Characteristics of ocean mesoscale eddies in the Canadian Basin from a high resolution pan-Arctic model

Abstract. Mesoscale eddies are ubiquitous in the Arctic Ocean and are expected to become more numerous and energetic as sea ice continues to decline. Yet, the spatio-temporal characteristics of these eddies are poorly documented. Here, we apply an eddy detection and tracking method to investigate mesoscale eddies in the Canadian Basin over the period 1995–2020 from the output of a high resolution (1/12°) regional model of the Arctic - North Atlantic. Over that period, about 6,250 eddies are detected per year and per depth level and are distributed about equally between cyclones and anticyclones. On average, these eddies last 10 days, travel 11 km and have a radius of 12.1 km. These statistics hide strong regional and temporal disparities within the eddy population studied. In the top 85 m, the seasonal, decadal and interannual variability in the number of eddies and in their mean characteristics follow that of the sea ice cover. In contrast, below the upper pycnocline, the eddy number and properties show a weakened seasonality. At all depths, eddy characteristics and generation rate show a strong asymmetry between the slope and the centre of the Canadian Basin. The upper 85 m show an increase in the number of eddies generated along the slope, while a net diminution of the number of eddies generated is visible within the pycnocline layer along the slope presumably due to the stabilizing effect of the slope. An increased number of eddies are generated in the vicinity of the cyclonic boundary current in the AW layer. The vast majority of eddies have no temperature signature with respect to their environment, although a significant portion of long-lived eddies, located along the Chukchi shelf break, have a non-negligible temperature anomaly and penetrate into the Beaufort Gyre, thus suggesting a mechanism for the penetration of heat into the gyre. The number of eddies generated within the upper 85 m increases by 34 % over the 25 year of simulation, with the largest increase occurring in the open ocean and marginal ice zone. The number of eddies between the upper and lower pycnoclines increases by 45 %, with a strong year-long increase in 2008, presumably in response to the Beaufort Gyre spin-up in 2007–2008. The number of eddies in the Atlantic Waters (AW) layer shows an overall increase of 41 % with little interannual variability. Finally, the analysis shows that the dominance of anticyclonic eddies within the Beaufort Gyre reported from measurements with Ice Tethered Profilers is partly due to a spatial sampling bias. This model-based eddy census can thus help interpret some of the discrepancies found between observational studies by providing a consistent spatio-temporal characterization of mesoscale eddies in the Canadian basin.