the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 23 Sep 2026
Evaporitic carbonates record surface melting in Antarctica
Abstract. Changes in Pleistocene Antarctic temperatures often coincide with variations in Northern Hemisphere summer insolation. While models invoking global CO₂ changes and shifts in oceanic and atmospheric circulation explain the temperature coherence between the poles, the role of Southern Hemisphere insolation in local Antarctic temperatures remain unclear. Here we present a temporal and geochemical record of Antarctic surface melting recorded by evaporitic carbonate formation from eight sites spanning the Amundsen Sea to the Ross Sea and 365m - 2000m in elevation. Isotopic data indicate water sourced from surface melt that weathers local rock and saturates carbonate through evaporation. U–Th dates restrict carbonate formation to three of the five most recent periods of high Southern Hemisphere summer insolation. These observations calibrate the effective albedo of darkened surfaces near nunataks and identify a Southern Hemisphere summer insolation threshold at which surface melt can occur under polar conditions.
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Status: open (until 03 Dec 2026)
- RC1: 'Comment on egusphere-2026-4455', Anonymous Referee #1, 29 Oct 2026 reply
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- 1
This study present novel data from evaporitic calcite crusts found in nunataks at 365-2000 m elevation in Antarctica. The formation of these calcite crusts requires the presence of liquid water, and as such, determining their period of growth can provide a chronology for which conditions were suitable for their growth. Here, the authors use 13C and 18O measurements to infer the process by which they develop (evaporation of liquid water) and U/Th dating method to obtain ages of the calcite crusts. 11 out of 14 samples are of Holocene age (2-6ka) and three samples at elevation >1400 m had ages of 43ka, 92.9ka and 97.8ka. The authors attempt to link their age distribution to periods where summer air temperatures were >0C, which would allow for the melting of snowpack, chemical weathering with local rocks and subsequent formation of evaporitic calcite crusts. No relation was found, and the authors then attempt to correlate the U/Th age distribution of summer insolation (because a thin snowpack can melt even if air temperatures are <0C due to energy transfer to the ground underneath; the authors could mention the studies from Antarctica that presented evidence of this).
However, the study fails to properly describe the assumptions in their approach. Namely, the formation of these calcite crusts in nunataks requires: 1) the presence of snow on the ground, 2) favourable conditions to melt snow, and 3) most importantly, that these areas remained nunataks for the past 100ka. Judging by Fig. 1B, at least this site seems to very close to the current elevation of the WAIS. Many studies documented that the East and West Antarctic Ice Sheet were hundreds of meters thicker during the last glacial maximum. As such, before attempting to correlate the U/Th age distribution of the evaporative calcite crusts with climatic conditions, the authors need to convince the readers that these areas remained in fact nunataks throughout the late Pleistocene and Holocene. If these areas were covered by ice at any point during this timeframe, then the U/Th age distribution of the calcite crusts might reflect periods when the EAIS and WAIS were thinner and therefore, they could be proxies of ice thickness in these mountainous areas. I therefore recommend substantive revisions to the manuscript.
Minor detail. The presentation of methods and results should follow that in the discussion: 13C and 18O (for process by which the calcite crusts formed), 87Sr/86Sr (for chemical weathering and source of Ca), and U/Th ages (time-series).