SOFAR float trajectories in the tropical Atlantic 1989-1992

Abstract

Neutrally buoyant SOFAR floats at nominal depths of 800 m, 1800 m, and 3300 m were tracked acoustically for 3.7 years in the vicinity of the western boundary and the equator of the Atlantic Ocean. Trajectories and summaries from the whole experiment are shown along with detailed trajectories from the second setting of the listening stations, October 1990 to September 1992. Some highlights are mentioned below. Trajectories at 1800 m revealed a swift narrow southward flowing deep western boundary current (DWBC) extending from 7°N across the equator. Two floats directly crossed the equator in the DWBC and went to 10°S. Two other floats left the DWBC near the equator and drifted eastward. Three floats entered the DWBC from the equatorial current system and drifted southward. No obvious DWBC or swift equatorial currents were observed by the 3300 m floats. The 800 m floats plus some surface drifters measured seven anticyclonic eddies as they translated northwestward along the coast of South America in a band from the equator to 12°N. One of the floats (28) entered the Caribbean where tracking stopped. This float was again tracked as it drifted across the mid-Atlantic Ridge and entered the Canary Basin near 34°N 28°W after a gap of 2.7 years. We infer that this float went westward though the Caribbean and northeastward in the Gulf Stream. Float 17 drifted northward from 10°N to 22°N in an eastern boundary current off the coast of West Africa. Floats between 6°N-6°S (roughly) drifted long distances zonally in the equatorial current system.