Anaerobic N2 production in Arctic sea ice

Rysgaard, Søren, Ronnie Nøhr Glud

Limnol. Oceanogr., 49(1), 2004, 86-94 | DOI: 10.4319/lo.2004.49.1.0086

ABSTRACT: We quantified anaerobic N2 production through bacterial denitrification and anaerobic NH4+ oxidation (anammox) in first-year ice from Young Sound (74°N) and in an ice floe off Northeast Greenland (79°N). Bacterial denitrification activity (100-300 nmol N L-1 sea ice d-1) occurred in the lower 0.5 m of the sea ice, which had high concentrations of NO3-, NH4+, and dissolved organic carbon (DOC). Despite sea-ice algal production in the lower sea-ice layers, heterotrophic activity resulted in a net O2 consumption of 13 µmol O2 L-1 sea ice d-1 in the lower 0.5-m ice layers. Together with melting of deoxygenated ice crystals, this led to anoxic conditions in the brine system favoring conditions for anaerobic NO3- reduction. Numbers of anaerobic NO3--reducing bacteria in the same ice layers were high (1.1 x 105 cells ml-1 sea ice, corresponding to 1.2 x 106 cells ml-1 brine). Area-integrated denitrification rates were 10-45 µmol N m-2 sea ice d-1, which corresponds to 7-50% of the sediment activity in the area. Although the proportion of anammox to total N2 production was up to 19% in layers of the ice floe from the Greenland Sea, the integrated rate only accounted for 0-5% of total NO3- reduction at the investigated localities.

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