PHYSICAL AND BIOLOGICAL VARIABILITY OF THE NORTHERN ARABIAN SEA DURING WINTER

PHYSICAL AND BIOLOGICAL VARIABILITY OF THE NORTHERN ARABIAN SEA DURING WINTER.

S.Prasanna Kumar, N. Ramaiah, Mangesh Gauns, V.V.S.S. Sarma, P.M. Muraleedharan, S. Raghukumar, M. Dileep and M. Madhupratap

National Institute of Oceanography
Dona Paula, Goa, India.

Abstract

Recent time-series hydrographic observations at a nominally fixed location in the northern Arabian Sea (21^oN, 64^oE) during winter (February) 1997 indicated the prevalence of cold SST and deep MLD resulting from the winter cooling and convection. Availability of nitrate in the surface layers and high concentration of chlorophyll in the euphotic zone as well as their in-phase variability with MLD and wind indicated that carbon fixation in the euphotic zone is primarily controlled by physical forcing. Inter-annual variability emerged out of a comparison between data of winter 1997 with 1995 and show that a small variability in SST (+ 1^oC) could lead to large changes in biological productivity. Satellite data on AVHRR SST and TOPEX / POSEIDON altimeter suggests that this inter-annual signal occurs on a basin-wide spatial scale. With the termination of winter cooling and starting of warming in the inter-monsoon, the Arabian Sea becomes less productive. During this period micro organisms proliferate; a feeding mode through microbial loop appears to be inherent to mezoooplankton of the area.