Influences of Topography on the Modeling of Abyssal Water Masses. Part I: Effects of Channel Representation

Abstract

Connections between basins below 4000 m, which may or may not be resolved in computer-generated model topography, have been found to have a considerable impact on the movement of Antarctic Bottom Water and on deep ocean temperatures. Blocked ridges produce sharply stepped tracer distributions and a complete absence of Antarctic influence in the North Atlantic. With channels opened, mass transports through them are of the right order, but interbasin gradients are too small and the water is too dense. Because mixing processes in the channels are poorly represented, some modification of channel properties may be necessary in order to achieve realistic water property distributions. This may be done by making local adjustments of diffusive and viscous coefficients, by the use of single width channels (which may be included inadvertently or by design in topography generation and which allow diffusive and limited advective exchanges between basins), and, when vertical resolution allows it, by an appropriate choice of sill depth at the interbasin channels. The various methods work by controlling the mixing of bottom water with deep water by advection and diapycnal diffusion.