3.1.3. Chlorophyll-a
Pre-Monsoon (March-May) and Northeast Monsoon (November - February) are
low productive periods in the SEAS along the southwest coast of India
(Supplementary Figure 3). This situation is caused by surface layer
stratification through solar heating during the Pre-Monsoon and the
intrusion of low saline oceanic Bay of Bengal waters during the
Northeast Monsoon22. Both these cause meagre nutrient
availability in the upper euphotic column creating low phytoplankton
biomass (chlorophyll-a) concentration22. The
situation significantly changes by late-May/June as a result of coastal
upwelling, and enhanced chlorophyll-a concentration starts
appearing along the entire coastline by June and persists up to October.
GoM has always moderate to the high level of chlorophyll-a present in the nearshore waters along the Indian coast. Enhancement of
chlorophyll-a in the GoM starts by late-May, just after the
Pre-Monsoon, and it peaks during July-August and then declines by
September-October. During the Northeast Monsoon, though the
chlorophyll-a concentration decreases in the offshore waters in
the GoM, its moderate concentration persists in the shelf waters along
the Indian coastline as a continuity of the water masses intruded from
the Bay of Bengal through the Palk Bay.