SULFUR CYCLING WITHIN A SMALL ARCTIC LAKE IN WESTERN GREENLAND: POTENTIAL INSIGHTS INTO EARLY PLUVIAL PERIODS ON MARS

Isolated lacustrine depositional environments were common in craters during early periods in Martian history. The underlying permafrost and lack of surface drainage would have allowed individual lakes to evolve distinct chemical signatures. Our analogue study has focused on seven small lakes (<1 km²; 4-12 m depth) located over a distance of about 6 km along a steep-walled, faulted valley overlying a structural shear zone. This area extends southwest from the terminal moraine of Russells Glacier to Søndre Strømfjord near Kangerlussuaq, Greenland. The lakes in this study area represent similar geochemical isolation and restricted sediment input compared to early Martian lacustrine environments. Through intensive study of these lakes under open-water (summer) and ice-covered (winter) conditions from 2011–2013 we will provide the first complete sulfur budgets for lake systems in these landscapes.

Here we present detailed water column profiles of [SO₄^2-] and [H₂S] in addition to their stable isotope (δ³⁴S) values for Epidote Vein Valley (EVV) Upper Lake. In summer open-water conditions, EVV Upper Lake is stratified, with a well-developed thermocline and oxycline at 2.5 m depth. Sulfate concentrations decreased with depth (244 to 142 μM), while concentrations of dissolved sulfide were low and increase slightly from 0.5 μM to 3 μM with depth. In winter during ice-covered conditions lake waters were completely anoxic and isothermal, with [H₂S] increasing modestly with depth from 33 to 70 μM. The winter [SO₄^2-] were higher compared to summer and decreased slightly with depth (from 450 to 320 μM). Lake δ³⁴S_SO4 values were also higher in winter +18.8‰ compared to summer values +6.4‰. The δ³⁴S_H2S of winter waters yielded values of -20.5 to -19.6‰. The ~40‰ offset in δ³⁴S values from sulfate to sulfide indicates active microbial sulfate reduction in the winter EVV Upper Lake water column. Monitoring multiple sulfur biogeochemical properties will yield a further understanding of various reservoir and kinetic isotope effects associated with the products of microbial sulfur cycling within Upper EVV Lake. Understanding microbial ecosystem dynamics in these Greenlandic lakes and how they respond to extreme seasonality and long-term climate change may lead to further insights into interpretations of crater lake deposits on Mars.