Abstract
Abstract. The S27 ice core, drilled in the Allan Hills Blue Ice Area of East Antarctica, is located in southern Victoria Land, ∼80 km away from the present-day northern edge of the Ross Ice Shelf. Here, we utilize the reconstructed accumulation rate of S27 covering the Last Interglacial (LIG) period between 129 ka and 116 ka (where ka indicates thousands of years before present) to infer moisture transport into the region. The accumulation rate is based on the ice-age–gas-age differences calculated from the ice chronology, which is constrained by the stable water isotopes of the ice, and an improved gas chronology based on measurements of oxygen isotopes of O2 in the trapped gases. The peak accumulation rate in S27 occurred at 128.2 ka, near the peak LIG warming in Antarctica. Even the most conservative estimate yields an order-of-magnitude increase in the accumulation rate during the LIG maximum, whereas other Antarctic ice cores are typically characterized by a glacial–interglacial difference of a factor of 2 to 3. While part of the increase in S27 accumulation rates must originate from changes in the large-scale atmospheric circulation, additional mechanisms are needed to explain the large changes. We hypothesize that the exceptionally high snow accumulation recorded in S27 reflects open-ocean conditions in the Ross Sea, created by reduced sea ice extent and increased polynya size and perhaps by a southward retreat of the Ross Ice Shelf relative to its present-day position near the onset of the LIG. The proposed ice shelf retreat would also be compatible with a sea-level high stand around 129 ka significantly sourced from West Antarctica. The peak in S27 accumulation rates is transient, suggesting that if the Ross Ice Shelf had indeed retreated during the early LIG, it would have re-advanced by 125 ka.
Highlights
The West Antarctic Ice Sheet (WAIS) is grounded on bedrock that currently lies below sea level and is vulnerable to rising temperatures (Mercer, 1968; Hughes, 1973)
We extend the existing Site 27 (S27) δ18O of atmospheric O2 (δ18Oatm) measurements by adding new δ18Oatm values at 45 depths, including one that overlaps with earlier data, in order to understand the stratigraphic integrity of the record at ∼ 180 ka and further improve the gas chronology
Each of the δ18Oatm minima and maxima associated with orbital-scale insolation variations between 105 and 245 ka is successfully identified in S27, including the δ18Oatm peak around 180 ka that was previously missing in Spaulding et al (2013)
Summary
The West Antarctic Ice Sheet (WAIS) is grounded on bedrock that currently lies below sea level and is vulnerable to rising temperatures (Mercer, 1968; Hughes, 1973). The stability of the WAIS remains poorly understood and constitutes a major source of uncertainty in projecting future sea-level rises in a warming world (Dutton et al, 2015a; DeConto and Pollard, 2016). One way to constrain the sensitivity of ice sheets to climate change is to explore their behavior during past warm periods. The Last Interglacial (LIG) between 129 ka and 116 ka (where ka indicates thousands of years before present) is a geologically recent warm interval with an average global temperature 0 to 2 ◦C above the preindustrial level (Otto-Bliesner et al, 2013). While the WAIS must have contributed to the LIG sea-level high stand (Dutton et al, 2015a, and references therein), quantifying these contributions is challenging and the timing of such WAIS changes (early versus late in LIG)
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