USAP-DC

This work will constrain WAIS elevation during the last interglacial in Marie Byrd Land (MBL) using shallow drilling to obtain bedrock samples from the ice-rock interface and measuring cosmogenic nuclide concentrations. The 26Al/10Be ratio is not sensitive to recent short periods of exposure or cover and thus quartz-bearing bedrock cannot be used to resolve exposure during MIS 5. In contrast, the bedrock on the southern flank of Mt. Waesche consists of young lava flows with existing 40Ar/39Ar ages < 350 ka; at least one flow with suitable lithology extends beneath the ice. Tephra chronology and bands of proximal volcanic debris in the adjacent blue ice area indicates volcanic eruptions within 107 ka at Mt. Waesche. The ice-covered lava flows near the ice margin are not likely to be significantly older. Thus, any 3He and36Cl in sub-ice bedrock requires exposure during the late Pleistocene. Although ice sheet models predict ice elevations 40 m lower during the LGM, exposure at deeper depths would be attributable to down draw during MIS 5. Two field seasons are proposed. The first would involve a GPR survey of the subglacial topography <100m under the blue ice area where we propose to drill, and mapping and dating the adjacent exposed lava flows in order to trace lava flows of known age and composition below the ice margin and locate appropriate drilling sites. 40Ar/39Ar and exposure ages of the subaerial lava flows would be measured during the following year. The second season would focus on drilling 8 boreholes (two transects) with the Winkie drill from near the ice margin to 80 m depth to obtain rock cores from the subice lava flows. 40Ar/39Ar ages of rock cores will determine the timing of eruption, whereas comparison with exposure ages of the same cores will constrain the timing and minimum extent of past down draw of the WAIS in MBL. In addition, deeper GPR surveys and subglacial rock lithologies might also reveal evidence of lava/ice interactions and independently place constraints on lower ice levels during past eruptions. Finally, investigators will compare results with modeled ice elevation histories and estimate the isostatic crustal response in order to convert our observed relative elevations to actual past ice elevations.

Person	Role
Zimmerer, Matthew	Investigator and contact
Campbell, Seth	Investigator
Mitrovica, Jerry	Investigator

Antarctic Earth Sciences	Award # 1745015
Antarctic Earth Sciences	Award # 1744949
Antarctic Earth Sciences	Award # 1744927

USAP-1745015_1

None in the Database