Turbulent Dissipation Rate and Mixing Variations in the Polar Front of the Southern Ocean

Lauren Newell Ferris1, Donglai Gong1, Takashi Ijichi2, Sophia Merrifield3, Justin Shapiro4 and Louis St Laurent4, (1)Virginia Institute of Marine Science, Gloucester Point, VA, United States, (2)Woods Hole Oceanographic Institution, Woods Hole, MA, United States, (3)University of California San Diego, Scripps Institution of Oceanography, La Jolla, CA, United States, (4)Applied Physics Laboratory University of Washington, Seattle, WA, United States
The Southern Ocean is the only sector of the global ocean that connects all three major ocean basins through the Meridional Overturning Circulation (MOC). Mixing processes are believed to play a prominent role in moderating and transforming water masses in this region, with implications extending to the global thermohaline circulation. Despite its importance, mixing processes in the Southern Ocean have been under-sampled, largely due to its remote location and severe conditions. With the maturing of autonomous platforms, there is now an opportunity to collect high-resolution spatial and temporal measurements in the full range of forcing conditions.

A small, proof-of-concept study called Autonomous Sampling of Southern Ocean Mixing (AUSSOM) was conducted in the Drake Passage region between the end of Austral Winter and the beginning of Austral Spring in 2017-1018. Records of meteorological forcing and upper ocean turbulence were collected spanning several months. A glider with microstructure sensing was used to collect a 6-week turbulence record spanning 800 km from the Shackleton Fracture Zone to the Falkland Plateau, and is perhaps the longest continuous glider-turbulence record, and the largest turbulence dataset, ever collected. Measurements indicate variations in turbulent dissipation levels are associated with the seasonal change in forcing, the spatial variation of water masses across the front, and changes in the physical mechanisms of mixing. Our analysis indicates no single parameterization of upper-ocean turbulent mixing can account for the range of dissipative processes occurring in the Polar Front.