Mushy Ice and Saltier Seas: Coupled Impacts of Sea Ice Thermodynamics in Antarctic Coastal Regions

The oceans around Antarctica are covered by sea ice for half the year, yet there exist a few locations along the coast that remain ice free for much of the year. While small in relative spatial footprint, Antarctic polynyas have an outsize impact on Earth’s climate system and on the Southern Ocean biological system. Physically, coastal polynyas around the Antarctic form as cold, downslope winds continually push ice away from the coast. We use data from the Community Earth System Model version 2 (CESM2) to characterize regional differences in modeled polynya features and the resulting impacts on the ocean and atmosphere. We analyze two preindustrial CESM2 experiments with different sea ice physics to better understand the effect of the newly adopted sea ice physical parameterization, which formulates sea ice as a mushy mixture of solid ice and salty water. We find that with the new “mushy layer” sea ice physics there is substantial increase in coastal sea ice frazil and snow ice production in CESM2 as compared to the older physics, which was used in CESM1. Additionally, the subsurface ocean water is denser with the “mushy” thermodynamics as a result of increased brine rejection and that there is a statistically significant increase of ~0.5Sv in Antarctic Bottom Water Formation. However, impacts on the ocean biogeochemistry are minimal and primarily related to small areas with summer ice concentration differences. While there are no significant changes in the atmospheric circulation, there are decreases in turbulent heat flux into the atmosphere with the “mushy” thermodynamics, which impacts atmospheric mixing and atmospheric boundary layer height.