Rapid changes in surface water carbonate chemistry during Antarctic sea ice melt

Abstract

The effect of sea ice melt on the carbonate chemistry of surface waters in the Weddell–Scotia Confluence, Southern Ocean, was investigated during January 2008. Contrasting concentrations of dissolved inorganic carbon (DIC), total alkalinity (TA) and the fugacity of carbon dioxide (fCO₂) were observed in and around the receding sea ice edge. The precipitation of carbonate minerals such as ikaite (CaCO₃·6H₂O) in sea ice brine has the net effect of decreasing DIC and TA and increasing the fCO₂ in the brine. Deficits in DIC up to 12 ± 3 ¼mol kg^-1 in the marginal ice zone (MIZ) were consistent with the release of DIC-poor brines to surface waters during sea ice melt. Biological utilization of carbon was the dominant processes and accounted for 41 ± 1 ¼mol kg^-1 of the summer DIC deficit. The data suggest that the combined effects of biological carbon uptake and the precipitation of carbonates created substantial undersaturation in fCO₂ of 95 ìatm in the MIZ during summer sea ice melt. Further work is required to improve the understanding of ikaite chemistry in Antarctic sea ice and its importance for the sea ice carbon pump.