Satellite Retrieved Spatio-temporal Variability of Phytoplankton Size Classes in the Arabian Sea

Abstract

The long-term trend in satellite retrieved phytoplankton size classes (PSC) such as picophytoplankton (PP), nanophytoplankton (NP), and microphytoplankton (MP) was studied in the three zones falling under different ecological provinces in open ocean regions of the Arabian Sea. A regionally tuned three-component “abundance” model was used to compute PSC biomass from Moderate Resolution Imaging Spectroradiometer onboard Aqua (MODISA) satellite data for the period of 17 years (2003 to 2019). The overall trend indicated the highest concentration of all PSC in the northern Arabian Sea (ARAB province) which gradually decreased to the southern region (MONS province). All PSC biomass showed a peak during the winter monsoon period in ARAB province attributed to the recurring algal bloom. The long-term temporal trend showed relatively lower concentration (most of the times PP > NP in ARAB. In contrast, MONS displayed PSC rank order as PP > NP > MP. A sharp decline in the concentration of MP biomass was observed during the onset of summer monsoon period in comparison with other PSC in MONS.