Effective diffusivities within oceanic thermohaline staircases

Abstract

A scale for the thickness of layers in regular “diffusive”‐type thermohaline staircases, derived from dimensional analysis, is found to collapse oceanic data. Combining this scale with laboratory‐derived double‐diffusive flux laws, we formulate effective diffusivities for salt, heat, and density. The diffusivities depend on the Turner number Rρ, but are independent of the Brunt‐Vaisala frequency. For Rρ near 1 the diffusivities for salt and heat are approximately equal (≃10−4 m2 s−1). They decrease roughly as Rρ−4 and Rρ−2, respectively, over the oceanic range 1≤Rρ≤10.