Dissolved gases in frozen basal water from the NGRIP borehole: implications for biogeochemical processes beneath the Greenland Ice Sheet

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Little information exists on biogeochemical transformations in aquatic ecosystems beneath polar ice sheets (i.e., water-saturated sediments, streams, rivers, and lakes) and their role in global elemental cycles. Subglacial environments may represent important sources of atmospheric CO2 and/or CH4 during deglaciation, thus acting as amplifiers in the climate system. However, the role of subglacial environments in global climate processes has been difficult to assess given the absence of biogeochemical data from the basal zones of inland polar ice sheets. Here, we report on the concentrations of CO2, CH4, and H2 in samples of refrozen basal water recovered at a depth of ~3,042 meters below the surface during the North Greenland Ice Core Project (NGRIP). CH4 and H2 concentrations in the NGRIP samples were approximately 60- and 700-fold higher, respectively, relative to air-equilibrated water, whereas CO2 was ~fivefold lower. Metabolic pathways such as (1) methanogenesis, (2) organic matter fermentation, carboxydotrophic, and/or methylotrophic activity, and (3) CO2 fixation provide plausible biotic explanations for the observed CH4, H2, and CO2 concentrations, respectively.