MICROPALEONTOLOGICAL ANALYSIS OF SEDIMENTS FROM BENEATH SUBGLACIAL LAKE WHILLANS AND THE UPSTREAM SECTORS OF THE WHILLANS AND KAMB ICE STREAMS, WEST ANTARCTICA

In January of 2013 the WISSARD (Whillans Ice Stream Subglacial Access Research Drilling) project recovered sediment cores from Subglacial Lake Whillans (SLW) in West Antarctica. We report preliminary micropaleontological analyses of SLW sediments, augmented by analysis of sediments previously recovered from beneath the upstream camps of the Whillans Ice Stream (WIS) and Kamb Ice Stream (KIS). Samples are being analyzed for diatoms, sponge spicules, and organic-walled microfossils. Absolute abundance (particles per gram dry sediment) of identifiable diatoms and diatom fragments in different size classes were calculated to compare and contrast each environment. Sponge spicules are being analyzed for taphonomic effects from subglacial transport and shearing. Palynomorphs are analyzed for abundance and diversity.

In SLW the upper 30 cm is softer and more water-rich than the underlying sediments. However, little variation in microfossil and fragment abundance or taphonomy is noted, which is in agreement with the stratigraphic homogeneity evident from geochemical and geological analyses performed to date. SLW contains 1.52x10⁶ to 1.13x10⁷ diatoms per gram, compared with 6.43x10⁶ to 4.63x10⁸ at upstream WIS and 6.13 10⁷ to 1.58x10⁸ at KIS. The abundance and preservation of the diatoms and spicules at SLW suggests relatively long distance transport from the marine sediment source, with evidence of high shear strain, following the subglacial shearing index of Scherer et al. (2005). Upper Miocene diatoms dominate all of the samples, though older and younger diatoms are noted as well. The WIS samples exhibit the highest diversity of diatoms, including Paleogene freshwater diatoms. KIS sediments have the highest abundance of whole diatoms, but they are characterized by low diversity, indicating local erosion of an Upper Miocene deposit. Palynomorphs in all of the samples demonstrate a sizable contribution of Eocene terrigenous material. The quantitative analysis of microfossils preserved in these sediments is revealing a complex set of subglacial processes. Constraining the heterogeneity of subglacial sedimentary environments and sediment transport is providing important data for understanding and modeling current and past WAIS behavior.