June '97 Summary Cruise Narrative Science Party List Browse SeaSoar Sections

The primary goal of this cruise was to make observations of processes which may remove shelf water and associated biota from the southern flank of Georges Bank, with priority given to obtaining observations of interactions between Gulf Stream rings and the shelf break front. Prior to sailing, satellite imagery revealed two ring-like features near the southern flank of the bank. A warm-core ring was positioned just west of the Great South Channel, while a less distinctly formed feature occupied the region to the east, near the 100 m isobath (see 26 June 1997 image). As the western ring was outside the study area, we chose to sample the eastern feature, beginning near Ron Schlitz's moored array and working eastward with a series of three 'radiator' sampling grids. Grid locations were chosen to sample: 1) the leading edge of interaction between Gulf Stream and the shelf waters, perhaps including the zone of flow reversal on the bank, 2) the region of maximum shear between Gulf Stream water in the feature and the mean flow on the Bank and 3) the region where the flow associated with the warm feature separates from the shelf, where imagery suggests streamers of cold water extend off-bank. Flow patterns and satellite imagery obtained during these initial surveys indicated that the feature was more plume-like (rather than ring-like) in character, with westward flows in the western region and eastward flows further east. Based on the results of the initial survey and motivated by our interest in shelf water removal, we chose to use the remainder of our time executing repeated radiator surveys spanning the maximum shear region and the separation zone to the east of the feature. Four repeats of the survey pattern allowed us to document both spatial variability and the temporal evolution of the warm-water intrusion onto the Bank. During this period, the primary warm plume produced a tendril which extended on-bank to the 60 m isobath. Fortunately, this feature was captured in our repeat sampling pattern. Lastly, while en route back to Woods Hole, we recovered a drifting guard buoy belonging to Peter Smith (Bedford Institute of Oceanography).