A Theory of the Interhemispheric Meridional Overturning Circulation and Associated Stratification

• Published in: Journal of Physical Oceanography
• Main Authors: Nikurashin, M, Vallis, G
• Format: Article in Journal/Newspaper
• Language: English
• Published: Amer Meteorological Soc 2012
• Subjects: Earth Sciences; Oceanography; Physical Oceanography; Antarctic; Antarc*
• Online Access: https://doi.org/10.1175/JPO-D-11-0189.1; http://ecite.utas.edu.au/80085

A quantitative theoretical model of the meridional overturning circulation and associated deepstratification 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 deepstratification and overturning streamfunction in terms of the surface forcing and other parameters ofthe problem. It relies on a matching among three regions: the circumpolar channel at high southernlatitudes, 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 NorthAtlantic Deep Water and Antarctic Bottom Water. It suggests that whereas the strength of themiddepth overturning cell is primarily set by the wind stress in the circumpolar channel, mid depthstratification results from a balance between the wind-driven upwelling in the channel and deepwater formation at high northern latitudes. Diapycnal mixing in the ocean interior can lead towarming and upwelling warm of deep waters. However, for parameters most representative of thepresent ocean mixing seems to play a minor role for the middepth cell. In contrast, the abyssal cellis intrinsically diabatic and controlled by a balance between the deep mixing-driven upwelling andthe residual of the wind-driven and eddy-induced circulations in the Southern Ocean.The theory makes explicit predictions about how the stratification and overturning circulationvary with the wind strength, diapycnal diffusivity and mesoscale eddy effects. The predictionscompare well with numerical results from a coarse-resolution general circulation model.