The influence of iron and sulfur minerals on sub-ice biogeochemical processes at Lake Bonney, Antarctica and Bench Glacier, Alaska

Abstract

This research investigated the influence of iron- and sulfur-containing minerals on biogeochemical processes in two contrasting glaciated catchments. In Theme 1, I explored the role of iron-bearing minerals in an abiotic methanogenesis reaction as a possible source to an unexplained methane pool in Lake Bonney (LB), Antarctica. In Theme 2, I examined the effect of iron-sulfide minerals on biological activity in subglacial sediments from Bench Glacier (BG), Alaska. The presence of iron and sulfur minerals potentially drives abiotic and biotic processes in both glaciated systems, though the magnitude of these processes is not fully understood. Theme 1 considers the methane in LB's water column, which has isotopic values consistent with an abiotic (thermogenic) source. Peak methane concentration occurs just below the depth of subglacial brine inflow from adjacent Taylor Glacier (TG). My experiments indicate direct basal ice melt, rock comminution, and methane production from the reaction of TG sediment with organosulfur compounds are not major sources of methane to LB. The likely source is crustally-derived methane supplied to the subglacial environment at TG, trapped by the overlying ice, then carried to the lake within subglacial brine outflows. My work also demonstrated how naturally occurring organosulfur compounds in LB will produce methane when reacted with TG glacial sediments at close to in situ temperature. Though this reaction is unlikely a major methane source in western LB, isotopic analysis of dissolved methane in LB's eastern lobe indicate this process may be occurring in the lake. For Theme 2, I isolated a species of Polaromonas which oxidizes thiosulfate to sulfate under aerobic conditions at near subglacial temperatures. This is the first demonstration of sulfur oxidation in this genus, and it is only the second organism with this ability to be isolated from a subglacial environment. My experiments showed this species can utilize thiosulfate sourced solely from the abiotic oxidation of the iron-sulfide mineral pyrite in an aqueous setting. This is the first time a glacial isolate has been shown to exhibit this capability.