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

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Science  29 Apr 2005:
Vol. 308, Issue 5722, pp. 685-688
DOI: 10.1126/science.1108678

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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 m2/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 m2/s, consistent with salt fingers and well above the mixing ascribable to mechanical turbulence.

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