On the freshwater forcing of the thermohaline circulation in the limit of low diapycnal mixing

Keeling, RF.  2002.  On the freshwater forcing of the thermohaline circulation in the limit of low diapycnal mixing. Journal of Geophysical Research-Oceans. 107

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abyssal ocean, antarctic circumpolar current, atmospheric co2, climate stability, Drake Passage, general-circulation, indian-ocean, interbasin exchange, intermediate water, large-scale circulation, mixed boundary conditions, overturning circulation, southern-ocean, thermohaline circulation, world ocean


[1] A conjecture is offered on the stability characteristics of the thermohaline circulation in the limit of very low diapycnal mixing. In this limit the action of the winds on the Antarctic Circumpolar Current (ACC) can sustain a deep overturning pattern known as the "reconfigured conveyor,'' consisting of upwelling around Antarctica and sinking in the North Atlantic, as shown by the work of Toggweiler and others. It is conjectured that in this limit, northern sinking should be stabilized in an "on'' state because of the penetration of freshwater into the ocean interior via isopycnal layers that outcrop to the surface within and south of the ACC. This conjecture is supported by qualitative arguments and by a hydraulic model for the reconfigured conveyor. The hydraulic model takes into account the freshwater budgets of the Atlantic basin, Antarctic surface waters, and the remaining oceans. It also takes into account, in simple terms, wind-driven Antarctic upwelling, eddy transports and mixing within the ACC, changes in pycnocline depth, the role of temperature forcing, and advective feedbacks on salinity. The hydraulic model suggests that multiple "on/off'' states of the reconfigured conveyor are possible but only if the deep waters that form in the Northern Hemisphere are fresher than the intermediate waters that form in the vicinity of the ACC in the Southern Hemisphere, a condition that is not satisfied in the modern ocean.






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