Abstract

Small-scale turbulent motions in the Southern Ocean play a vital role in setting the abyssal stratification and in determining the response of climate models to anthropogenic forcing. However, few direct observations of turbulent mixing in the Antarctic Circumpolar Current (ACC) exist. Further more, observations of the sources and mechanisms underlying the intensity and distribution of turbulent kinetic energy dissipation in the ACC are scarce. Consequently in 2009, the Diapycnal and Isopycnal Mixing Experiment in the Southern Ocean (DIMES), was initiated. DIMES is a mutli-component US/UK project focused on understanding patterns and processes of mixing in two contrasting regimes (the SE Pacific and the SW Atlantic) of the ACC .

In this presentation, we report on turbulent mixing observations collected using free-falling microstructure instruments as part of the DIMES experiment. Turbulent dissipation rates, which vary between _{10-10 W kg-1 and} 10-9 W kg-1, are found to be strongly related to the strength of bottom current speeds and the local topographic roughness. This observation, alongside detailed analysis of internal wave field properties, supports the hypothesis that abyssal turbulent dissipation is attributed to the breaking of internal waves generated by ACC - topography interactions. However, local turbulent dissipation accounts for only a small proportion of the energy flux predicted by linear theory, opening questions as to the fate of much of the bottom-generated internal wave energy. This study represents the largest comparison of turbulent dissipation measurements and internal wave characteristics in the Southern Ocean, to date.