Continental weathering and secular evolution of redox-sensitive isotope systematics

Project Background
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. The student 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.

Candidate Requirements
This project would suit a candidate interested in understanding Earth System Science, past climate and isotope geochemistry.

Training
The student will receive thorough training in isotope geochemistry and modelling by Andersen and Millet. This includes that the student 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, the student will have access to the DTP training courses, as well as a range of Cardiff University Student Development courses, to maximise transferable skills. The student is also expected to present project results to national and international conferences. Finally, the student will have the opportunity to demonstrate both in the classroom and in the field.
Combined, the training package of the project will give the student an excellent basis for the rest of their career.