Atlantic pycnocline theory scrutinized using a coupled climate model

Abstract

Simulations with changed Southern Ocean wind-stress, oceanic vertical mixing, surface freshwater forcing and global warming confirm the basic equations of Gnanadesikan's (1999) theory for the Atlantic: one vertical scale, the pycnocline depth D, contributes inversely proportional to low-latitudinal upwelling and linearly to Southern Ocean eddy transport. The maximum Atlantic overturning is confirmed to be quadratic in D but is also shown to be linear in a meridional density difference. Our simulations strongly suggest that the theory needs to be complemented by a dynamical equation for since changes in both D and δp are significant and mutually independent. While, under global warming D varies strongly and δp is practically constant, the situation is reversed for altered surface freshwater fluxes. Similarly, variations in the meridional length scale of Southern Ocean outcropping require a dynamical equation in order to capture the fundamental behavior of the Atlantic meridional overturning circulation. © 2010 by the American Geophysical Union.