TITLE: Production and remineralisation of Dissolved Organic Matter.

SUPERVISOR
Erik Buitenhuis
University of East Anglia (UEA)

PROJECT DESCRIPTION
The most recent climate models include representations of ecosystem processes, both on land and in the oceans. Ecosystem processes are now seen as vital to a better understanding of the various climate feedbacks. Here we propose to investigate the feedback between climate and the oceanic carbon cycle through the degradation of organic matter by bacteria. This work will be undertaken in the framework of the Dynamic Green Ocean Project, an international project aimed at developing a community model of ocean biogeochemistry for applications to Earth system problems.

The third PhD student will determine the cycling of dissolved organic matter and its dependence on nutrient ratios:
(a) determine the excretion rates and C:N:P:Fe ratios of phytoplankton produced DOM. These experiments will use samples of the N and P limited continuous cultures of the other two PhD projects and of the iron-light colimitation experiments of the post-doc. Since the projects are planned to only partially overlap in time, samples will be frozen until used.
(b) determine, together with the post-doc, the dependence of bacterial remineralisation and bacterial growth efficiency on the nutrient ratios of the POM and DOM. These experiments will measure preferential remineralisation over time, taking up to a year, to address the dependence on the nutrient ratios both from varying production ratios by phytoplankton and as the ratios change over the course of the experiment. Bacterial production will be measured by radiolabeled thymidine incorporation, POC and PON will be measured by CHN analysis, DOC and DON by HTC TOC analysis and P and Fe in POM and DOM by alkaline hydrolysis followed by nutrient analysis. The dependence of remineralisation rate and growth efficiency on the nutrient ratios of the POM and DOM has a big impact on the partitioning of carbon between export and re-entering the microbial loop, therefore quantifying this partitioning will provide an important constraint on biogeochemical models.
(c) synthesize ocean observations of DOM and POM concentration for C, N and P.
(d) perform sensitivity studies of the model within the range of experimentally determined vital rates and evaluate the results against the observations.

The Ph.D. student will gain experience in both experimental biological oceanography and modelling marine biogeochemistry and feedbacks with global climate change, and with the analysis of oceanographic observations for model validation. The student will work as part of a small but dynamic and highly international group and in collaboration with a worldwide network of marine ecologists and ocean modellers.

Funding: An ERC Starting grant application has been sent to the EU, applying for funding starting October 2009. In addition, candidates can apply for funding from the School of Environmental Sciences.

How to apply: If you are interested in this project, please contact Erik Buitenhuis. See also the extra guidance notes for PhD students.