SEASONAL VARIABILITY IN OXYGEN AND NUTRIENTS IN THE CENTRAL AND EASTERN ARABIAN SEA

Extensive observations made in the central and eastern Arabian Sea und er JGOFS (India) programme suggest strong seasonal variations in conce ntrations of oxygen and nutrients in the water column. In the intermed iate waters (depth range 150-800 m) oxygen concentrations were lowest during winter (with values near zero at similar to 400 m) in relation to those in the other two seasons (intermonsoon and southwest monsoon) . This together with nitrate distributions revealed the occurrence of intense reducing conditions in intermediate waters during winter becau se of the sluggish water movement and high surface productivity, Secon dary nitrite, an indicator of occurrence of denitrification was presen t at oxygen levels < 10 mu M. Nitrate deficits reached a maximum of 10 mu M in winter, whereas, it was half this value in monsoon, The avera ge deficits suggest increasing reducing conditions in the order monsoo n (1.6 mu M), intermonsoon (3.7 mu M) and winter (4.0 mu M).