Thermohaline Adjustment and Advection in an OGCM*

Abstract

The response of an ocean general circulation model to the onset of deep-water formation in the North Atlantic Ocean is explored. The processes of baroclinic adjustment to the new deep water mass and the advection of the new deep water mass are compared in both space and time. The baroclinic adjustment is gauged by following the anomalies in the 0–2000 dbar layer thickness and the advection is measured with the aid of idealized passive tracers. Baroclinic adjustment follows the classical boundary layer path and all locations north of the Antarctic Circumpolar Current begin to feel the effects within 20 years. Heat transport in the North Atlantic responds on the adjustment timescale. Advection does not follow the boundary layer path and is much slower: the timescale for NADW to reach the North Pacific Ocean is on the order of 1000 years. While the baroclinic signal is much faster, the initial response is much smaller and probably could not be detected over the random noise in the pressure field outside of the Atlantic basin. Both processes weaken as they move farther from the forcing region.