Carbon Oxidation and Denitrification Rates in Sediments of the Chukchi Sea

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The northward flow through the Bering Strait transports nitrate-rich Pacific waters into the Arctic basin. This influx supports the richest productivity found in the Arctic. It has been hypothesized that export of part of this productivity could supply significant amounts of organic matter to the central Arctic. Part of the productivity is consumed within the Chukchi Sea via sedimentary carbon oxidation, and the rates in the U.S. region of the Chukchi are moderately high. However, new measurements of sedimentary sulfate reduction rates indicate that past estimates were several-fold low. Furthermore, conversion of inorganic nitrogen to N2 by denitrification in these sediments appears to be rapid. Thus, the sediments in the American Chukchi may oxidize more of the productivity and remove more of the nitrogen than previously thought. Furthermore, a large pool of organic rich sediments underlies much of the Russian Chukchi Sea, suggesting that even larger areas of sedimentary consumption, perhaps with even greater rates of oxidation and denitrification, may occur in the Russian areas. The organic rich areas of the U.S. and Russian Chukchi Sea will be sampled throughout the ice-free regions in mid summer of 1996. At each site, sediment-water fluxes of O2, N2, N2O, inorganic nutrients, TCO2, and alkalinity will be measured in replicate flux experiments. Vertical profiles of sulfate reduction rates will be determined by current 35SO4 tracer techniques. Porosity, organic matter content and pore water distributions of key solutes will also be determined. These data would expand our knowledge of sedimentary carbon oxidation and denitrification rates and their role in the productivity cycle in the Chukchi Sea. The improved estimates of these sedimentary processes will better estimate the potential for this region to export significant quantities of organic matter to the rest of the Arctic basin.