Search

The Western Arctic Ocean is a host to major ocean circulation systems, many of which generate eddies that can transport water masses and corresponding tracers over long distances from their formation sites. However, comprehensive observations of critical eddy characteristics are currently not available and are limited to spatially and temporally sparse in situ observations. Here we use high‐resolution spaceborne synthetic aperture radar measurements to detect eddies from their surface imprints in ice‐free sea surface roughness, and in sea ice patterns throughout marginal ice zones. We provide the first estimate of eddy characteristics extending over the seasonally ice‐free and marginal ice zone regions of the Western Arctic Ocean, including their locations, diameters, and monthly distribution. Using available synthetic aperture radar data, we identified over 4,000 open ocean eddies, as well as over 3,500 eddies in marginal ice zones from June to October in 2007, 2011, and 2016. Eddies range in size between 0.5 and 100 km and are frequently found over the shelf and near continental slopes but also present in the deep Canada Basin and over the Chukchi Plateau. We find that cyclonic eddies are twice more frequent compared to anticyclonic eddies at the surface, distinct from the dominating anticyclonic eddies observed at depth by in situ moorings and ice‐tethered profilers. Our study supports the notion that eddies are ubiquitous in the Western Arctic Ocean even in the presence of sea ice and emphasizes the need for improved ocean observations and modeling at eddy scales. Plain Language Summary: Ocean eddies play an important role in the transport of heat, salt, and pollutants over long distances from their formation sites. However, their observations in the Arctic Ocean are complex due to severe weather and sea ice cover. Here we present results of high‐resolution satellite observations over the ice‐free ocean and in the marginal ice zones. Detailed eddy characteristics are for the first time presented for the Western Arctic Ocean. These results provide observational evidence that eddies are ubiquitous in this Arctic region even in the presence of sea ice and emphasize the need for improved ocean observations and modeling at eddy scales. Key Points: First account of eddies in the Western Arctic Ocean is presented based on satellite observations over open ocean and marginal ice zonesEddies range in size between 0.5 and 100 km and are ubiquitous over deep and shelf regions of the Western Arctic OceanCyclonic eddies are twice more frequent compared to anticyclones [ABSTRACT FROM AUTHOR]

The halocline of the Beaufort Gyre varies significantly on interannual to decadal time scales, affecting the freshwater content (FWC) of the Arctic Ocean. This study explores the role of eddies in the Ekman-driven gyre variability. Following the transformed Eulerian-mean paradigm, the authors develop a theory that links the FWC variability to the stability of the large-scale gyre, defined as the inverse of its equilibration time. The theory, verified with eddy-resolving numerical simulations, demonstrates that the gyre stability is explicitly controlled by the mesoscale eddy diffusivity. An accurate representation of the halocline dynamics requires the eddy diffusivity of 300 ± 200 m2 s−1, which is lower than what is used in most low-resolution climate models. In particular, on interannual and longer time scales the eddy fluxes and the Ekman pumping provide equally important contributions to the FWC variability. However, only large-scale Ekman pumping patterns can significantly alter the FWC, with spatially localized perturbations being an order of magnitude less efficient. Lastly, the authors introduce a novel FWC tendency diagnostic-the Gyre Index-that can be conveniently calculated using observations located only along the gyre boundaries. Its strong predictive capabilities, assessed in the eddy-resolving model forced by stochastic winds, suggest that the Gyre Index would be of use in interpreting FWC evolution in observations as well as in numerical models. [ABSTRACT FROM AUTHOR]

This study is motivated by Arctic Ocean observations of sub-mixed layer eddies found at large distances from their assumed formation region of a surface ocean front. Eddy formation is explored through high-resolution numerical simulations of surface fronts, separating two mixed layers, with a range of configurations similar to those observed in the Arctic Ocean. This study finds that frontal instabilities lead to the development of self-propagating dipoles, which have the potential to propagate far from the front if interactions with other eddies are avoided. However, most dipoles are unbalanced, consisting of a dominating surface cyclone and a weaker anticyclone below, and thus propagate on curved trajectories with eventual recirculation back to the front. Their maximum separation distance from the front depends on the ratio of self-advecting velocities ϵ; balanced dipoles that have ϵ ≈ 1, and the ability to propagate far from the front. For dipoles generated numerically, this study estimates ϵ using analytical solutions of a 2½-layer quasigeostrophic model for Gaussian vortices. The distribution of the ratio ϵ for these dipoles is found to be skewed toward higher values (i.e., cyclones are dominant in dipoles). Sensitivity experiments suggest that shallow fronts that separate mixed layers of approximately equal depths favor the development of balanced dipoles that can self-propagate over long distances. [ABSTRACT FROM AUTHOR]