This work aims to understand the link between the seafloor morphology and sub-seafloor stratigraphy of the Eastern Bransfield Basin (EBB; Antarctic Peninsula) with the water masses circulation established since the opening of the basin at around 3.3 Ma. Bottom currents (contourite) features identified from swath bathymetry data and parametric echo-sounder profiles acquired in the DRAKE2018 and POWELL2020 cruises are correlated with published information about water masses circulation and hydrological data. The EBB is the easternmost sector of the Bransfield Strait, oriented SW-NE and bounded by the Antarctic Peninsula to the southeast and the South Shetland and Elephant islands to the north and northwest. Contourite features are identified based on their sedimentary stacking pattern and morphological characteristics. They locate at distinctive depth levels in the EBB. A large mounded drift has been identified in an intra-slope platform in the SE margin, at water depths of 1000-1500 m. It is 35 km long and 20 km wide and is bounded by erosional contourite moats. These features are interpreted to result from the southwestward flow of the East Basin Deep Water (EBDW) at intermediate depths, formed by a mix of water masses from the Weddell Sea. Plastered drifts topped by contourite terraces occupy depths of 1100-1200 m along the SE margin of the basin, and are related to the high-energy oceanographic regime formed at the transitional boundary between the EBDW and the East Bransfield Bottom Water (EBBW). Contourite features on the deep, flat seafloor of the EBB at 2000-2300 m water depth are also formed by the EBBW. Mounded contourite drifts prograde and thin towards the outer limits of the basin, where contourite moats are interbedded with mass transport deposits. These contourite features have been generated by the episodic entrance of bottom water masses from the Central Basin and their mix with deep water masses flowing from the NE. This work reveals the highly dynamic oceanographic circulation in the Bransfield Strait, which has been established as tectonic processes led to the opening and deepening of gateways in the narrow basins at the tip of the Antarctic Peninsula and South Scotia Sea. Understanding the onset and temporal variability of the oceanographic pattern is of key importance to study the impact of deep-sea gateways in global oceanographic and climatic models.

4th Deep Water Circulation Research Conference. Edinhburgh, 24-26 May 2023