Assessment of Turbulent Mixing Associated With Eddy-Wave Coupling Based on Autonomous Observations From the Arctic Canada Basin

Abstract

Interaction between mesoscale eddies and near-inertial internal waves can contribute to enhanced turbulence mixing but quantitative knowledge from in situ observations is still lacking. This study reveals how eddy/near-inertial wave interactions (ENIs) can affect the variability of turbulent mixing in the ice-covered Canada Basin of the Arctic Ocean. We use data from five Ice-Tethered Profiler with Velocity (ITP-V) systems that autonomously obtained vertical profiles of horizontal velocity as well as temperature and salinity, which enabled quantification of ENI-caused turbulent mixing using a fine-scale parameterization. From the ITP-V observations in 2013–2015, 67 anticyclones were detected, of which 90% had a deep core at 150–250 m depth. The remaining eddies had a shallow core, typically embedded in the Pacific Summer Water (PSW). Just over one third of the eddies showed evidence of ENI with enhanced near-inertial internal wave amplitude (NIW) near the eddy cores. For these ENI cases, the parameterized turbulence dissipation rate was O (10−10–10−8 W kg−1), the larger estimates being several orders of magnitude greater than the background level. For the deep eddies, the ENI process can largely be accounted for by the classical theory, NIWs are trapped inside the negative relative vorticity core of anticyclones. For one shallow eddy, the NIW signal was greatest below the core. We postulate that a vertically elongated system of NIWs cannot be constrained vertically within such small-cored eddies. It is also interpreted that the wave enhancement below the core was supported by the isopycnal slope near the PSW through its geostrophic shear.