Natacha Bourg will present her thesis on Friday 13 December 2024 à 10:00 at the Amphithéâtre M - Campus de La Garde, on the following topic: Interactions between boundary currents, fronts and eddies in the Northern Current and the East Australian Current. Transport dynamics and application to the journey of Physalia spp.
Composition of the Jury
Rapporteurs Bruno Blanke (LOPS, Brest France), Clothilde Langlais (CSIRO, Hobart Australia)
Examiners Luis Ferrer (AZTI, Pasaia Spain), Daniel Conley (UoP, Plymouth UK)
Directors Anne Molcard, Amandine Schaeffer (UNSW, Sydney Australia)
Summary
Edge currents, characterised by high speeds and numerous dynamic interactions with continental margins, are the main drivers of oceanic variability in the coastal regions they cross. The first part of this thesis focuses on High Frequency RADAR observations of the North Current in the North-Western Mediterranean and the East Australian Current in the South Pacific Ocean. We study the seasonal and interannual variability of the current and the development of mesoscale eddies in the North Current system. In particular, we are examining the separation dynamics of the East Australian Current, its frontal characteristics and its impact on surface chlorophyll-a concentration. Because of their large extent and position along the continental shelf, the edge currents are important because they act both as barriers and as transport belts for passive matter. The second part focuses on Physalia spp, a pseudopassive stinging organism floating on the ocean surface that regularly reaches the Australian coast. We were able to estimate the relative impact of meteorological and marine variables on their stranding. Based on laboratory experiments, we are establishing a parameterisation for the drift of 3D models of Physalia spp. induced by the wind. This result, integrated into a Lagrangian tracking model based on scenarios typical of the East Australian Current, enables us to determine the cumulative influence of wind and current on the trajectories of the Physalia The results presented in this thesis contribute to our knowledge of two onboard currents, characterised by different scales and modes of variability, and illustrate their role in the transport of passive matter through the study of the drift of Physalia spp.