SIGNATURES OF STIRRING AND MIXING NEAR THE GULF-STREAM FRONT

Citation
Gl. Hitchcock et al., SIGNATURES OF STIRRING AND MIXING NEAR THE GULF-STREAM FRONT, Journal of marine research, 52(5), 1994, pp. 797-836
Citations number
53
Categorie Soggetti
Oceanografhy
Journal title
ISSN journal
00222402
Volume
52
Issue
5
Year of publication
1994
Pages
797 - 836
Database
ISI
SICI code
0022-2402(1994)52:5<797:SOSAMN>2.0.ZU;2-H
Abstract
In October, 1986 the surface waters adjacent to the Gulf Stream front were surveyed with an undulating profiler to describe the finescale st ructure of the mixed layer. The profiler was a Seasoar equipped with a CTD and fluorometer. The survey first defined the structure of a cycl onic eddy which resembled frontal eddies of the South Atlantic Bight i n sea surface temperature imagery. The Seasoar transects revealed, how ever, that the cyclonic eddy lacked a cold dome typically seen in fron tal eddies. Farther downstream the Seasoar defined the structure of st reamers of Gulf Stream and Shelf water wrapped about the southern edge of a warm-core ring. The streamers had lateral and along-axis dimensi ons on the order of approximate to 10 km and 100 km, respectively, and were bordered by narrow intrusive features. The temporal history of t he streamers was described from SST imagery, and the surface flow deri ved from ship's drift vectors. CTD casts taken while following an isop ycnal float provided a means to examine the structure of the intrusive features. Interleaving was evident at the boundaries of the streamers and intrusive features where high conductivity Cox numbers were conce ntrated, suggesting elevated microstructure activity. The Turner angle distribution, indicating either saltfingering or diffusive convection , did not correlate well with the Cox number distribution. This is int erpreted as evidence that lateral, rather than diapycnal, mixing was t he process mediating the exchange of properties at the boundaries of c ontrasting water types. In contrast to physical properties, the distri bution of fluorescence showed relatively less structure in the surface layer between the ring and Gulf Stream front. In the surface layers o f the two streamers the pigment and bacterial biomass, and the diatom species composition, were typical of Slope water communities. We hypot hesize that small-scale mixing processes concentrated at the boundarie s of the streamers were the mechanism by which Slope water plankton we re seeded into streamers of different hydrographic origins. Presumably , high netplankton growth rates allowed the Slope water species to dom inate the communities in the streamers.