How does stably-stratified shear-driven turbulence mix our oceans and estuaries?

Amongst its many harmful effects, global warming directly impacts ocean temperatures, causing an increase that disrupts worldwide circulation. This disruption is worrying, both in the short and long term, because the present circulation patterns perform vital functions to sustain Earth’s hospitable climate. To address this, advanced mathematical and computer models are used to predict climate evolution. The models, however, require improvement in understanding turbulent mixing in stably stratified shear flows, where different water currents with varying salinity or temperature interact chaotically.

To advance understanding, the project will follow a three-step approach. First, a reduced-scale laboratory model of these flows will be used, allowing precise control over variables such as flow geometry and density differences. Second, the laboratory findings will be interpreted through mathematical models of turbulent mixing to extrapolate results to real-scale ocean flows, leveraging “dimensional analysis” techniques similar to those used in engineering. Third, the predictions will be validated by comparing them to actual measurements from ships, addressing the challenges of sparse and expensive ocean data.

Additionally, the project will apply the three-step approach to a shorter-term issue: saltwater intrusion in estuaries. Rising sea levels, increased droughts, and extreme weather events are exacerbating saltwater encroachment in densely populated deltas, such as the Thames Basin in the UK. Therefore, the research aims to develop more accurate models of mixing in saltwater intrusions to help mitigate this pressing problem.