A Salt Finger Tracer Release Experiment

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0081502 SchmittAn extensive field experiment will be conducted in the area of the extensive thermohaline staircase in the western tropical Atlantic to investigate the role of double diffusion in subsurface water mass transformation. A purposeful tracer (Sulfur hexafluoride SF6) will be released into a layer near the middle of the staircase to obtain a robust 9-month measurement of vertical mixing and lateral dispersion. Surveys of fine- and microstructure with a profiling instrument will determine the dissipation rates of turbulent kinetic energy and thermal variance. Formulae for the relationship of these dissipation rates to vertical diffusivity depend dramatically on whether the source of energy for mixing is salt fingering or turbulence. This experiment will determine the relative contribution of these two sources to the vertical mixing of tracer, salt and heat. A moored CTD/Current profiler will be used to relate fine- and microstructure surveys to the long term tracer dispersion. The hope is that the work will lead to improved parameterizations of diapycnal mixing for general circulation and climate prediction models.