  This study examines the mesoscale and submesoscale circulations along the
continental slope in the northern Gulf of Mexico at depths greater than 1000 m.
The investigation is performed using a regional model run at two horizontal
grid resolutions, 5 km and 1.6 km, over a three year period from January 2010
to December 2012. Ageostrophic submesoscale eddies, and vorticity filaments
populate the continental slope, and they are stronger and more abundant in the
simulation at higher resolution, as to be expected. They are formed from
horizontal shear layers at the edges of highly intermittent,
bottom-intensified, along-slope boundary currents and in the cores of those
currents when they are confined on steep slopes. The horizontal resolution
influences the representation of the lateral and vertical transport of
neutrally buoyant tracers. This is exemplified by a passive dye deployed near
the Macondo Prospect, where the Deepwater Horizon rig exploded in 2010, and at
the largest known natural hydrocarbon seep in the northern Gulf, few hundred
kilometers to the west of the rig wellhead. The first site is characterized by
weak mean currents and, in the high resolution run, by intense submesoscale
eddies that form to the west of the Macondo Prospect. GC600, on the other hand,
is surrounded by a complicated bathymetry, and its flow is highly variable. The
trapping exerted by the submesoscale eddies and vorticity filaments near the
rig constrain the spreading in the vicinity of the Macondo Prospect, and as a
result, patchiness in the passive tracer distributions differs in the two
integrations, despite similar diffusivities expressing the average spreading
rate. The tracer released at GC600, on the other hand, is dispersed more
effectively in the first six months in the higher resolution case due to
enhanced near-bottom turbulent mixing.
