Observing storm-induced sediment resuspension processes in the mid-atlantic bight with Slocum Gliders

Abstract

Storm-induced sediment resuspension events are examined using physical/optical sensors deployed on Slocum Gliders. Two types of storm response are found. In summer, the intense seasonal stratification limits sediment resuspension even during hurricanes. In contrast, winter storms suspend sediment throughout the full water column. The fall transition between seasons starts with surface cooling that preconditions the shelf for mixing during fall storms. Focusing on a classic fall northeaster, sediment resuspension was limited to below the weakening pycnocline early in the storm. After the pycnocline was eroded, particles immediately filled the water column. The optical signals suggest that suspended particles are likely similar materials, which implies the reduced slope of the backscatter profiles is caused by an increase in vertical transport or turbulent mixing. Wave bottom orbital velocities during this time were decreasing, and glider vertical velocities show no indication of enhanced vertical velocities reflecting full water column Langmuir cells. We conclude the enhanced mixing is related to the interaction of the surface and bottom boundary layers as the stratification is eroded, and the observed variability is associated with the tide.