USAP-DC

Stone/1341728 This award supports a project to determine if the West Antarctic Ice Sheet (WAIS) has thinned and collapsed in the past and if so, when did this occur. This topic is of interest to geologists who have long been studying the history and behavior of ice sheets (including the WAIS) in order to determine what climatic conditions allow an ice sheet to survive and what conditions have caused them to collapse in the past. The bulk of this research has focused on the last ice age, when climate conditions were far colder than the present; this project will focus on the response of ice sheets to warmer climates in the past. A new and potentially transformative approach that uses the analysis of atoms transformed by cosmic-rays in bedrock beneath the WAIS will allow a definitive test for ice free conditions in the past. This is because the cosmic rays capable of producing the necessary reactions can penetrate only a few meters through glacier ice. Therefore, if they are detected in samples from hundreds of meters below the current ice sheet surface this would provide definitive proof of mostly ice-free conditions in the past. The concentrations of different cosmic ray products in cores from different depths will help answer the question of how frequently bedrock has been exposed, how much the ice sheet has thinned, and which time periods in the past produced climatic conditions capable of making the ice sheet unstable. Short bedrock cores beneath the ice sheet near the Pirrit Hills in West Antarctica will be collected using a new agile sub-ice geological drill (capable of drilling up to 200 meters beneath the ice surface) that is being developed by the Ice Drilling Program Office (IDPO) to support this and other projects. Favorable drilling sites have already been identified based on prior reconnaissance mapping, sample analysis and radar surveys of the ice-sheet bed. The cores collected in this study will be analyzed for cosmic-ray-produced isotopes of different elements with a range of half-lives from 5700 yr (C-14) to 1.4 Myr (Be-10), as well as stable Ne-21. The presence or absence of these isotopes will provide a definitive test of whether bedrock surfaces were ice-free in the past and due to their different half-lives, ratios of the isotopes will place constraints on the age, frequency and duration of past exposure episodes. Results from bedrock surfaces at different depths will indicate the degree of past ice-sheet thinning. The aim is to tie evidence of deglaciation in the past to specific periods of warmer climate and thus to gauge the ice sheet's response to known climate conditions. This project addresses the broad question of ice-sheet sensitivity to climate warming, which previously has been largely determined indirectly from sea-level records. In contrast, this project will provide direct measurements that provide evidence of ice-sheet thinning in West Antarctica. Results from this work will help to identify the climatic factors and thresholds capable of endangering the WAIS in future. The project will make a significant contribution to the ongoing study of climate change, ice-sheet melting and associated sea-level rise. This project has field work in Antarctica.

Person	Role
Stone, John	Investigator and contact

Antarctic Glaciology

Award # 1341728

USAP-1341728_1

Deployment	Type
Pirrit Hills subglacial drilling	general deployment

Data_Management_subglacial_drilling.pdf

Repository	Title (link)	Format(s)	Status
ICE-D	Cosmogenic nuclide data, Mt Axtell	None	exists
ICE-D	Cosmogenic nuclide data, Mt Tidd	None	exists
ICE-D	Cosmogenic nuclide data, Mt Turcotte	None	exists
ICE-D	Cosmogenic nuclide data, Mt Goodwin	None	exists
ICE-D	Cosmogenic nuclide data, Harter Nunatak	None	exists
ICE-D	Cosmogenic nuclide data, John Nunatak	None	exists
USAP-DC	Pirrit Hills subglacial bedrock core RB-2, cosmogenic Be-10, Al-26 data	None	exists

1. Spector, P., Stone, J., Pollard, D., Hillebrand, T., Lewis, C., & Gombiner, J. (2018). West Antarctic sites for subglacial drilling to test for past ice-sheet collapse. The Cryosphere, 12(8), 2741-2757. (doi:10.5194/tc-12-2741-2018)
2. Spector, P., Stone, J., Pollard, D., Hillebrand, T., Lewis, C., & Gombiner, J. (2018). West Antarctic sites for subglacial drilling to test for past ice-sheet collapse. (doi:10.5194/tc-2018-88)