Hydrodynamics of pollutant and organic carbon settling: implications for dispersal and concentration in oceans

Understanding the transport, deposition, and burial processes of anthropogenic pollutants (e.g. micro– and nanoplastics), and organic carbon, are major challenges to predicting marine pollution hotspots and quantifying blue carbon stocks. Burial of particulate terrestrial organic carbon in marine sediments removes CO2 from the atmosphere, which helps to regulating climate over geologic time scales. Spatial and temporal variability in deposition means that quantification of these blue carbon stocks remain highly uncertain. Burial efficiency of organic carbon depends on the exposure time to oxygen, which is tied to suspension settling rates that remain poorly constrained. Similarly, the hydrodynamics and settling rates of microplastic particles, which range in shape and composition, have not been studied. Sea surface accumulations of plastics account for ~1% of the estimated global marine plastic budget, and the remaining 99% ends up in the deep seafloor. Much of this material occurs as microplastics: small (<1 mm) fragments and fibres, yet the distribution of these particles in the marine environment is poorly understood.

Therefore, there is an urgent need to understand how organic carbon and pollutants are dispersed and sequestered in the open marine environment. Advances in understanding of their hydrodynamic behaviour have the scope to inform the development of models that aim to forecast the dispersal and storage of these particles. Because very little is known about the settling of microplastics and other low density particles with complex morphologies, such as clay flocs and organic carbon particles, the student will design novel physical experiments using state-of-the-art settling tanks and particle imaging velocimetry (PIV) equipment in the Sorby Lab Suite. An existing measurement system that has been developed to measure the dynamics of falling ice particles will be adapted. The Sorby Lab Suite has a unique capability to measure these particle dynamics using an existing proven experiment system. The physical experiments will be used to inform and develop direct numerical simulation (DNSexperimentsin which the Navier–Stokes equations are numerically solved without any turbulence model, to investigate dispersal patterns over longer timescales and greater spatial scales.