Microbial nitrogen cycling on the Greenland Ice Sheet

[摘要] Nitrogen inputs and microbial nitrogen cycling were investigated along a 79 km transect into the Greenland Ice Sheet (GrIS) during the main ablationseason in summer 2010. The depletion of dissolved nitrate and production ofammonium (relative to icemelt) in cryoconite holes on Leverett Glacier,within 7.5 km of the ice sheet margin, suggested microbial uptake andammonification respectively. Positive in situ acetylene assays indicatednitrogen fixation both in a debris-rich 100 m marginal zone and up to 5.7 kmupslope on Leverett Glacier (with rates up to 16.3 μmolesC₂H₄ m⁻² day⁻¹). No positive acetylene assays weredetected > 5.7 km into the ablation zone of the ice sheet. Potentialnitrogen fixation only occurred when concentrations of dissolved andsediment-bound inorganic nitrogen were undetectable. Estimates of nitrogenfluxes onto the transect suggest that nitrogen fixation is likely of minorimportance to the overall nitrogen budget of Leverett Glacier and ofnegligible importance to the nitrogen budget on the main ice sheet itself.Nitrogen fixation is however potentially important as a source of nitrogento microbial communities in the debris-rich marginal zone close to theterminus of the glacier, where nitrogen fixation may aid the colonization ofsubglacial and moraine-derived debris.

[学科分类] 地球化学与岩石