Is There a Meridional Overturning Cell in the Pacific and Indian Oceans?

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Abstract
The diagnostic quasi-island model of Nof addressing the exchange between the South Atlantic and the Southern Ocean is extended to the exchange between the Pacific–Indian Ocean system and the Southern Ocean. The new calculations suggest that, in a similar fashion to the Atlantic Ocean, the Indian and Pacific Oceans have a meridional overturning cell with a transport of 18 ± 5 Sv (1 Sv ≡ 106 m3 s−1). In contrast to the Atlantic in which there is deep water formation resulting in a cell that extends all the way from the surface to the bottom, however, the Indian and Pacific circulation cell is shallow in the sense that it does not occupy the entire water column. As in the Atlantic case, the cell is driven by both winds and thermohaline processes, but the calculation does not require solving the complete wind–thermohaline problem. The computational method takes Africa, Asia, and Europe to compose a “pseudo island”; that is, the combined continent is entirely surrounded by water but has no net circulation around it. The continuation of sea level around the continent allows one to compute analytically the zonal upper-layer transport that is first forced meridionally from the Southern Ocean to the Pacific and Indian Oceans and then forced down to lower levels. Although there are no direct observations to support or refute the idea of a shallow cell in these oceans, the concept is consistent with earlier inverse calculations, with the observed distribution of silicate, and with earlier general circulation experiments. The main weaknesses of the calculation are the level-of-no-motion assumption (which is particularly questionable in high latitudes) and the neglect of form drag on the Bering Strait sill.