Impact of Surface Waves on Mixing and Circulation in a Summertime Lead

Abstract. Surface waves are becoming more prevalent in the Arctic as sea ice cover reduces. Here we use 3D turbulence-resolving simulations to explore how surface waves affect upper ocean dynamics, and hence surface conditions, as they propagate along summertime leads (narrow regions of open ocean between melting sea-ice cover). We separate the ocean dynamics into turbulent motions which dominate vertical kinetic energy, and a mean cross-lead circulation which drives near-surface downwelling within the lead. Without waves, along-lead winds create weak mixing and an asymmetric circulation where a sinking plume within the lead is balanced by upwelling that extends under the ice to the right of the wind vector. The presence of waves enhances both mixing and circulation by localizing, strengthening and deepening the downwelling plume and turbulent vertical velocities, increasing vertical buoyancy fluxes, and creating an upwelling cell to the left of the wind which significantly alters surface conditions beneath the left lead edge. Waves also drive a sharp front and convection within the lead. Physically-based scalings are proposed for the mixing and circulation changes to capture the effects of various system parameters including lead width, which has a leading-order impact on both turbulence and circulation. The wave-driven changes to turbulence and circulation are present even for relatively weak (developing) waves, although the biggest changes are seen for strong (equilibrium) waves.