Double-diffusive convection (DDC) is a phenomenon that can occur in fluids in which buoyancy is affected by two constituents that diffuse at different rates. Many readers of Oceanography magazine will be at least somewhat familiar with the topic of oceanic DDC, probably in the form of “salt fingers” (SF), a variety that can arise when surface waters are warmer and more saline than waters below, as is the case in broad reaches of the ocean, especially in the subtropics. A second variety, called the “diffusive layering” (DL) mode, requires that the warmer water lie below the cooler water, a common situation at high latitudes. In addition, both SF and DL can exist at the boundaries between interleaving water masses, a situation that can occur anywhere that lateral gradients of temperature and salinity occur. Thus, many areas of the ocean appear to be susceptible to DDC, and observations suggest that DDC is commonly present in such regions, especially if background turbulence is relatively low. This would be a mere curiosity but for the fact that the divergence of DDC-mediated fluxes may be large enough to have significant effects on the background system.

Kelley, D. 2015. Review of Double Diffusive Convection, by T. Radko. Oceanography 28(1):179–180, https://doi.org/10.5670/oceanog.2015.25.

Hogg, N.G., and R.X. Huang, eds. 1995. Collected Works of Henry M. Stommel. American Meteorological Society, Boston, MA, USA, 683 pp.
1. Stern, M.E. 1975. Ocean Circulation Physics. Academic Press, San Diego, CA, 246 pp.
2. Turner, J.S. 1973. Buoyancy Effects in Fluids. Cambridge University Press, Cambridge, UK, https://doi.org/10.1017/CBO9780511608827.

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