Double diffusion in the Mediterranean Sea: Observation and parameterization of salt finger convection

Abstract

For the Mediterranean Sea a large set of historical conductivity‐temperature‐depth casts has been investigated for the occurrence of double‐diffusive vertical mixing due to salt finger convection. All casts were screened in terms of the density ratio Rρ, providing probability distributions of Rρ for the upper 1000‐dbar range of eight geographical areas. Vertical profiles of the salt finger‐driven diffusivities kS and kT of salinity and temperature have been evaluated from the statistics of Rρ and a presumed mixing law, and analytic expressions are provided, which can be used to parameterize the effects of salt finger mixing in ocean circulation models of the Mediterranean. In most areas the diffusivity profiles exhibit an absolute maximum below the core of the Levantine Intermediate Water. Toward the surface the diffusivities decrease rapidly, while the downward decay is less pronounced. A different behavior is found in the Tyrrhenian and Adriatic Seas, where the diffusivities remain high also at greater depth.