INTERBASIN EXCHANGE OF BOTTOM WATER IN OCEAN GENERAL-CIRCULATION MODELS

The abyssal part of the thermohaline circulation can pass through narr ow channels between ocean basins, which can potentially be resolved by high-resolution ocean models such as the Fine Resolution Antarctic Mo del. However, in the FRAM, as in other models, topographic smoothing f illed in these channels, severely weakening the abyssal circulation an d altering the baroclinic structure at shallower depths. The authors d escribe a model covering the Vema Channel region of the South Atlantic , which was nested in the FRAM, with a straight, single gridpoint chan nel joining the Argentine and Brazil Basins. Initialization with the F RAM results produced a weak northward flow through the channel, which decayed after 6 months. Spinning up the model toward the FRAM results produced southward flow, whereas spinning up toward the Levitus climat ological fields of temperature and salinity produced northward flow of similar strength to observations. An experiment with higher cross-cha nnel resolution gave a similar result. Topographic smoothing therefore results in incorrect abyssal flow and, therefore, thermohaline circul ation in the present generation of both eddy-resolving and climate oce an general circulation models.