Abstract
Ocean mesoscale eddies play a key role in the large-scale transport and redistribution of important oceanic tracers such as nutrients and anthropogenic carbon. This thesis investigates the properties, mechanisms, and parameterizations of important mesoscale eddy-induced effects on these tracers, including stirring, dispersion, frontogenesis and mixing. The first chapter describes how mesoscale eddies affect the stirring and dispersion of idealized tracers in a realistic model of the Gulf Stream region, by using a novel advection-based framework. The proposed framework models the eddy tracer forcing, which represents the net effect of eddies on tracer distribution, and involves anisotropic stirring and dispersion. The second chapter examines the relative importance of mesoscale eddies and large-scale currents in the formation and evolution of a large-scale tracer front, associated with the eastward extension of a western boundary current. The study demonstrates that the eddies act to sharpen the front, whereas the large-scale advection counteracts this effect. The eddy-driven frontogenesis is then described in terms of the novel advective framework. The third chapter compares the Lagrangian and Eulerian diagnostics of eddy mixing rate (diffusivity) and uses Lagrangian particles to estimate the Eulerian eddy diffusivity in an idealized eddy-resolving double-gyre model. The Lagrangian diffusivity estimated from particle trajectories is shown to differ from the Eulerian diffusivity estimated from the flux-gradient relation. A novel approach to calculating the Eulerian diffusivity from Lagrangian particles is then proposed. The thesis advances the understanding of the effects of mesoscale eddies on oceanic tracers with an emphasis on eddy-induced tracer advection, potentially improving the tracer simulations in ocean climate models, and provides a new way to utilize Lagrangian measurements to generate Eulerian eddy diffusivity maps.