COLD ANTICYCLONIC EDDIES FORMED FROM COLD POOL WATER IN THE SOUTHERN MIDDLE ATLANTIC BIGHT

AVHRR satellite imagery of the southern Mid-Atlantic Eight during May 1993 revealed a large area of cold water over the shelf break and slop e that appeared to spin up into a series of southward propagating anti cyclonic eddies. The eddies had diameters of 35-45 km at the surface a nd moved southward at about 20 cm/sec. A radial TOYO CTD (to 50m) and ADCP velocity (to 400m) transect was conducted across the southern-mos t of these eddies. The upper 50 meters had minimum temperatures of les s than 7 degrees C and salinities of about 33 pss, characteristics sim ilar to cold pool waters usually found over the continental shelf. ADC P velocity data from one of-the eddies revealed anticyclonic flow exte nding to a depth of about 250m. The transport of cold pool water by th e eddies was estimated to be 0.1 to 0.2 Sv which is of the same order as the annual mean alongshore transport of shelf water in this region. The origin of the deeper water within the eddy is unlikely to be the continental shelf because the shelf break is less than 100 m. The dept h and velocity profiles along the TOYO transect were consistent with t he constant potential vorticity eddy model of Flierl (1979) although t he source of the eddy kinetic energy is uncertain. The cause for the e xodus of cold pool water from the shelf, which extended northward to a t least 38 degrees N, is unclear but must involve the establishment of an alongshore baroclinic pressure gradient against the usual southwes tward shelf flow. It is possible that the intrusion of Gulf Stream wat ers onto the shelf near Cape Hatteras was a precursor of this off-shel f transport. The southern-most eddy was marked by high biological prod uctivity and very high oxygen supersaturation. The phytoplankton bloom detected within the exported cold pool water, located over the contin ental slope, suggests a mechanism whereby production fueled by nutrien ts derived from the shelf can be locally exported into deep water. (C) 1998 Elsevier Science Ltd. All rights reserved.