Lagrangian Current Measurements within the Eastern Margin of a Warm-Core Gulf Stream Ring

Abstract

Two satellite-tracked buoys drogued at 10 m depth were deployed within shelf water, close to the shelf/slope front in late summer 1980. Position and sea-surface temperature data from the two buoys were combined with surfaco-water mass analysis based an high resolution infrared satellite imagery. Buoy trajectories and surface-water mass analysis suggest that both buoys traversed a region of shelf water while moving to the southwest at less than 25 cm s−1. Stronger currents up to 54 cm s−1 from warm-core ring 80-A were encountered near 38°N latitude. These currents caused the buoys to move anticyclonically along the ring's eastern margin within a well defined shelf-water entrainment. Buoy sea-surface temperatures and positions showed good correlation with frontal boundaries based on satellite imagery. This was shown for both the ring shelf-water entrainment and another shelf-water feature located along the northern edge of the Gulf Stream. Volume transport of the ring entrainment was estimated to be 1.5 × 105 m3 s−1 (4700 km3 year−1). An estimated 40% of this yearly volume (1900 km3 year−1) could be shelf water, according to salt- and mass-balance considerations. The yearly estimate of 1900 km3 year−1, however, is too large according to estimates by other investigators, and because the entrainments are short-lived features. A proposed model uses three warm-core rings per year located in the Middle Atlantic Bight for 90 days each. If the rings entrain shelf water at the measured rate for 50% of the time, this amounts to 703 km3 year−1 or 30% of the total yearly shelf-water transport estimated by others.