- Laboratory for Global Marine and Atmospheric Chemistry
- School of Environmental Sciences
- University of East Anglia
- Norwich
- NR4 7TJ
- UK
Nicholas Stephens
Current Research
The Dynamic Green Ocean Model that is being developed, provides the ability to simulate ocean carbon cycling in terms of a physical (OPA) model. Although rapidly advancing the models being developed here, and as part of other research efforts are still relatively primitive. Often the all important biologically mediated feedback cycles are poorly understood and inadequately represented. In conjunction with other studies designed to better understand and implement the more important ocean processes, this study concentrates on the interaction of the nitrogen cycle on potential feedback regulation of the the nitrogen biogeochemistry on sources and sinks of carbon as exerted through marine based biology.
The current version of the model describes the main sources and sinks of nitrogen metabolism in the marine ocean with an enthuses on accounting for the processes of nitrogen fixation in the open ocean. Presently a model that can account for nitrogen fixation as represented by a functional planktonic type (PFT) should provide the ability to better describe fluxes of nitrogen and carbon, and provide a better understanding of the feedback processes exerted through diazotrophic (N2-fixing) growth. In developing the model components to describe N2 fixation in a marine ecosystem, the aim is also to better represent and understand the other fundamental nitrogen assimilatory/ dis-assimilatory processes such as denitrification and the relationship to the availability of other growth limiting nutrients like phosphorus and iron.
Research Activities
1) Presently a model is being developed based upon the first release PlankTOM5.0 code. This includes additional tracers, processes and a new PFT to describe N2 fixation. For more information concerning the models being developed by myself please read the more detailed descriptions on the other pages, or the modelling activities of other members of the group try the new Green Ocean Project Website.
http://lgmacweb.env.uea.ac.uk/green_ocean/jobs.shtml
2) Physiological models to describe the growth of Trichodesmium spp.in terms of nitrogen and carbon assimilaion. This includes the development of models to describe the interrelationships between the assimilation of differnt nitrogen sources in a generic cell type. This idea is taken further to describe the diazocytic conditions in terms of nitrogen and carbon metabolism in a bundle sheath.
3) Following the processing of filtered samples to determine cellular quota (N:C) in Gloeothece and in particular the relationship to some of the photosynthetic parameters have led to some interesting results. It is now possible to update the original studies modelling the interrealtionsships between the different nitrogen assimilatory pathways following some parameterisation experiments. The results themselves reinforce the idea that it is the assimilatory (post-transport reactions) rather than the transport processes that have greater significance with respect to developing physiology models.
4) The evaluation and validation of biogeochemical models. These are ongoing discussions and collaborations within the group and through the AMEMR workshop in February 2007.
5) More comprehensive representations of the marine nitrogen cycle and implications over differing timescales.
6) The influence of dust and aerosol on marine biogeochemistry.
Other interests include the immuno-labelling and fluorescent labelling of nitrogenase, and the cellular rythmns and metabolism of diazotrophic cells. This is additional research that is in various stages of discussion and preparation.