Changing sea ice in Antarctic coastal polynyas in the Community Earth System Model (CESM)

Abstract:

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. Polynyas span a range of spatio-temporal scales from large, persistent polynyas to smaller, ephemeral polynyas that open on daily to monthly scales. We focus data from the Community Earth System Model version 2 (CESM2) to characterize regional differences in modeled polynya features. 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 production in CESM2 as compared to the older physics, which was used in CESM1. We investigate the coupled impact this change in coastal sea ice production has on ocean mixing and as a source of heat and moisture to the atmosphere. Additionally, we use CESM2 ensemble data from Coupled Model Intercomparison Project Phase 6 (CMIP6) transient climate experiments. By analyzing daily sea ice concentration over the historical and future period to identify regional polynya-like features in the model and catalogue their size, location, temporal duration, and variability throughout the year and describe how polynyas may change with a changing climate.