How Saharan dust clouds that turn skies orange also nourish nature

It looked like something from Mars as the skies turned orange over much of Europe and parts of the UK last week. This was dust whipped up from the Sahara and carried across Europe on southerly winds, making a mess of cars and windows and providing a welcome spring bonus for the car-washing industry. While spectacular, it was not that unusual.

The Sahara is the world’s biggest producer of dust, which can be blown far and wide, especially in spring when seasonal winds rake the desert. In fact, clouds of the dust can be swept across the Atlantic on the trade winds, and more than 20m tonnes reach the Amazon each year. That dust is a precious fertiliser that nourishes the rainforest with much-needed iron and phosphorus minerals. In fact, by a strange symmetry, the Saharan dust adds about the same amount of phosphorus to the Amazon each year that is flushed out to sea by flood waters.

The dust also fertilises the vast numbers of microscopic phytoplankton in the Atlantic, the tiny algae that soak up huge amounts of carbon dioxide. When the phytoplankton eventually die, the remains sink to the bottom of the ocean, where the carbon stays locked away, helping fight climate breakdown.