Comparative study of the variability of the phytoplankton biomass in two upwelling zones of the western Arabian Sea from 2003 to 2020.

This study investigates the monthly and interannual variations in chlorophyll-a (Chl-a) concentrations in the Oman and Somalia upwelling zones using satellite data from 2003 to 2020. Bivariate Wavelet Coherence (BWC) and Multiple Wavelet Coherence (MWC) analyses were applied to identify the key factors influencing Chl-a concentration changes. The results show that Ekman pumping and Ekman transport induced by the southwest monsoon are crucial for phytoplankton blooms along the coast and offshore in both upwelling zones. BWC analysis revealed that the mixed layer depth (MLD) is the best single oceanic factor explaining the interannual fluctuations in Chl-a concentrations in the Oman upwelling zone, while sea surface temperature (SST) is the best factor in the Somalia upwelling zone. MWC analysis showed that the combinations of MLD-EPV (Ekman pumping velocity), MLD-SLA (sea level anomaly), MLD-Niño 3.4, and MLD-SST are most strongly associated with Chl-a variations in the Oman upwelling zone.