The ocean contains two major interhemispheric basins, containing the Pacific and the Atlantic oceans, as well as the smaller, primarily Southern Hemisphere, basin containing the Indian ocean, all connected via the Antarctic Circumpolar Current (ACC). Wind-driven gyres exist in all the major basins, and the Atlantic has a robust overturning circulation. How does it all fit together? There is no universally accepted picture, and certainly no quantitative theory. Rather, observations and numerical simulations have been used to put together a qualitative picture, as illustrated in figure 2.6. The circulation illustrated should be regarded as a highly schematic representation, perhaps even as a metaphor, of the real ocean circulation, in part because of the presence of ocean eddies discussed below. Also, only the more global features are illustrated; thus, we see a cross-hemispheric circulation in the Atlantic, but not its vertical structure, which we'll talk about more in chapter 4. However, the figure does illustrate the main features of the global circulation: a meridional overturning circulation, the sinking of cold dense water in the North Atlantic and off Antarctica, and the western boundary currents.
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