Structure of ocean circulation between the Galápagos Islands and Ecuador

Abstract

From 27 March to 5 April 2009, upper ocean velocities between the Galápagos Islands and Ecuador were measured using a vessel mounted ADCP. A region of possible strong cross-hemisphere exchange was observed immediately to the east of the Galápagos, where a shallow (200 m) 300 km wide northeastward surface flow transported 7-11 Sv. Underlying this strong northeastward surface current, a southward flowing undercurrent was observed which was at least 600m thick, 100 km wide, and had an observed transport of 7-8 Sv. Next to the Ecuador coast, the shallow (<200 m) Ecuador Coastal Current was observed to extend offshore 100 km with strongest flow, 0.33ms-1, near the surface. Immediately to the west of the Ecuador Coastal Current, flow was directed eastward and southward into the beginnings of the Peru-Chile Countercurrent. The integral of the surface currents between the Galápagos and Ecuador agreed well with observed sea level differences. Although the correlation of the sea level differences with large scale climate indices (Niño3 and the Southern Oscillation Index) was significant, more than half of the sea level variability was not explained. Seasonal variability of the sea level difference indicated that sea level was 2 cm higher at the Galápagos during late winter and early spring, which could be associated with the pattern of northward surface flows observed by R/V Knorr.