Despite the thousands of kilometers that separate them, the Algerian Sahara desert and the Amazon rainforest are linked: each year, a natural cycle transports millions of tons of sand from the African continent to the South American continent. A contribution that the largest equatorial forest in the world needs to flourish.
A sandstorm part of the Algerian Sahara desert
Each year, 22,000 tons of phosphorus contained in sand from the Sahara cross the Atlantic Ocean to land in the Amazon, reports a US study published in the journal Geophysical Research Letters. This is the first quantification of the transatlantic transport of this chemical element over more than 4,000 km, from Africa to South America.
Because it grows on poor soil, the Amazonian forest sees its productivity limited by the availability of nutrients such as phosphorus. In addition, heavy rainfall accentuates the deprivation of the soil of these elements each year.
The Amazon forest
In its analysis based on data collected between 2007 and 2013 by the remote sensing satellite CALIPSO (Cloud Aerosol Lidar and Infrared Pathfinder Satellite Observations) and the radar satellite CloudSat, the team of researchers estimates that these phosphorus losses are compensated by the deposits natural dust. Those coming from the Bodélé depression, located in the southern center of the Sahara desert in northern Chad, are of particular interest: this ancient lake bed contains enormous deposits of dead microorganisms loaded with phosphorus. According to scientists, the sand is lifted by sandstorms into the upper atmosphere, then it is transported to the Amazon by air currents.
Dust influences the climate and vice versa
Over the observed period, the trend is very variable. The researchers have indeed noted up to 86% difference between the highest quantity (2007) and the lowest (2011) of naturally carried sand. Precipitation could explain this variation. Two hypotheses are possible: either the rains favor the growth of vegetation which reduces soil erosion, or the quantity of dust is linked to the modes of circulation of the winds.
“We know that dust is very important in many ways,” said the study’s lead author, Hongbin Yu, a researcher at NASA’s Goddard Space Flight Center, Greenbelt and University of Maryland, at College Park (USA). “It is an essential component of the Earth system. Dust will affect climate and at the same time climate change will affect dust,” he continues.
Phosphorus represents only 0.08% of the 27.7 million annual tons of “migrating dust”. Other elements such as potassium, calcium or magnesium are therefore supposed to be part of the journey. This first estimate enriches knowledge on the behavior and role of dust in the environment and on its effects on the climate.
Translated from : https://topdestinationsalgerie.com/comment-le-sable-du-sahara-algerien-fertilise-la-foret-amazonienne/