Project Rationale Marine phytoplankton, support almost all oceanic ecosystems. The dynamics of plankton populations are therefore a key component of the global carbon cycle. Simple models of infection coupled to ecology  have highlighted the potentially important role of virus infection of oceanic phytoplankton in the cycling of nutrients and carbon. Since virus-triggered death and rupture of phytoplankton retains organic carbon in surface waters, it may decrease the amount of atmospheric carbon that is sequestered in the deep ocean by the ‘biological pump’, of which the flux of sinking phytoplankton cells is a key component. The global significance of viruses in the carbon cycle can only be understood through oceanic ecosystem models that account for this “viral loop”, which requires the integration of eco-epidemiological models of phytoplankton with large-scale ocean general circulation and biogeochemical models. Such understanding is necessary to assess how viruses may influence predictions of the carbon cycle and to inform future climate change scenarios [2,3]. This project presents an excellent opportunity for students with a mathematical background that are interested in moving into Environmental Sciences; as well as to students from Biological, Earth or Chemical Sciences interested in learning mathematical and computational modelling.
Methodology The methodology combines the use of theoretical biology with mathematical and computational modelling, in order to address questions on the marine biogeochemical carbon cycle. The student will be encouraged to develop their own ideas but the methods and aims of the PhD studentship are:
1. Review extant population biology models of viral infection of phytoplankton, and select the model best aligned for use with global-scale marine biogeochemistry models. This may require modifying the theoretical structure, equations and parameter values of the selected model for the context of biogeochemical modelling. Simple modelling techniques will be used to achieve this, and to perform a preliminary assessment of the impact of virus on plankton ecology, including the biological pump. 2. Integrate the resulting coupled virus-biogeochemistry model within a global circulation model using the state-of-art Transport Matrix framework. This allows fast, computationally-efficient simulations using an offline ocean circulation model, and facilitates the tuning of this new model. This activity may require changes to the underlying biogeochemical model code. 3. Use this modified global biogeochemical model to investigate the effect that the viral loop has on carbon export fluxes to the deep ocean, using use of results from the original reference model for comparison.
Training The INSPIRE DTP programme provides comprehensive personal and professional development training alongside extensive opportunities for students to expand their multi-disciplinary outlook through interactions with a wide network of academic, research and industrial/policy partners. The student will be registered at the University of Southampton and hosted at the National Oceanography Centre. Specific training will include: use of HPC facilities at the NOC; use of global circulation and biogeochemical models; use of the Transport Matrix framework; epidemiological modelling; biological-chemical-physical interactions; computer model coding and analysis.
Please check https://inspire-dtp.ac.uk/how-apply for details.
 C.J. Rhodes and A.P. Martin. The influence of viral infection on a plankton ecosystem undergoing nutrient enrichment. Journal of Theoretical Biology, 265(3):225-237, 2010.  Lionel Guidi et al. Plankton networks driving carbon export in the oligotrophic ocean. Nature, 532:465-470, 2016.  M. Middelboe and C.P.D. Brussaard. Marine viruses: Key players in marine ecosystems. Viruses, 9(10):302, 2017
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