Picture: Breaking wave. Credit: Todd Turner (Unsplash).

Internal waves are everywhere in the oceans. Like waves on the surface of the ocean that break on the beach, internal waves travel in the ocean interior, sometimes propagating great distances. As they propagate, they interact with other waves and with the average flow (ocean currents, fronts, and eddies) until they dissipate or break.

Most of the energy of internal waves dissipates as ocean turbulent mixing but a fraction is exchanged with the mean surrounding flow while the travel. Importantly, internal waves provide a link between large-scale forcing (wind and tides) and small-scale dissipation (turbulent mixing). The transport of momentum and energy by internal waves within the ocean is a key process in the meridional overturning circulation.

Major gaps exist in our understanding of the pathways between the generation and the breaking of internal waves in the Southern Ocean. This has important implications for the distribution of internal wave-driven turbulent mixing, for the sensitivity of ocean mixing rates, and for the representation of ocean mixing in numerical models. The documentation of internal waves pathways and life cycles is limited. Indeed, direct observations and sampling of the spatially inhomogeneous and temporally intermittent internal wave in four dimensions is very complex.

To address the questions around internal wave-driven mixing and energy pathways, we used observations of internal waves from a turbulent mixing hotspot in the Southern Ocean. With these observations, we identified and characterised both internal wave and the background environment. Our work shows that the Antarctic Circumpolar Current strongly influences the life cycle of internal waves. This strong current advects internal waves, modifies the wave characteristics through wave-mean flow interactions, and sets-up critical layers for the waves. Our findings suggest that it is important to represent mesoscale flow impacts when parameterizing internal wave-driven mixing in the Southern Ocean.

  • Paper: Waterman, S., Meyer, A., Polzin, K. L., Naveira Garabato, A. C., & Sheen, K. L. (2021). Antarctic circumpolar current impacts on internal wave life cycles. Geophysical Research Letters, 48, e2020GL089471. https://doi. org/10.1029/2020GL089471