Scope of activities

In-situ microstructure observations and indirect estimates in the Arctic Ocean have shown mixing levels in the central Arctic Basins to be an order of magnitude below those in other oceans, with mixing 'hotspots' and enhanced vertical heat flux in shallow seas and on the continental shelves. Energy for mechanical mixing originates from wind and tidal forcing, which generate internal waves and the internal tide. As sea-ice declines, we have seen surprisingly little change in the average mixing levels associated with wind-generated internal waves, likely due to suppression by strong near-surface stratification, although episodic mixing events associated with high-energy waves may be increasing in frequency. Tidal mixing in the central Arctic Ocean is limited due to the critical latitude for M2 preventing a freely propagating internal tide. However, over rough topography, there is strong evidence of enhanced tidal mixing. Internal wave packets with periods shorter than the tidal period have been observed using SAR satellite data in the White, Barents, and Kara Seas. 
 
Due to the low levels of turbulent mixing in the central Arctic Basins, double-diffusive processes (driven by the differing molecular diffusivities of heat and salt) play an important role in setting water properties. In the Canadian Basin, an extensive laterally and temporally coherent double-diffusive staircase sits above the Atlantic Water temperature maximum. Staircase structures have also been observed more sporadically in the Eurasian Basin. Generally good agreement has been found with laboratory derived double-diffusive flux laws, allowing us to estimate vertical heat flux through the staircases. Using Ice-Tethered Profiler data, the spatial extent of double-diffusive staircases has been determined. Staircases are not observed near the Basin margins or in the flanks of eddies, where shear and turbulent mixing levels are likely high enough to erode the individual layers. Combining results for wind- and tidal-driven mixing with our knowledge of double-diffusive processes provides a more complete picture of mixing and vertical heat flux in the Arctic Ocean, although in-situ measurements remain extremely sparse and many of these processes are active areas of research. 
 

The goal of the Mixing team is to establish an Arctic Ocean mixing baseline product using existing in-situ observations and inferred mixing levels. Our plan is to provide a spatial map of current observations and a gridded product representing the best available estimates of mixing (turbulent diffusivity and dissipation) and/or vertical heat flux, with uncertainties and variability, to be continuously updated as new measurements become available. The mixing baseline product our group is working to establish is not intended to provide a complete picture of Arctic Ocean mixing, but rather a snapshot of our best knowledge to date.


Team leaders

Hayley Dosser
Yale University

An T Nguyen
UT Austin


Accomplishments

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Questions?

Contact Andrey Proshutinsky, Senior Scientist, Woods Hole Oceanographic Institution at aproshutinsky@whoi.edu.