Strong winds frequently whip up dust as they funnel through a break in the Tibesti and Ennedi massifs and across the Bodélé Depression, the lowest point (land elevation) in Chad. By one estimate, dust storms cloud the skies over the ancient lakebed roughly 100 days each year.
On January 20, 2021, the Visible Infrared Imaging Radiometer Suite(VIIRS) on the NOAA-20 spacecraft captured striking imagery of one of those storms. The image above shows dust from the Bodélé streaming through the gap in the mountains as it rides northeasterly winds.
The dust itself is mostly comprised of particles of quartz and the remains of ancient diatoms—microscopic organisms that lived in ancient Lake Mega Chad. About 7,000 years ago, the lake spanned an area larger than all of the Great Lakes combined.
Bodélé dust is of particular interest to scientists because diatoms are rich in phosphorous, a nutrient essential to plant growth. Since the Bodélé is such an abundant source of dust, and its plumes often cross the Atlantic Ocean, scientists have long thought that dust from this area fertilized the nutrient-limited soils of the Amazon rainforest.
Recent research suggests that idea may not be entirely right. A more detailed analysis of data from several satellites and models indicates that much of the Bodélé dust settles over Africa or gets washed out of the atmosphere by rain before reaching South America. The researchers found that most of the dust that does reach the Amazon comes instead from El Djouf, a west African desert in Mauritania and Mali. That area is roughly 2500 kilometers (1,600 miles) west of Bodélé.
References & Resources
- Bristow, C. & Moller, T. (2017) Testing the auto-abrasion hypothesis for dust production using diatomite dune sediments from the Bodélé Depression in Chad. Sedimentology, 65 (4), 1322-1330.
- EOS (2020, August 28) Saharan Dust Reaching the Americas Comes from El Djouf. Accessed January 20, 2020.
- NASA (2015, February 22) NASA Satellite Reveals How Much Saharan Dust Feeds Amazonâs Plants. Accessed January 20, 2020.
- NASA Earth Observatory (2019, December 21) Bodélé Dust.
- NASA Earth Observatory (2020, January 9) A Dusty Journey.
- Yu, Y. et al. (2020) Disproving the Bodélé Depression as the Primary Source of Dust Fertilizing the Amazon Rainforest. Geophysical Research Letters, (47) 13.
- Yu, Y. et al. (2018) Identification and Characterization of Dust Source Regions Across North Africa and the Middle East Using MISR Satellite Observations. Geophysical Research Letters, (45) 13.
NASA Earth Observatory image by Lauren Dauphin, using VIIRS data from NASA EOSDIS LANCE, GIBS/Worldview, and the Suomi National Polar-orbiting Partnership. Story by Adam Voiland.
