Dust storms bring a cool climate (Image: NASA/SPL)

DUST is all that’s needed to plunge the world into an ice age. When blown into the sea, the iron it contains can fertilise plankton growth on a scale large enough to cause global temperatures to drop. The finding adds support to the idea of staving off climate change by simulating the effects of dust – perhaps by sprinkling the oceans with iron filings.

Iron-rich dust falling on the ocean has long been known to spark blooms of plankton, and researchers suspect the process could have intensified the ice ages that have occurred over the past few million years.

The thinking goes that, during warm periods, much of the Southern Ocean is an oceanic desert because it lacks the iron crucial for plankton growth. That changes at the start of ice ages, when a wobble in the planet’s orbit causes an initial cooling that dries the continents, generates dust storms – particularly in central Asia – and sends dust onto the surface of the Southern Ocean.


The plankton that then bloom take the carbon they need from the water, causing the oceans to absorb carbon dioxide from the atmosphere to compensate. This cools the atmosphere further, creating yet more dust-producing regions, and the cycle continues, sinking Earth into an ice age.

When the planetary wobbles, known as Milankovitch cycles, eventually choke off the cooling, the feedback goes into reverse: continents warm, dust storms subside, the Southern Ocean is starved of iron, and CO 2 levels in the atmosphere rise again.

Evidence for the theory can be found in ice cores from Antarctica, which show lots of dust in the air coinciding with low atmospheric CO 2 levels during recent ice ages. But this record goes back only 800,000 years.

Now Alfredo Martinez-Garcia at the Swiss Federal Institute of Technology in Zurich and colleagues have used marine sediment cores taken from an area of the Atlantic Ocean just north of the Southern Ocean to look back 4 million years. They say dust levels have been twice as high during deep glaciations throughout that time (Nature, DOI: 10.1038/nature10310).

“Dust deposition in the Southern Ocean increased with the emergence of the deep glaciations that characterise the late Pleistocene,” says Martinez-Garcia.

John Shepherd of the National Oceanography Centre in Southampton, UK, says the study “confirms the magnitude of the role of iron” in the onset of severe glacial conditions.

Fertilising the oceans with iron filings has been suggested as one method to combat climate change. So far, however, real-world tests have created only small blooms of plankton.

Shepherd says the tests have been on too small a scale to demonstrate any lasting effect. “It would be of great scientific interest to do some larger-scale longer-term experiments.” The new evidence, he says, suggests that it should work.