The salts dissolved in the world’s oceans have profound effects, from the large scale, where evaporation-precipitation patterns have the opposite buoyancy effect to thermal forcing, to the microscale, where molecular diffusion of heat is 70 times faster than that of salt. It has often been assumed that this difference can only matter at the smallest scales, so that heat and salt are mixed in exactly the same way by turbulence. However, the different molecular diffusivities are the basis for a variety of phenomena known as double-diffusion, and these can lead to important differences between heat and salt fluxes, with consequences for much larger scales. In particular, density fluxes the “wrong way”: Kp < 0.

Ruddick, B. 1997. Differential fluxes of heat and salt: Implications for circulation and ecosystem modeling. Oceanography 10(3):122–127, https://doi.org/10.5670/oceanog.1997.04.

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