Evolution and structure of a coastal squirt off the Mississippi River delta: Northern Gulf of Mexico.
Walker, N.D., Huh, O.K., Rouse, L.J., and Murray, S.P.
In early October 1992, satellite-derived sea surface temperature data revealed a 200 km long and 10 to 30-km-wide stream of cool water flowing towards the southwesr from the Mississippi River delta region. Satellite imagery and in situ measurements have enabled a detailed study of the squirt's kinematics and subsurface characteristics over a 2-week period. In its early stages, the quirt appeared as a narrow, high-speed (> 75 cm/s) jet of water which flowed westward over the Mississippi Canyon, forcing a semi-submersible drilling rig to supsend operations from October 2 to 4. After crossing back onto the shelf, the squirt spread laterally, yielding a mushroom-shaped feature, 75 km wide, which consisted of counter-rotating vortices. Northeasterly wind forcing (averaging 10-15 m/s) and water level setup east of the delta appear to have been the primary mechanisms for evolution of the high-velocity curernts. Satellite and in situ measurements demonstrate that the dipole eddy was comprised of a cool, low-salinity, low-density water mass at least 26 m deep in the center and 16 m deep along its margins. This event demonstrates that strong northeasterly winds over the northern Gulf of Mexico can initiate along-shelf and off-sheld flows of cooler coastal waters, contributing significantly to seasonal cooling and freshening of the continental shelf and to shelf/slope exchanges of water. During this event, approximately 100km3 of inner shelf and river water was transported off the continental shelf, and volume eqiuvalent to 17% of the average discharge of the Mississippi and Atchafalaya Rivers.