Dynamical pathways of Antarctic Bottom Water in the Atlantic

A reduced-gravity model is developed to represent the flow of Antarctic Bot tom Water (AABW) over realistic bathymetry in an Atlantic domain. The dynam ics are based on the steady, planetary-geostrophic, shallow-water equations , including a linear bottom friction and a uniform diapycnal upwelling thro ugh the top of the model layer. The model solutions are broadly consistent with observations of the distribution and transport of AABW. The flows occu r predominantly along potential vorticity contours, which are in turn broad ly oriented along bathymetric contours. The characteristic weak flow across potential vorticity contours of the Stommel-Arons model is present as a sm all addition to this stronger forced mode along potential vorticity contour s. As a consequence, mass balance is maintained not by hypothesized western boundary currents as in the Stommel-Arons model, but by the interplay betw een topographic slope currents and interior recirculations. In particular, a transposition is found in the flow of AABW from the western side of the B razil Basin south of the equator to the western flank of the Mid-Atlantic R idge north of the equator. This is also consistent with an analytical resul t derived by extending the Parsons mechanism to an abyssal layer overlying arbitrary bathymetry. The authors suggest that the results provide a more c onvincing zero-order picture than the Stommel-Arons model for the circulati on of AABW and perhaps for abyssal water masses in general.