Shoal Bathymetry Influence on Offshore Transport and Mixing

Ocean dynamics on continental shelves are strongly influenced by topographic features. Particularly, interactions between shoals and their surrounding flow play an important role in supporting cross-shelf exchange and mixing in the coastal ocean. Despite this, there remains uncertainty about the role these shoals play in transporting fluid offshore, and how shoals spur vertical and horizontal mixing. In this work, we use a series of large eddy simulations to simulate flow over shoals, analyzing the offshore transport of momentum and tracers, and the generation of eddy kinetic energy upstream and downstream. Our simulations are centered around a reference case of the Diamond Shoals off of North Carolina, using boundary conditions prescribed from observations. Our results show that the shoal serves as an extension of the coastline, diverting flow offshore and generating turbulence that enhances mixing. By testing variations in shoal geometry, we find that offshore transport and mixing are driven by the vertical and horizontal extent of the shoal bathymetry relative to the surrounding shelf.