Growth and Decay of High-Biomass Algal Bloom in the Northern Arabian Sea

Abstract

The annual episodes of high-biomass algal bloom are a known phenomenon in the northern Arabian Sea. In the present study, we demonstrate growth and decay of bloom using long-term satellite-retrieved parameters such as chlorophyll-a (chl-a), sea surface temperature (SST), phytoplankton absorption (aph), detritus–coloured dissolved organic matter absorption (adg) and model-derived mixed layer depth (MLD). Chl-a, the index of phytoplankton biomass, showed an inverse relationship with SST with a lag of 2–8 days between lowest SST and highest chl-a. The deepening of MLD associated with high chl-a and low SST indicated a role of convective mixing in the formation of bloom. The average SST of ~ 25 °C was found to be a favourable condition for such open ocean bloom. The lag was more towards eastern boundary of the basin, indicating variable intensities of convective mixing influencing spatial extent of bloom. The positive correlation between aph and adg indicated simultaneous production and degradation showing delay of 3–10 days from peak production to degradation.