USAP-DC

Efforts to improve sea level forecasting on a warming planet have focused on determining the temperature, sea level and extent of polar ice sheets during Earth’s past warm periods. Large uncertainties, however, in reconstructions of past and future sea levels, result from the poorly constrained climate sensitivity of the Antarctic Ice sheet (AIS). This research project aims to develop the use of subglacial precipitates as an archive the Antarctic ice sheet (AIS) past response to climate change. The subglacial precipitates from East Antarctica form in water bodies beneath Antarctic ice and in doing so provide an entirely new and unique measure of how the AIS responds to climate change. In preliminary examination of these precipitates, we identified multiple samples consisting of cyclic opal and calcite that spans hundreds of thousands of years in duration. Our preliminary geochemical characterization of these samples indicates that the observed mineralogic changes result from a cyclic change in subglacial water compositions between isotopically and chemically distinct waters. Opal-forming waters are reduced (Ce* <1 and high Fe/Mn) and exhibit elevated 234U/238U compositions similar to the saline groundwater brines found at the periphery of the AIS. Calcite-forming waters, are rather, oxidized and exhibit δ18O compositions consistent with derivation from the depleted polar plateau (< -50 ‰). 234U-230Th dates permit construction of a robust timeseries describing these mineralogic and compositional changes through time. Comparisons of these time series with other Antarctic climate records (e.g., ice core records) reveal that calcite forming events align with millennial scale changes in local temperature or “Antarctic isotopic maximums”, which represent Southern Hemisphere warm periods during low Atlantic Meridional overturning circulation. Ultimately, this project seeks to develop a comprehensive model as to how changes in the thermohaline cycle induce a glaciologic response which in turn induces a change in the composition of subglacial waters and the mineralogic phase recorded within the precipitate archive.

Person	Role
Blackburn, Terrence	Investigator and contact
Tulaczyk, Slawek	Co-Investigator
Hain, Mathis	Co-Investigator
Rasbury, Troy	Co-Investigator

Antarctic Earth Sciences	Award # 2045611
Antarctic Earth Sciences	Award # 2042495

USAP-2042495_1

None in the Database

1. Piccione, G., Blackburn, T., Tulaczyk, S., Rasbury, E. T., Hain, M. P., Ibarra, D. E., Methner, K., Tinglof, C., Cheney, B., Northrup, P., & Licht, K. (2022). Subglacial precipitates record Antarctic ice sheet response to late Pleistocene millennial climate cycles. Nature Communications, 13(1). (doi:10.1038/s41467-022-33009-1)