Internal wave turbulent mixing variability in the Antarctic Circumpolar Current estimated from fine-scale observations in Drake Passage

Manuel Othon Gutierrez-Villanueva, University of California San Diego, Scripps Institution of Oceanography, La Jolla, CA, United States, Teresa K Chereskin, SIO/UCSD, La Jolla, CA, United States and Janet Sprintall, Univ California San Diego, La Jolla, CA, United States
Abstract:
Turbulent mixing plays a dominant role in the Southern Ocean meridional overturning circulation, which impacts the distribution of heat, carbon, nutrients, and other tracers. Mixing is enhanced at locations where the Antarctic Circumpolar Current (ACC) encounters abrupt topography, which favors the generation and breaking of internal waves (IWs). Drake Passage is a hot spot of turbulent mixing. We present preliminary results of turbulent mixing due to breaking IWs in Drake Passage from a series of full-depth CTD/LADCP casts undertaken in November 2007-2011 as part of the cDrake experiment. We applied the vertical kinetic energy (VKE) spectrum parameterization (Thurnherr et al. 2015) to the full-depth casts to estimate dissipation rates of turbulent kinetic energy \(\epsilon_{VKE}\). In general, \(\epsilon_{VKE}\) \(>1 \times 10^{-9}\) W kg\(^{-1}\) near the bottom is concentrated where the mean position of the Polar Front crosses the Shackleton Fracture Zone. High dissipation values are also found in the Polar Front Zone near the surface, suggesting that wind-generated near-inertial IWs penetrate below the mixed layer and eventually break in the thermocline. Dissipation rates \(\epsilon\) are estimated employing the widely-used shear/strain fine-scale parameterization and compared with \(\epsilon_{VKE}\) as a function of depth, topographic roughness, position of the ACC fronts and kinetic energy. This allows us to elucidate possible discrepancies between the VKE spectrum and the shear/strain fine-scale parameterizations, as well as assist in identifying the possible mechanisms influencing the spatial variability of turbulent mixing in Drake Passage.