Effect of Precipitation on Chlorophyll-a in an Upwelling Dominated Region Along the West Coast of India

The South Eastern Arabian Sea (SEAS) is an upwelling-dominated region, where the seasonally-reversing winds and currents are the major physical forces driving primary production. The region is characterized by high primary productivity during the summer monsoon season (June to September), when the winds and currents favor upwelling. The coast is notable for the presence of monsoonal rivers. During summer monsoon, nutrient-rich riverine water is discharged in great quantity into coastal waters. The heavy inflow of turbid, nutrient-rich water into coastal regions during the summer monsoon facilitates primary production, augmenting phytoplankton biomass. In the present study, we investigated the relative roles of upwelling and precipitation that drive productivity along the south-west coast of India. The available remote sensing data sets for chlorophyll-a (Chl-a), precipitation, silicate and wind were used for the period 1998 to 2016. The Chl-a anomaly showed positive correlation with upwelling index and precipitation except during 2003 and 2012. During these years, negative anomalies for Chl-a and precipitation were observed even though the upwelling index showed positive anomalies. So the enhancement in Chl-a was nominal during those specific years even when the upwelling was very strong. This indicates the role of riverine nutrients from heavy precipitation during summer monsoon that contributes significantly to coastal productivity apart from upwelling in SEAS.