the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 04 Nov 2024
Changes in precipitation and temperature patterns related to the state of the North Atlantic Ocean during the Medieval Climate Anomaly
Abstract. In a warmer climate, uncertainties persist regarding regional precipitation responses and a potential weakening of the Atlantic Meridional Overturning Circulation (AMOC). This study examines the Medieval Climate Anomaly (~800–1399 CE) warm period to uncover hydroclimate patterns and their links with the North Atlantic Ocean variability, including AMOC, Sea Surface Temperature (SST), and the Inter-Tropical Convergence Zone (ITCZ) at centennial (100-years) scales. Analyzing change-sensitive multi-proxy data reveals that North Atlantic Ocean conditions play a significant role in influencing hydroclimate variability across Europe and North America, potentially by regulating atmospheric heat and moisture transport. Specifically, we show that warm SST conditions correspond to warmer climates on both continents, while low SST periods are associated with a southward shift of the ITCZ, potentially initiating cooler climates and hydrological variations. However, the state of the AMOC remains unclear, despite indications of subtle weakening in some records. Exploring hydroclimate suggests that continental-scale precipitation variations are linked to temperature changes, but regional responses are uncertain. Notably, warmer/slightly warmer climates are primarily linked to more humid conditions, especially in mid-latitude regions. Conversely, slightly colder climates tend to result in more arid conditions. Comparing model assimilation with proxy data reveals significant discrepancies, suggesting that either the models fail to adequately capture key processes or the proxy data contain substantial uncertainties. While our findings provide valuable insights into regional hydroclimate changes and variability in the North Atlantic Ocean state under a warmer climate, they also emphasize the necessity for more in-depth research on regional precipitation variability and the identification of appropriate proxies for tracking AMOC signals.
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RC1: 'Comment on cp-2024-68', Anonymous Referee #1, 24 Feb 2025
Review of "Changes in precipitation and temperature patterns related to the state of the North Atlantic Ocean during the Medieval Climate Anomaly" (cp-2024-68)In this paper the authors are interested in temperature and hydroclimate of the MCA and compare a range of proxy data sources with a paleoclimate data assimilation product and a model simulation. In general I think the paper does a decent job of accomplishing the stated goals and the conclusions are in line with the somewhat ambiguous and somewhat conflicting results of the underlying data.
PaleoView data source: This source appears to just be a way of accessing the TRaCE21ka simulation? Some places in the paper the authors appear to categorize it as a data assimilation product like PHYDA (e.g., lines 270-271) but that is not accurate. They authors need to make it more clear that PaleoView is the TRaCE21ka simulation data alone and is not modified by proxy data in the same way that PHYDA is.
Reference to "grid" values throughout the text: I recommend using something like "continental average" (or perhaps some abbreviation indicating regional average) to indicate that this is a regional averaged value. Calling it "grid" is a little strange or unclear what is meant if you are also using "point" estimates because the terms grids and points are often used interchangeably or are at least closely related.
Hydroclimate variables: I'm confused as to why the authors used the variable label "P-E" throughout the comparisons between proxy, model, and reconstructed data. Having some proxies be approximately P-E is plausible enough but then the TRaCE21ka data is just temperature or precipitation (so missing E) and PHYDA is PDSI, which is much more complicated than P-E. I think the authors should indicate in Figs 8,9, Table 1 that these values are not actually P-E. This may also account for some of the discrepancies that the authors see in their analyses between the data sources.
ITCZ: So the ITCZ is a deep-tropical phenomena yet very little proxy data analyzed here is from the tropics. It was unclear to me how it was justified and used to be an indicator of the ITCZ? Also I noticed that the authors frequently use ITCZ for assessing North Atlantic variability. I don't think this makes sense given that the ITCZ and North Atlantic are dynamically and geographically separate things.
Citation: https://doi.org/10.5194/cp-2024-68-RC1 -
AC1: 'Reply on RC1', Shailendra Pratap, 19 Jul 2025
Dear Reviewer,
I hope this message finds you well. Thank you very much for taking the time to evaluate our manuscript and for your thoughtful feedback and positive response. We sincerely appreciate your constructive comments, which have helped us improve the quality of the work.
Please find our detailed responses to your comments attached as a PDF file in the supplementary materials.
Thank you very much.
Sincerely,
Shailendra Pratap
On behalf of all co-authors
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AC1: 'Reply on RC1', Shailendra Pratap, 19 Jul 2025
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RC2: 'Comment on cp-2024-68', Anonymous Referee #2, 23 May 2025
In this manuscript Pratap and co-authors seek to explore variations in temperature, hydroclimate and ocean circulation, primarily in the north Atlantic during the middle portion of the Common Era. This is achieved through the synthesis of previously-published records and their comparison to a data assimilation product (PHYDA ) and a CCSM3 simulation spanning the past 21,000 years (accessed via PaleoView). The focus on the time from 800-1400 C.E., during the so-called Medieval Climate Anomaly, arguing that it is warm climate.
I am generally supportive of synthesis efforts and data-model comparison efforts. Every source of paleoclimate data has it's strengths and weaknesses, and combining them can often amplify mutual signals and minimize noise. However, the value of such syntheses should be to yield new insight and I find that Pratap and co-authors do not successfully achieve this. While I find no fatal flaws in their analyses, I also do not see that this study brings much new insight to the community. Given that other synthesis studies exist using similar data (e.g Moffa-Sanchez et al., 2019; https://doi.org/10.1029/2018PA003508), the authors do not make a clear case for what this study adds. Many conclusions seem either fairly well established (e.g. warm SST corresponds with warm continental temperature, cool SST drives the ITCZ southward, etc.) or are ambiguous (e.g. "the sensitivity of AMOC tracers across both space and time require further investigation"). Thus, I suggest the authors either more clearly articulate how their work advances understanding relative to previous synthesis studies or hold off on publication until they have a result that does advance knowledge.
A more specific concern regards how the authors approach the PHYDA data at its comparison to their work. The authors state that PHYDA is included to "assess the reliability of model-based paleoclimate outputs," and I fear they may be interpreting PHYDA as a model. Consistent with this, they suggest that poor correlations between their data and PHYDA highlight "the need for improvements in model performance." Rather, PHYDA is a data assimilation product that likely includes many of the same datasets considered by Pratap et al, but arguably synthesizes these data in a more sophisticated and physically-realistic way.
Citation: https://doi.org/10.5194/cp-2024-68-RC2 -
AC2: 'Reply on RC2', Shailendra Pratap, 19 Jul 2025
Dear Reviewer,
I hope this message finds you well. Thank you very much for taking the time to evaluate our manuscript and for providing encouraging feedback and a positive response. We sincerely appreciate your thoughtful comments, which have helped us improve the quality of our work.
Please find our detailed responses to your comments attached as a PDF file in the supplementary materials.
Thank you.
Kind regards,
Shailendra Pratap
On behalf of all co-authors
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AC2: 'Reply on RC2', Shailendra Pratap, 19 Jul 2025
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