SUBGLACIAL PRECIPITATES RECORD EAST ANTARCTIC ICE SHEET RESPONSE TO PLEISTOCENE CLIMATE CYCLES

The East Antarctic ice sheet (EAIS) is the Earth’s largest freshwater reservoir and its volume contributes significantly to past and future sea level. However, because existing ice overprints geologic evidence from times when the ice sheet volume was smaller than today, it is difficult to constrain how the EAIS has responded to past warm periods. Here, we report a 100kyr record of chemical changes in basal water beneath the EAIS using subglacial chemical precipitates. The subglacial precipitates discussed here formed beneath the ice in the Wilkes Basin and are now exhumed at Elephant Moraine, a supraglacial moraine that forms as sediment rich basal ice from the base of the EAIS is brought to surface. Several precipitates from this location exhibit laminations of carbonate and opal, suggesting their deposition in water bodies with varying chemical compositions. Combining ²³⁴U-²³⁰Th ages on opal layers with elemental imaging, we derive a timeseries describing opal-calcite mineralogic transitions within these precipitates. The major finding of this study is that this record of chemical change in the hydrologic system beneath Antarctica closely matches Pleistocene glacial-interglacial climate cycles, suggesting that Antarctic subglacial precipitates record EAIS response to global climate cyclicity. Wavelet analysis on this record of opal-calcite transitions indicates that the EAIS responds to 25kyr, 40kyr, and 100kyr orbital cycles. Geochemical models exploring the mechanism for opal-calcite transitions in subglacial environments suggest that the observed changes in mineralogy are the result of periodic melting and freezing beneath the EAIS, thereby recording the EAIS response to warming and cooling.