Biogeochemistry of snowmelt in an Antarctic glacial ecosystem

Abstract

Solute mass balance, hydrochemical data, and hydrological process data are used to present the first detailed account of catchment biogeochemistry in an Antarctic melt season. The study was undertaken in a small glacial catchment in the maritime Antarctic (Signy Island, South Orkney Islands), where extreme ecosystem changes have been observed at the ice margin. Here melting caused a snowpack solute elution phase characterized by the production of extremely concentrated solutions just centimeters from the snow surface. These were equivalent to 2% marine water and dominated by sea‐salt aerosol. Nutrients were also present but were rapidly sequestered in snowpack and ice marginal environments. Thus the decoupling of nutrient dynamics from other snowpack solutes seems to occur almost immediately after melt and testifies to the presence of a glacial ecosystem. Although significant, the estimated rates of nutrient uptake were low (0.025 gNH4‐N/m2/yr and 0.0011 gPO4‐P/m2/yr, equivalent to 66 and 74% of total annual atmospheric inputs) and, in the case of NH4+, 2–3 orders of magnitude lower than those reported for temperate snowpacks. However, the data also demonstrated significant NO3− production (0.030 gNO3‐N/m2/yr or 3 times total atmospheric inputs) that appears to be associated with zones of high rock‐water contact at the ice margin. After the early snowpack elution phase, nutrient cycling was also greatly influenced by inputs from penguin and seal excreta. Thus local marine ecosystems enhance the nutrient content of meltwaters and fertilize the glacial, terrestrial, and aquatic ecosystems that are responding to climate change in the maritime Antarctic.