| 18 Nov 2025
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.
In this manuscript, the authors discuss the impact of waves on mixing in conditions representative of the sea ice, where leads are present. I think this is an interesting work that falls well within the scope of TC and that, with a few minor updates, it should be suitable for publication.
- One point was not completely clear for me regarding the model setup: is the ice fixed, or moving? If it is fixed, then I suppose this means that effects such as the relative motion of ice floes and the associated "pumping" effect is missing (see for example https://doi.org/10.1029/2018JC014500 , https://doi.org/10.1063/5.0088953 )? This can typically generate quite a lot of mixing / eddies in particular when the floes and openings are quite small relative to the incoming wavelength? I think this could be made clearer and discussed, including discussing both i) can some additional mechanisms be present in the real world, ii) which regimes (wavelength to lead width / floe size for example) exist for which these would play a role.
- It is interesting that you choose to keep the Coriolis force - given the spatial and temporal scales that are considered here, does it really play a role, or is it present just as a "carry over" from the base model used?
- If I understand correctly, you only look at one particular case of relative wind and wave direction - basically wind and waves propagating alongside the lead. Is this understanding correct? I think it is only named "in passing" in a sentence in 2.1. Actually, I think this is a quite "strong" / "limiting" hypothesis - I do not see a reason a priori for the wind and waves to propagate alongside the leads, and results may look quite different if wind and waves propagate for example perpendicular to the leads, or at an angle with each other. Of course, doing LES for a wide range of relative wind and waves orientation with respect to the leads may be too much work for a single paper, so it is fine to pick up a specific case as you do here - but this should be made very clear, and highlighted / discussed more in my opinion.
- I am used to LES in aerodynamics as a way to model (without resolving them) the smallest scales (for example mm / sub-mm scales) but resolving the larger eddies. I am less familiar with LES in ocean sciences, so my understanding may be a bit off. Still, I am surprised that one can "just" pick up such a large mesh size (1x1x0.5 m3). I think you may need to discuss more why / if the LES grid size / resolution is adequate (in particular, what are the smallest scales expected, what is the LES cutoff, and is it appropriate). If I understand correctly, this should be validated by comparing the different scales in the turbulent cascades, and determining what needs to be resolved vs. what can be modeled.
- Fig. 3 may be a bit confusing - each arrow should have a clear reason for being here, at present it seems like there are "many, decorating" arrows. Consider taking an iteration through the figures to make sure all elements are necessary / meaningful / explained.
- If one trusts the simulations and the fact that the LES is properly applied and models an appropriate range of scales, then the results should be also trustworthy and the discussion / analysis parts which use quite standard analysis techniques, hence, should be generally robust. Therefore, I have no major comments on the results per se, and these seem anyways quite well aligned with what one would expect a priori.