Sack Lunch Seminar (SLS)

The Southern Ocean is one of the most energetic regions of the world ocean due to intense winds and storm forcing, strong currents in the form of the Antarctic Circumpolar Current (ACC) interacting with steep topography, and enhanced mesoscale activity. Consequently, the Southern Ocean is believed to be a hotspot for enhanced oceanic mixing. Previous work based on finestructure parameterizations has suggested that strong mixing is also ubiquitous below the mixed layer.

Results from a US/UK field program, however, showed that enhanced internal wave finestructure and turbulence levels are not widespread, but limited to frontal zones where strong bottom currents collide with steep largeamplitude
topography. Direct measurements of turbulence showed that previous estimates of mixing rates in the upper 1km are biased high by up to two orders of magnitude. Despite the prevalence of energetic wind events, turbulence driven by downward propagating nearinertial wave shear is weak below the mixed layer. Inefficient wind forcing at nearinertial frequencies and seasonally varying upper ocean stratification likely contribute to the observed weak mixing rates. Double diffusive processes and turbulence both contribute to buoyancy flux, elevating the effective mixing efficiency above the canonical value of 0.2 in the upper 1km. Ultimately, this work informs largescale modeling efforts through parameterizations of mixing processes in the highly undersampled Southern Ocean.