Seasonal and Interannual Variability Between Upper Ocean Processes and the Slope Current in the Region Around the Cosmonauts Sea off East Antarctica

The impacts of large-scale climate variability on the current system and meridional transport in the Cosmonauts Sea off East Antarctica are studied by employing the satellite-observed absolute dynamic topography (ADT) data and reanalysis hydrographic data. Three currents converge in the Cosmonauts Sea: the Antarctic Circumpolar Current (ACC), the Weddell Gyre Eastern Branch (WGeb) and the Antarctic Slope Current (ASC) containing the Antarctic Slope Front (ASF) topographically locked in the slope region. Strong seasonal and interannual variations are associated with these currents. The ACC and ASC are both stronger in autumn and weaker in spring and summer, while the WGeb extends eastward in winter and retreats in summer. On the interannual timescale, the Southern Annular Mode (SAM) reinforces the westerlies during its positive phase, pushing the ACC southward and suppressing westward ASC, and vice versa. The results on related mechanisms suggest the significant barotropic modulations induced by the winds on ocean dynamics from both the sea surface and interior ocean. The westerlies could affect the meridional sea level gradient through Ekman transport convergence, inducing the geostrophic adjustment of currents. Moreover, the vorticity input from the wind field produces meridional water transport under the topographic and planetary beta-effects, potentially influencing the structure of the ASF and associated ASC. This frontal adjustment is superimposed on the background barotropic variations and causes strong local responses of the currents to the remote wind forcing, which indicates a propagation of variability signals from large-scale barotropic circulations to frontal-scale baroclinic currents in the ocean interior. Seasonal and interannual variations in the large-scale wind field can affect the strength and position of the current system in the region around the Cosmonauts Sea off East Antarctica. The Antarctic Circumpolar Current (ACC), the Weddell Gyre Eastern Branch (WGeb) and the Antarctic Slope Current (ASC) meet around the Cosmonauts Sea. The surface current velocities and variations based on satellite-observed sea surface height (SSH) data are computed, and the potential forcing mechanisms are analyzed. The strengths of the ACC and ASC change similarly in different seasons but oppositely in different years, along with the changes in the wind belts over the Southern Ocean. The results from studies indicate that the wind field plays an important role in forcing water motions, not only at the sea surface to change the SSH but also at depth to influence the water mass structure. These processes could further regulate the ACC and the ASC, enabling the large-scale wind field to force into the narrow current jets associated with water mass fronts and topographic slopes. Three main currents converging in the Cosmonauts Sea form an integrated circulation system with interconnected variations Winds exert critical barotropic modulations on water transport in both the surface and deep layers Adjustment of Antarctic Slope Front north of Cape Ann can be triggered by interior ocean transport variations driven by wind stress curl