Irreversible Stirring and Mixing of Tracers by Oceanic Internal Gravity Waves

Oceanic internal waves are often thought to be ineffective in stirring and mixing tracer fields such as heat, salt, carbon, and other nutrients. Due to their oscillatory nature, waves are expected to merely displace tracers periodically around their mean position. However, observations of enhanced lateral tracer dispersion at submesoscales (<10 km), where energetic internal waves are abundant, urge better understanding of the role of waves in dispersing oceanic tracers. Using theoretical and numerical methods, this study examines the impact of waves and their amplitudes on the lateral dispersion of passive tracers. We show that two or more waves can irreversibly stir and mix tracers. A broadband spectrum of waves further enhances stirring and mixing. Tracer dispersion in general is seen to become more efficient with increasing amplitude of waves. These findings stem from kinematic non‐interacting waves and dynamic nonlinearly interacting waves. Our results highlight the effectiveness of finite‐amplitude internal waves in tracer stirring and underscore the need to resolve or parameterize wave‐induced lateral mixing in large‐scale ocean models.