Tidal Dynamics of Capbreton Canyon and Their Influence on Resuspension of Sediment

Abstract

This thesis uses observations to investigate the tidal dynamics and sediment transport processes within Capbreton Canyon, a submarine canyon located in the southeastern Bay of Biscay. Submarine canyons serve as key conduits for sediment movement from the coastal shelf to the deep sea but the exact mechanisms involved are still poorly understood. This study focuses on the interactions between internal waves and the canyon's complex topography which can result in increased levels of internal wave energy close to the seafloor able to cause sediment resuspension. Observations for this study were collected during the PLUMEFLOC campaign aboard the RV Pelagia covering depths from 500m to 4000m. The key variables evaluated include temperature, salinity, current velocity, as well as optical and acoustic backscatter from multiple CTDs, ADCPs and OBSs. These variables are used to investigate the structure of the water column and to identify regions of heightened internal wave energy. Based on these findings, wavelet analysis revealed highly complex baroclinic conditions with varying tidal frequencies dominating the temperature and current velocity signal at different locations along the thalweg of the canyon. A particular focus was placed on observations from a bottom lander deployed along the thalweg of the canyon at a depth of 2500m, where highly nonlinear phenomena such as breaking internal waves and bores were observed. Throughout the measurement period, periodic transitions between wave steepening and wave breaking are found with upcanyon propagating bores showing signs of sediment resuspension. However, not all internal tidal bores observed during the study led to sediment resuspension, indicating that further research is necessary to understand the specific conditions and factors that contribute to this phenomenon.