A deep cyclonic gyre in the Australian-Antarctic Basin

• Published in: Progress in Oceanography
• Main Authors: McCartney, Michael S., Donohue, Kathleen A.
• Format: Text
• Language: unknown
• Published: DigitalCommons@URI 2007
• Subjects: Abyssal circulation; Antarctic circumpolar current; Boundary currents; Gyres; Southeast Indian ocean sector; Southern ocean; Wind-driven Circulation; Antarctic; Australian Antarctic Basin; Australian-Antarctic Basin; Drake Passage; Flinders; Indian; Kerguelen; Southern Ocean; The Antarctic; Antarc*; Antarctica
• Online Access: https://digitalcommons.uri.edu/gsofacpubs/1225; https://doi.org/10.1016/j.pocean.2007.02.008

The traditional image of ocean circulation between Australia and Antarctica is of a dominant belt of eastward flow, the Antarctic Circumpolar Current, with comparatively weak adjacent westward flows that provide anticyclonic circulation north and cyclonic circulation south of the Antarctic Circumpolar Current. This image mostly follows from geostrophic estimates from hydrography using a bottom level of no motion for the eastward flow regime which typically yield transports near 170 Sv. Net eastward transport of about 145 Sv for this region results from subtracting those westward flows. This estimate is compatible with the canonical 134 Sv through Drake Passage with augmentation from Indonesian Throughflow (around 10 Sv). A new image is developed from World Ocean Circulation Hydrographic Program sections I8S and I9S. These provide two quasi-meridional crossings of the South Australian Basin and the Australian-Antarctic Basin, with full hydrography and two independent direct-velocity measurements (shipboard and lowered acoustic Doppler current profilers). These velocity measurements indicate that the belt of eastward flow is much stronger, 271 ± 49 Sv, than previously estimated because of the presence of eastward barotropic flow. Substantial recirculations exist adjacent to the Antarctic Circumpolar Current: to the north a 38 ± 30 Sv anticyclonic gyre and to the south a 76 ± 26 Sv cyclonic gyre. The net flow between Australia and Antarctica is estimated as 157 ± 58 Sv, which falls within the expected net transport of 145 Sv. The 38 Sv anticyclonic gyre in the South Australian Basin involves the westward Flinders Current along southern Australia and a substantial 33 Sv Subantarctic Zone recirculation to its south. The cyclonic gyre in the Australian-Antarctic Basin has a substantial 76 Sv westward flow over the continental slope of Antarctica, and 48 ± 6 Sv northward-flowing western boundary current along the Kerguelen Plateau near 57°S. The cyclonic gyre only partially closes within the Australian-Antarctic Basin. ...