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On the interactions between the Mississippi River plume and the Gulf of Mexico offshore circulation

Rafael Schiller, Villy Kourafalou, Patrick Hogan, Nan Walker
University of Miami - RSMAS
(Abstract received 12/17/2010 for session X)

The Mississippi River (MR) is the major source of freshwater, nutrients and pollutants for the Gulf of Mexico (GoM). The MR plume influences both the ecosystems of the northern GoM region and remote coastal areas (Florida Keys), the latter due to interactions and offshore removal by the GoM mesoscale circulation. In this study, we investigate the dynamical processes controlling the fate of the MR plume, in particular the conditions that favor cross-marginal transport. A high resolution (1/50 deg) model of the northern GoM region was developed using HYCOM. A realistically-forced simulation (nested in a data-assimilative regional GoM-HYCOM model) reveals that the offshore removal is a frequent plume pathway. Eastward, wind-driven currents promote large freshwater transport towards the shelfbreak and the DeSoto Canyon, where mesoscale eddies interact with the buoyant plume and effectively entrain the riverine waters. Freshwater transport estimates show that the offshore removal by eddies can be as large as the wind-driven shelf transport. The proximity of eddies to the shelfbreak is a sufficient condition for offshore removal, and shelf-to-offshore interaction is facilitated by the steep bottom topography near the MR Delta. Strong eddy-plume interactions were observed when the Loop Current System impinged against the shelfbreak, causing the formation of coherent, narrow low-salinity bands that extended toward the Gulf interior. The offshore pathways depend on the position of the eddies near the shelf edge, their life span and the formation of eddy pairs that generate coherent cross-shelf flows.

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2011 LOM Workshop, Miami, Florida February 7 - 9, 2011