Distribution of dissolved oxygen in the western Bay of Bengal

S.W.A. Naqvi, S.N. DeSousa, S.P. Fondekar, C.V.G. Reddy

Abstract



Distribution of dissolved oxygen in the western Bay of Bengal has been studied using the data collected during the cruises of R V Gaveshani from August to September, 1976. Surface distribution of dissolved oxygen, oxygen saturation and temperature revealed the presence of intense upwelling off Visakhapatnam where oxygen concentration was found to be about 15% less than the saturation values. Distribution at 50 and 100 m indicated the deepening of isothermal layer in the central region and the presence of an offshore divergence off Visakhapatnam. Low values ( 0.5 ml/l) were observed at 200 m especially near the shelf break probably because of higher rate of oxidation of organic matter associated with high productivity of the shelf and slope waters. Two oxygen minima were observed in the south-western Bay of Bengal at 100-250 m and 400-600 m, separated by a layer of relatively high oxygen water at 250-350 m. This has been attributed to advection of waters relatively rich in oxygen from equatorial region. In the north-western Bay, however, only one minimum was observed. Very low ( 0.1 ml/l) oxygen concentrations were observed occasionally in the intermediate layers; these were invariably associated with quite significant nitrate concentrations thereby ruling out any possibility of sulphate reduction

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