During winter, thin sea ice is formed in coastal polynias, areas of open-water within a sea ice pack and important sites of dense shelf water formation. In the Mertz Glacier polynia (138°E-147°E, East Antarctica), we examined the effects of an extreme calving event, the last Mertz glacier calving, on the regional sea ice distribution. The high-frequency variability of sea ice concentration was studied for years 1992 to 2011 from passive microwave satellite data with fine spatial (6.25 km and 12.5 km) and temporal (1 day) resolutions. Our results showed that the last calving of the Mertz glacier tongue in February 2010 greatly modified the size and shape of the polynia with a significant westward shift in the regional ice regimes. We also identified a post-calving transition state characterised by a 70%-decrease in polynia area from the pre-calving mean. In the eastern part of the study area, our findings are in agreement with other studies predicting an important decrease in polynia activity. In the western part, where the main polynia activity has shifted after the calving, the new sea ice distribution is expected to have a major impact on local sea ice production, dense shelf water sinking, and potentially the regional thermohaline circulation. With extreme climatic events predicted to occur more frequently, long-term monitoring of the regional icescape could be used to evaluate the vulnerability of Antarctic physical processes and related ecosystems.