Lead supervisor: Oliver Shorttle, Earth Sciences
Co-supervisor: John Maclennan, Earth Sciences; Marie Edmonds, Earth Sciences; Ery Hughes, Volcanology Team, Te Pū Ao | GNS Science, Aotearoa New Zealand
Brief summary:
This project will provide novel constraints on volcanism’s most important environmental forcing: its carbon flux to the atmosphere.
Importance of the area of research concerned:
Earth’s environmental history is a story of carbon regulation, whereby feedbacks in the fluxes of carbon between atmospheric and rock reservoirs have sustained a habitable planet for over 4 billion years. At the heart of the terrestrial carbon cycle is volcanic degassing of mantle carbon, which acts as a long-term forcing on Earth’s climate. However, the amount of carbon released by volcanism remains uncertain, in part due to the very property that makes carbon such an important element: its tendency to enter the gas phase. This means that basalts, our best tool for interrogating mantle chemistry, have frequently lost their primary CO2 before we can measure it. This work will therefore focus on deciphering the degassing history of basalts in order to constrain their initial carbon concentrations and hence the carbon flux from volcanoes.
Project summary :
How reliable are crystal archives as recorders of magma carbon content? There are significant limitations to the most ubiquitous approaches of estimating the carbon content of primary magmas. Seawater noble gas contents provide a bulk estimate of upper mantle carbon, and its flux, but cannot easily resolve the mantle sources contributing to it. In contrast carbon/trace-element ratios in melt inclusions can resolve heterogeneous mantle sources, but their carbon contents are frequently lowered by CO2 degassing. The aim of this project is to provide new constraints on the flux of carbon from Earth’s mantle by employing novel analytical tools to trace degassing, and by targeting key sample localities in Iceland.
What will the student do?:
This project will involve field work, geochemical micro-analysis, and modelling. Melt inclusions from key localities will be investigated for their volatile, trace element and carbon isotope composition: Icelandic eruptions will be targeted because of their extreme geochemical variability and associated elevated CO2 contents. The student will undertake fieldwork in Iceland to collect new material for analysis and draw on existing well-characterized collections. Sample will be characterised at Cambridge's state-of-the-art micro-analytical suite, using scanning electron microscopy, electron microprobe and Raman spectroscopy. Trace elements and carbon analysis of melt inclusions will be measured at the NERC ion probe facility. Models of carbon degassing will be developed and applied to each eruption to estimate its pre-degassed carbon content.
References - references should provide further reading about the project:
Matthews, S., Shorttle, O., Rudge, J.F. & Maclennan, J. 2017. Constraining mantle carbon: CO2-trace element systematics in basalts and the roles of magma mixing and degassing. Earth and Planetary Science Letters, vol. 480, pp.1-14. doi:10.1016/j.epsl.2017.09.047
Marty, B., 2012. The origins and concentrations of water, carbon, nitrogen and noble gases on Earth. Earth and Planetary Science Letters, vol.313-314, pp.56-66. doi:10.1016/j.epsl.2011.10.040
Miller, W.G.R., Maclennan, J., Shorttle, O., Gaetani, G., Le Roux V., & Klein, F.. 2019. Estimating the carbon content of the deep mantle with Icelandic melt inclusions. Earth and Planetary Science Letters, vol. 523. doi:10.1016/j.epsl.2019.07.002
Applying
You can find out about applying for this project on the Department of Earth Sciences page.