Observations of small eddies in the Beaufort Sea

Abstract

The horizontal and vertical variations of velocity, temperature, density, and turbulent kinetic energy dissipation in the central Beaufort Sea were measured with helicopter‐borne expendable current profilers and conductivity‐temperature‐depth units. Almost all velocity differences larger than 0.05 m s−1 could be consistently interpreted as being due to nearly circular eddies with a diameter of 10–20km, a thickness of 50–500 m, peak velocities of 0.07–0.3 m s−1, and little expression at the top of the ocean. Four such eddies were found. Two anticyclones were found and accurately sampled. Two cyclones were found but were only poorly sampled; both were beneath and close to one of the anticyclones. Relative vorticity could be computed for two anticyclones and one cyclone. Within experimental error, the two anticyclones, and all historical Beaufort Sea anticyclones, had a relative vorticity of −ƒ and thus zero potential vorticity at the center. The cyclone had a central relative vorticity of about 0.5ƒ and thus a different value of potential vorticity than the surrounding fluid. One anticyclonic eddy (B) was sampled seven times over a period of 23 days. Its measured velocity and density fields were in approximate gradient wind balance. Its central core contained values of temperature, nitrate, and silicate that were different from those outside the core at the same density. It moved eastward at about 0.02 m s−1 through the surrounding fluid. Measurements of turbulent kinetic energy dissipation were almost always less than the noise level of the instrument (about 10−9 W kg−1), corresponding to a mean dissipation much less than this and a minimum decay time due to turbulence much longer than 0.3 year. The nondimensional strength (Rossby number) and shape (Burger number) of anticylcone B are very similar to those of other Beaufort Sea anticyclones and similar to those of small mid‐latitude eddies. Each of the eddies observed here was centered on a temperature maximum associated with one of the warm water masses that advect into the Arctic Ocean. The two anticyclones were centered on temperature maxima originating in the Pacific Ocean, whereas the two cyclones were centered on temperature maxima from the Atlantic Ocean. This is consistent with the hypothesis that the eddies are formed as these water masses enter the Arctic Ocean.

Scales and dynamics of Submesoscale Coherent Vortices formed by deep convection in the northwestern Mediterranean Sea

“…Similarly, Carpenter and Timmermans [2012] computed the aspect ratio (H/ R) of a density perturbation introduced into uniformly stratified waters and found: Bu5½ln ð10Þ=p 2 ' 1. These numerical and theoretical considerations are consistent with observational studies made at various places of the world's ocean describing SCVs [D'Asaro, 1988a;Timmermans et al, 2008;Bower et al, 2013;Pelland et al, 2013;Bosse et al, 2015]. The large aspect ratio close of deep anticyclonic SCVs can thus be explained by those constraints on the Burger number and the low stratification of the deep basin.…”

“…Their rotation sets transport barriers that drastically reduce the lateral exchanges between their core and the surrounding waters [Rhines and Young, 1983;Provenzale, 1999]. They are, therefore, extremely efficient in transporting physical and biogeochemical tracers characteristics of their generation site over long distances [D'Asaro, 1988a;Testor and Gascard, 2003;Bower et al, 2013;L'Hegaret et al, 2016]. However, due to their small horizontal extension and their little surface signature, a fine-scale description of the SCVs remnant of wintertime convective events, especially along the vertical axis, is still lacking.…”

Structure and dynamics of mesoscale eddies over the Laptev Sea continental slope in the Arctic Ocean

“…Arctic Ocean eddies can travel several thousand kilometers from their origins over a period of several years, preserving the properties of water trapped inside their cores (e.g., Newton et al, 1974;Manley and Hunkins, 1985;D'Asaro, 1988). 15 Dmitrenko et al (2008) analyzed temperature and salinity distributions in the core of a warm AW eddy observed at a mooring over the Laptev Sea slope, and concluded that it was formed in the vicinity of St. Anna Trough-i.e., ~1100 km west of the mooring site.…”

Confluence and redistribution of Atlantic water in the Nansen, Amundsen and Makarov basins

“…This supports again the hypothesis that the deep inversions are formed from cross-frontal interactions between the Barents Sea branch water and the water column beneath the Fram Strait inflow core. Documentation of eddies in the Central Arctic are rare and available so far only for the Canadian Basin (Newton et al, 1974;D'Asaro, 1988;Muench et al, 2000). High resolution numerical simulations show that eddies might spin off also from the Atlantic water boundary current north of the Barents Sea (Wieslaw Maslowski, pers.…”