RAPID: Fine- and Microstructure Observations in Conjunction with a GEOTRACES Section along 40 degrees S in the Atlantic

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This project funds the acquisition and analysis of fine- and microstructure data in conjunction with the UK funded GEOTRACES A10 section along 40S in the South Atlantic. A combination of vertical profiling and glider platforms will be used. The resulting data will be used to estimate regional diapycnal mixing and isopycnal stirring rates. It is anticipated that there will be significant regional variability in response to variations in tides, eddies, topographic morphology and mean geostrophic currents. Estimates of diapycnal mixing will be aided by radiation balance equations and estimates of isopycnal stirring will be informed by comparison to published scalings.Intellectual MeritThere is a great deal of uncertainty regarding the details of how oceanic budgets of heat, mass, momentum, energy, potential vorticity or passive tracers are balanced, particularly at the submesoscale and especially with regards to the roles of nonlinearity versus wave radiation and the role of internal waves versus geostrophic motions. The proposed work will address this uncertainty by documenting fine- and microstructure fields along the GEOTRACES A10 section and will quantitatively investigate the relationship to, and dependence upon, variability on larger spatial and temporal scales. Measured diapycnal mixing rates will be compared to radiation balance equation based estimates of turbulent production associated with the regional internal wave climate. Isopycnal stirring rates will be compared to published scalings based upon both weakly nonlinear and turbulent analyses.Broader ImpactsResults of the proposed research will contribute to the understanding and prediction of global climate change and the carbon cycle. Efforts will be in direct support of the GEOTRACES program as the biogeochemical budgets that are the focus of that study depend upon diapycnal mixing and isopycnal stirring rates. The project will provide direct estimates of these and will assist with the interpretation. It will also assist with the development and implementation of turbulent mixing and isopycnal stirring parameterizations for general circulation models used to predict the ocean climate response. Specifically, the characterization of diapycnal mixing and isopycnal stirring derived from the microstructure observations will be incorporated by collaborators at Oxford University in their general circulation model simulations of tracer transport.