Role of tides on the formation of the Antarctic Slope Front at the Weddell-Scotia Confluence

Abstract

The structure of the Antarctic Slope Front (ASF) and the associated Antarctic Slope Current (ASC) on the Scotia Sea side of the Weddell-Scotia Confluence (WSC) is described using data from a hydrographic survey and three 1 year long moorings across the continental slope. The ASC in this region flows westward along isobaths with an annual mean speed of ∼0.2 m s-1, with time variability dominated by the K1 and O1 tidal diurnal constituents, a narrowband oscillation with ∼2-week period attributable to the spring/neap tidal cycle, and seasonal variability. Realistic and idealized high-resolution numerical simulations are used to determine the contribution of tides to the structure of the ASF and the speed of the ASC. Two simulations forced by realistic atmospheric forcing and boundary conditions integrated with and without tidal forcing show that tidal forcing is essential to reproduce the measured ASF/ASC cross-slope structure, the time variability at our moorings, and the reduced stratification within the WSC. Two idealized simulations run with tide-only forcing, one with a homogeneous ocean and the other with initial vertical stratification that is laterally homogeneous, show that tides can generate the ASC and ASF through volume flux convergence along the slope initiated by effects including the Lagrangian component of tidal rectification and mixing at the seabed and in the stratified ocean interior. Climate models that exclude the effects of tides will not correctly represent the ASF and ASC or their influence on the injection of intermediate and dense waters from the WSC to the deep ocean. Key Points: Tides set mean properties of Antarctic Slope Front in Weddell-Scotia Confluence Volume convergence by tidal rectification, plus mixing, creates Slope Current Shelf water properties in Weddell-Scotia Confluence modified by tides