Stable deep-ocean circulations

Vertical circulations (upwelling or downwelling) in the ocean can be either unstable (i.e. the result of temperature and/or density differences) or stable. Unstable flows are known as thermohaline circulations (Section 11.5) and they are equivalent to atmospheric convection, which drives the Hadley cell, for instance (Section 12.6). The Hadley cell is thermally direct, because ascent and latent energy release occurs in the ascending branch of the circulation cell.

The best-known stable ocean circulation is the shallow upwelling forced by wind along a coastline or along the equator. Such a circulation is thermally indirect, because in the ascending branch the water is colder. The Ferrel cell in the atmospheric general circulation is indirect also. Another indirect ocean circulation cell is the Deacon cell in the Southern Ocean (1). This circulation results from correlated zonal differences of density and flow, due to horizontal eddies.

(1) Karoly, D.J., P.C. McIntosh, P. Berrisford, T.J. McDougal & A.C. Hirst 1997. Similarities of the Deacon cell in the Southern Ocean and Ferrel cells in the atmosphere. Quart. J. Roy. Meteor. Soc. 123, 519-26.