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Cambridge NERC Doctoral Training Partnerships

Graduate Research Opportunities
Brief summary: 
An innovative and exciting project which will explore the relationship between long-term climate and mantle convection.
Importance of the area of research concerned: 
It is widely recognized that mantle convection generates vertical movements of the Earth's surface, which vary as a function of space and time throughout geologic history. Recent analysis of oceanic basins reveals that these transient movements have wavelengths of 1000s of kilometers and amplitudes of 100s of meters. This dynamic topography varies on timescales of 1-10 million years, which means that the shape and depth of oceanic basins change. From a climate and ocean science perspective, there is considerable interest in understanding why the carbonate compensation depth (CCD), which determines the depth at which the supply of carbonate from the surface is balanced by dissolution, varies since it is an important variable in carbon cycle models. During Cenozoic times, there is excellent evidence that CCD fluctuates in the Atlantic and Pacific oceans. These fluctuations are usually interpreted as a consequence of changes in weathering, climate and sea level. It has been proposed that the changing pattern of dynamic topography could play a crucial role in moderating the apparent CCD, especially during Cenozoic times.
Project summary : 
This project will address this interdisciplinary problem using two approaches. First, a global reconstruction of observed dynamic topography will be generated for the oceanic realm by analyzing new and legacy seismic reflection and wide-angle records. Isostatic calculations will be used to measure residual depth anomalies from these records. Stratigraphic constraints will then be used to determine the temporal evolution of these anomalies which are a proxy for dynamic topography. Secondly, spatial changes in the percentage of carbonate sediment will be carefully reconstructed by analyzing a global inventory of Deep-Sea Drilling Program (DSDP), Ocean Drilling Program (ODP), and Integrated Ocean Drilling Program (IODP) core sites. Initially, this analysis will focus on exploiting known oceanographic proxies for water mass structure.
What will the student do?: 
Processing, analysis and interpretation of dynamic topography will be carried out on seismic surveys using a suite of existing software tools developed at the Department of Earth Sciences. Seismic processing and visualization packages will be used to measure sedimentary and oceanic crustal thicknesses with a view to determining and applying the necessary isostatic corrections. In this way, a global map of observational dynamic topography will be constructed with attendant uncertainties. This map will form the basis for analyzing and interpreting CCD measurements. Existing core site measurements will be collated and analyzed with a view to constructing a global database of CCD measurements. A combined quantitative analysis of geophysical and geochemical measurements will be used to develop a full understanding of the link between mantle and oceanic processes.
References - references should provide further reading about the project: 
Van Andel, T.H., 1975. Mesozoic/Cenozoic calcite compensation depth and the global distribution of calcareous sediments. Earth and Planetary Science Letters, vol. 26, 187-194.
Hoggard, M.J., White, N., and Al-Attar, D., 2016. Global dynamic topography observations reveal limited influence of large-scale mantle flow. Nature Geoscience, vol. 9}, 456-463.
Campbell, S.M., Moucha, R., Derry, L.A. & Raymo, M., 2018. Effects of dynamic topography on the Cenozoic carbonate compensation depth. Geochemistry, Geophysics, Geosystems, vol. 19, 1025-1034.
You can find out about applying for this project on the Department of Earth Sciences page.
Professor Nicky White
Department of Earth Sciences Graduate Administrator
Dr Alex Piotrowski