Carbon distributions and fluxes in the North Water, 1998 and 1999

As part of the first investigation of the North Water region of Baffin Bay to specifically examine carbon cycling in this unique and highly productive area, we found that the distributions of carbon within these waters were controlled by a complex system of transport and biological processes. We systematically collected samples throughout the North Water during April–July 1998 and August–September 1999 and analyzed them for total dissolved inorganic carbon (DIC), alkalinity, dissolved organic carbon, and total suspended particulate carbon. Consistent with biogenic drawdown, surface DIC concentrations dropped by as much as 250 μmol kg−1 during the summer and began to increase again by the end of September. Although the surface waters were supersaturated with carbon dioxide in early spring, extensive ice cover limited CO2 outgassing at that time. As the ice cleared, decreasing surface DIC concentrations supported significant fluxes of CO2 into the ocean. In late September and early October, when ice again was beginning to cover the area, the surface waters were still undersaturated in CO2, implying that the North Water could be a net sink of atmospheric carbon, if winter air–sea fluxes are minimal. There is strong evidence that horizontal advection plays an important role in controlling DIC distributions, although we were unable to independently quantify the advective fluxes. Based on the observed changes in total carbon concentrations and estimates of air–sea fluxes, we found that carbon was lost from the surface waters between April 1998 and October 1999, probably due to both biological and advective export.