Uptake of atmospheric carbon dioxide in Arctic shelf seas: evaluation of the relative importance of processes that influence pCO 2 in water transported over the Bering–Chukchi Sea shelf

Abstract

The uptake of atmospheric carbon dioxide in the water transported over the Bering–Chukchi shelves has been assessed from the change in carbon-related chemical constituents. The calculated uptake of atmospheric CO 2 from the time that the water enters the Bering Sea shelf until it reaches the northern Chukchi Sea shelf slope (∼1 year) was estimated to be 86±22 g C m −2 in the upper 100 m. Combining the average uptake per m 3 with a volume flow of 0.83×10 6 m 3 s −1 through the Bering Strait yields a flux of 22×10 12 g C year −1. We have also estimated the relative contribution from cooling, biology, freshening, CaCO 3 dissolution, and denitrification for the modification of the seawater pCO 2 over the shelf. The latter three had negligible impact on pCO 2 compared to biology and cooling. Biology was found to be almost twice as important as cooling for lowering the pCO 2 in the water on the Bering–Chukchi shelves. Those results were compared with earlier surveys made in the Barents Sea, where the uptake of atmospheric CO 2 was about half that estimated in the Bering–Chukchi Seas. Cooling and biology were of nearly equal significance in the Barents Sea in driving the flux of CO 2 into the ocean. The differences between the two regions are discussed. The loss of inorganic carbon due to primary production was estimated from the change in phosphate concentration in the water column. A larger loss of nitrate relative to phosphate compared to the classical ΔN/ΔP ratio of 16 was found. This excess loss was about 30% of the initial nitrate concentration and could possibly be explained by denitrification in the sediment of the Bering and Chukchi Seas.