Variability of Cross-Slope Flow in the Desoto Canyon Region

Cross-slope flow is critical for governing heat and material exchange, including pollutants and biota, between the coastal and deep ocean. This study focuses on characterizing the variability of cross-slope near-bottom flow in the DeSoto Canyon region, where the BP's Macondo well exploded in April 2010, using a multi-decadal HYbrid Coordinate Ocean Model (HYCOM) simulation of Gulf of Mexico circulation. Due to change in shelf orientation east and west of the canyon, wind-driven vertical motions are mostly related to a component of the local wind vector along an angle that may deviate from the local isobaths, with smaller deviations from the along-isobath direction to the east of the canyon and bigger departures to the west. This implies that upwelling is associated with along-isobath winds east of the canyon but shelf waves propagating from the eastern shelf, where northwesterly winds are upwelling favorable, influence cross-slope flow to the west of the canyon. Beyond the shelf break, where the Loop Current and its eddies can directly impact the depth of isotherms, the isotherms are deepened underneath the Loop Current and anticyclones but uplifted on their inshore periphery. The Loop Current also interacts with the west Florida shelf and generates a high pressure gradient that extends northward along the continental slope into the study domain. Consequently, large-scale and persistent upwelling and downwelling events take place over the continental slope of the domain. The vertical excursions mostly range from ±35 to ± 50 m for the shallow isopycnals but can reach to over ± 100 m. Most distinct upwelling and downwelling events are short duration on the order of days, however there is a significant chance for persistent events, which can be induced by either remote or direct interaction of the Loop Current and/or eddies with the slope.