Cross Surfzone/Inner-shelf Dye Exchange (CSIDE) Experiment: AUV Observations of Flow Structure

The exchange of tracers (nutrients, pollutants, pathogens, larvae, phytoplankton, and sediment) in the inner continental shelf is particularly complex and has important implications for continental shelf ecosystems and for nearshore water quality. Vortical structures associated with transient seaward flowing currents (rip currents) have been shown to represent the dominant exchange mechanism between the surfzone and the inner-shelf. However, the spatial structure of these vortical features in cross-shelf transport has not been resolved and a paradigm for how these structures evolve in stratified inner-shelf waters is lacking. Autonomous Underwater Vehicles (AUVs) have tremendous potential for resolving spatio-temporal flow structure in the inner-shelf. Here we present AUV observations collected during a series of surfzone dye release experiments carried out during the fall of 2015 at Imperial Beach, California (CSIDE experiment). Repeat line surveys were carried out using a REMUS 100 AUV to resolve dye, temperature and salinity distributions outside of the surfzone. Surfzone/inner-shelf flow structures were targeted using fine resolution grid surveys and a fixed instrumentation array was employed to resolve the spatio-temporal wave field. Preliminary results highlighting the effects of inner-shelf stratification on the vertical structure these vortical features are discussed and potential dissipation mechanisms are explored.