Spatial and Subannual Variability of the Antarctic Slope Current in an Eddying Ocean–Sea Ice Model

Abstract

The Antarctic Slope Current (ASC) circumnavigates the Antarctic continent following the continental slope and separating the waters on the continental shelf from the deeper offshore Southern Ocean. Water mass exchanges across the continental slope are critical for the global climate as they impact the global overturning circulation and the mass balance of the Antarctic ice sheet via basal melting. Despite the ASC’s global importance, little is known about its spatial and subannual variability, as direct measurements of the velocity field are sparse. Here, we describe the ASC in a global eddying ocean–sea ice model and reveal its large-scale spatial variability by characterizing the continental slope using three regimes: the surface-intensified ASC, the bottom-intensified ASC, and the reversed ASC. Each ASC regime corresponds to a distinct classification of the density field as previously introduced in the literature, suggesting that the velocity and density fields are governed by the same leading-order dynamics around the Antarctic continental slope. Only the surface-intensified ASC regime has a strong seasonality. However, large temporal variability at a range of other time scales occurs across all regimes, including frequent reversals of the current. We anticipate our description of the ASC’s spatial and subannual variability will be helpful to guide future studies of the ASC aiming to advance our understanding of the region’s response to a changing climate. The Antarctic Slope Current (ASC) circumnavigates the Antarctic continent following the continental slope and separating the waters on the continental shelf from the deeper offshore Southern Ocean. Water mass exchanges across the continental slope are critical for the global climate as they impact the global overturning circulation and the mass balance of the Antarctic ice sheet via basal melting. Despite the ASC’s global importance, little is known about its spatial and subannual variability, as direct measurements of the velocity field are sparse. Here, we describe the ASC in a global eddying ocean–sea ice model and reveal its large-scale spatial variability by characterizing the continental slope using three regimes: the surface-intensified ASC, the bottom-intensified ASC, and the reversed ASC. Each ASC regime corresponds to a distinct classification of the density field as previously introduced in the literature, suggesting that the velocity and density fields are governed by the same leading-order dynamics around the Antarctic continental slope. Only the surface-intensified ASC regime has a strong seasonality. However, large temporal variability at a range of other time scales occurs across all regimes, including frequent reversals of the current. We anticipate our description of the ASC’s spatial and subannual variability will be helpful to guide future studies of the ASC aiming to advance our understanding of the region’s response to a changing climate.