PhD opportunity: Assessing the effects of ocean acidification on carbon export in the marine realm

Dept/School: Cardiff School of Earth and Ocean Sciences, Cardiff University
PhD Supervisor(s): Dr S Barker, Dr A Ridgwell
Funding Availability: Funded PhD Project (European Students Only)
Application Deadline: 28 January 2011

Roughly 30% of the CO2 emitted through industrial processes is taken up by the worlds oceans. While this means that atmospheric CO2 levels are somewhat lower than they would have been otherwise, it is also causing a lowering of ocean pH (a phenomenon known as ocean acidification, OA). The export flux of organic carbon from the surface to deep ocean represents a critical component of the global carbon cycle by providing a means to drawdown CO2. However, this flux may be vulnerable to changes in the production and export of biogenic carbonate from the surface ocean, which itself may be susceptible to the effects of OA. This project aims to assess this mechanism and its potential role within the broader impacts of OA.

Initially the student will investigate and quantify the relationships between vertical fluxes of the major phases sinking to the deep sea (the so-called ballast effect). This will be achieved through statistical analysis of a range of mechanistic models for vertical particle transport. The results from this exercise will then be used to inform a range of climate models (including the GENIE Earth System model) in terms of their implementation of ballasting. The student will investigate the potential role of ballasting for changes in atmospheric CO2 in both the past (e.g. Glacial-Interglacial changes or the Palaeocene-Eocene Thermal Maximum) and the future (e.g. the IPCC emissions scenarios).

The candidate will be given training in the techniques related to the project (including the use and development of computer models). The supervisors have the requisite skills and expertise to provide this training.

Wider implications:
Central to trustworthy and robust predictions of future global marine impacts of Ocean Acidification (OA) is a ‘correct’ representation of the marine carbon cycle. Representations of organic and inorganic fluxes between the surface and deep ocean are a major source of uncertainty for the current generation of climate models used for predicting and understanding the complex interactions between atmospheric CO2 and the marine carbon cycle. This project will address these uncertainties directly and therefore provide an important step towards the improvement of climate models.

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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