Spatiotemporal dynamics of polynyas and their relationships with phytoplankton blooms in the Ross Sea, Antarctica

Phytoplankton bloom is closely tied to the seasonal evolution of Antarctic coastal polynyas, yet a phenology-based framework linking polynya dynamics to bloom spatiotemporal patterns and phase-specific environmental drivers has been missing. This study uses satellite-derived sea ice concentration and chlorophyll-a (Chl-a) data from 2002 to 2023 to examine the polynyas evolution in the Ross Sea and their relations with phytoplankton blooms. We characterize spatiotemporal polynya dynamics quantitatively based upon double-logistic functions and phenological metrics. Environmental drivers including photosynthetically active radiation (PAR), sea surface temperature (SST), wind speed (WS), and wind direction (WD) are integrated to assess their influence on different bloom phases. Results show significant increases in polynya areas (up to 1240.57 km² per year) from 2002 to 2023. Polynyas exhibit a spatial pattern of slow northward advance and rapid southward retreat. Over the past two decades, they have tended to advance earlier, retreat later, and have longer open water durations (~6 d per decade). A strong positive correlation is found between polynya advance and bloom initiation, with regionally varying regression slopes exceeding 2 d per decade. Environmental drivers of Chl-a show distinct regional and phenological differences: in the Ross Sea Polynya, PAR is the dominant positive factor during both growth and decline phases, whereas SST and WD show significant negative effects during the decline phase. In the Terra Nova Bay Polynya, growth-phase Chl-a is significantly influenced by environmental variables. These findings enhance our understanding of polynya‒bloom interactions in the Ross Sea.