The Bodélé Depression

The Bodélé Depression is a palaeolake basin situated in northern Chad. Digital elevation models have highlighted a series of palaeoshorlines once prominent as palaeolake Megachad’s borders. Megachad was formerly the largest lake in Africa covering in excess of 350,000 km² but has since dried up exposing a largely diatomite surface (Bristow et al, 2009). TOMS (Total Ozone Mapping Spectrometer) Aerosol Index data illustrates the Bodélé Depression to be a critical mineral aerosol source throughout the year (Washington and Todd, 2005). Entrainment of dust into the atmosphere from this major source region forms an important component of the Earth’s climate system because of its potential to influence, for example, the radiation budget. Extreme erodibility and strong surface winds account for the magnitude of the dust plumes over the Bodélé. Engelstaedter et al (2006) suggest that anthropogenic activity is also responsible for the great entrainment of dust. Firstly through land use changes such as through agriculture, mining, water management or vehicular activity, and secondly through our contributions to climate change which in turn modify dust emissions.

      African aerosol indices and Bodele dust (From UCL and NASA)

Dust from the Bodélé Depression is also known to influence biogeochemical cycling. Koren et al (2006) advise that 40 million tons of dust are transported to the Amazon from the Sahara each year. With a considerable proportion of Saharan dust accounted for from the Bodélé, it is clear a significant proportion of Amazonian dust is from this region. Furthermore, Koren et al state that the Amazon basin has a dependence on the mineral fertilisation from Saharan dust sources. Washout of nutrients in heavy rainstorms makes a steady supply of mineral essential to maintain rainforest equilibrium.