Defining Antarctic polynyas in satellite observations and climate model output to support ecological climate change research

Abstract. Antarctic polynyas are key components of Antarctic marine ecosystems, influencing light and nutrient availability and open water access for marine predators. Thus, changes in the physical characteristics of polynyas can influence how these ecosystems respond to a changing climate. Here, we explore how to identify polynyas using satellite and Earth System Model data, and we assess the impacts of using different polynya-identification metrics (sea ice concentration or thickness). Our results show optimal metrics for polynya definition will depend on the temporal and spatial resolution of the data, as well as the season and region of interest. These results highlight the importance of identifying polynyas on grids of the same type and resolution when comparing polynyas from different data products. We find that sea ice thickness is more suitable for identifying polynyas in model data in winter months in contrast to spring months when both sea ice thickness and concentration may be suitable metrics. We then use the Community Earth System Model Version 2 (CESM2) to investigate ecosystem function within polynyas and find that there is enhanced phytoplankton productivity in modeled polynya features in both hindcast and fully coupled simulations, with springtime polynyas remaining an important control on Antarctic productivity under future climate change.