Lead supervisor: John Taylor, DAMTP
Co-supervisor: Ali Mashayek, Earth Sciences; Adrian Martin, NOC Southampton
Brief summary:
This project will use high resolution numerical simulations to explore the physical processes that contribute to the formation and sinking of marine snow particles in the surface ocean.
Importance of the area of research concerned:
The ocean plays a very important role in the global carbon cycle. About half of the global primary production is performed by microscopic marine algae called phytoplankton. Some of the organic matter that is produced by phytoplankton aggregates into clusters called marine snow, which then sink into the ocean interior. The resulting flux of carbon out of the surface ocean represents a significant long-term sink in the global carbon cycle.
Ocean currents have a significant impact on phytoplankton and slowly drifting marine snow. In particular, recent studies have found that swirling eddies with scales between 1-10km, known as the submesoscale (see image), have strong vertical circulations and rapidly transport particles out of the surface ocean (e.g. Omand et al. 2015, Taylor et al. 2020). Despite this progress, the influence of submesoscale eddies on the formation of marine snow aggregates is unknown. Climate models cannot resolve the small-scale physics responsible for marine snow formation and missing knowledge about the processes involved contributes to uncertainty in the effectiveness of the biological pump in a changing climate.
Project summary :
The objective of this project, joint between the University of Cambridge and the National Oceanograpy Centre, will be to explore the influence of submesoscale (1-10km) dynamics on the formation and transport of marine snow aggregates. Submesoscales cause buoyant material to accumulate (e.g. microplastics and buoyant phytoplankton cells), while also energizing small-scale turbulence. Both factors are expected to enhance collision rates between organic particles, thereby enhancing the formation rate of marine snow particles. This project will test this hypothesis using high resolution simulations that resolve submesoscale eddies and small-scale turbulent motions. The project will provide important new insights into the formation mechanisms of marine snow particles and will ultimately inform improved parameterizations of particle formation and carbon export in global climate models.
What will the student do?:
This work will use OceanBioME.jl (https://github.com/OceanBioME/OceanBioME.jl), a software package recently developed by the Ocean Dynamics group at the University of Cambridge. Importantly for this project, OceanBioME includes particle-based biogeochemical models to interact with the flow physics. In this project the student will use OceanBioME to simulate the movement of individual marine snow particles in a flow with active submesoscales and 3D turbulence. The particle formation rate will be modeled using data reported in Takeuchi et al., 2019.
The student will conduct a series of numerical experiments by varying parameters governing the physics and biogeochemistry and will use the output to diagnose the functional dependence of the marine snow aggregation and export rates on these parameters. The model results will be tested using available field data (e.g particle backscatter measurements from ocean gliders). The results will then be used to inform new parameterizations for marine snow in global climate models.
References - references should provide further reading about the project:
Omand, M.M., D’Asaro, E.A., Lee, C.M., Perry, M.J., Briggs, N., Cetinić, I. and Mahadevan, A., 2015. Eddy-driven subduction exports particulate organic carbon from the spring bloom. Science, 348(6231), pp.222-225.
Takeuchi, M., Doubell, M.J., Jackson, G.A., Yukawa, M., Sagara, Y. and Yamazaki, H., 2019. Turbulence mediates marine aggregate formation and destruction in the upper ocean. Scientific Reports, 9(1), p.16280.
Taylor, J.R., Smith, K.M. and Vreugdenhil, C.A., 2020. The influence of submesoscales and vertical mixing on the export of sinking tracers in large-eddy simulations. Journal of Physical Oceanography, 50(5), pp.1319-1339.
Applying
You can find out about applying for this project on the Department of Applied Mathematics and Theoretical Physics (DAMTP) page.