A census and properties of mesoscale Kuril eddies in the altimetry era

Abstract

The ocean-side area of the Kuril Islands is a region with high bioproductivity and rich fishing and a convergence of transformed subtropical and subarctic waters with significant impact on weather and climate. Waters of different origin mix in the region including Kuroshio Extention, Japan Sea, Oyashio, Okhotsk Sea and Alaskan Stream waters. Despite the important role of Kuril eddies (KE) in transporting heat, salt, nutrients and their biological activity, there are still major gaps in our knowledge of the properties and dynamics of these energetic and mesoscale features in the northwestern Pacific Ocean. Using altimetry data during 1993–2021, we conducted the first systematic census of KE with the help of the automatic eddy tracking algorithm AMEDA. We separated KE into four groups according to their places of formation in relation to the Kuril-Kamchatka Trench and found a strong inhomogeneous spatial distribution of the Kuril cyclones (KC) and anticyclones (KAC). Different kinematic properties of KE have been studied and analyzed. The Trench has been found to play a role of an eddy guide for long-lived eddies with a comparatively small number of KE being able to cross the Trench. The highest occurrence frequency of KAC was observed along the Trench, especially in the area east off the Bussol Strait, whereas KC occurred more frequently along the ocean side of the Trench. Among the observed long-lived KE, there were more than 90% of eddies with the nonlinearity parameter exceeding 1 implying that the majority of KE are coherent vortices transporting water with its properties. The relative concentrations of waters of different origin inside KAC and KC cores were computed for each group applying the new Lagrangian algorithm. It allowed us to detect transportation of subtropical water in the KE cores to north and subarctic water to south over the distance of the order of 1000 km and more.