Oscillating environmental responses of the eastern Arabian Sea

Abstract

Characteristics of two distinct physical processes, the coastal upwelling and convective overturning, which enhance phytoplankton productivity in the west coast of India, are discussed in this study. Systematic <i>in-situ </i>data collected during the two contrasting monsoon (summer and winter) periods were utilized for the study. During summer monsoon, the colder (27°C), less oxygenated (<190 μM), nitrate rich (NO₃-N >2 μM) waters were evidenced in the upper layers of the southwest coast of India, along with higher level of primary production (surface - 76 mgC m^-3d^-1 & column -1629 mgC m^-2d^-1) and chlorophyll <i>a </i>(surface - 1.2 mgm^-3 & column -45.7 mgm^-2). In contrast, during winter, the upper thermohaline layer of the northeastern Arabian Sea exhibited colder sea surface temperature (SST, 25-26°C), and deeper mixed layer depth (MLD, >70 m). This area was distinguished by less oxygenated (<180 μM), nitrate rich (>2μM) and high productive (surface - >10 mgC m^-3d^-1 & column - >800 mgC m^-2 d^-1) waters. I can be stated that the physically forced chemical changes occurred in the upper layers of both southeastern and northeastern Arabian Sea, appeared in an oscillating manner with respect to monsoonal changes, seemed to trigger the enhancement of phytoplankton productivity of the area.