Southern Ocean – Rates and Mechanisms of Turbulent Dissipation and Mixing – the Diapycnal and Isopycnal Mixing Experiment (DIMES)

Australia: The Land Where Time Began

Southern Ocean – Rates and Mechanisms of Turbulent Dissipation and Mixing – the Diapycnal and Isopycnal Mixing Experiment (DIMES)

In this study the authors¹ used microstructure and finestructure data that had been collected as part of the Diapycnal and Isopycnal Mixing Experiment in the Southern Ocean (DIMES) to analyse the spatial distribution of turbulent dissipation rates and internal wavefront characteristics across 2 contrasting regimes of the Antarctic Circumpolar Current (ACC). The results indicated that mid-depth turbulent dissipation rates increase O(1 x 10^-10 W kg^-1 in the Southeast Pacific to O(1 x 1^—9 W kg^-1) in the Scotia Sea, which typically reach 3 x 10^-9 W kg^-1 within a kilometre of the seabed. It has been found that enhanced levels of turbulent mixing are associated with near-bottom flows that are strong, rough topography, and regions where the internal wavefield has enhanced energy, a less-inertial frequency content and a dominance of energy that is propagating upwards. It is strongly suggested by these results that a major role in determining the spatial distribution of turbulent dissipation in the ACC is played by the internal waves that are bottom-generated. Wave radiation theory is used to calculate the energy flux that is associated with the generation process of bottom internal wave generation, which has been found to vary between 0.8 mW m^-2 in the Southeast Pacific and 14 mW m^-2 in the Scotia Sea. Of this energy 10%-30% is typically found to dissipate within 1 km of the seabed. Comparison between turbulent dissipation rates that have been inferred from finestructure parameterisations and estimates derived from microstructure it is suggested there is a significant departure from wave-wave interaction physics in the near-field of wave generation sites.