Lagged influence of spring southern annular mode on late-summer Antarctic fast ice variability

Antarctic fast ice is essential for ice shelf stability and the formation of Antarctic Bottom Water, which are critical for global ocean circulation. Despite its importance, the variability of fast ice has not been extensively studied. Here, we investigate the influence of the Southern Annular Mode (SAM) on fast ice variability in March. We find that circum-Antarctic fast ice variability in March is significantly associated with the strength of SAM in the previous September, particularly in the regions of Dronning Maud Land (DML), the Amundsen Sea (AS), and the Australian sector (Aus). In DML and AS, positive SAM induces northward sea ice drift near the coast, which can contribute to reduced surrounding sea ice during spring. This sea ice loss is further amplified by increased net solar radiation associated with reduced albedo. In turn, ocean swell near the coast increases during summer, contributing to the reduction of fast ice in March. In contrast, fast ice variability in the Aus region is less linked to coastal sea ice loss. Instead, in this region, where north–south-oriented coastal features are prominent, fast ice formation is associated with westward pack ice advection driven by the Antarctic Coastal Current. Positive SAM enhances eastward sea ice drift, hindering westward ice advection and reducing springtime fast ice, ultimately leading to decreased fast ice in March.