Pathways of the North Atlantic Current from surface drifters and subsurface floats

Abstract

The North Atlantic east of the Grand Banks presents a thermal front from 40° to 50°N between the warm North Atlantic Current (NAC) and the cold Labrador Current. Here we use the trajectories of 84 isopycnal RAFOS floats deployed on the 27.2 and 27.5 σT surface in 1993–1995 and 218 surface drifters deployed by the International Ice Patrol and the Institut für Meereskunde (Kiel, Germany) between 1978 and 1993 to understand the pathways of the NAC. The mean flow pattern, kinetic energy, directional stability, and most probable path through 1° by 1° boxes are derived for each of the three surfaces. Speed and kinetic energy decrease with depth, although directional stability is comparable at all levels. The axis of the NAC, which follows the 4000 m isobath along the western boundary, is described by mean kinetic energy (MKE) values surpassing 100 cm2 s−2 at the surface or 50 cm2 s−2 on the float surfaces and correspond to regions with directional stabilities in excess of 60%. Maximum values of eddy kinetic energy are found just offshore of the maximum MKE associated with the NAC main pathway and decrease rapidly to the east. Two cyclonic meanders are identified at 44°N, 45°W near the Newfoundland Seamounts and at 46°N, 42°W near Flemish Cap. The main difference between the patterns derived for the surface drifters and floats was the greater eastward extent of the cyclonic trough at 44°N and intensity of the Mann Eddy (42°N, 44°W) during the float sampling period (1993–1995).