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Cambridge NERC Doctoral Training Partnerships

Graduate Research Opportunities
 
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) and Nd isotopes have been used to understand Earth processes including ocean circulation, marine chemical cycling, continental weathering, and continental crust formation. They have primarily been used as a marine tracer of lithologic source and therefore many studies have focused on the liberation of REE during the weathering of crystalline rocks. However a substantial portion of REE in sediments and sedimentary rocks resides within authigenic and biogenic marine phases. The incorporation of REE into these authigenic and biogenic phases is poorly understood but is likely controlled in part by scavenging from seawater, while the post-depositional stability of these phases is linked to chemical weathering, water-rock interaction, and redox changes. Chemical weathering through geological time is likely to have implications for past changes in climate, ocean nutrient availability, and igneous processes and compositions. This PhD will focus on the fundamental processes which control water-sediment exchange of REE, and examine the implication for its long term cycling, oceanic budgets, and the interpretation of climate records.
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 sedimentary reservoirs of REE compositions and 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?: 
The student will begin by making laboratory experiments to examine scavenging and release of REE onto marine sediments and its dependence on grain size, mineralogy, particle surface chemistry, and water compositions. 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. Combined literature data and new elemental and isotopic data will form the basis for the development of models of the geochemistry of sedimentary reservoirs through geological time, with possible implications for weathering, redox, and continental crust evolution through geological time.
References - references should provide further reading about the project: 
Hindshaw, R.S., Tosca, N.J., Piotrowski, A.M., and Tipper, E.T., (2018) Clay mineralogy, strontium and neodymium isotope ratios in the sediments of two High Arctic catchments (Svalbard). Earth Surface Dynamics 6, 1, 141-161, DOI: 10.5194/esurf-6-141-2018.
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.
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
Applying
You can find out about applying for this project on the Department of Earth Sciences page.
Dr Edward Thomas Tipper
Dr Oliver Shorttle
Department of Earth Sciences Graduate Administrator
Dr Alex Piotrowski