L' approccio Sistemi Dinamici a trasporto e mixing in oceano aperto: dagli esponenti di Lyapunov agli elefanti di mare

Presenting strong inhomogeneities, mesoscale phenomena play an important role in the open ocean . They structure the marine landscape with consequences on the repartition of nutrients and phytoplankton communities. Such repartition is largely determined by the horizontal transport induced by surface currents. In this thesis surface currents detected from satellite altimetry are studied from a dynamical systems point of view. This approach is used to analyze how surface water masses may be trapped by mesoscale eddies. A semi-Lagrangian diagnostic which combines the Eulerian Okubo-Weiss criterion with the analysis of water parcels trajectories is used to partition the ocean into regions with different retention times is defined and studied. Different retention times appear to influence the behaviour of a tagged marine predator (an elephant seal) along a foraging trip. The comparison between predator trajectory and eddy retention time suggests that water trapping by mesoscale eddies, detected from satellite altimetry, may be an important factor for monitoring the spatial repartition of the trophic chain in the open ocean.