Sources and Sinks of Carbon and Nitrogen in Antarctic Subglacial Aquatic Environments


Trista J. Vick-Majors1, Amanda Achberger2, Alex Michaud1, Mark Skidmore1, Eric Boyd1, John Dore1, Wayne Gardner3, Kaijun Lu3, Brent Christner2, and John C. Priscu1

1Montana State University, Bozeman, MT 2Louisiana State University, Baton Rouge, LA 3Univeristy of Texas Marine Science Institute, Port Aransas, TX


Recent recognition of the widespread nature of liquid water beneath the Antarctic ice sheet has generated new interest in subglacial aquatic environments as microbial habitats. These environments have been shown to contain active ecosystems and encompass stores of organic matter and nutrients of unquantified significance to Earth’s biogeochemical cycles. We report here on microbial transformations of organic matter in Subglacial Lake Whillans (SLW), which lies beneath ~800 m of ice in West Antarctica in a relic marine embayment.


Heterotrophic C production and respiration (estimated as incorporation + respiration of 14C-labelled leucine) together represent a C sink of ~8 x 1011 µmol C yr-1 over the 60 km2 area of SLW. Freshly produced organic C derived from chemoautotrophic primary production (estimated from 14C-bicarbonate incorporation in the dark) provides ~1 x 1011 µmol C yr-1. Upward diffusion from the underlying sediments provides an additional source of dissolved organic C (~2 x 1010 µmol C yr-1). These data together with results of excitation-emission matrix spectroscopy indicate that contemporary chemosynthetic production in the water column is the main organic carbon source in SLW.


Microbial diversity data and Δ17O of NO3- of ~0‰ indicate that ammonia oxidizing Archaea are important primary producers and that microbial activity is the primary source of nitrate in the SLW water column, respectively. Primary production in SLW was sensitive to the addition of nitrapyrin, a known inhibitor of ammonium oxidation. Rates of ammonium utilization, which include ammonium oxidation and metabolic incorporation, were nine times greater than rates of microbial ammonium regeneration suggesting that the major source of ammonium is relic material stored in the SLW sediments rather than microbial recycling within the water column. Collectively, our data suggest that the SLW ecosystem is supported by a combination in in situ production and organic matter stored in the relic marine sediments underlying the lake.


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