Some aspects of the oxygen-deficient conditions and denitrification in the Arabian Sea

Abstract

Utilizing a fairly large amount of recently collected data, some outstanding questions concerning the Arabian Sea denitrification problem are addressed. The true level of dissolved oxygen, determined colorimetrically, are about an order of magnitude lower than those reported previously from the oxygen minimum zone. Lateral advection of waters from south into the oxygen-deficient layer is suggested by the presence of an intermediate oxygen maximum discernible even at very low oxygen levels. An unusual minimum in nitrate and a corresponding maximum in nitrite are observed occasionally within the depth range 700-1.200 m at several stations, generally located in the northeastern Arabian Sea. These features probably resulting from seasonal changes in primary production, lateral advection of waters from the slope region off the Indian coast, or an in-situ production of organic matter