Eddies in the Canada Basin, Arctic Ocean, Observed from Ice-Tethered Profilers

Abstract

Five ice-tethered profilers (ITPs), deployed between 2004 and 2006, have provided detailed potential temperature and salinity S profiles from 21 anticyclonic eddy encounters in the central Canada Basin of the Arctic Ocean. The 12-35-m-thick eddies have center depths between 42 and 69 m in the Arctic halocline, and are shallower and less dense than the majority of eddies observed previously in the central Canada Basin. They are characterized by anomalously cold and low stratification, and have horizontal scales on the order of, or less than, the Rossby radius of deformation (about 10 km). Maximum azimuthal speeds estimated from dynamic heights (assuming cyclogeostrophic balance) are between 9 and 26 cm s Ϫ1, an order of magnitude larger than typical ambient flow speeds in the central basin. Eddy -S and potential vorticity properties, as well as horizontal and vertical scales, are consistent with their formation by instability of a surface front at about 80°N that appears in historical CTD and expendable CTD (XCTD) measurements. This would suggest eddy lifetimes longer than 6 months. While the baroclinic instability of boundary currents cannot be ruled out as a generation mechanism, it is less likely since deeper eddies that would originate from the deeper-reaching boundary flows are not observed in the survey region.

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

“…Relatively high rotational speed (up to 13 cm/s) at the uppermost 77-m depth level at the M1g mooring site suggests that these eddies may extend well above this level, through the CHL to the base of the SML. Eddies generally occupy a similar depth range in the Canadian Basin (Timmermans et al, 2008;Spall et al, 2008;Kawaguchi et al, 2012). Our analyses of data from the Laptev Sea slope show that eddies can frequently be found significantly deeper, including deeper part of the AW layer.…”

“…6). The lifting/lowering of the isopycnal surfaces and the density anomaly at a specific depth can be used as a "first-guess" criterion to identify eddies crossing the mooring; this is similar to how eddies are identified in ITP records (e.g., Timmermans et al, 2008;Carpenter and Timmermans, 2012;Zhao et al, 2014). However, joint wavelet 10 analysis of density and velocity series at M1f suggests that ~20 % of isolated density anomalies were not accompanied by corresponding increases in rotational velocities.…”

“…Higher values of the rotational speed were reported for eddies found in the Canadian Basin (Krishfield et al, 2002;Pickart et al, 2005;Timmermans et al, 2008;Kawaguchi et al, 2012). For example, Kawaguchi et al (2012) reported V rot as large as 57 cm/s for a large-scale (~60-70 km in diameter) eddy observed at the boundary of the Chukchi and Beaufort seas, with an associated value of Ro ≈ 0.1.…”

The Rossby radius in the Arctic Ocean

“…The eddy described by Kawaguchi et al (2012) was (apparently) an unusually large one, doubling these values. An empirical quantification of this description is given by Timmermans et al (2008). Hoskins et al (1985) suggest an approach (the pursuit of which is beyond the scope of the present study) whereby an explanation of these observations may be developed.…”

Two Configurations of the Western Arctic Shelfbreak Current in Summer

“…Plueddemann and R. Krishfield 2007, personal communication;Timmermans et al 2008). It is now known that such features are usually associated with subsurface eddies of Pacific Water.…”