Tracking the Green Sahara: Assessing periods of humidity in North-West Africa using speleothem geochemistry

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The arid Saharan belt running across North Africa is an important part of today's climate system. However, changes in past climate and potential future variations are currently poorly understood. This is largely due to the lack of well-dated paleoclimate records and historical instrumental data from the region. Recent work has given evidence for a period of humidity in Western Sahara during the Holocene as well as recurrent moist periods and 'greening' of North Africa during the late Pleistocene. However, the processes which provided moisture to the region at these times are not well understood. Past variations in humidity are thought to have had important influences on early human migration within Africa and future changes may have societal implications for modern populations living in the area. This project will assess the timing of past humid periods relative to other climatic changes, and the sources of the moisture during these periods. Stalagmites are powerful, high-resolution paleoclimate archives which can be absolute dated to produce annually resolved records of regional climate change. This project will contribute to the currently lacking geospatial coverage of speleothem records in NW Africa, complementing other terrestrial paleoclimate archives such as lake deposits. Additional work will also be undertaken on previously collected samples from southern Morocco to further understand the extent of climate change during important climate events within the Holocene, such as the African Humid Period. These samples were collected from a previous excursion and are available for further analysis in department. Fieldwork to collect stalagmites will be undertaken in Morocco and potentially in Western Sahara and Algeria, taking into account FCO travel advice to these countries. A record of paleoclimate will then be constructed in the lab from the geochemistry of stalagmites, using stable isotope ratios, trace element concentrations and sample petrography. Speleothems grow as a consequence of the input of water into a carbonate karst system. Analysis of growth to non-growth periods in stalagmites, as well as changes in growth speed, are therefore a valuable indicator of changes in regional humidity. By performing a holistic interpretation of changes in stable isotope ratios and the timing of growth periods in stalagmites across North Africa, the migration of the hyper-arid Saharan belt and the occurrence of periods of humidity may be observed. Individual analysis of records would also contribute to previous interpretations of climate. For example, observing geospatial changes in stalagmite 18O would infer possible moisture sources and transport across NW Africa both in the past and towards the present. An understanding of the controls and extent of climate change in North Africa are important for constraining the relationship between regional hydrology and global climate variations. This project will aim to reconstruct climate change between the Atlas Mountains and Sahara Desert using speleothems to advance our understanding of the region.