Ocean circulation, Ocean heat transport

Take away ideas and understandings

• Ocean circulation is produced by the wind stress acting on the sea surface and by buoyancy (heat and freshwater) fluxes between the ocean and atmosphere.

• The former induces the wind driven ocean circulation, the latter the thermohaline circulation.

• The wind driven flow is by far the more energetic and for the most part resides in the upper kilometer.

• The sluggish thermohaline circulation forces ocean overturning reaching in some regions to the sea floor, resulting in the formation of the major water masses of the global ocean: North Atlantic Deep Water and Antarctic Bottom Water.

• The wind stress produces Ekman Layer transport in the surface layer (upper 100 to 300 meters) of the ocean, which redistributes the buoyant surface water producing sea level hills in convergence regions, depressions in divergent regions, of about 1 meter amplitude. These irregularities in sea level induce horizontal pressure gradients, initiate the wind driven geostrophic currents.

• The ocean currents are for the most part geostrophic, meaning that the horizontal pressure gradients are balanced by the Coriolis Force.

• Ocean overturning, product of buoyancy exchange with the atmosphere, form specific water masses which spread at depth throughout the ocean. The thermohaline circulation engages the full volume of the ocean into the climate system, by allowing all of the ocean water to 'meet' and interact directly the atmosphere, that is to exchange heat and freshwater with the atmosphere.

Link to detailed lecture notes