Biological response of the sea around Sri Lanka to summer monsoon

Abstract

Chlorophyll-a concentration (chl a) maps derived from the Ocean Color Monitor (OCM) on board Indian Remote Sensing Satellite (IRS-P4) and Seaviewing Wide field of View sensor (SeaWiFS) show increased chl a in the waters around Sri Lanka during summer monsoon. Physical processes that can lead to the phytoplankton bloom are investigated using upper ocean temperature profiles and satellite derived winds, sea surface temperature (SST) and sea level anomalies (SLA). There is a chl a bloom attached to the southern coast of Sri Lanka accompanied by cool SST, low SLA and upsloping of isotherms towards the coast. Coastal upwelling driven by monsoon winds is identified as the physical mechanism causing nutrient enrichment in the surface layer. The Southwest Monsoon Current (SMC) which flows eastward south of Sri Lanka and then into the Bay of Bengal advects the upwelled water eastward along its path. The chl a rich waters from the Indian coast also advects along with the SMC towards Sri Lanka. East of Sri Lanka the open ocean upwelling associated with the Sri Lanka Dome is also found to be an important process that upwell nutrients.