SUBGLACIAL LAKE SEDIMENTS FROM MIS 5 ACCESSED AT A SUPRAGLACIAL MORAINE

Remote sensing has revealed an active subglacial hydrologic system beneath the Antarctic ice sheet, with large lakes, saturated sediments, and channels connecting these water bodies from domes to the ice sheet edges. Here we report the first occurrence of subglacial lake sediments found as erratics exhumbed in basal ice sections found at supraglacial moraines. We utilize the geochronologic and geochemical data for two paired sedimentary accumulations deposited in a subglacial water body in Wilkes Basin, East Antarctica to explore feedback between climate and basal lake conditions. Both samples contain textures consistent with lacustrine deposition, with calcite and opal primary bedding, interrupted by layers rich in clastic dropstones. Occurrence of these three components is cyclic. Importantly, the dropstones are observed to impact the laminated unconsolidated sediment, implying the samples formed beneath a body of water deep enough to allow the dropstone clastics to accelerate to a sufficient velocity to penetrate the underlying sediment.

In this presentation, we report the ²³⁴U-²³⁰Th dates for multiple horizons from the two samples. The resulting age model requires a precipitation rate of 5 mm/yr, with a total duration of 5kyr during interglacial stage MIS 5. Compositional maps acquired using SEM Energy Dispersive Spectra reveal the cyclic nature of the sedimentary bedding. Based on spectral analysis of these chemical data, primary opal-calcite transitional bedding occurs over decadal to centennial timescales, while siliciclastic dropstones are delivered on longer period cyclicities. Ongoing efforts look to link the observed periodicities with possible forcing mechanisms. This work demonstrates a novel sampling archive for subglacial lake sediments and records a detailed history of past subglacial processes.