Abstract

The dense water outflow from the Southern Ocean continental shelf is closely associated with the strength and position of the Antarctic Slope Front. Here we explore the short-term variability of the Antarctic Slope Front system and the mechanisms that regulate cross-slope exchange processes using high temporally- and spatially-resolved measurements from three ocean gliders deployed in 2012. Orkney Islands, are grouped regionally and composited by isobaths. There is consistency in the front position around the Powell Basin while the magnitude of the velocity field shows substantial variability, up to 2.2 times its mean value. The along-slope transport of the Antarctic Slope Current (upper 1000 m) varies between 0.2 and 5.9 Sv and does not exhibit a regional pattern. High eddy activity in the slope region contributes to the variability of the Slope Current. In most of the study area the flow is bottom intensified, even in the absence of bottom water export form the shelf. Common to all sections within the Powell Basin is a potential vorticity gradient on isopycnals. The vertical buoyancy gradient makes the main contribution to the potential vorticity, and is enhanced in the dense water layer. A susceptibility of the flow to baroclinic instabilities is identified over the slope, mainly in the presence of dense flow. Glider transects west of the South Orkney Islands indicate a northward flow, which differs from previous estimates of the mean circulation’s orientation. This study provides some of the first observational confirmation of the high frequency variability associated with an active eddy field that has been suggested by recent numerical simulations in this region.