Phytoplankton dynamics in the Antarctic marginal ice zone: Trends and drivers

The Southern Ocean's Marginal Ice Zone (MIZ) plays a crucial role in carbon cycling through its influence on phytoplankton biomass and distribution. Here we investigate the impact of climate change on phytoplankton dynamics in the MIZ using satellite-derived chlorophyll-a (Chl-a) data from 1997 to 2020. We observed significant (P < 0.05) increases in Chl-a concentration across most sectors of the MIZ. We observed a significant expansion (>30 %) in the spatial extent of high-biomass areas within the MIZ, with the highest increase in the Ross Sea. However, these trends are spatially variable, with offshore regions showing significant increases, while trends in shelf and coastal waters are mixed, including areas of decrease and non-significance. This indicates the potential for heightened productivity in the Antarctic Ocean region, leading to the export of additional carbon in the future. Furthermore, we establish connections between climate drivers and Chl-a trends, emphasizing the impact of freshening and stratification on Chl-a concentration. These changes in salinity and water column structure are critical factors influencing phytoplankton growth and distribution. Our findings contribute to a better understanding of the interlinked interactions between phytoplankton, sea ice dynamics, and climate variability in the MIZ. By explaining the links between environmental changes and biological responses, this study emphasizes the importance of these relationships for future climate change assessments.