Assessing the millennial and centennial variability of the West African Monsoon during the late Quaternary: palaeodata and modelling approach


  • Supervisors: Dr Fabienne Marret-Davies, University of Liverpool
    Prof Andy Morse, University of Liverpool


  • External Supervisors:

  • Contact:

    Dr Fabienne Marret-Davies, University of Liverpool f.marret@liverpool.ac.uk

  • CASE Partner:

Application deadline: 10 January 2020

Introduction:

The tropical West African climate is mainly controlled by insolation and the convection due to thermal differences between the ocean and the adjacent continent; in turn, this has a control on the amount of precipitation. Interannual to seasonal variability of the West African Monsoon (WAM) has been observed, and has shown a strong impact on the water availability and consequently on ecosystems and societies [1]. On a longer time-scale, monsoon dynamics have varied in relation to glacial-interglacial cycles, modulated by orbital forcing, in particular the impact of the precession driving changes through the summer insolation [2]. The Quaternary history of the WAM variability has been mainly documented from marine records as very few continental sites provide a long record of the WAM history and are not always continuous. However, the temporal resolution of these marine records is rather low [3] and does not encapsulate the millennial and centennial variability observed further north such as the Dansgaard-Oeschger events [4].

Coupled ocean-atmosphere general circulation models (GCMs) were developed to simulate past environmental conditions with variable and fixed boundary conditions, in order to understand the mechanisms forcing the changes. Different types of models, from intermediate complexity models (e.g. GENIE-1) able to simulate transient climate over long periods to earth system models (e.g. LOVECLIM) incorporating an increasing number of the biosphere-atmosphere components, have helped to better understand forcing mechanisms but also the importance of palaeodata from climate proxies for better constrain the simulation outputs [5]

Project Summary:

This project aims to determine the response of the WAM to abrupt climatic events as well as warmer than present day conditions. A sedimentary marine core collected off Gabon (off the Ogooué River) will be analysed in high resolution for key-time periods to answer the following questions:

  • Can we detect the millennial D-O events in the monsoon activity and does it respond or lead the Greenland interstadials?
  • How the WAM responded to warmer conditions such as during the last Interglacial period, 115,000-130,000 years ago?
  • How fitting are environmental reconstructions from paleodata and model simulations for the WAM? 

The approach for this project is twofold: i) to provide paleodata of the West Africa monsoon activities and variability and ii) to assess model outputs with reconstructed environmental conditions. 

Pollen and other palynomorphs will be analysed and used to quantify climate conditions using the available pollen dataset (modern and fossil) to adapt the MAT (Modern Analogue Technique) and the Inverse mode technique [5] with BIOME4 [6].

Secondly, this proposal seeks to assess GCMs simulation outputs with previously published palaeodata and herein. Over the last decades, model simulations of precipitation patterns have increased in number and complexity, from snapshots to transient outputs. With access to different model databases and published results (all data are available through the databases hosted in PMIP, QUEST and NOAA), the student will be able to extract simulations and compare the outputs with reconstructed palaeoenvironmental conditions.

References:

[1] Giannini, A., Salack, S., Lodoun, T., Ali, A., Gaye, A.T., Ndiaye, O. (2013) A unifying view of climate change in the Sahel linking intra-seasonal, interannual and longer time scales. Environmental Research Letters, 8 (2), art. no. 024010.

[2] Kutzbach JE, Harrison SP, Coe MT (2001) Land–ocean–atmosphere interactions and monsoon climate change: a palaeo-perspective. In: Schulze E-D, Heimann M, Harrison SP, Holland E, Lloyd J, Prentice IC, Schimel DS (Max-Planck-Institute for Biogeochemistry J, Germany) (eds) Global biogeochemical cycles in the climate system. Academic Press, San Diego, pp 73–83.

[3] Hessler, I., Dupont, L., Bonnefille, R., Behling, H., González, C., Helmens, K.F., Hooghiemstra, H., Lebamba, J., Ledru, M.-P., Lézine, A.-M., Maley, J., Marret, F., Vincens, A. (2010) Millennial-scale changes in vegetation records from tropical Africa and South America during the last glacial. Quaternary Science Reviews, 29 (21-22), pp. 2882-2899.

[4] Brown, E. T., T. C. Johnson, C. A. Scholz, A. S. Cohen, and J. W. King (2007). Abrupt change in tropical African climate linked to the bipolar seesaw over the past 55,000 years, Geophys. Res. Lett., 34, L20702

[5] Guiot, J., Wu, H.B., Garreta, V., Hatté, C., Magny, M. (2009) A few prospective ideas on climate reconstruction: From a statistical single proxy approach towards a multi-proxy and dynamical approach. Climate of the Past, 5 (4), pp. 571-583

[6] Kaplan, J.O., Bigelow, N.H., Prentice, I.C., Harrison, S.P., Bartlein, P.J., Christensen, T.R., Cramer, W., Matveyeva, N.V., McGuire, A.D., Murray, D.F., Razzhivin, V.Y., Smith, B., Walker, D.A., Anderson, P.M., Andreev, A.A., Brubaker, L.B., Edwards, M.E., Lozhkin, A.V. (2003) Climate change and Arctic ecosystems: 2. Modeling, paleodata-model comparisons, and future projections. Journal of Geophysical Research D: Atmospheres, 108 (19), pp. ALT 12-1 - 12-17

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