Thanks to Dust from the Sahara

May 6, 2014 | Posted in: Science

Desert, Konstantin Makovsky

Desert, Konstantin Makovsky

“When we try to pick out anything by itself, we find it hitched to everything else in the Universe.” John Muir

 

The desert does not bring to mind the fecundity of tropical jungles. These two ecosystems seem to be inherently incompatible, completely without connection to one another. What could endless burning sands have to do with a world of humid air, lush plants, and innumerable animal life? Well, this is Earth, and every part of the planet, no matter how small or how large, is interconnected to the whole. So, here’s the surprising story of how desert feeds jungle.

The Sahara desert is frequented by powerful windstorms brewed up by the boiling heat of the moisture-less sands. These winds shift and shape the desert dunes, making mountains out of innumerable tiny grains of sand and dirt. These winds are so restless and so strong that they lift up fine soil from the dunes, carrying it up into the atmosphere to collect as tons and tons of dust. Held aloft in these powerful winds, the dust from the Sahara is pushed into the Atlantic trade winds, beginning an epic journey over the vast Atlantic ocean.

Dust from the Sahara carried by winds over the Atlantic, photo courtesy of NASA.

Dust from the Sahara carried by winds over the Atlantic, photo courtesy of NASA.

Much of this wind-lofted dust falls into the ocean, providing a plentiful portion of the iron, calcium, and especially the rare phosphorous that plankton depend on. This desert dust sprinkled into the ocean, like seasoning into a giant soup, ensures that the plankton (and subsequently, all the larger species that feed on this minute organism) continue to thrive.

But some of the fine dust remains in the trade winds, blown along with the occasional locust hitching a ride, all the way to the continents on the other side of the Atlantic:

“[This dust] reaches Brazil. It reaches the Caribbean Islands. It reaches Florida, Georgia, Alabama, and the Carolinas. It comes not just in dribs and drabs but by the ton, about a billion metric tons each year.” William Bryant Logan, Air: The Restless Shaper of the World

Exotic Landscape, Henri Rousseau.

Exotic Landscape, Henri Rousseau, 1908.

This dust from the Sahara, a land without plants to leech the nutrients from the desert sands, is carried by winds all across the great ocean to reach the rainforests of Brazil and the deciduous forests in southern North America. These dusts settle into the soils, providing a rich mineral infusion of calcium, potassium, nitrogen, iron, and vital phosphorous, all of which are crucial for the forests’ survival.

“The soils of the rain forest are old, very old. The rainfall leaches the nutrients through them very quickly. Phosphorous–always the first of the major plant nutrients to be exhausted–is virtually unavailable in the soils. Only the annual transport of the dust from Africa brings this crucial mineral and so permits the great trees and their colonies of epiphytes to grow.” Logan

Orchids are epiphytes, growing on trees and pulling in minerals from the air. Cattleya Labiata, from Paxton's Flower Garden, volume 1, plate 24.

Orchids are epiphytes, growing on trees and pulling in minerals from the air. Illustration of Cattleya labiata, from Paxton’s Flower Garden, Volume 1, Plate 24.

Nothing on our planet (or in the universe for that matter) is separate or independent from everything else. The deserts of the world are all supplying nutrients carried by the wind to ecosystems at a deficit for minerals. The epicenter of diversity on our planet, the precious rainforests, are only continuing to grow because of their connection with a desert nearly devoid of plant life on the other side of an ocean.

This post was informed by:
Air: The Restless Shaper of the World, William Bryant Logan

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