Satellite-based observations of intense chlorophyll-a bloom in response of cold core eddy formation: A study in the Arabian Sea, Southwest Coast of India

Mesoscale phenomena are highly energetic features of ocean dynamics and circulation patterns. Their influence on biological and biogeochemical processes varies widely from advective transport and also from the generation of variations in the environment that affect biological and chemical rates. This study investigates the surface chlorophyll-a (Chl-a) bloom affect in the case-1 (open ocean) waters of Arabian Sea off the southwest coast of India in response to the cold core eddy in the post-monsoon 2016 using satellite-based observations. The 8-day composite of Chlorophyll-a (Chl-a), Sea Surface Height Anomalies (SSHA), Sea Surface Temperature (SST) and the wind field vectors were analyzed to study the Chl-a bloom characteristics and eddy mechanism. The results show that a very high concentration of Chl-a (6 mg/m-3) bloom occurred during the cold-core eddy formation which lasted for more than a month. Analysis revealed that the Chl-a bloom is attributed to the combined effect of surface and subsurface processes such as cyclonic structure of cold-core eddy, high Ekman pumping velocity, negative values SSHA, decreased values of SST, and nutrient injection from subsurface to the surface. Our study concluded that the presence of pre-existing cyclonic cold-core eddy, decreased SST and high Ekman pumping velocity played a major role in the formation of Chl-a bloom in the study area.