Monday, February 11, 2008

Dust storms in Sahara trigger huge plankton blooms in eastern Atlantic

Science Daily: Scientists on board RRS Discovery are at sea studying the Saharan dust that blows off the coast of Africa - triggering huge plankton blooms in the eastern Atlantic. Saharan dust is rich in nitrogen, iron and phosphorus and acts as a fertilizer on the production of plankton. Dr Eric Achterberg from National Oceanography Center at the University of Southampton is leading the research cruise and studying the dust’s effect on nutrients, plankton production and the food chain.

The quantity of dust involved, about 500 million tonnes per year, is sufficient to affect the climate. By partly absorbing and partly reflecting sunlight, the dust particles heat the air but cool the ocean surface. They also encourage cloud formation, which reinforces the reflection of light back into space.

Such effects can be far-reaching: hurricanes in the Caribbean begin their life off north west Africa, with atmospheric dust being one of many factors influencing their early development. Wind-blown dust from the Sahara desert plays a crucial role in fertilizing large areas of the Atlantic Ocean. The delivery of nutrients, and some metals common on land but scarce in the open ocean, stimulates the production of massive plankton blooms.

'Dust storms are sporadic events,' said Eric Achterberg. 'And Saharan dust can come from many sources – it can be mixed with soot, from grassland and forest fires; and it can change its chemical and physical properties as it is carried in the atmosphere, at different heights and different moisture conditions. These complications make it difficult to include the dust effects in climate models.'…

Photo of dust plume off the African coast by NASA, 1998, Wikimedia Commons

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