Isotopic evidence of microbial sulfur cycling in sediments associated with springs on the margin of a saline, alkaline, lake in south central Oregon

Warner Valley is a closed-drainage basin located between the high lava plains on the Oregon Basalt Plateau and the North American Basin and Range Province where shallow evaporitic lakes and playas are common. Coleman Lake, just south of Warner Valley, is a saline, alkaline, dry lakebed receiving inflow only from rain, snow, and two perennial springs on the west shore. Foskett Spring and Dace Spring are mesothermal springs (about 18 °C) with narrow outflow channels dissipating into wetlands. Stringer mats of white, filamentous, sulfur-oxidizing bacteria and an intermittent sulfidic odor are characteristic of the wetland below Foskett Spring in winter.;Despite sulfate concentrations only about 350 ppm in Dace and Foskett Springs, there is isotopic evidence of a microbial sulfur cycle preserved in the sediments along the flow path. A combination of basaltic landscape, semi-arid climate, and closed-drainage lakes allows useful comparisons with crater lakes on ancient Mars. The objective of the proposed research is to quantitatively extract, purify, and measure the concentration and isotopic composition of sulfur-containing minerals and dissolved-sulfur constituents in springs, seeps and wetlands located on the margin of the Coleman dry lakebed as insight into plausible evidence of past microbial life on Mars.;Six sediment cores of 0.3 to 0.6 meter in length were collected and used for sequential extraction of sulfur in various oxidation states (sulfate, elemental sulfur, monosulfide and disulfide) and for measurement of sulfur isotope ratios. Results are used to predict the preservation potential for chemical and isotopic signatures in sediment during burial and along the discharge path. Three processes are identified and discussed: drainage patterns into and out of Coleman Valley, local sulfur enrichment of sulfur in sediment by microbial metabolism, and redistribution of wind-blown sulfates from regional evaporitic deposits.