Southeastern Arabian Sea bordering the southwest coast of India is a dynamic region influenced by the seasonally reversing monsoon system. Phytoplankton biomass of the surface waters of this region is distinctly influenced by the changes in different physical forcing mechanisms. In this paper, the variability in the phytoplankton biomass and its offshore extent in the southeastern Arabian Sea during summer monsoon season was analysed using the merged satellite chlorophylla (chl-a) concentration data provided by Ocean Colour Climate Change Initiative (OC CCI) during the last two decades from 1998 to 2017. The highest chla concentrations near the coast were observed during the summer monsoon season of 2002 and 2009-2011. Years with low chla concentration appeared to increase from 2012 onwards, with 2013 and 2016 showing an exception. The zonal extent of high chla , which on average was up to 75 oE was found to extend westwards up to 73 oE from the coast in recent years. The increase in surface chla concentration is a regular phenomenon during the summer monsoon season, the offshore extent of which is influenced by prevailing physical forcing mechanisms.

 Phytoplankton, chl-a, summer monsoon