Geochemical estimates of denitrification in the Arabian Sea and the Bay of Bengal during WOCE

Abstract

High quality World Ocean Circulation Experiment (WOCE) data are used in conjunction with an isopycnal mixing model to calculate nitrate deficits due to denitrification in the oxygen minima of both the Arabian Sea and the Bay of Bengal. Basin-scale, integral denitrification rates are estimated by combining the nitrate deficits with water mass ages computed for the same regions based on the chlorofluorocarbon (CFC-11) distributions. Nitrate deficits exceeding 12 μmol kg-1 are observed for the Arabian Sea during the 1995 southwest monsoon. The estimated basin-scale nitrate deficit integrated over the oxygen minimum layer is 63±20 Tg N, and the annual loss rate is 21±7 Tg N y-1. The basin-scale nitrate deficit is about half other, recent inventory estimates, with most of the discrepancy in the bottom half of the oxygen minimum below the secondary nitrite maximum. No signature of active, water column denitrification was observed in the Bay of Bengal during the 1995 northeast monsoon. Copyright 1997 by the American Geophysical Union.