Lead supervisor: Nicholas Tosca, Earth Sciences
Co-supervisor: Justin Strauss, Dartmouth College
Brief summary:
This project will use cutting-edge analytical and experimental techniques to test a central hypothesis related to the evolution of life on Earth.
Importance of the area of research concerned:
As an essential nutrient for all life on Earth, changes in the availability of seawater phosphate over geological timescales are thought to have regulated biospheric productivity and ecosystem structure. For example, increases in marine phosphate availability in the Neoproterozoic Era (1,000–538 million years ago), inferred from the total concentration of P in mudstones, are thought to have driven the emergence of eukaryotic algae. However, the causes are not well understood because the concentration of P in mudstones is difficult to relate to seawater phosphate concentrations. This project will apply new analytical methods to probe the distribution and mineral hosts of phosphate in shallow water carbonate rocks and in mudstones, which together provides valuable new constraints on ancient seawater phosphate concentrations. These new data will re-shape our understanding of biological diversification and nutrient availability through a critical interval in Earth's history.
Project summary :
This project will focus on one question: how much P was available in ancient seawater? One aspect of the project will focus on acquiring well preserved carbonate samples from Canada, Svalbard, and Australia and employing a range of advanced characterisation techniques to constrain the distribution and speciation of P in carbonate rocks. These techniques will also be applied, for the first time, to siliciclastic rocks. An additional aspect will address key processes that modulated P concentrations in ancient sediments through geochemical experimentation and theory. The results will be explored through a range of biogeochemical modelling techniques.
What will the student do?:
The project includes three components, which can each be emphasised to different degrees according to the student's preference for the type of work involved: (1) undertake field work to study and sample well-preserved Proterozoic carbonate successions; (2) undertake analytical work to characterise P in ancient sedimentary rocks. This will include, bulk mineralogical and geochemical analysis, solid state NMR spectroscopy, synchrotron-hosted micro-XRF and XANES, and SEM-EDS; (3) design and implement key geochemical experiments and models to fill in key knowledge gaps regarding how P is cycled in carbonate depositional environments and in anoxic siliciclastic settings.
References - references should provide further reading about the project:
Syverson, D. D. et al. Nutrient Supply to Planetary Biospheres From Anoxic Weathering of Mafic Oceanic Crust. (2021) Geophys Res Lett 48.
Roest-Ellis, S., Richardson, J. A., Phillips, B. L., Mehra, A., Webb, S. M., Cohen, P. A., Strauss, J.V., Tosca, N.J. (2023). Tonian Carbonates Record Phosphate-Rich Shallow Seas. Geochemistry, Geophysics, Geosystems, 24(5). https://doi.org/10.1029/2023gc010974
Crockford, P., & Halevy, I. (2022). Questioning the Paradigm of a Phosphate-Limited Archean Biosphere. Geophysical Research Letters, 49(17). https://doi.org/10.1029/2022gl099818
Applying
You can find out about applying for this project on the Department of Earth Sciences page.