Turbulence and Mixing Statistics and Dynamics in the Southeastern Beaufort Sea

Stephanie Waterman1, Jeff R Carpenter2, Benjamin Scheifele1 and Lucas Merckelbach2, (1)University of British Columbia, Earth, Ocean and Atmospheric Sciences, Vancouver, BC, Canada, (2)Helmholtz-Zentrum Geesthacht, Institute of Coastal Research, Geesthacht, Germany
Abstract:
Characterizing ocean mixing is made challenging by the patchy and episodic nature of ocean turbulence and a scarcity of direct measurements, especially in the Arctic Ocean. Here we present over 20,000 observations of the turbulent dissipation rate, ε, alongside corresponding mixing rate estimates, derived from near-continuous shear and temperature microstructure measurements collected from a glider over 11 days in the southeastern Beaufort Sea. Our observations reveal a high degree of variability in turbulent rates, with a relatively small number of strongly turbulent events that exist within an otherwise weakly- or non-turbulent background field. In 21% of the data, ε is below the detectable level of 10-12 Wkg-1 for temperature microstructure; in the remainder of the data, ε varies over five orders of magnitude. Generally weak turbulence combines with strong stratification to imply that mixing dynamics are frequently dominated by buoyancy effects: buoyancy Reynolds number estimates suggest that characterizing the mixing rate as turbulent is appropriate for only ~7% of the data. These turbulent diffusivity estimates however make a disproportionate contribution to mixing overall: they increase the (arithmetic) mean diapycnal mixing rate by three orders of magnitude over the molecular diffusivity of salt, and they may be as large as O(10-5) m2s-1 locally. Our observations reveal variability on all resolved scales, however below 100 m depth turbulence appears modulated most strongly by tidal forcing. Overall, our study serves to demonstrate the importance of having numerous observations to accurately characterize the nature of turbulence and mixing in the region.