Review: CHADRILL proposal

In this blog post, I am going to a review a recent article by Florence Sylvestre et al. titled 'The Lake CHAd Deep DRILLing project (CHADRILL) – targeting ∼ 10 million years of environmental and climate change in Africa'. As the title suggests, the article focusses on the proposed drilling of ~1800m of sediments near Lake Chad's coastline. 

 The proposal 
CHADRILL was proposed at an International Continental Scientific Drilling Program (ICDP) sponsored workshop in late September 2016 in Aix-en-Provence. The workshop was attended by 56 scientists from 11 countries. The rationale behind the proposed drilling is the potential importance of the moisture variability record in light of historic variations in greenhouse gas concentration and northern hemisphere ice extent. In addition, the investigation plans to look at the influence of orbital forcing and ENSO on regional climate. Looking back at periods when orbital variables were similar to those today can aid future climate change predictions. Furthermore, looking back at a sediment record spanning the Miocene-Pliestocene could provide insight into the water availability on the African continent when atmospheric CO2 is high and there is a lack of northern hemisphere ice sheet coverage.

A cradle of humanity?
The LCB is thought to be one of the cradles of humanity. Hominid fossils found in the basin include Australopithecus bahrelghazali and Sahelanthropus tchadensis which date back to the Late Miocene. The presence of hominid remains in the LCB could provide clues to explain how environmental triggers, such as water availability could have influenced human evolution.

Evidence from the Lake Chad region suggests that the ancient Esohabi River in Libya connected the LCB with the Mediterranean Sea. Climate models suggests that the Esohabi River was the same size as the present-day Nile and was fed by North African monsoonal rains. This link is hypothesised to relate to the movement of hominids towards the Mediterranean. The Nile passage was formerly thought to be the only route early humans could have taken to traverse the Sahara which acted as a barrier to northward migration from the African Tropics. Although, it is not known whether the Sahara was in fact a continuous barrier to northward dispersal at this time because the region is thought to have been populated during humid phases such as the African Humid Period.

Drilling plans
Drilling is set to take place close to the location of the 1973 geotechnical Bol borehole. The reasoning behind this location is that it is the site with the most detailed records of the lithology to be drilled in the LCB. Moreover, the 1973 site is likely to provide the most continuous sequence as it is located near the LCB's depocentre, probably why it was also chosen in 1973. The main target of the CHADRILL project is to retrieve a complete sample of lacustrine sediment between depths of 70 and 300m. If successful, recovery of deposits from between 300 and 670m is also planned, as well as from between 0 and 70m from the sand dunes.

 'The record preserved in Lake Chad has implications for a climate system that spans half the globe' (Sylvestre et al. 2018, p73)

The Lake Chad palaeoclimate record will hopefully extend back to the Miocene and provide important new information on water avaibility north of the equator. Proposed drilling in the LCB will be useful in conjunction with another potential palaeoclimate record south of the equator, from Lake Tanganyika. Together, these new records could provide new insight into environmental change across the continent over an extended timescale.

Lake Chad and ... Mars?
It has been suggested that sediments around Lake Chad are similar to those which were discovered on the 2011-2012 Curiosity Mars mission. This has led to the idea that the freshwater systems of LCB could be used as a comparison for similar systems on Mars. Hence, looking into deposits around Lake Chad could further our understanding of the beginning of life Earth, Mars and other planets.

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