Particle Size Distributions and Attenuation on a Stratified Inner Continental Shelf.

摘要

High resolution, cross-shelf physical and bio-optical ship surveys were conducted during the summer stratified season off the southern coast of New Jersey. On 13 July 1999, a small storm passed over the study area generating the largest waves of the summer field season. Compared to pre-storm levels, scattering measured with an Attenuation-Scattering at 9 wavelengths sensor (ac-9) in depths less than 15 m doubled on 14 July 1999. This increase was accompanied by strong vertical mixing inshore and increases in suspended sediment concentrations measured with a Laser In Situ Scattering Transmissometer (LISST-100). A particulate load maximum was observed offshore in the thermocline. The location and vertical distribution of the maximum was unexpectedly asymmetric between the up and downcasts. The observations indicated that the asymmetry was caused by particle entrainment, disaggregation, and mixing by the sampling cage housing the instruments as it was lowered and raised through the water column. A method to remove the profiling effect appeared to accurately reproduce the concentration and vertical distribution of suspended particles. The measurements suggested that some of the larger entrained particles were disaggregated to form concentrations of smaller particles on the upcasts. Given the location of the LISST within the profiling sea cage, only the downcasts produced undisturbed estimates of the vertical distribution of concentration and size classes.