PhD opportunity: Constraining marine carbon fluxes and their effect on atmospheric CO2

Dept/School: Cardiff School of Earth and Ocean Sciences, Cardiff University
Project Supervisor(s): Dr S Barker, Dr A Ridgwell
Application Deadline: 30 June 2010

Ocean Acidification (OA) is a major concern for modern society. However, it is clear from the geological record that the Earth’s oceans have witnessed many episodes of acidification (or the reverse) in the past. Some of these have been caused by external perturbations to the climate system (for example the massive injection of carbon during the Palaeocene-Eocene Thermal Maximum ~55Ma) while others were driven by internal physical and / or biogeochemical processes, such as the well-known glacial-interglacial cycles of atmospheric CO2. There is an array of uncertainties surrounding the processes involved in OA. This project is concerned with the interplay between two of the most important of these.

The ‘biological pump’ describes the transport of organic carbon from the surface to deep ocean. An increase in the strength of this pump will cause a decrease in atmospheric CO2. The inorganic pump describes the transport of biogenic carbonate to the deep sea. Production of CaCO3 by plankton in the surface ocean causes a reduction in dissolved inorganic carbon (DIC) but also in Total Alkalinity (TA). The resultant decrease in the ratio of TA / DIC actually causes an increase in CO2 thus a strengthening of the inorganic pump would cause atmospheric CO2 to rise. Knowledge of how these processes have and will respond and interact with OA is of obvious importance. Furthermore there is growing evidence that they are not independent.

Ballasting is the term given to the capacity of various mineral phases to literally provide ballast for the sinking of organic matter to the deep sea. Various studies have documented the association of organic carbon transport to the vertical flux of carbonate shells (i.e. a direct link between the organic and inorganic pumps). However the precise quantitative relationships between the various phases involved are poorly constrained. This project aims to improve our knowledge of the precise relationships between potential ballasting minerals and organic carbon fluxes and to use this information to inform state-of-the-art climate models in their implementation of this potentially important parameter.

Initially the student will use the most up-to-date database of global sediment trap results to investigate and quantify the relationships between vertical fluxes of the major phases sinking to the deep sea. Following this the student will use their results to investigate their implications for the global carbon cycle. The student will investigate changes both in the past and those predicted for the future using Earth system models of intermediate complexity. By choosing examples from the past, the student will be able to assess the quantitative relationships they have determined. They will then have some confidence in the incorporation of their parameterisations in model simulations used to assess the future consequences of OA.

Full training in various data-based and computer modelling techniques will be provided, including attending an ocean acidification modelling workshop held at Bristol that will provide a practical background in configuring and analyzing experiments surrounding climate change and ocean circulation in an Earth system model (‘GENIE’).

Funding Notes
This fully-funded project forms part of a major new study (led by Bristol University) to investigate the future effects of ocean acidification, as part of the new national OA Programme sponsored by NERC and DEFRA. As well as being part of the vibrant UK OA research community, the successful candidate will be entrained into the EU OA project (‘EPOCA’) and have access to its training workshops and meetings. There will also be opportunities for presenting results at international conferences and the successful candidate will be encouraged to apply for relevant workshops and summer-schools (e.g., SOLAS).

Archer, D. & Maier-Reimer, E. Effect of deep-sea sedimentary calcite preservation on atmospheric CO2 concentration. Nature 367, 260-263 (1994).
Barker, S., Higgins, J. A. & Elderfield, H. The future of the carbon cycle: review, calcification response, ballast and feedback on atmospheric CO2. Philos. Trans. R. Soc. Lond. Ser. A-Math. Phys. Eng. Sci. 361, 1977-1999, DOI: 10.1098/rsta.2003.1238 (2003).
Klaas, C. & Archer, D. Association of sinking organic matter with various types of mineral ballast in the deep sea: implications for the rain ratio. Glob. Biogeochem. Cycle 16 (4), 63-1 – 63-14 (doi :10.1029/2001GB001765) (2002).
Ridgwell, A. et al. Marine geochemical data assimilation in an efficient Earth System Model of global biogeochemical cycling. Biogeosciences 4, 87-104 (2007).
Ridgwell, A., Zondervan, I., Hargreaves, J. C., Bijma, J. & Lenton, T. M. Assessing the potential long-term increase of oceanic fossil fuel CO2 uptake due to CO2-calcification feedback. Biogeosciences 4, 481-492 (2007).

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