Contributions of Intermediate Waters, Deep Waters and Shallow Wind-driven Gyres to the Overturning Circulation and Heat Transport

L D Talley (Scripps Institution of Oceanography, UCSD, La Jolla, CA 92093-0230; ph. 619-534-6610; fax 619-534-9820; Internet: ltalley@ucsd.edu)

The ocean's meridional heat transport across subtropical latitudes can be broken into contributions arising from: (1) the shallow overturning in the subtropical gyres to the base of thermocline, (2) overturning into the intermediate depth layer (500 to 2000 meters) in the North Atlantic, North Pacific and area around Drake Passage, and (3) overturning into the deep layer in the North Atlantic (Nordic Seas overflows) and around Antarctica. Based on the temperature difference between the inflowing warm and outflowing cold waters in the intermediate and deep overturning cells, and the formation rates for each of these water masses, the net heat transport associated with all intermediate water formation is equivalent in size to that for all deep water formation. Intermediate waters are associated with about 0.5 PW of northward transport in the northern hemisphere and about 0.5 PW of southward transport in the southern hemisphere. Deep waters are associated with about 0.4 PW of northward transport in the North Atlantic and about the same amount southward in the Southern Ocean (probably divided amongst the three ocean basins there).

Using various direct estimates of heat transport across subtropical latitudes, and these estimates of the intermediate and deep overturning components, the residual is an estimate of the heat transported by the shallow gyre overturning. This is about 0.5 PW for the North Pacific and North Atlantic subtropical gyres and about 0.2 PW for each of the three southern hemisphere subtropical gyres.