Variability of Eddy Formation off the West Greenland Coast from a 1/60° Model

Abstract

Abstract Eddies generated off the west Greenland coast modulate the deep convection in the Labrador Sea, while there are still open questions related to their formation mechanisms. Using 11 years (2008–18) of output from a NEMO model configured with a 1/60° nest in the Labrador Sea, we present the patterns of baroclinic and barotropic instability off the west Greenland coast. We highlight the generation of Irminger Rings at Cape Desolation and boundary current eddies at the location of the Overturning in the Subpolar North Atlantic Program (OSNAP) West section. In between these formation sites, eddy energy attenuation occurs along the West Greenland Current (WGC). Overall, baroclinic instability dominates in the upper 1000 m and is twice as strong as the barotropic instability. Seasonally, the instabilities are generally twice as strong in winter compared to summer. Interannually from 2008 to 2018, the instabilities generally show a strengthening trend, with values in 2018 two to three times as strong as those in 2008. We found that on an interannual time scale, the strengthening of WGC and the steepening of its velocity contours enhance the barotropic instability, and the intrusion of the upper Irminger Sea Intermediate Water (uISIW) on the Irminger Water enhances the baroclinic instability by increasing the horizontal density gradient. On a seasonal time scale, variability of the eddy momentum and density fluxes modulate the barotropic and baroclinic instability, respectively. From observation-based datasets, we also found that the downstream eddy kinetic energy is highly correlated with the uISIW transports, suggesting that the amount of uISIW affects the eddy formation. Using a very high-resolution numerical model, our study provides new insight into the variability and mechanisms of eddy formation along the west Greenland coast. Significance Statement Vigorous eddy activity exists off the west Greenland coast. The eddies flux buoyancy to the interior Labrador Sea and thus weaken the convection, which feeds the lower limb of the Atlantic meridional overturning circulation. Given uncertainties in the eddy formation mechanisms, by using an ocean model with very high resolution that resolves those eddies, we show the factors that control the production and variability of the eddy formation off the western coast of Greenland. The eddy formation generally strengthens over the years 2008–18, which is a result of the intrusion of intermediate water on the continental slope and a stronger boundary current. The eddy formation shows a seasonal cycle—it is generally the strongest in winter and weakest in summer, which is modulated by the seasonal variability of eddy momentum and density fluxes.