Annalisa Bracco Georgia Institute of Technology I will discuss some of the open challenges of modeling the surface and deep sea circulation, and the water column exchanges in the northern Gulf of Mexico. Using a suite of numerical simulations run at different horizontal and vertical resolutions with the inclusion of passive Lagrangian and Eulerian tracers, I will show that vertical transport and horizontal mixing are strongly impacted by the details of the dynamics resolved by the model. The evolution of tracers released close to the surface or below the mixed layer along the continental slope, for example, differs enormously whenever the simulation resolves only the mesoscale circulation or is capable of representing submescale (1-10km) processes and instabilities.Implications of this work are not limited to deep spill forecasts, or to simulating the Gulf of Mexico biogeochemical dynamics and processes, but may extend to the broad climate modeling community.