— The ice core is analysed for aluminium particles (Image: DRI / McConnell)
The ice core was extracted from James Ross Island, at the tip of the Antarctic Peninsula (Image: DRI/McConnell)
Satellite pictures (left) shows that brown dust plumes can extend at least 600 km over the Southern Ocean (brownish colour) from Patagonia; measurements of the amount of dust in the atmosphere shows it is comparable to what would be produced in very dusty regions such as the Sahara desert (Image: NASA / University of Maryland Baltimore / Santiago Gassó)
The Antarctic Peninsula became a dustier place during the 20th century, according to researchers who have tracked the dust back to Patagonia.
Increased desertification in the South American country, and overgrazing by the large number of sheep raised there in the early-1900s, may be to blame, the researchers speculate. The consequences of the process are as yet unknown.
Aluminium dust is eroded off the Earth's crust and lifted into the air by the winds, and form part of clouds of dust that move around the planet. So when researchers examining a 120-metre-long ice core extracted from the Antarctic Peninsula found that levels of aluminium had more than doubled during the 20th century, they deduced that the dust must have been deposited there by dust clouds from faraway places.
Joe McConnell at the Desert Research Institute in Nevada, US, and colleagues set about trying to locate the source of the dust.
Hot and dry
The team compared the variations in aluminium levels to variations in 20th-century weather and found that the aluminium matched Patagonia weather. For example, more deposited aluminium dust in Antarctica seemed to accurately follow periods of hotter, drier weather in Patagonia.
McConnell believes that a rise in sheep farming in Patagonia early in the 20th century, and the inevitable overgrazing that ensued, caused the region to become more desert-like. This, he says, means the soil is drier and more likely to release clouds of aluminium-carrying dust.
McConnell's findings may prove useful in aerosol research. How aerosols interact with the weather and cause it to change is a notoriously uncertain field of research because of a lack of historical data available to build models with.
Affect on climate
"McConnell's data is very interesting," says Paul Ginoux at the Geophysical Fluid Dynamics Laboratory in Princeton, New Jersey, US, who is using the new findings. He explains that this is the first continuous record of dust levels that has been made available to him and his modelling colleagues.
But Ginoux says it is very difficult to know how larger dust clouds over the Southern Ocean where satellite pictures show dust clouds move after they are lifted off Patagonia (see image, right) could affect the climate.
"Over Africa, dust clouds warm the atmosphere and cool the Earth's surface, which reduces precipitation," says Ginoux, "but over the Southern Ocean, aerosol concentrations are very low." He says this could mean that the dust clouds have had no effect on local climate. At the moment, it is simply too uncertain to say what, if any, effect the dust has on the Antarctic climate and ice melting rates.
In fact, the greatest significance of McConnell's findings could lie at the bottom of the sea.
Plant plankton in the Southern Ocean suck carbon dioxide out of the air during photosynthesis, and when they die or are consumed by other organisms, some of that carbon ends up on the ocean bed. It is well known that the amount of iron available to the plankton is what limits their growth. And the iron is carried across the ocean in the same clouds of dust that carry aluminium.
So more dust may mean more plankton, and therefore a bigger conveyor belt sinking carbon dioxide to the bottom of the ocean one of the Earth's biggest carbon sinks.
Journal reference: Proceedings of the National Academy of Sciences (DOI: 10.1073/pnas.0607657104)
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