Chaotic Transport and Mixing by Ocean Gyre Circulation

Abstract

This paper reviews some recent development of the Lagrangian modeling of chaotic transport and mixing by the gyre-scale (basin-scale) ocean circulation, by use of some contemporary ideas and tools. Lagrangian trajectories in a simple oceanic flow can exhibit complex behaviors, called the chaotic advection. This chaotic advection can induce the chaotic transport and mixing in the fluid particles and finer structures in the tracer fields. The chaotic transport and mixing by gyre-scale circulation motion was proposed as one of fundamental mechanisms for the chaotic or fractal behaviors of the quasi-Lagrangian drifter trajectories observed in oceans, and water mass and water property exchanges on the gyre-scale or basin scale. It is this chaotic (or stochastic) nature of the Lagrangian trajectories that provides a possible linkage between the large-scale motion and the finer structure in the tracer fields. The results showed the fundamental importance of transients of the large scale oceanic motion in the Lagrangian transport and mixing processes. Some basic ideas and methodology were introduced in relation to the Lagrangian modeling of the water mass and water property exchanges. The discussion was focused on the chaotic transport and mixing by the gyre-scale (basin-scale) motion with some references to that by the meso-scale motions. The chief purpose of the paper is to introduce main ideas and methodology behind this Lagrangian modeling, rather than to give a complete literature review on the chaotic transport and mixing in physical oceanography or on the gyre-scale transport and mixing. A simple gyre scale ocean circulation model, mimicking the upper North Atlantic, was used to highlight the ideas and the results were found to be favorably comparable to observations.