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E413: The impact of dynamic topography on chemical weathering (Lead Supervisor: Ed Tipper, Earth Sciences)

Supervisors: Ed Tipper (Earth Sciences) and Nicky White (Earth Sciences

Importance of the area of research:

On long time scales chemical weathering acts as a sink for atmospheric carbon, regulating the climate. During weathering Ca and Mg from silicate minerals are released, subsequently transported to oceanic basins and deposited as Ca and Mg carbonates, transferring carbon from the atmosphere into the carbonate rock reservoir. Uplift of rock stimulates chemical weathering by supplying fresh rock to the zone of weathering. Thus, it has been suggested that tectonics is a major control on long- term climate. Most notable is the hypothesis that the uplift of the Himalayas contributed to the cooling trend of the Cenozoic.

Project summary:

Convectively supported uplift has recently been recognised as acting on short (1000s of km's) wavelengths and relatively rapid (10's of Ma's) timescales. This project will investigate to what extent this affects the chemical weathering of the continents.

Africa acts as a natural laboratory to study dynamic topography. It's ‘basin and swell' topography has long been recognised as caused by mantle convection and it is largely unaffected by plate tectonic processes. River profile inverse modelling has revealed pulses of uplift associated with greater physical erosion and off-shore sedimentation. This suggests tectonics is acting as a first order control on physical erosion. The focus of this project will be how the uplift of Africa has affected a) present day chemical weathering and b) how this may have varied in time.

What the student will do:

Offshore cores through the continental shelf collected by scientific or industrial drilling could hold an archive of weathering within specific catchments over the Cenozoic. Correlating proxies of weathering (e.g. δ7Liclay) with the predicted uplift history may elucidate how uplift has affected weathering. This could be augmented with classical indicators of sedimentary maturity and provenance.

Comparing this to present day chemical fluxes in rivers surrounding a convectively supported dome (e.g. Bié dome, Angola) will calibrate these results. This could be used to estimate the magnitude of carbon sunk by weathering from these regions.

The above approaches would be compared with models of chemical weathering (e.g. West et al. 2005). River profile inversion produces a predicted history of physical erosion which can be compared to deltaic sedimentary fluxes. This history could be fed into chemical weathering models along with a reconstructed climatic history to create a modelled history of chemical weathering.

Please contact the lead supervisor directly for further information relating to what the successful applicant will be expected to do, training to be provided, and any specific educational background requirements.

References:

Paul, J.D., Roberts, G.G., White, N., 2014. The African landscape through space and time. Tectonics 33, 898-935. doi:10.1002/2013TC003479

Raymo, M.E., Ruddiman, W.F., 1992. Tectonic forcing of late Cenozoic climate. Nature 359, 117-122. doi:10.1038/359117a0

West, A.J., Galy, A., Bickle, M., 2005. Tectonic and climatic controls on silicate weathering [rapid communication]. Earth Planet. Sci. Lett. 235, 211-228. doi:10.1016/j.epsl.2005.03.020

Follow this link to find out about applying for this project.

Other projects available from the Lead Supervisor can be viewed here.

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