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Year-round variability in the Ross Gyre (RG), Antarctica, during 2011-2015, is derived using radar altimetry. The RG is characterized by a bounded recirculating component and a westward throughflow to the south. Two modes of variability of the sea surface height and ocean surface stress curl are revealed. The first represents a large-scale sea surface height change forced by the Antarctic Oscillation. The second represents semiannual variability in gyre area and strength, driven by fluctuations in sea level pressure associated with the Amundsen Sea Low. Variability in the throughflow is also linked to the Amundsen Sea Low. An adequate description of the oceanic circulation is achieved only when sea ice drag is accounted for in the ocean surface stress. The drivers of RG variability elucidated here have significant implications for our understanding of the oceanic forcing of Antarctic Ice Sheet melting and for the downstream propagation of its ocean freshening footprint.

Plain Language Summary The Ross Gyre is one of the main current systems of the Southern Ocean and conveys heat toward the cold continental shelves of the Antarctic Pacific sector, thus impacting the stability of diverse ice shelves. Due to the seasonal sea ice cover, measurements are sparse and little is known about the variability of the gyre's circulation and its driving forces. Here we use satellite radar altimetry to generate new light on the Ross Gyre variability. Two key aspects are identified: (i) large-scale variability of the sea surface height driven by the zonal winds that flow around Antarctica and (ii) changes in area and strength of the gyre, which are linked to a regional center of low pressure that modulates the local meteorology and sea ice conditions. This same pressure system regulates the strength of the coastal currents, which potentially impacts on the distribution of key oceanic properties toward the Ross Sea. The processes identified in this study have strong implications for our understanding of the oceanic forcing of Antarctic Ice Sheet melting and for the downstream propagation of its ocean freshening footprint.