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Cold Carbon Sink: Slowing Global Warming with Antarctic Iron

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Recent research shows that melting icebergs in the ocean around Antarctica may actually slow global warming. The iron particles they carry feed algae blooms that suck up CO2. Could man-made algae blooms in the frigid waters help combat climate change?

The catch was cold and lifeless, there wasn't a single fish flopping in the net. When the haul came to rest on the deck of the HMS Endurance in southern Atlantic off the coast of Antarctica, the only sound was a dull creak.

Then polar researchers picked up sledgehammers and set to work on their catch, a block of ice measuring more than 10 meters (33 feet) long. They chipped away at the ice until they had reached deep enough into its interior, and there they made an exciting discovery.

The  HMS Endurance  in the Antarctic.
AP

The HMS Endurance in the Antarctic.

Under a scanning electron microscope, tiny iron particles became visible. "These particles measure only a fraction of a millimeter," team leader Rob Raiswell explains, "but they have great importance for the global climate."

A geochemist at the University of Leeds, Raiswell had set out with the British naval icebreaker Endurance in order to investigate a hypothesis long circulated among polar researchers. The idea holds that icebergs transport tiny iron particles within their frozen mass. As the gigantic hunks of ice slowly thaw, they release these particles into the Southern Ocean. There, according to the conjecture, these iron compounds have an incredible effect, bringing the waters surrounding Antarctica into bloom.

CO2 Sinking to the Ocean Floor

The ocean that surrounds the ice-encrusted continent is full of nutrients such as nitrogen. The only element lacking for plankton to be able to bloom there is iron. Until now, wind was the only proven source of iron in the Southern Ocean, blowing much-needed iron oxide and other metal oxides from the dusty deserts of the southern continents. The quantities moved by this method, however, are miniscule.

"This is the first time we've been able to prove the presence of trace elements in icebergs," Raiswell explains. With their discovery off the coast of the Antarctic Peninsula, the scientists revealed a powerful mechanism that has been operating under the waves for millions of years: icebergs fertilize the ocean around the South Pole with microscopic particles containing iron. Algae are then able to bloom, and they in turn absorb the greenhouse gas carbon dioxide from the Earth's atmosphere via photosynthesis. Some of the algae then sinks to the ocean floor.

"This helps to slow down global warming," says Raiswell. The researcher has approximated the amount of CO2 disposed of through this process. Icebergs, he calculates, currently dump around 120,000 tons of iron into the Southern Ocean, causing 2.6 billion tons of CO2 to be removed from the atmosphere. This massive amount corresponds to the greenhouse gases emitted from power plant smokestacks, home chimneys and automobile exhaust pipes in India and Japan combined.

"The Earth itself seems to want to save us," Raiswell comments. He sees this self-healing process as having "significant" potential, although it is "by no means sufficient" to halt global warming.

Getting the Algae to Bloom

According to Raiswell's calculations, the effect will increase in the coming decades, as more and more ice breaks off from ice sheets due to rising temperatures. This is happening especially along the Antarctic Peninsula, which has seen a rapid temperature increase of 2.5 degrees Celsius (4.5 degrees Fahrenheit) in the last 50 years. Every percentage point increase in the amount of ice that breaks off, an additional 26 million tons of CO2 is removed from the atmosphere.

Carbon storage in the Antarctic depths.
DER SPIEGEL

Carbon storage in the Antarctic depths.

Meanwhile, ice is moving out from the interior of the Antarctic continent faster than ever before, grinding across the rocky bedrock and releasing iron-oxides such as schwertmannite. Iron from these minerals then allows algae in the ocean to bloom in greater quantities.

Still, this naturally occurring iron fertilization doesn't come close to tapping the nutrient-rich but iron-poor Southern Ocean's full potential to act as a CO2 sink. The iron-deficient area covers 50 million square kilometers (20 million square miles). If this entire expanse were to be artificially fertilized with several million tons of iron oxide, the ocean could remove three and a half gigatons of carbon dioxide from the atmosphere. This amounts to an eighth of the yearly emissions created by burning oil, gas and coal.

Among scientists and environmental entrepreneurs, a plan has long been in the works to fertilize the ocean around Antarctica with iron sulfate, using large tankers. The, scheme is controversial since environmentalists fear such geo-engineering could knock the ecosystem out of balance. American oceanographer Mary Silver even predicts possible large-scale proliferation of poisonous algae. For this reason, the UN Convention on Biological Diversity in May 2008 called for a moratorium on such plans, at least until further scientific results are available.

A unique new project now aims to close this knowledge gap. The German research icebreaker Polarstern will set out for Antarctica from Cape Town at the beginning of January. Leader of the project is Victor Smetacek from the Alfred Wegener Institute for Polar and Marine Research (AWI). An Indian-German team of 49 people will accompany him.

Fiddling with the Planet

The plan is to create an artificial plankton bloom north of the island of South Georgia using several tons of iron sulfate. "It will be the largest bloom produced to date," Smetacek says. So large, in fact, that it will be possible to observe it from space with special satellites, and it will attract large swarms of krill from the south.

Smetacek plans to put a great deal of metrological effort into investigating how much algae in fact sinks to the bottom of the ocean. To do this, he will focus on a particular species of algae that grows along the coast. Spores of this species are enclosed by a silicon dioxide shell, and they also incorporate carbon dioxide into their organic inner parts. When the spores then sink through the water, even fish can hardly digest them. "Then the greenhouse gas is sure to be out of the earth's atmosphere for several hundred years," Smetacek explains.

Smetacek has also suggested the establishment of an authority at the United Nations to oversee future iron fertilization projects undertaken to save the climate. The researcher doesn't want to leave this matter in the hands of industry, allowing companies simply to buy their way out of other climate-related obligations with a tanker full of iron sulfate. "The issue is too complex not to be supervised by scientists," he says.

To critics who call this too much playing around with the planet's natural workings, Smetacek replies: "Their objections will be swept away when our powerlessness in the face of climate change becomes apparent."

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