Tania Pereira Vázquez ( Ph.D. student):Diagnosis of the Western Boundary Current System of the Weddell Gyre from a global eddy-resolving ocean model

The major feature of the Weddell Sea, located east of the Antarctic Peninsula in the Southern Ocean, is a cyclonic gyre driven by wind and thermohaline forcing as well as topographic steering. To a great extent, the Western Boundary Current System (WBCS) of the Weddell Sea gyre splits into different branches before its arrival to the Scotia Sea, east of the Bransfield Strait. Importantly, one of these branches leakages near-freezing subsurface waters into Bransfield Strait. These waters are known as Transitional Weddell Sea Water (TWW) and have been recently suggested to maintain regionally low rates of glacier retreat within the Bransfield Strait. In this work we use historical observations and a global eddy-resolving ocean model (GLORYS12V1, available at https://marine.copernicus.eu) to understand further the governing variations of the WBCS before its arrival to the Scotia Sea. We focus on the ADELIE transect (Figure 1), a key location which captures the hydrography and dynamic of the western branch of the gyre before water masses start exiting the basin. Model-based estimates indicate the volume transport across this transect is on average about 20.2 ± 2.8 Sv over the period 1993-2018. These values agree well with previous studies (see Table 1). Also, a strong seasonal cycle is revealed with an amplitude about 7-8 Sv stronger during the winter (31 Sv) as compared to summer (24 Sv). This seasonal cycle is in agreement with a strengthening of the wind stress curl forcing the gyre. These results encourage us to explore through ongoing analyses the modelled interannual variability of the WBCS, assessing the impact that wind and thermohaline forcing’s may have on controlling this variability. We are currently extending these analyses with a data from a Weddell Sea limited region ocean ice shelf model (NEMO), which enable different thermohaline scenarios under which the Weddell Sea gyre responds.