North Atlantic Ocean surface currents

Abstract

Close to 1800 surface drifters are used to investigate the 15 m circulation of the North Atlantic Ocean. The data are used to describe structures of the average Eulerian circulation and of the associated eddy variability. The data resolve scales on the order of 50 km, which have hitherto not been systematically described, in particular, near shelf breaks and near the most intense currents, the Gulf Stream, the North Atlantic Current (NAC), and the frontal currents of the subpolar gyre. This reveals a complex series of quasi‐permanent eddies, meanders, and recirculation patterns. Gulf Stream intensity is portrayed as changing abruptly near 54°W, east of which, it is identified as two current branches centered near 39° and 41.5°N, the northern one connecting more directly with the NAC, and the southern one with the recirculation gyre and the Azores Current (AC). Many features of the currents are controlled by topography, in particular, currents are often intensified near shelf breaks or parallel to ridges in the subpolar gyre. However, the largest northward branch of the NAC in the Icelandic basin is located near the deepest bathymetry, not near steep bathymetry. Other currents, in particular, in the subtropical gyre, are less clearly related to topography: for instance, the AC is featured as a zonal eastward current extending far west of the Mid‐Atlantic Ridge (MAR) to at least 55°W and possibly 63°W. In the interior and away from topographic features the eddy kinetic energy (EKE) is the largest where the mean currents are the largest. In the subpolar gyre, there are striking differences in EKE between southward flowing currents (the Labrador and east Greenland Current) and the northward flowing currents (west Greenland Current and branches of the NAC), which have higher EKE. The areas of weakest variability are located in the southwest part of the subpolar gyre, northeast of Iceland, and in the eastern Atlantic south of 45°N. The AC eddies and the mesoscales south of the Canary Islands transect this eastern eddy desert. Drifter trajectories are used as realizations of Lagrangian particles in the vicinity of current cores. These illustrate the variety of paths or connections between different current systems and demonstrate cross‐stream dispersions.