Impacts of Antarctic summer sea-ice extremes.

Antarctic sea ice plays many crucial roles in the physical environments and ecosystems of Antarctica and the Southern Ocean. In this study, we synthesize the physical, biogeochemical, ecosystem, and societal impacts of summers with extreme low Antarctic sea-ice coverage. These extreme events result in the loss of multiyear landfast ice and changes in sea-ice seasonality. Following extreme low sea-ice events, we find surface warming of the Southern Ocean and changes to the formation rate of Antarctic Intermediate Water, likely affecting heat and carbon uptake. Ice-shelf calving is negatively correlated with sea-ice area, so that years with less sea ice show increased calving. Prolonged open water affects the magnitude and seasonality of surface-phytoplankton blooms. The impacts on higher trophic levels are species-specific and occur through habitat loss and changes to prey availability. Extreme sea-ice lows will adversely impact krill, a foundational prey species that relies on sea ice for nourishment and refuge. The loss of stable landfast ice in austral spring and summer hampers Antarctic operations and resupply missions. Understanding the full impacts of recent, and future, sea-ice extremes is of utmost importance and requires an enhanced observational network that spans the physical and ecological systems of Antarctica and the Southern Ocean.