A Theory of the Interhemispheric Meridional Overturning Circulation and Associated Stratification
Nikurashin, M and Vallis, G, A Theory of the Interhemispheric Meridional Overturning Circulation and Associated Stratification, Journal of Physical Oceanography, 42 pp. 1652-1667. ISSN 0022-3670 (2012) [Refereed Article]
A quantitative theoretical model of the meridional overturning circulation and associated deep
stratification in an interhemispheric, single-basin ocean with a circumpolar channel is presented.
The theory includes the effects of wind, eddies, and diapycnal mixing, and predicts the deep
stratification and overturning streamfunction in terms of the surface forcing and other parameters of
the problem. It relies on a matching among three regions: the circumpolar channel at high southern
latitudes, a region of isopycnal outcrop at high northern latitudes and the ocean basin between.
The theory describes both the middepth and abyssal cells of a circulation representing North
Atlantic Deep Water and Antarctic Bottom Water. It suggests that whereas the strength of the
middepth overturning cell is primarily set by the wind stress in the circumpolar channel, mid depth
stratification results from a balance between the wind-driven upwelling in the channel and deep
water formation at high northern latitudes. Diapycnal mixing in the ocean interior can lead to
warming and upwelling warm of deep waters. However, for parameters most representative of the
present ocean mixing seems to play a minor role for the middepth cell. In contrast, the abyssal cell
is intrinsically diabatic and controlled by a balance between the deep mixing-driven upwelling and
the residual of the wind-driven and eddy-induced circulations in the Southern Ocean.
The theory makes explicit predictions about how the stratification and overturning circulation
vary with the wind strength, diapycnal diffusivity and mesoscale eddy effects. The predictions
compare well with numerical results from a coarse-resolution general circulation model.
meridional overturning circulation, deep stratification, conceptual theory, water masses, thermohaline circulation