LAUSR

Abstract South Eastern Arabian Sea (SEAS) is an upwelling dominated region, where the distribution of chlorophyll-a (Chl-a) is mainly controlled by basin scale to mesoscale processes associated with seasonal reversal of winds and currents. The analysis of long-term satellite-derived Chl-a data revealed inter-annual variability in association with extreme climatic events. In the present study, satellite imageries were applied to study the long term Chl-a variability in SEAS followed by ascertaining the influence of extreme climatic events. Chl-a data were obtained from Ocean Colour Climate Change Initiative (OC-CCI) which provides high resolution cloud free data for the Arabian Sea during summer monsoon season (June to September). Satellite measurements of Sea Level Anomaly (SLA), Sea Surface Temperature (SST) and sea surface wind data were also compiled from various sources. The monthly data for the above environmental variables during the years 1998 to 2016 were analysed as representatives of the possible causative physical processes influencing the variability in Chl-a. The time series and Hovmoller analysis revealed that the maximum variability occurred during summer monsoon. This study revealed that the interannual variability in Chl-a was prominently influenced by the underlying processes involved in coastal upwelling. The extreme climatic events such as ENSO and IOD were particularly taken into account to understand the the interannual variability in Chl-a and associated environmental variables. The relative variability in Chl-a and associated environmental variables with these events was prominent during strong El Nino, La Nina and IOD. Cross Correlation Function (CCF) analysis points out that Chl-a content is negatively correlated with IOD to an extent of one month or less whereas, ENSO doesn’t indicate such relations. Hence, the variability associated with IOD showed pronounced influence than ENSO. The study elucidates the interannual variability of Chl-a and the overall influence of associated extreme events in SEAS.