Geological Society of America

T102 It's a Cold, Cold World: Permafrost and Glacial Hydrogeology

Monday, 20 October 2014
8:00 AM - 12:00 PM
110

GREENLAND BASAL BIOGEOCHEMISTRY AND MICROBIOLOGY BASED ON THE ANALYSIS OF SUBGLACIAL DRAINAGES IN THE KANGERLUSSUAQ REGION

Paper number: T102-7
Program: Technical Sessions
Time: 9:30 AM – 9:45 AM

Authors

Ronald S. Sletten Presenting Author
University of Washington, Seattle, WA
Karen Junge
University of Washington, Seattle, WA
Birgit Hagedorn
University of Alaska Anchorage, Anchorage, AK
Brent Christner
Louisiana State University, Baton Rouge, LA
Markus Dieser
Boseman, MT
Karen Cameron
Department of Geochemistry, Copenhagen
Kyla Choquette
University of Alaska, Anchorage, AK
Erik Broemsen
Louisiana State University, Baton Rouge, LA
Lu Liu
University of Washington, Seattle, WA
Zoe Harrold
Montana State University, Boseman, MT

Abstract

Our study investigates concurrently microbial communities and geochemistry to assess the biological role in weathering at the water-ice-rock interface. We collect outflow samples over an entire melting season from the base of the Russell Glacier, an outlet glacier of the SW Greenland Ice Sheet that has a considerable subglacial drainage contribution. Bulk outflow waters are slightly depleted in dissolved oxygen and contain dissolved methane (2.7 to 83 μM), indicating a range of oxic to anoxic conditions along the glacier margin. The presence of methane, along with the dominance of methane-consuming bacteria based on reverse transcribed (RT) 16S rRNA sequence libraries and particulate methane monooxygenase RT-mRNA amplicons, confirms that methanotrophic bacteria are viable members of the subglacial ecosystem. Nevertheless, uncertainty still exists whether in situ production or release from thawing sediments is the source of methane. In the latter case, there is potential for greater amounts of methane release with further thawing. In either scenario, methane is believed to be biogenic, supported by δ¹³C-CH₄ values between -64‰ and -62‰.

Highly reactive bioavailable iron determined through sequential extraction of suspended sediments and dissolved Fe(II) is negatively correlated with dissolved oxygen and positively with total ion concentration, suggesting that mineral dissolution and either microbial-mediated or abiotic oxidation of iron occur. Furthermore, it is assumed that depletion of oxygen and high ion concentrations indicate that these waters have a strong contribution from the subglacial environment where oxygen supply is limited. High sulfate concentrations in the outflow indicate that sulfide oxidation is also a major reaction in this environment.

Inverse modeling of the drainage waters suggests that various weathering reactions can account for the measured water chemistry. These modeling studies are consistent with carbon reduction in the subglacial environment; however, sorting out distinct processes by inverse modeling of average drainage waters does not provide an unique solution and other data must be taken into account. Toward this goal, we plan to analyze sub/intra glacial waters along an elevation transect for chemical and microbial composition.