Marine nitrogen cycling- Some recent observations in the northwestern Indian Ocean

Abstract

Published estimates of the rate of denitrification in the Arabian Sea have been evaluated and some new data on the nitrogen cycle have been presented Secondary nitrite maxima and nitrate reduction appear to be associated with oxygen concentrations of less than 3 mu mol dm super(-3) A vertical section of the nitrate deficit along the latitude 17 degrees N highlights and unusual feature of denitrification in the Arabian Sea That is, contrary to the pattern expected from the data on primary productivity, the process appears to be most intense not along the continental margin off the Indian Coast but some distance away This is probably due to the presence of a hitherto undetected subsurface counter-current It is shown that, provided that denitrification in the Arabian Sea conforms to the global trend, the high rate derived in a recent study from the exports of nitrate deficits out of the denitrification zone (approximately 30 Tg y super(-1)) is probably the closest estimate of the true value