Reduced trapping efficiency of mesoscale eddies under eddy-eddy interactions

Abstract Oceanic mesoscale eddies are commonly assumed to act as coherent structures that trap and transport water masses over long distances. However, recent Lagrangian studies suggest that long-lived coherent structures in the ocean are much more limited than implied by Eulerian eddy boundaries. In this study, surface drifters are used to examine the material transport capabilities of mesoscale eddies, and it is found that drifters initially enclosed by eddies tend to rapidly leak out after only a few days on average, indicating that these drifters are not effectively trapped and coherently transported by mesoscale eddies. Furthermore, a series of numerical experiments suggests that while an isolated eddy can effectively transport initially enclosed water parcels, significant water leakage occurs in the presence of multiple eddies, which may be associated with eddy–eddy interactions. And the degree of this leakage is found to be positively correlated with the intensity of the background strain field. Our results suggest that, in realistic multi-eddy environments, eddy stirring may contribute more significantly to material transport than eddy trapping, with broad implications for heat and biogeochemical tracer redistribution and for the representation of eddy transport in climate models.