Material Transport in Oceanic Gyres. Part I: Phenomenology

Abstract

Abstract Material spreading and mixing by oceanic mesoscale eddies are analyzed in an idealized, numerical model of the wind-driven, midlatitude oceanic circulation. The main focus is on the regime with large Reynolds number, Re, and vigorous mesoscale eddies, although brief comparisons are made with less turbulent solutions at smaller Re. The analyses are based on ensembles of Lagrangian particle trajectories. The authors find that tracer transport by mesoscale eddies differs in many ways from the commonly used model of homogeneous, isotropic eddy diffusion. The single-particle dispersion, which describes the spreading process, is generally anisotropic and inhomogeneous and in most places it is not diffusive (i.e., not linear in time) during intermediate-time intervals after tracer release. In most of the basin and especially in the deep layers, subdiffusive single-particle dispersion occurs due to long-time trapping of material by coherent structures such as vortices near the strong currents and planeta...