Frontal structure and transport in the northwestern Weddell Sea

Abstract

Hydrographic data from the Antarctic Drifter Experiment: Links to Isobaths and Ecosystems (ADELIE) project are analyzed to determine the frontal structure and transport along a section across the continental shelf and slope in the northwestern Weddell Sea. The flow is dominated by three barotropic northward flowing currents: the Antarctic Coastal Current, the Antarctic Slope Front and the Weddell Front. The strongest baroclinic flows are confined to the region between the Slope Front and the Weddell Front over the steepest part of the continental slope. The Antarctic Coastal Current flows over the continental shelf near a local steepening in the bathymetry and has a transport of ~1.3 Sv. The Antarctic Slope Front is found approximately 25 km offshore of the shelf break in 800 m of water. The Slope Front, which is associated with a transport of ~4 Sv, exhibits peak velocities above the bottom that reach 35cm s^(-1)as detected by lowered acoustic Doppler profiler (LADCP) measurements. A third northward current is found between the 2500 and 3000 m isobaths, corresponding to a local break in the topography. Potential temperature–salinity diagrams show that the change in water mass properties across the deep front is similar to the change found across the Weddell Front in the northern Weddell Sea. This suggests that the deep front is a crossing of the Weddell Front further upstream in the Weddell Gyre. The Weddell Front accounts for ~17 Sv of northward transport across the section. A deep outflow is observed all along the continental slope between the Slope Front and the Weddell Front. Transport within the deep outflow is localized in two to three distinct cores that are tied to topographical features. The total transport across the ADELIE section is 46 ± 8 Sv. This value exceeds previous estimates because the full-depth and de-tided LADCP measurements allowed the narrow (~20 km) frontal currents to be resolved, leading to more accurate estimates of the barotropic component of the flow. We discuss the physical processes that may lead to the formation and maintenance of these fronts.