Capturing Oceanic Submesoscales, Stirring, and Mixing with Sound and Simulations

The global oceans act as a sponge, soaking up significant amounts of the excess heat and carbon that have been added to the atmosphere due to human activity. Our oceans therefore play a key role in buffering the magnitude of climate change. However, the future storage capacity of the ocean sponge is uncertain, alongside the distribution of nutrients and oxygen, key ingredients for a healthy marine ecosystem. To address these uncertainties, we need to better understand how the oceans flow deep below the surface layers - in particular current flows that span scales of tens of metres to hundreds of kilometers, otherwise known as submesoscales. Submesoscale currents matter because they provide a pathway to harness energy from the winds and tides and use it to stir and mix different water masses around the globe, along with the heat, carbon and nutrients that they carry. Despite their importance, little is known about ocean submesoscales because of their intermediate size and intermittent nature. This means they are both difficult to capture in nature or model with computers.

In this project, my team will conduct a pioneering experiment that will capture for the first time the full range of current flows that exist beneath the surface ocean layers, alongside the mixing and stirring that they generate. A targeted sea-going programme using active acoustics will sample the ocean at unprecedented resolutions (two orders of magnitude better than other techniques) and fully capture submesoscale currents. Similar to how bats echo-locate, a ship at the surface releases sound pulses into the water and records reflections from water layers. Acoustic measurements will be combined for the first time with cutting-edge robotics, vessel-mounted and moored instrumentation. In parallel, state-of-the-art model simulations will be both validated and improved using our new ocean observation data. The result will be the most realistic representation of the sub-surface ocean to date. The simulations will be used to quantify submesoscale initiation, ubiquity and interactions, and assess their role in driving energy and property exchanges in the global ocean. The experiment will take place at a global hotspot of ocean activity: the Brazil-Malvinas Confluence off the coast of Argentina. Here sub-tropical waters from the Atlantic collide with polar waters from the Southern Ocean. Water mass exchanges at this confluence, which are likely driven by submesoscale currents, play a key role in the distribution of heat, salt, carbon and life sustaining nutrients and oxygen throughout the global oceans.

By revealing interior ocean dynamics in unparalleled detail at the Brazil-Malvinas Confluence, COSSMoSS will shed light on a significant missing piece of the scientific ocean puzzle helping us to better understand our future biosphere and climate.