SULFUR CYCLING WITHIN A SMALL ARCTIC LAKE IN WESTERN GREENLAND: POTENTIAL INSIGHTS INTO EARLY PLUVIAL PERIODS ON MARS
Here we present detailed water column profiles of [SO42-] 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 [SO42-] were higher compared to summer and decreased slightly with depth (from 450 to 320 μM). Lake δ34SSO4 values were also higher in winter +18.8‰ compared to summer values +6.4‰. The δ34SH2S 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.