Lead supervisor: Ed Tipper, Earth Sciences
Co-supervisor: Alex Piotrowski, Earth Sciences; Oliver Shorttle, Earth Sciences
Brief summary:
Constraining the Rare Earth Element (REE) geochemistry of seawater and sediments and how weathering, ocean chemistry, and climate changed their cycling on geological timescales
Importance of the area of research concerned:
Rare Earth Elements (REE) have a central role in reconstructing Earth system processes, from how the Earth first solidified from a molten ball, to tracing the modern supply of sediments to the oceans. REE’s are also now highly in demand as part of the green energy transition, making it critical that we understand their distribution and cycling through the Earth system. In investigating REE in Earth’s surface environment, many studies have focused on their mobilisation during the weathering of crystalline rocks. However, a substantial portion of REE in modern sediments and sedimentary rocks resides within secondary phases formed in aqueous environments at low tmperature. The incorporation of REE into these secondary phases is poorly understood but is likely controlled in part by scavenging from seawater. This project will place new constraints on the mobilisation of REE’s at Earth surface conditions, both to understand their modern cycling and to aid in their use as a proxy for past climate. The project will couple novel stable isotopic tracers that are sensitive to the formation of secondary phases to direct measurement of REE’s and their isotopes.
Project summary :
This project will explore how the REE budget and Nd isotopic composition of seawater and marine authigenic phases changed because of processes including scavenging, weathering, and sedimentary cycling. The student will make geochemical measurements to characterise the REE compositions of sedimentary reservoirs and the processes that have led to their variability through time, with a focus on understanding chemical weathering and water-rock exchange. New geochemical tools will be utilized to improve our understanding of these processes: low-temperature stable isotopic fractionation of magnesium and lithium offer the potential to constrain water-rock interaction at low temperatures. When applied alongside Nd isotopes, these tools will allow us to identify how weathering and other low temperature processes have affected the REE composition of sedimentary reservoirs over geological time.
What will the student do?:
Experiments: The student will develop a series of laboratory experiments to quantify the scavenging and release of REE (chemical equilibrium) onto marine sediments and its dependence on grain size, mineralogy, particle surface chemistry, and water compositions (pH and chemical composition). Chemical analysis on both fluids and particles will be conducted by ICP-MS/OES. Natural samples: The student will also use suspended sediments from the largest rivers in the world to characterize crustal composition. The student will also measure sedimentary rock compositions from older portions of the geological record, and examine its mineralogical and chemical heterogeneity and changes through time. Isotopic analysis of lithium, magnesium and Nd isotopes will determine a time integrated weathering history of crustal sediments. Data analysis and modelling: Combined literature data and new elemental and isotopic data will form the basis for the development of models (using the R or Python programming languages for example) of the geochemistry of sedimentary reservoirs through geological time, with implications for weathering, redox, and continental crust evolution through geological time
References - references should provide further reading about the project:
Hindshaw, R.S., et al, (2019) Experimental constraints on Li isotope fractionation during clay formation, Geochimica et Cosmochimica Acta, Vol. 250, pp. 219-237, https://doi.org/10.1016/j.gca.2019.02.015
Larkin, C.S., Piotrowski, A.M., Hindshaw, R.S., Bayon, G., Hilton, R.G., Baronas, J,, Dellinger, M., Wang, R., Tipper, E.T., (2021) Constraints on the source of reactive phases in sediment from a major Arctic river using neodymium isotopes. Earth and Planetary Science Letters 565, 116933. https://doi.org/10.1016/j.epsl.2021.116933
Hindshaw, R.S., Aciego, S.M., Piotrowski, A.M., and Tipper, E.T. (2018) Decoupling of dissolved and bedrock neodymium isotopes during sedimentary cycling. Geochemical Perspectives Letters, 8. pp. 43-46. ISSN 2410-3403 https://www.geochemicalperspectivesletters.org/article1828/
Applying
You can find out about applying for this project on the Department of Earth Sciences page.