Modeling water column structure and suspended particulate matter on the Middle Atlantic continental shelf during the passages of Hurricanes Edouard and Hortense

The present contribution is motivated by the desire to elucidate the processes that contributed to the evolution of observed thermal structure and resuspension of particulate matter during and after the passages of two hurricanes, Edouard and Hortense, within a two-week period in late-summer 1996. A unique set of high temporal frequency measurements of the vertical structures of physical and optical properties was obtained at a mooring site near the Middle Atlantic Bight continental shelf-break (70 m water depth). These data provided insight and initial conditions for the physical model used for this study. The model accounted for wind and bottom current generated turbulence, surface waves, wave-current interactions, tides, and depth-dependent density-driven circulation. We find that the most important process controlling the thermal water column structure during and following the passage of Hurricane Edouard was the wind stirring. Differences between the model results and the observations of thermal structure may have been caused by advection, which is not included in this one-dimensional model. There is also clear evidence of internal tides in the observations, whereas the model could not reproduce this effect. A suspended particulate matter (SPM) model is included as a module of the physical model to examine sediment resuspension processes. It is concluded that wave-current bottom shear stress was clearly the most important process for sediment resuspension during and following both hurricanes. Discrepancies between modeled and observed SPM are attributed to the presence of biological material in the surface waters and changes in sediment properties (flocculation and de-flocculation) during and following the passages of the hurricanes.