Phytoplankton dynamics in east Arabian Sea

By Lauren Biermann (Plymouth Marine Laboratory) and Vinaya Kumari (Central Marine Fisheries Research Institute, Mangalore Regional Centre)

Productivity influences life in the ocean by driving its chemical cycles and sinking atmospheric carbon dioxide. Changes in these processes/cycles are associated with fluctuations in other biological variables such as Chlorophyll-a (Chl-a) and net primary productivity, as well as marine resource distribution and abundance.

In oceanic environments, it is important to study the coupling of physical and biological processes to understand how the temporal and inter-annual variations occur, and what the forcing mechanisms are behind these variations.

To understand the changes in biotic communities along the Arabian Sea, trends in Sea Surface Temperature (SST), Chl-a and NPP were investigated (Figure 1).

The CMEMS GlobColour (Global Ocean Chlorophyll) product, a Level-4 monthly reprocessed chlorophyll and primary productivity data at 4km spatial resolution, and the CMEMS Sea Surface Temperature and Sea Ice Analysis (OSTIA) product, which provides Level-4 monthly SST data at 0.25-degree resolution, were used. GlobColour is based on Sentinel3/OLCI measurements, and OSTIA SST data are created using Sentinel3/SLSTR measurements next to other sources of measurements.

The results shown in Figure 2 illustrate how increases in SST are associated with reduced Chl-a and NPP in the Arabian Sea, while cooler SST values tend to coincide with higher Chl-a and NPP. Highest NPP occurred during the months of March and August, and were lowest in June and October, when SST values peaked at around 30°C.

This case study was produced and presented by Dr Vinaya Kumari during the EUMETSAT virtual Copernicus Marine Data Stream (CMDS) training course in October 2020.