The current system in the Cosmonaut Sea off East Antarctica is subjected to large-scale climate change, which in turn affects the nutrient availability and productivity of the region. The Copernicus merged absolute dynamic topography (ADT) data were employed to analyze the variability of major currents and potential driving mechanisms behind. The main currents in the Cosmonaut Sea are revealed to be the Antarctic Circumpolar Current (ACC), the Weddell Gyre Eastern Branch (WGeb) and the Antarctic Slope Current (ASC); and strong seasonal and interannual variations are also found associated with these currents. ACC and ASC both are stronger in autumn and weaker in spring and summer, while the WGeb expends eastward in winter and retreats in summer. At the interannual timescale, the Southern Annular Mode (SAM) could reinforce westerlies during its positive phase, pushing ACC southward and suppressing westward ASC, and vice versa. Studies on related mechanisms suggest the crucial role of winds in the barotropic modulation of ocean dynamics. The westerlies affect the meridional gradient of the sea level through Ekman transport, inducing the change of barotropic geostrophic currents. The changing atmospheric and oceanic circulations have possible influence on the southward Sverdrup transport maintaining the Antarctic Slope Front (ASF) crucial to the ASC thereafter. The WGeb might also perform an intermediate role in the southward cascading of variability from ACC to ASC. This indicates that the response of regional ocean dynamics to circumpolar atmospheric variations could be understood from the view of cascading processes.