LIGHT MICROSCOPY ANALYSIS OF WEST ANTARCTIC SUBGLACIAL SEDIMENTS: BIOGENIC SILICA PRESERVATION AND THE POTENTIAL FOR MICROBIAL COMMUNITY INTERACTIONS

The NSF funded Whillans Ice Stream Subglacial Access Research Drilling (WISSARD) project collected sediment core samples from Subglacial Lake Whillans (SLW), a subglacial lake that is part of the Whillans Ice Stream, West Antarctica in 2013. Analysis of sediment cores and the water column revealed active microbial communities beneath the ice sheet (Christner et al, 2014). By examining silica sponge spicules in Antarctic subglacial environments this project provides deeper understanding of the type of microbial community present in this subglacial setting and environmental interaction. We present preliminary results on down-core changes in a 40 centimeter sediment core from SLW.

This project focuses on tracking pitting structures, axial canal width, and mineral precipitants on sponge spicules down core to understand the connection between the geosphere and biosphere at SLW. We use fossil sponge spicules (likely Miocene in age based on common ages of fossil diatoms in sediments) from SLW to understand microbial interactions with subglacial tills. Etch pitting, and mineral precipitants of opaque minerals are observed in light microscopy, which could be a byproduct of microbial interaction. A parallel study on Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy is performed to determine elemental composition of opaque minerals observed in light microscopy (LM). LM provides observations of interactions with the axial canal which cannot be observed in SEM.

Preliminary research on over 200 sponge spicules from intervals down-core indicate microbial interaction decreases with depth. Initial trends in pitting structures and mineral precipitants follow a similar trend to microbial community profiles, which provides support for our hypothesis that microbes are specifically targeting proteinaceous material preserved within biosiliceous structures. These analyses are providing important information for understanding nutrient sources for subglacial communities.