How Saharan Dust Fertilizes the Amazon: Diatoms for the Win in an Unexpected Way!
How Saharan Dust Fertilizes the Amazon: Diatoms for the Win in an Unexpected Way!
When you think about how the Amazon rainforest maintains it’s incredible biodiversity and productivity, you probably do not imagine millions of tons of dust travelling 10,000 miles across the Atlantic Ocean from the Sahara Desert. But that is what happens every year in one of Earth’s most fascinating natural supply chains. The Sahara Desert and the Amazon rainforest, exist in an unexpected partnership, connected through an atmospheric delivery system, so large that it compensates for nearly all of the nutrients lost to intense rainfall.
The Paradox: A Lush Forest on Barren Soil
The Amazon presents an ecological puzzle. Despite being known as a hotbed of biodiversity and unbridled vegetative growth, the rainforest grows in extraordinarily nutrient poor soils. Approximately 90 percent of Amazonian soils suffer from severe phosphorous deficiency.
This deficiency makes sense hydraulically. The 60-120 inches of rainfall that the Amazon receives annually (hence the name), also leaches and strips nutrients from the soil. Millions of years of this relentless rainfall has left the region nutrient starved.
The forest somehow manages to thrive despite these constraints. The forest system does well to recycle nutrients decaying organic matter before it gets stripped away by rainwater, but it is not enough to make up for the losses. Where are the necessary nutrients coming from?
The Answer: Saharan Dust
The answer came from satellites capable of tracking atmospheric aerosols. In 2015, atmospheric scientist Hongbin Yu and colleagues at the University of Maryland found that the Saharan dust provided the missing piece. Using the CALIPSO satellite, researchers quantified a stunning fact: approximately 27 million tons of Saharan dust reach the Amazon basin annually.
More importantly, these dust particles carry an estimated 22,000 tons of phosphorus each year which is precisely the amount estimated to be lost from the Amazon through rainfall and river discharge.
The Bodélé Depression: Ancient Diatom Graveyard Turned Nutrient Factory
The source of this nutrient windfall is something called the Bodélé Depression in northeastern Chad. This vast, flat expanse of ancient lack bed contains some of Earth’s most phosphorus-rich sediments which accumulated from millions of years of aquatic productivity when Lake Mega Chad covered the region.
The depression is layered with fossilized diatoms that thrived in the ancient lake. When these organisms died, and their silica shells accumulated on the lake bottom, they created sediment layers that are rich in phosphorous and other nutrients. When the lake eventually evaporated, as the regional climate shifted to drier conditions, these nutrient rich sediments remained.
Today, powerful trade winds call the Harmattan blast across the Bodélé during the dry season and easily lift the dry sediments into the atmosphere to transport them thousands of miles from Africa to South America.
The journey takes about a week, and when the dust plumes reach the moisture-rich atmosphere over the Amazon, the particles are deposited in the rains. The dust even participates in helping catalyze cloud formation as well as providing some shade to the upper canopy protecting against excessive evaporation during dryer seasons.
An Elegant System
This system represents a global cause and effect that has taken millions of years to perfect and sustain. It is so elegantly simple, but at the same time so very complex and global.
And to think that it started with a tiny microbe called a diatom. These primary producers were working within an ecological niche and unknowingly aggregated and collected a wealth of nutrients from their environment during numerous bloom and bust cycles. Only to later have their skeletal remains picked up by global winds and spread to another continent to fuel a famously biodiverse terrestrial ecosystem.
It is a stretch to compare the concentrated diatoms from a dried ancient lake to the diatoms found in our Fish Brew Bold FLO and Rise & Thrive, but this example does show how outsized of an impact a tiny primary producer like a diatom can have!