Satellite Observations Of Oceanic Shelf-Slope Exchange

Abstract

The transport of water masses and energy along and across the shelf edge has significance for both the abiotic and biotic components of local and distant regions of the Texas-Louisiana continental shelf in the northwestern Gulf of Mexico. Sequential Infrared images obtained by NOAA satellite Advanced Very High Resolution Radiometer (AVHRR) instruments have been used to examine the structure and assess motion of surface waters during episodic events at the shelf edge along the Brownsville Front. Transport seaward and shelfward is associated with the counterclockwise rotation around the Texas Plume, a seaward extension of the Front in the vicinity of Alaminos Canyon. When it occurs, this feature is a spatially-localized dynamic event. Submesoscale, counter-clockwise rotating eddies have been observed arrayed along the Front from the longitude of Brownsville to that of Atchafalaya Bay. These features represent spatially sequential, advecting mixing mechanisms that translate eastward along the shelf edge and induce shelf-slope exchange. Larger, clockwise-rotating Loop Current eddies bring about converse exchange through their clockwise rotation as they move westward along the shelf edge. In circumstances where organized motion along the Brownsville Front is weak, exchange has been observed in terms of interlaced seaward and shelfward hammer-head formations that reach across the shelf edge. Without westward penetration of the Loop Current or a Loop Current eddy west of the Mississippi Delta’s longitude, surface waters seward of the Louisiana Bight are shown to move due south and reach the vicinity of Campeche Bank.