Challenges in identifying Antarctic coastal polynyas in satellite observations and climate model output to support ecological climate change research

Antarctic coastal 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 challenges inherent in identifying climatologically and biologically relevant Antarctic coastal polynyas on gridded data in both satellite and Earth System Model data. We find that it is critical to consider grid type and resolution, season, metric and threshold when defining polynyas. Regridding data, both spatially and temporally, can have significant impacts on identified polynya statistics. The spatial distributions of Antarctic coastal polynyas are significantly correlated between the two observational products as well as between the observational products and the model data. The Earth System Model we use here captures coastal polynya-like features that occupy ∼ 3 % of the area of the winter sea ice zone and contribute ∼ 17 %–21 % of the total sea ice zone marine net primary productivity (NPP). Temporal self- and cross correlations of integrated polynya areas and numbers are inconsistent across observational and modelling products. Trends in polynya areas are not robust, changing significance, magnitude and sign across threshold, grid and product.