Microstructure turbulence and diffusivity parameterization in the tropical and subtropical Atlantic, Pacific and Indian Oceans during the Malaspina 2010 expedition

Measurements of microstructure turbulence were carried out, in the upper 300 m, in the tropical and subtropical Atlantic and Pacific oceans during the Malaspina 2010 expedition, by using a microstructure turbulence (MSS) profiler. Diapycnal diffusivity (Kρ) was estimated from dissipation rates of turbulent kinetic energy (ε) measured by the MSS profiler, and also from hydrographic and meteorological data by using the K-profile parameterization (KPP). In the mixing layer, averaged Kρ (169×10−4m2s−1) and ε (16.8×10−8Wkg−1) were three and one orders of magnitude higher, respectively, compared to the ocean interior (0.59×10−4m2s−1 and 1.0×10−8Wkg−1). In general, the KPP showed a good agreement with diffusivity estimates derived from microstructure observations, both in the mixing layer and in the ocean interior. The KPP also reproduced the main regional patterns observed in the ocean interior. The analysis of turbulence generation mechanisms below the mixing layer showed that shear-induced mixing was more important in those regions influenced by the equatorial undercurrent, where averaged diffusivity was 2.27-3.62×10−4m2s−1. Favorable conditions for salt fingers formation were more frequently observed in the Atlantic, where, as a consequence of this process, diffusivity could increase up to 20%. This result could have important implications for the transport of heat and dissolved substances in these regions.