Summer and winter denitrification rates in western Arctic shelf sediments

We report estimates of sedimentary denitrification rates from the Bering, Chukchi and Beaufort Seas made during August-September 1992, and rates obtained in the Beaufort Sea off Pt. Barrow, Alaska, under late wintertime conditions (March 1993). The estimates made during August-September were based on both deployments of an automated in situ benthic flux chamber tripod and on pore water chemical profiles from cores analyzed aboard the R/V Alpha Helix. Wintertime observations were obtained using scaled-down versions of the in situ flux chamber that were deployed through land-fast ice. The results of these determinations suggested that there was no drastic decrease in shelf denitrification rates at the end of winter off Pt. Barrow despite the fact that a supply of ''new'' organic material to the sediments via primary production had not occurred for several months. In addition, the ensemble of our data suggest appreciable year-round average rates (similar to 1 mg-atom N-2 m(-2) day(-1)) that fall within the range of modern estimates for moderately productive midlatitude shelf regions, and are about 40% as high as values reported for the Washington (NE Pacific) shelf. The results have some significance for understanding the oceanic combined nitrogen budget because denitrification in shallow and hemipelagic sediments is a major loss term and because the Arctic Ocean and its marginal and adjacent seas (such as the Bering Sea) contain 25% of the ocean's shelf sediments and 14% of the ocean sediments with depths between 0.2-1 km, despite the fact that this region accounts for only 4% of the total oceanic surface area. (C) 1997 Elsevier Science Ltd.