Observations of offshore shelf-water transport induced by a warm-core ring

Abstract

Gulf Stream warm-core rings often are observed to entrain water from the continental shelf and transport filaments of shelf water out over the continental slope. In June 1982 the R. V. Endeavor made a transect through one such shelf-water “streamer” that was seen from satellite thermal imagery to the east of warm-core ring 82B. Acoustic doppler current profiles together with repeated CTD stations were made through the streamer. The CTD system was also equipped with a dissolved oxygen sensor and transmissometer. We were able to make an unprecedented section of velocity and water mass structure of the shelf-water filament. The offshore velocity structure observed was complicated with velocities ranging from 10 to 50 cm s −1, temperatures, in a sub-surface temperature minimum, of less than 8°C, surface salinities less than 33‰, with high levels of suspended particulate matter and manganese, and with shelf-water properties as deep as 100 m in the center of the streamer. Transports calculated in different temperature and salinity classes showed a total volume transport of waters in the filament of 0.8–0.9 × 10 6 m 3 s −1 for water with a salinity <35‰. Thermal imagery shows that the streamer was not “wrapped around” the ring but was advected by the ring and deposited at the inshore edge of the Gulf Stream. Using adjacent stations not in the streamer, but in the Slope Water, as a reference for water that presumably replaced the above amount of shelf water, estimates have been made of the net exchange of heat, salt, particulates, dissolved oxygen and Mn due to the offshore transport of shelf water by 82B. These estimates indicate that warm-core rings are capable of inducing significant exchange across the Shelf/Slope Water front off the northeast coast of the U.S.A.