Image1_Updated geostrophic circulation and volume transport from satellite data in the Southern Ocean.JPEG

Introduction: A geodetic estimation of the surface geostrophic currents can be obtained from satellite data by combining sea surface height measurements obtained from altimetry missions with geoid data from gravity missions. These surface geostrophic currents serve as a reference for inferring a comprehensive three-dimensional (3D) geostrophy by propagating them downwards using temperature and salinity profiles.

Methods: In this work, we revisit this problem for the Southern Ocean, estimating the 3D geostrophy near full depth in 41 layers, with a 1° spatial resolution and monthly temporal resolution, covering the 12 years from 2004 to 2015. We analyze the obtained 3D geostrophy over the Southern Ocean region, where the Antarctic Circumpolar Current (ACC) and its several fronts are depicted, as well as other major currents such as the Agulhas Current, the Brazil-Malvinas Current, or the East Australian Current. From the 3D geostrophic currents, we also estimate the associated water volume transport (VT) and present the results for the ACC and the Drake Passage in the context of existing literature.

Results: Our analysis yields a mean VT estimate of 15.9 ± 0.1 Sv per 1° cell within the ACC region and 149.2 ± 2.2 Sv for the Drake Passage ([60.5°S, 54.5°S] x [303.5°E]). Importantly, our study includes a comprehensive validation of the results. The spatial resolution of our space-data-based approach enables us to provide VT estimates for various paths followed in the different in situ campaigns at the Drake Passage, thereby validating our findings.

Discussion: The analysis demonstrates a remarkable agreement across different measurement locations, reconciling the differences in estimates reported from different campaigns. Moreover, we have estimated the barotropic and baroclinic components of the currents and their associated VT.