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. sults 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 (∼ 1 mg-atom N2 m−2 day−1) that fall within the range of modern estimates for moderately productive mid-latitude 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 oceanʹs 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.