Southern Ocean polynyas in CMIP6 models

Abstract. Polynyas facilitate air–sea fluxes, impacting climate-relevant properties such as sea ice formation and deep water production. Despite their importance, polynyas have been poorly represented in past generations of climate models. Here we present a method to track the presence, frequency spatial distribution Southern Ocean 27 models participating Climate Model Intercomparison Project Phase 6 (CMIP6) two satellite-based products. Only half form open-water (OWPs), most underestimate area. As satellite observations, three show episodes high OWP activity separated by decades no OWP, while other unrealistically create OWPs nearly every year. In contrast, coastal polynya area is overestimated models, with least accurate representations occurring coarsest horizontal resolution. We that presence or absence linked changes regional hydrography, specifically linkages between convection and/or shoaling upper column thermocline. Models an Antarctic Circumpolar Current transport wind stress curl too frequent OWPs. Biases representation continue exist which has impact on ocean circulation ventilation should be addressed. However, emerging iceberg discharge schemes, more adequate vertical grid type overflow parameterisation are anticipated improve associated prediction future.