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C420: Quantifying the impact of atmospheric dust on vegetation and hydro-climate in the Amazon rainforest during the last 20,000 years. (Lead Supervisor: Francesco Muschitiello, Geography)

Supervisors: Francesco Muschitiello (Geography), Christine Lane (Geography) and William D'Andrea (Lamont Doherty Earth Observatory, Columbia University)

Importance of the area of research:

The Amazon rainforest constitutes half of the planet's remaining rainforests. It is one of Earth's richest biological resources and a key ecosystem controlling Earth's climate, whereby small changes in vegetation cover can have a large impact on the carbon cycle and atmospheric circulation. Here, changes in vegetation cover and diversity can alter the regional hydrological cycle via changes in surface radiation. Thus, small shifts in forest productivity can severely impact the South American monsoon system, which largely contributes to the hydro-climate of the continent controlling the frequency of floods and droughts with important socio-economic implications. Tree growth and productivity across the Amazon are regulated by the availability of nutrients, which depend highly on deposition of dust from North African sources in response to changes in rainfall over the Sahel and Sahara deserts. However, the chain of feedback linking dust nutrients, vegetation cover, and hydro-climate in the Amazon is still poorly understood and is potentially vulnerable to climate change, especially considering the uncertainty surrounding future precipitation projections for tropical North Africa.

Project summary:

The project aims to use marine palaeoclimate records to provide a better insight into the sensitivity of Amazon rainforests to changes in dust nutrient supply from North African deserts during the last 20k years, and to quantify forest-climate interactions that link changes in forest ecosystem productivity to the variability of the South American monsoon system. The project is divided into four objectives: (1) compiling published regional palaeo-hydro-climate parameters; (2) quantifying Saharan dust fluxes from marine archives combining grain-size, Th and Sr isotope measurements; (3) quantifying from the same archives Amazon palaeo-precipitation and vegetation shifts using plant-derived sedimentary δD and δ13C isotopic tracers, respectively; (4) comparing the compiled and analysed data to climate model output using a fully-interactive vegetation model including biochemical processes.

What the student will do:

The successful candidate will first focus on compiling and evaluating published South American hydro-climate data covering the last 20k years. The candidate will then focus on generating multi-proxy records from two marine sediment cores off north-eastern Brazil and a number of core top sediments from the equatorial Atlantic (already available through the supervisors’ collaborators). The candidate will produce records of dust, lipid biomarker abundance, and leaf-wax stable hydrogen and carbon isotopes (δD and δ13C) and will use modern core top sediments to validate the use of the isotope data to quantitatively infer changes in Amazon rainfall and vegetation cover. Finally, the candidate will focus on performing spatial and temporal analyses of the compiled and analysed data that will serve as benchmark for validation of climate model experiments (generated by EC-Earth) using a fully-interactive vegetation model with an explicit representation of biochemical cycles.

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:

Davies, F.J., Renssen, H., Blaschek, M., Muschitiello, F., 2015. The impact of sahara desertification on arctic cooling during the Holocene. Climate of the Past 11, 571-586. doi:10.5194/cp-11-571-2015

Malhi, Y., Roberts, J.T., Betts, R.A., Killeen, T.J., Li, W., Nobre, C.A., 2008. Climate Change, Deforestation, and the Fate of the Amazon. Science 319, 169-172. doi:10.1126/science.1146961

Yu, H., Chin, M., Yuan, T., Bian, H., Remer, L.A., Prospero, J.M., Omar, A., Winker, D., Yang, Y., Zhang, Y., Zhang, Z., Zhao, C., 2015. The fertilizing role of African dust in the Amazon rainforest: A first multiyear assessment based on data from Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations. Geophysical Research Letters 42, 1984–1991.

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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