Chaotic Advection, Mixing, and Property Exchange in Three-Dimensional Ocean Eddies and Gyres

Genevieve Brett, Ph.D., 2018
Larry Pratt, Co-Advisor
Irina Rypina, Co-Advisor

This work investigates models of two oceanographic flows: an overturning submesoscale eddy and the Western Alboran Gyre. For the first, I quantify the importance of diffusion as compared to chaotic advection for tracers using three methods: scaling arguments; statistical analysis of trajectory ensembles; and Nakamura effective diffusivity. I find that chaotic advection dominates over turbulent diffusion only in wide chaotic regions, which always occur near the center and outer rim of the cylinder. The second flow is a realistic numerical model of the Western Alboran Gyre, which I examine from both Eulerian and Lagrangian perspectives. I find that advection is the dominant term in Eulerian budgets for volume, salt, and heat in the gyre, while viscous diffusion dominates the vorticity budget. I then construct a moving three-dimensional Lagrangian gyre boundary from stable and unstable manifolds, computed on several isopycnals and stacked vertically. The regions these manifolds cover is the stirring region, where water is exchanged with the gyre over days to weeks. The stirring region can reach the northern coast. Using a gate, I calculate the continuous advective transport across the Lagrangian boundary in three dimensions for the first time. Challenges in closing Lagrangian budgets are described.