Project EARTH-17-GMH2: Stalagmite reconstruction of past Saharan aridity

Supervisors:  Gideon Henderson and Chris Day

The belt of desert stretching across North African is a significant feature of today’s climate system, influencing not only this region, but Mediterranean climates to the North and monsoon to the south.  Dust generation in the area also influences climate through its impact on radiative forcing in the atmosphere, and through addition of nutrients to the Atlantic Ocean.  Past changes in this region are thought to have played an important part in the evolution and migration of humans and earlier hominins, and future changes will have an important socio-economic impact across a large swath of the globe.  Climate change in this region is known to occur, on timescales ranging from the decadal to geological.  At shorter timescales, changes in the African monsoon at the southern edge of the Sahara are poorly understood, but have huge impacts for food supply.  On longer timescales, the whole of the Saharan region is known to have been much wetter, and covered with grassland and lakes, in different climate conditions.  Producing such dramatic responses from climate models is very hard, and the processes that drive change in this region are poorly understood.  This situation is not helped by the sparse nature of modern instrumental data in the region, and by lack of well-dated paleclimate records, particularly for periods before the Holocene.

This project will reconstruct climate in north-west Africa using stalagmite records from caves in Morocco and neighbouring countries.  Stalagmites can be very precisely dated with U-Th techniques, and provide information about past climate at annual (and sometimes even seasonal) timescales (e.g. Liu et al. 2013).  In regions that are arid today, their very presence signifies periods of past wetter conditions, and dating of such material provides important constraints on the relationship of such changes to other global climate parameters (e.g. Vaks et al. 2010, 2013).

We have a collection of stalagmite samples from three caves in Morocco, forming a triangle across the country and sampling sites presently under very arid conditions.  Existing work on these samples has demonstrated their potential to accurately constrain past wet periods and, through the use of 18O and other geochemical proxies, to assess possible moisture sources during these periods.  There is much still to be done on these sites, however, to fully unlock their potential, and there are many other cave sites in Morocco and adjoining countries that would add powerful additional information.

This project would initially focus on U-Th dating and proxy measurement on existing stalagmite samples from Morocco, but would also involve fieldwork to collect further samples.  It could also be expanded, should this be of interest to the student, to include a modelling component to more firmly connect results to modern climate understanding.  Such modelling would be conducted in collaboration with colleagues with relevant expertise in the School of Geography, and would benefit from Oxford’s formal partnership with the Met Office through use of their models.

Further Reading:

Liu, Y.H., Henderson, G.M., Hu, C.Y., Mason, A.J., Charnley, N., Johnson, K.R. and Xie, S.C. (2013) Links between the East Asian monsoon and North Atlantic climate during the 8,200 year event. Nature Geoscience 6, 117-120.

Vaks, A., Gutareva, O.S., Breitenbach, S.F.M., Avirmed, E., Mason, A.J., Thomas, A.L., Osinzev, A.V., Kononov, A.M. and Henderson, G.M. (2013) Speleothems reveal 500,000-year history of Siberian permafrost. Science 340, 183-186.

Vaks, A., Bar-Matthews, M., Matthews, A., Ayalon, A. and Frumkin, A. (2010) Middle-Late Quaternary paleoclimate of northern margins of the Saharan-Arabian Desert: reconstruction from speleothems of Negev Desert, Israel. Quaternary Science Reviews 29, 2647-2662.