Wednesday, January 23, 2013
Environmental Science and Engineering Seminar
A Theory of the Meridional Overturning Circulation and Associated Stratification of the Ocean
Maxim Nikurashin, Physical Oceanographer, Institute for Marine and Antarctic Studies, University of Tasmania
A theoretical model of the meridional overturning circulation and associated deep stratification in interhemispheric 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 problem parameters. The theory describes both the mixing- and wind-driven components of the overturning circulation and relies on a matching among three regions of the ocean: the circumpolar channel at high latitudes in the Southern Hemisphere, a region of isopycnal outcrop at high latitudes in the Northern Hemisphere, and the ocean basin at low and mid latitudes between them.
The theory suggests that whereas the strength of the mid-depth overturning cell is primarily set by the wind stress locally in the circumpolar channel, stratification at mid-depth results from a balance between the rate of wind-driven upwelling in the southern circumpolar channel and the rate of the deep water formation at high northern latitudes. The abyssal cell, on the other hand, is intrinsically diabatic and controlled by a balance between the mixing-driven upwelling in the abyssal ocean and the residual between the wind-driven and eddy-induced circulations in the Southern Ocean. Overall, the stratification of the worlds oceans below the main thermocline is critically dependent on the dynamics occurring in the Antarctic Circumpolar Channel.