Water mass pathways and transports over the South Scotia Ridge west of 50°W

Abstract

During the ESASSI cruise carried out in January 2008, a sector of the South Scotia Ridge west of the South Orkney Islands was surveyed with a spatial resolution of 1–2 nm (1 nm≡1852 m) over the continental slopes and of about 5 nm elsewhere. We use the ESASSI-08 data set to quantify the export and regional pathways of waters from the Weddell Sea into the Scotia Sea west of 50°W, where the intermediate and deep waters are characterized by being colder and fresher than those crossing the deeper gaps east of the South Orkney Islands. An inverse model initialized with ship-borne ADCP velocities is applied to temperature and salinity profiles to obtain a better estimation of the flow pattern. The model domain encloses the region between Elephant Island and 50°W, and is delimited north and south by the flanks of the ridge. The value obtained for the full-depth net transport into the Scotia Sea is 7±5 Sv (1 Sv≡10 6 m 3 s −1), with heat- (‘enthalpy’ for a non-zero volume transport) and salt-anomaly fluxes of 14±5 TW and (0.8±0.4)×10 6 kg s −1 relative to mean property values of −0.29 °C and 34.56, respectively. The clockwise circulation within the Hesperides Trough enables the along isopycnal exchange of properties between the involved water masses and some diapycnal mixing between the deepest layers. Approximately one-third of the volume transport measured along the northern wall of the trough recirculates inside the trough. The other two-thirds are suggested to outflow into the Scotia Sea, mainly through the deepest gap west of the South Orkney Plateau.