Abstract

Time series of current velocity and temperature from several depths at a site near the center of Drake Passage show features that can plausibly be interpreted as current rings. Between June 1975 and January 1976, five cyclonic rings from the Continental Water Boundary and one anticyclonic ring from the Polar Front passed over the site. The diameters of the rings varied from 30 km to 130 km, and all of them extended vertically to a depth of at least 2500 m. The rings exhibited maximum spin velocities of about 20 cm sec−1 at 1000 m depth and 10 cm sec−1 at 2500 m. Their translatory motion, which was toward the north at about 4 cm sec−1, contained a westward component relative to the ambient flow. The magnitude of the westward component suggests that it may have resulted from an interaction between rings and the sea floor, which slopes downward to the northeast at the mooring site. The total available mechanical energy of the rings (kinetic plus potential) varied from 6.2 × 1013 j in the smallest ring to 9.9 × 1014 in the largest. The available heat, relative to the Antarctic Zone, was several orders of magnitude larger: −3.0 × 1017 j for the smallest ring and −3.6 × 1018 j for the largest. The numbers indicate that current rings may play an important role in dissipating the kinetic energy of the circumpolar fronts and that they may be responsible for a significant poleward flux of heat in the Southern Ocean.

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