the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 29 Sep 2023
Reconstructing Younger Dryas Ground Temperature and Snow Thickness from Cave Deposits
Paul Töchterle
Anna Baldo
Julian B. Murton
Frederik Schenk
R. Lawrence Edwards
Gabriella Koltai
Gina E. Moseley
Abstract. The Younger Dryas Stadial was characterized by a rapid shift towards cold-climate conditions in the North Atlantic realm during the last deglaciation. While some climate parameters including atmospheric temperature and glacier extent are widely studied, empirical constraints on permafrost temperature and snow thickness are limited. To address this, we present a regional dataset of cryogenic cave carbonates (CCCs) from three caves in Great Britain that formed at temperatures between −2 and 0 °C. Our CCC record indicates that these permafrost temperatures persisted for most of the Younger Dryas. By 15 combining ground temperatures with surface temperatures from high-resolution, ground-truthed model simulations, we demonstrate that ground temperatures were approximately 6.6 ± 2.3 °C warmer than the mean annual air temperature. Our results suggest that the observed temperature offset between permafrost and the atmosphere can be explained by an average snow thickness between 0.2 and 0.9 m, which persisted for 233 ± 54 days per year.
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Paul Töchterle et al.
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RC1: 'Comment on cp-2023-72', Anonymous Referee #1, 02 Nov 2023
Reviewer comments on CP-2023-72, „Reconstructing Younger Dryas Ground Temperature and Snow Thickness from cave deposits” by Töchterle et al.
I have read with great interest the discussion paper by Töchterle et al., using Cryogenic Cave Carbonates (CCCs) to reconstruct past permafrost conditions during the Younger Dryas in Great Britain. The manuscript is well written, the analytical methods are sound and overall, the drawn conclusions appear to be well-justified. I have only some minor comments that may help to improve the manuscript.
My first "major" comment concerns the uncertainty propagation of the temperature (offset) estimates. It is unclear to me how propagated uncertainties are calculated (L241ff). While the temperature offset uncertainty for the proxy reconstructions appears to be calculated by the sum of the errors of MAGT and MAAT, this seems to be different for the offset for the CESM. Likewise, in L280 a different uncertainty for the temperature offset is given (most likely a typo), but please clarify.
Secondly, I would also ask the authors to provide more context on the involved models and methods to estimate Younger Dryas snow cover (L270ff). The model used in part (1) (“Analytical approach”) seems to be kind of a black box, and it would be good to include more explanations of the components and assumptions of the model. In part (2) I was wondering if the grid cells used as modern analogues were also checked if they are “analogues” also in terms of seasonality? The seasonal T differences appear to have been extreme according to the model, so this could also affect the results.
Lastly, I miss a more summarizing, concluding statement, what the results actually mean? For example, how “new” or “(un-) expected” are the results? The current version of the manuscript leaves the reader a bit lost on how to assess the numbers of snow days per year or the derived snow thickness etc...
In addition, I have some minor comments along the text:
L17/18: I would provide a statement/context in the abstract, what these results actually mean.
L23 Maybe state a number of what is meant by “extremely cold” of “most severe cooling”
L38ff Sometimes it is unclear, if the statements refer only to Britain, Northern Europe in general, or other areas. This relates a bit to the whole introduction, that it could be more clearly outlined how well YD climate/permafrost is investigated in Britain, in N Europe, and why it would be important/necessary to find out more about it…
Fig 1: Colors of the cave symbols are hard to see
L93ff Please provide also absolute min/max temperatures for the cave
L100 does this impact ventilation / temperature exchange?
L163ff Would it be possible to elaborate this in a bit more detail? In the site description, it is noted, that convective heat flux is not dominant for Nettle pot?
L241 How is the error estimated? Shouldn’t it be 3.1°C? (2.1 + 1°C)
L256 see previous comment (uncertainty?)
L257 also here related to previous comment (uncertainty?)
L274ff only one sentence to explain the model that produces the main result is very few information…
L280 now its +- 2.4°C?
L292 where these grid cells also checked if they compare well in terms of seasonality, i.e. min/max temperatures?
Citation: https://doi.org/10.5194/cp-2023-72-RC1 -
RC2: 'Comment on cp-2023-72', Anonymous Referee #2, 22 Nov 2023
The authors have completed a really nice study on cryogenic cave carbonates from three sites in the British Isles that constrain mean annual ground temperatures (MAGT) during the Younger Dryas interval. The CCC, compared to other estimates of mean annual air temperatures during the YD suggest that the ground must have been significantly warmer than the air, and a model suggests that a snow cover thickness of around 0.4 m over a long winter season could allow ground temperatures in the CCC thermal window. These data add evidence for YD conditions in the British Isles and North Atlantic region during a critical time interval in the last deglaciation. The authors provide some modern analog locations similar to what they estimated for the YD.
Overall, the results are solid and support the authors interpretation. I cannot identify any problems with the paper. The writing was clear (mostly, but see below), and the reasoning solid.
Perhaps the only substantive comment I have on the manuscript is that the paper ends abruptly at line 343. It seems to be missing a conclusion, or at least a paragraph to summarize the main findings and implications of the study. The authors might consider some broader questions related to their data in a summary paragraph of section.
Figure 1. Indicate that the isotherms are estimate YD isotherms. I got confused when I saw the figure because I assumed they were modern initially but I had to read carefully to find out not.
In the Modern Climate Data section, I feel there needs to be a better description of the permafrost data: what it is, why it was used, what time it represents. Is it only for the Britain? The study sites? Eurasia?
Figure 2. Records, plural? I only see one other paleoclimate record. Add the Cheng et al 2020 citation to caption.
Fig. 6 caption, I think it should read ±2.1 not +-2.1
To a reader not versed in the details of the TTOP method, it would be helpful to walk the reader through it using plain English.
Can the authors say anything about MAGT during the preceding Bolling period? It is interesting that the CCCs correspond so well to the YD, but what would have been the MAGT depression during the YD relative to the Bolling?
Citation: https://doi.org/10.5194/cp-2023-72-RC2
Paul Töchterle et al.
Paul Töchterle et al.
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