M. Mohrmann, C. Heuzé, and S. Swart (2021) Southern Ocean polynyas in CMIP6 models, The Cryosphere, vol 15, pp. 4281–4313, doi:10.5194/tc-15-4281-2021.
We use daily and monthly sea ice concentration and sea ice thickness output from 27 models that participated in the Climate Model Intercomparison Project phase 6 (CMIP6) to evaluate their representation of polynyas, i.e. openings in the winter sea ice, in the Southern Ocean. We find that:
- The daily sea ice thickness output has serious issues;
- Few models have very large open ocean polynyas, but open ocean polynyas feature in most models too often;
- The majority of models overestimate the area of coastal polynyas;
- For most models, the polynya occurrence and area is larger if using daily output instead of monthly, or if using sea ice thickness instead of concentration;
- Too few model families provided CM and ESM versions for us to be certain, but CM versions seem to have a better representation of coastal polynyas, likely because they can be run at higher resolution;
- The Southern Annular Mode and open ocean polynya activity are surprisingly not correlated in the models. Instead, we find a relationship with the Antarctic Circumpolar Current (ACC): the models with the largest open ocean polynya are the ones with the most realistic ACC, although it is unclear which process causes the other one.