How does dust from the Sahara fertilise the Amazon rainforest?
A dry lakebed in Chad sends tonnes of dust across the Atlantic to feed trees thousands of kilometres away.
▶ Start the storyA desert's dust can fertilise a rainforest because the Amazon's soil is short of , and the wind brings it from the Sahara. The Sahara is the largest source of , or wind-blown, dust in the world, producing roughly 400 to 700 million tons a year, almost half of all such desert dust reaching the ocean. That dust has been found as far away as the Amazon basin, Scandinavia and Japan. For the Amazon, whose soil is limited in phosphorus in many places, Saharan dust is a main source of that nutrient.
The best-known dust factory is the Bodélé Depression in Chad. It is a dry basin that is a major source of fertile dust essential for the Amazon rainforest, with some studies suggesting it supplies over half of the nutrient-rich dust that supports it. One research team, which had earlier timed the Bodélé's storms with NASA satellite images, reported in 2006 that it deposits up to 50 million tonnes of dust a year in South America.
up to 50 Mt/yr
The story goes back to the green Sahara. The dust comes from , tiny fossilized organisms, from a vast lake that once filled the region, Mega-Lake Chad. As the Sahara dried out and the lake shrank, its lakebed sediments baked into fine dust that the wind picks up. The wind has to blow at a minimum of about 36 kilometres an hour to start a storm.
The dust crosses the Atlantic in a hot, dry layer of air above the sea, so a drying climate far away gives green leaves a lift.
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Recap
The Sahara's dry lakebed dust is a nutrient delivery across the Atlantic to the Amazon.
💡 A trick to remember it · A dried-up lake in Chad is a flour mill in the sky: the wind grinds the old lakebed and posts it to the Amazon.
Surprising fact · Some studies suggest a single dry basin in Chad, the Bodélé Depression, supplies over half of the dust that feeds the Amazon.
Connects to
- 🏖️ How do sand dunes form, move and sometimes sing?
- 🔬 How does life survive in the Atacama Desert, and what does it teach us about Mars?
- ⚖️ Is the Amazon about to flip into savanna? Where scientists agree and disagree
- 🍂 Why is the soil under the world's richest forest so poor?
- 🦒 Was the Sahara really green once?
- Bodele depression
- Phytoplankton
Sources (3)
No source, no claim. Every fact in this lesson (17 claims) cites at least one of these.