Experimental Investigation of Differential Diffusion in Low Buoyancy Reynolds Number Oceanic Regimes

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0136116 MoumA comprehensive set of measurements of scalar gradient spectra from the towed microstructure instrument MARLIN, will be collected in regions of the abyssal ocean where a large range of both turbulence and stratification regimes is expected. The purpose of the study is to investigate the dependence of the ratio of salt diffusivity to heat diffusivity on buoyancy Reynolds number. To accomplish these objectives, two new sensors using well understood principles will be built and deployed on MARLIN. The first is a combined thermocouple/microscale conductivity probe. The second is an anisotropy probe using multiple thermocouple pairs. A complementary purpose for analyzing horizontal scalar fluctuations is to improve the interpretation of microstructure measurements. Many assumptions are commonly made to infer mixing and fluxes from one-dimensional, partially resolved scalar spectra, or to relate scalar spectra to turbulent kinetic energy dissipation rates (such as the assumption of isotropy, a universal spectral form for scalar gradients, and associated .constants). Used in conjunction with the present catalog of existing vertical spectra and spectra from turbulence simulations, these measurements will permit improvements in the ability of the microstructure community to reliably quantify the effects of small scale ocean processes.