N deficiency in a well-oxygenated cold bottom water over the Bering Sea shelf: influence of sedimentary denitrification

Anomalously low ratios of dissolved inorganic nitrogen (DIN) to dissolved inorganic phosphorus (DIP) were found in a well-oxygenated cold bottom water over the southeastern Bering Sea shelf during late summer. Our study shows that the anomalously low DIN/DIP ratios are caused by sedimentary denitrification. The estimated sedimentary denitrification rates, ranging from 0.7 to 1.5 mmol/m2/day, are similar to values previously reported for continental shelf regions. An annual rate of sedimentary denitrification in the Bering Sea shelf can be, at a low limit, in the order of 2.5 Tg N/yr. This corresponds to roughly one-third of the annual net supply of the nitrate to the Bering Sea shelf and, at least, 2.5% of annual global denitrification rate in oceanic sediments, implying that the sedimentary denitrification in the Bering Sea shelf could be a significant sink of nitrogen in both regional and global scales.