Triple oxygen isotope geochemistry and the evolution of the atmosphere
Atmospheric oxygen is fundamental to life as we know it, but its concentration has changed dramatically over Earth’s 4.5 billion year history. An amazing qualitative story has emerged, in which Earth’s atmosphere was devoid of free oxygen for the first 2 billion years of planetary history, with two significant increases in concentration at ~2.4 and ~0.55 billion years ago. Both oxygenation events were accompanied by extreme climatic effects – the “snowball earth” episodes – and paved the way for massive reorganization of biogeochemical cycles such as the Cambrian radiation of macroscopic life and oxygen’s subsequent regulation at levels amenable to macroscopic life. Despite these profound influences on the Earth system, we currently lack fundamental quantitative constraints on atmospheric oxygen levels over the past 2.4 billion years. This project, part of a broader 5 year program funded by the European Research Council, will develop new analytical methods to measure triple oxygen isotope geochemistry in key sedimentary samples and increase the database of measurements from which fundamental constraints can be derived.
Recent advances in Cavity Ringdown Spectroscopy have enabled the determination of 17-O excess in H2O to the astonishing precision of 10 parts per million. The fellow will develop classic methodology to induce isotope exchange between nitrate, sulfate, perchlorate and water, and quantify the 17-O excess via pre-post measurements on the H2O. This method Isotope Exchange – Cavity Ringdown Spectroscopy (IE-CRDS) should enable comparable or lower uncertainty than classic methods for samples with large 17-O excess, at a fraction of the cost and effort. Additional measurements, including interlab comparisons, will be carried out using the laser-ablation CO2-fluorination IRMS technique pioneered by project-partner Dr Huiming Bao in Louisiana, U.S.A.
The IE-CRDS methodology will be used in conjunction with IRMS to analyze 17-O excess in geological samples spanning post-GOE Earth history. The lab already has exciting samples from never-before-analyzed ~ 2.2 – 2.0 Ga evaporites obtained from fresh drill core in the Karelia province, Russia. To complement those, the fellow will conduct field work in northwest Namibia (Otavi province) and the southwest US (Pahrump Group, Death Valley) to obtain sulfate-related evaporitic samples spanning the Neoproterozoic (1.0 Ga – 543 Ma) record of Snowball Earth, the rise of animals, and the “second rise of oxygen”. Sampling campaigns to the western Alps/Apennines and the southwestern USA will enable collection of arid deposits of the Permo-Triassic periods (~300-200 Ma), spanning the largest extinction event in Earth history. Project partner Dr. Tony Prave has expert knowledge of these successions, and will help guide sampling strategies. We will make an additional field excursion to the ~ 2 million year old Atacama desert, Chile, to collect soil samples spanning a hyper-arid to arid rainfall gradient. These samples will provide a critical ground-truth needed to validate predictive oxygen isotope photochemical models, which will be developed concurrently by the research group.
We are looking to appoint a Postdoctoral Research Fellow with experience in field geology and isotope geochemistry. This is a 36 month, full time position, starting salary, £31,656 – £37,768 per annum, depending upon experience. For any enquiries about the project please contact Mark Claire (firstname.lastname@example.org). A start date is anticipated for January 1st, 2017, but is negotiable. Additional information on the project is available here: http://earthsci.st-andrews.ac.uk/study/project-2/
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To apply please see the posting on the University’s Job Vacancy site.
Interview Date: 14 November 2016
Closing Date: 24 October 2016
Please quote ref: AR1837SB
Further Particulars: AR1837SB FPs.pdf
School of Geography and Geosciences
Department of Earth and Environmental Sciences
Salary: £31,656 – £37,768 per annum
Start: January 2017 or as soon as possible thereafter
Fixed term for 3 years