Rw. Houghton et al., SHELF-SLOPE WATER FRONTAL STRUCTURE, MOTION AND EDDY HEAT-FLUX IN THESOUTHERN MIDDLE ATLANTIC BIGHT, Deep-sea research. Part 2. Topical studies in oceanography, 41(2-3), 1994, pp. 273-306
Results of an analysis of SEEP-II temperature and velocity data to inv
estigate the shelf-slope frontal structure, motion and eddy heat flux
in the southern Middle Atlantic Bight are presented. In the winter and
spring the inclination of the frontal boundary and the vertical veloc
ity shear, when averaged over periods greater than a week, approximate
ly satisfy the Margules' equation. Associated with the locally wind dr
iven cross-shelf excursions (similar to 20 km) of the foot of the fron
t are vertical displacements of the frontal boundary due to vorticity
constraints imposed by the bottom topography. Some of the smaller-scal
e frontal motions suggest wave-like disturbances propagating southward
along the continental margin. In April 1988 the most severe wind even
t recorded during SEEP-II displaced the foot of the front into the upp
er slope region and injected shelf water into the interior of the slop
e water column. On the mid-shelf cross-shelf eddy heat fluxes are negl
igible, as temperature variations and cross-shelf velocities are in qu
adrature. At the shelfbreak, however, depth-averaged heat fluxes, appr
oximately 4 x 10(6) W m(-1) onshore, are significantly different from
zero and comparable to the exchange estimated by Fairbanks using O-18
tracer data. In the winter and spring the eddy flux is greatest near t
he frontal boundary in the lower water column and is dominated by a fe
w large exchange events. In the summer the subtidal eddy flux is great
est just below the seasonal pycnocline in the upper water column, with
a peak in the 5-11 day band that may be a contribution from frontal i
nstabilities. Bottom Eulerian mean velocities are 1-2 x 10(-2) m s(-1)
offshore over the shelf and slope. Measured eddy fluxes are adequate
to achieve the advective-diffusive balance required to maintain the fr
ontal position in steady state.