Supervisor: Ed Tipper (Earth Sciences)
Importance of the area of research:
Chemical weathering regulates Earth’s carbon cycle and hence global climate over geological timescales. Ca and Mg from silicate minerals are released to the solute phase during chemical weathering. This solute Ca and Mg subsequently gets buried as Ca and Mg carbonates in ocean basins transferring carbon from the atmosphere to the carbonate rock reservoir. This simple reaction is thought to provide the climatic feedback that has maintained Earth’s climate equable over geological history. Quantitative models of silicate weathering processes coupled to estimates of carbon fluxes associated with silicate weathering are therefore fundamental to understanding Earth’s carbon cycle, and the feedbacks between the carbon cycle, climate and chemical weathering. Stable isotope ratios of elements such as Li, Mg and Si are making a major contribution to our understanding. Rivers such as the Ganges, Mekong and Red River are carbon hot-spots, transferring more carbon than many other areas of the world making them key locations to quantify weathering processes.
Stable isotope ratios like 26Mg/24Mg, 30Si/28Si and 7Li/6Li have emerged as promising tools to quantify chemical weathering on the continents. Large rivers provide a key source of solutes to the oceans and understanding their composition has implications for ocean chemistry. Major advances have been made by working at the large river basin scale. Recent developments have used coupled measurements of water and sediment to constrain the timing and location of weathering. This project will focus on a series of large river basins in SE Asia such as the Ganges, Irrawaddy, Salween Mekong and Red River, working on both our archive samples and conducting dedicated fieldwork.
What the student will do:
The project will involve significant amounts of both lab and field work. The student will be trained in the methods of the stable isotope ratio measurement by state-of-the-art MC-ICP-MS and in the chemical preparation methods that are pre-requisite to this. The student will begin by measuring samples on our archive water and sediment sample collection, where we have an extensive collection of samples from the rivers of SE Asia. In the first summer of the project there will be an expedition to one of the major river systems to collect a dedicated sample suite to include both water and sediment.
Key questions are:
1) What controls the stable isotopic compositions of large river systems?
2) Where does the weathering take place?
3) When does the weathering take place?
4) What is the link between the composition of the river water and suspended sediment
Tipper, E.T., et al., Positive correlation between Li and Mg isotope ratios in the river waters of the Mackenzie Basin challenges the interpretation of apparent isotopic fractionation during weathering. EPSL 333-334, 35-40 (2012)
Dellinger, M., et al., Lithium isotopes in large rivers reveal the cannibalistic nature of modern continental weathering and erosion. EPSL, 401, 359-372 (2014)
Tipper, E.T., et al., The Mg isotope budget of the modern ocean: Constraints from riverine Mg isotope ratios. EPSL 250, 241-253 (2006).
Other projects involving the supervisor(s) listed can be viewed here: