THE NORTHEAST WATER POLYNYA AS AN ATMOSPHERIC CO2 SINK - A SEASONAL RECTIFICATION HYPOTHESIS

During the multidisciplinary 'NEW92' cruise of the United States Coast Guard Cutter (USCGC) Polar Sea to the recurrent Northeast Water (NEW) Polynya (77-81 degrees N, 6-17 degrees W; July-August 1992), total di ssolved inorganic carbon and total alkalinity in the water column were measured with high precision to determine the quantitative impact of biological processes on the regional air-sea flux of carbon. Biologica l processes depleted the total inorganic carbon of summer surface wate rs by up to 2 mol C m(-2) or about 3%. On a regional basis this deplet ion correlated with depth-integrated values of chlorophyll a, particul ate organic carbon, and the inorganic nitrogen deficit. Replacement of this carbon through exchange with the atmosphere was stalled owing to the low wind speeds during the month of the cruise, although model ca lculations indicate that the depletion could be replenished by a few w eeks of strong winds before ice forms in the autumn. These measurement s and observations allowed formulation of a new hypothesis whereby sea sonally ice-covered regions like the NEW Polynya promote a unique biol ogically and physically mediated ''rectification'' of the typical (ice free, low latitude) seasonal cycle of air-sea CO2 flux. The resulting carbon sink is consistent with other productivity estimates and repre sents an export of biologically cycled carbon either to local sediment s or offshore. If this scenario is representative of seasonally ice-co vered Arctic shelves, then the rectification process could provide a s mall, negative feedback to excess atmospheric CO2.