Enhanced Diapycnal Mixing by Salt Fingers in the Thermocline of the Tropical Atlantic

Abstract

Diapycnal mixing plays a significant role in the ocean's circulation and uptake of heat and carbon dioxide, but has not been quantified in salt finger–driven thermohaline staircases. We recently performed a tracer release experiment in the western tropical Atlantic staircase at ∼400 m depth. The observed dispersion implies an effective diapycnal diffusivity for tracer and salt of 0.8 to 0.9 × 10 –4 m 2 /s. Temperature microstructure data interpreted in terms of a vertical production-dissipation balance yields a smaller effective diffusivity for heat of 0.45 (± 0.2) × 10 –4 m 2 /s, consistent with salt fingers and well above the mixing ascribable to mechanical turbulence.