Marine heatwaves during the pre-monsoon season and their impact on Chlorophyll-a in the north Indian Ocean in 1982-2021

Indian Ocean has been undergoing rapid warming in recent years, which increases the likelihood of Marine heatwave (MHW). MHWs are extreme warm ocean surface conditions in which temperature exceeds the 95th percentile for three or more consecutive days. We investigate MHW events occurred in Arabian Sea (AS) and Bay of Bengal (BoB) during pre-monsoon for 1982-2021 period, their impact on Chlorophyll-a (Chl-a) and net primary productivity (NPP). There were 42 (68) MHW events with a significant trend of 8.1 (6.3) MHW days dec in AS (BoB). There is a distinct decrease in Chl-a concentration associated with MHW, especially in medium and long duration events. In general, AS and BoB have witnessed more frequent and long-lasting MHWs in the 2002-2021 period, which reduce NPP of north Indian Ocean. A decrease in Chl-a and NPP, 10 % in AS and 2 % in BoB, is estimated, but only severe MHWs inflict a notable reduction.