Continental weathering and secular evolution of redox-sensitive isotope systematics
This research project is in competition for funding with one or more projects available across the NERC GW4 Doctoral Training Partnership (DTP). Usually the projects which receive the best applicants will be awarded the funding. Find out more information about the DTP and how to apply.
Application deadline: 7 January 2019
Start date: October 2019
DTP research theme: Changing Planet
The weathering of continental crust is a major driver of Earth’s climate. It helps regulate atmospheric CO2 content as well as provides soluble ions to the oceans. Thus, the weathering cycle over time have played an important role for the evolution of ocean chemistry and life.
Understanding the secular evolution of the chemistry of upper continental crust and the release of elements from weathering can therefor provide critical information of the long-term biogeochemical evolution of the surface Earth. However, continental weathering processes were very different in the Earth’s deep past relative to present day due to lower levels of atmospheric oxygen, different crustal chemical composition and the absence of vegetation at the surface.
This project focusses on investigating secular evolution in continental weathering over Earth History using redox sensitive isotope systematics of uranium, molybdenum and chromium in terrestrial samples.
Project aims and methods
The aim is to establish the secular evolution in the geochemistry and isotope systematics of Mo, U and Cr in terrestrial metasediments and paleosoils from the Archean, through the Proterozoic and into the Phanerozoic. The outcome of these analyses will be:
- establish the secular evolution in the release of redox-sensitive elements from an oxygen-lean to and oxygen-rich atmosphere. This will constrain the Precambrian U, Mo and Cr biogeochemical cycling and give estimates on atmospheric oxygen-levels.
- estimate the Mo, U isotope budgets for the upper continental crust over time. This will provide the counterpart to the deep recycling of isotopically anomalous Mo and U into the mantle via subduction.
- derive estimates of the isotope composition of the inputs of Mo and U to the oceans across Earth History. This will improve the reconstruction of global ocean anoxia from these redox-sensitive redox proxies.
The samples consist of a range of terrestrial detrital siliciclastic sediments and paleosols over Earth History. You will characterise samples and elemental concentrations as well as uranium, molybdenum and lead isotopes. Analytical work will be carried out in the newly set up Cardiff Earth Laboratory for Trace Element and Isotope Chemistry (CELTIC) at Cardiff University and Bristol Isotope Group.
This project would suit a candidate interested in understanding Earth System Science, past climate and isotope geochemistry.
You will receive thorough training in isotope geochemistry and modelling by Dr Andersen and Dr Millet. This includes that you will be trained in cutting-edge analytical techniques in the newly installed geochemistry analytical facilities at Cardiff University. Complementary analyses will be conducted at the Bristol Isotope Group.
In addition to project-specific training, you will have access to the DTP training courses, as well as a range of Cardiff University Student Development courses, to maximise transferable skills. You are also expected to present project results to national and international conferences. Finally, you will have the opportunity to demonstrate both in the classroom and in the field.
Combined, the training package of the project will give you an excellent basis for the rest of their career.
References and background reading list
- Andersen, M.B., Elliott, T., Freymuth, H., Sims, K.W., Niu, Y. and Kelley, K.A., 2015. The terrestrial uranium isotope cycle. Nature, 517, p.356.
- Andersen, M.B., Vance, D., Morford, J.L., Bura-Nakić, E., Breitenbach, S.F. and Och, L., 2016. Closing in on the marine 238U/235U budget. Chemical Geology, 420,11-22.
- Archer C, Vance D., 2008. The isotopic signature of the global riverine molybdenum flux and anoxia in the ancient oceans. Nature Geoscience.1,597.
- Frei, R., Gaucher, C., Poulton, S.W., Canfield, D.E., 2009. Fluctuations in Precambrian atmospheric oxygenation recorded by chromium isotopes. Nature 461, 250-253.
- McLennan, S.M. and Taylor, S.R., 1980. Th and U in sedimentary rocks: crustal evolution and sedimentary recycling. Nature, 285, 621.