The Ross Sea, the most productive region of phytoplankton around the Antarctic margin, supports the marine food web in the Southern Ocean. However, the long-term variability of chlorophyll-a production is not fully understood. Here we explored the long-term changes in austral summer chlorophyll-a concentrations in the Ross Sea region during the 1997–2023 period. The results indicate a clear east–west asymmetric change in chlorophyll-a concentration between 180°W–130°W: decreasing (increasing) in the west (east), which is dominated by the changes in wind forcing and sea ice coverage. Cyclonic wind anomalies drive regional sea ice divergence off Marie Byrd Land, while increasing coastal easterly winds off Marie Byrd Land and southerly wind anomalies in the western Ross Sea drive regional sea ice convergence. As a result, photosynthetically active radiation availability increased (decreased), promoting (limiting) phytoplankton growth in the eastern (western) zone. The warming sea surface temperature and potential increases in dissolved iron also may contribute to the chlorophyll-a blooms in the eastern zone.

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