – it would be easier to read if you also point the boundaries of the known phases (as example, Younger Dryas, Bølling, Allerød) of the Lateglacial period in these figures.
A: The Late-glacial climate episodes are added to the main discussion figure, Figure 3 and explanation to the caption.
Q: Figure 2 – please, could you add scale to the photo of B. nana leaves?
A: The scale is added to the figures.
Q: Caption to the Figure 1 – why did you select the time slice of 13300 cal yr BP to show the vegetation zones?
A: Yes, it was the most diverse local vegetation along the Baltic transect, showing communities from mixed forest to tundra. Short note added to Fig 1 caption.
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AC2: 'Reply on CC1', Leeli Amon, 19 Apr 2022
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RC2: 'Comment on cp-2021-133', Anonymous Referee #2, 15 Mar 2022
This is a really interesting paper that brings together a range of techniques to look at a very important question of seasonality in relation to climate forcing of vegetation and the seasonal patterns of climate change in a period of climatic instability. As such it is very much worthy of publication. The conclusions are at face value imporant and the proxy analyses is excellent. My issue with this paper, however, relates to the reporting and discussion around the chronology and the integration of the two sites. Firstly, altough lake Svetinu is published it would be very useful to have a summary figure of the chronology of this record and the chronological resolution of the palaeoecological data from Svetinu. Secondly, and most importantly, lake Kosilase has a lateglacial chronology based on only two radiocarbon dates, one close to the start of the interstadial and one close to the end. It is very unclear how these relate to the proxy samples. There is no real explanation of the chronological uncertainty on any of the lateglacial proxy data from Kosilase, or the uncertainty of the comparison of the data across the two lakes.
I understand that it is difficult to obtain radiocarbon dates but given this paper compares two sites with a discussion of how they record the timing of changes the lack of detail on the two chroinologies and the age model errors is a problem. I would really like to see the production of an age model for Kosilase, based on an IntCal20 calibration and a recalibraton of the age model for Svetinu using IntCal20. Moreover, the uncertainty on the calculaton of UI and inferred bud birst dates needs to be expressed in a table in the results.
Overall this is a rw
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AC3: 'Reply on RC2', Leeli Amon, 19 Apr 2022
We thank the reviewer for the comments.
Q: Firstly, although lake Svetinu is published it would be very useful to have a summary figure of the chronology of this record and the chronological resolution of the palaeoecological data from Svetinu. Secondly, and most importantly, lake Kosilase has a lateglacial chronology based on only two radiocarbon dates, one close to the start of the interstadial and one close to the end.
… I would really like to see the production of an age model for Kosilase, based on an IntCal20 calibration and a recalibraton of the age model for Svetinu using IntCal20.
A: The analysed part of Kosilase core is relatively short, only 20 cm but rich in subfossil leaves. We discussed and decided that according to our experience on the Baltic Late-glacial material two dates per 20 cm covering ca 700 years could give us a good estimation of chronology. Also, we do not compare the datasets closely, as we understand that the chronological resolution is different, but describing the trends. Initially we used IntCal13 for calibration because Lielais Svetinu agemodel was published with that. We now re-calibrated both datasets with IntCal20 (Figure below). For Kosilase median age values didn’t change, but age ranges at 95.4% probability changed slightly and we added new corrected dates to Table 1. Lake Lielais Svetinu recalibrated ages with IntCal20 differed from IntCal13 results 0- max. 50 years.
Q: The uncertainty on the calculaton of UI and inferred bud birst dates needs to be expressed in a table in the results.
A: The uncertainties are expressed as GDD5 model (r2=0.68, p = <0.001, RMSE = 62 GDD5), DOY model (r2 = 0.7, p = 0.002, RMSE – 3.8 days) and added in the text (lines 99-100).
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AC3: 'Reply on RC2', Leeli Amon, 19 Apr 2022
Leeli Amon et al.
Leeli Amon et al.
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