Sea ice impacts on spring bloom dynamics and net primary production in the Eastern Bering Sea

In the Eastern Bering Sea, changes in sea ice have been implicated in recent major upper-trophic level shifts. However, the underlying relationships between sea ice and primary producers have not been well tested. Here, we combine data from multiple satellite platforms, reanalysis model results and biophysical moorings to explore the dynamics of spring and summer primary production in relation to sea ice conditions. In the northern Bering Sea, sea ice consistently retreated in late spring, leading to ice-edge phytoplankton blooms in cold (0-1 °C) waters. However, in the southeastern Bering Sea, sea ice retreat was far more irregular. Although this did not significantly alter bloom timing, late retreat led to blooms at the ice-edge while early retreat led to blooms in open waters that were warmer (≤5.4 °C) and >70% more productive. Early sea ice retreat also led to higher productivity in summer, likely due to weaker thermal stratification. Overall, annual net primary production during warm years of early sea ice retreat was enhanced by 40-50% compared to years with late sea ice retreat in the southeastern Bering Sea. These findings suggest the potential for future sea ice loss to enhance overall carrying capacity of the southeastern Bering Sea ecosystem. Consistently warm blooms in the future may also channel more energy flow toward the pelagic, rather than benthic, environment. To date, however, neither sea ice extent nor the timing of its retreat have undergone long-term changes in the Eastern Bering Sea.