LAUSR

Phytoplankton size classes (PSC) patterns are distinctive, tightly coupled to environmental controls of the upper ocean layer, with sensitiveness toward the seasonal cycle. This letter focuses on the phenology of PSC to investigate the spatiotemporal assemblage of each PSC influenced by the environmental drivers over the Arabian Sea (AS). We applied an abundance-based approach on 16-year time series gap-filled satellite-derived chl- $a$ products to retrieve the PSC. Further, we estimated the PSC phenology indices for the AS as the timing of initiation, termination, duration, peak, and mean. The threshold criterion method is used to extract and map the PSC phenology indexes. The unique environmental adaptation of each PSC on both spatial and seasonal variability is highlighted and discussed based on the connection with the sea surface temperature (SST) and mixed layered depth (MLD). From the results, a new perspective is drawn on the PSC phenology patterns in the AS and how environmental controls influence each PSC.