Nanoparticles from melting glaciers could trap carbon

by Catherine Brahic from http://www.newscientist.com

The increasing number of icebergs breaking off Antarctica may have an unexpected benefit. According to one team of scientists, the bergs could feed carbon-loving plankton. If they are right, melting icebergs could - theoretically - slow global warming. Just how great an effect this would have remains to be seen.

Rob Raiswell of the University of Leeds, UK and colleagues trained high-resolution microscopes on ice sampled from icebergs in the Southern Ocean and the Antarctic glaciers from which they are born.

They found nano-sized particles of iron, between five and 10 millionths of a millimetre across. The team believe that because of the size and structure of the particles, the iron could be assimilated by phytoplankton.

“Most of the ground-up rock carried by icebergs is thought to be inert,” says Raiswell. “However, the high resolution microscopy shows there are small amounts of iron nanoparticles. They simply could not be seen except by these techniques.”

Phytoplankton need iron in order to grow, and the Southern Ocean is generally thought to be low on iron. But there is evidence that some Antarctic glaciers are flowing into the ocean faster because of climate change. This means more icebergs. If Raiswell’s findings are correct, more icebergs would mean more dissolved iron, therefore more phytoplankton, and more carbon dioxide sucked out of the atmosphere and into the oceans.

Plankton boost

“Dust has been thought to be the main outside source of iron to the Southern Ocean,” says Raiswell. He and his colleagues calculated that existing icebergs could double the supply of iron to the region.

The researchers will need to prove that the nano-iron can indeed boost plankton growth. Ken Denman of the Canadian Centre for Climate Modelling and Analysis says there is some debate over what form of iron phytoplankton can use. “For example, only a few percent of air-borne iron deposited in the oceans is believed to be readily utilisable by phytoplankton,” he says.

Denman also points out that climatologists think there is typically less iron in the oceans during warm inter-glacial periods. “Why would human-induced warming increase the iron supply whereas recent natural warming occurred at the same time as decreased iron and southern Ocean [phytoplankton], as far as we can tell from the ice cores?”

It is too early to say how much of an impact more icebergs will have. One problem is that not all plankton sinks to the bottom of the ocean and contributes to the deep-ocean carbon sink. Part of it is eaten by marine animals and returned to the water column in their excrement. Geochemists have only a poor idea of the amount of carbon that is cycled in this way.

Journal reference: Geochemical Transactions (DOI: 10.1186/1467-4866-9-7)

Sea levels set to rise faster than expected

Geneva, Switzerland: Even warming of less than 2°C might be enough to trigger the loss of Arctic sea ice and the meltdown of the Greenland Ice Sheet, causing global sea levels to rise by several metres.

Ahead of next week’s meeting of governments in Poznan, Poland for UN climate talks WWF analysis of the latest climate science comes to the dire conclusion that humanity is approaching the last chance to keep global warming below the danger threshold of 2°C.

”The latest science confirms that we are now seeing devastating consequences of warming that were not expected to hit for decades,” said Kim Carstensen, WWF Global Climate Initiative leader.

“The early meltdown of ice in the Arctic and Greenland may soon prompt further dangerous climate feedbacks, accelerating warming faster and stronger than forecast.

“Responsible politicians cannot dare to waste another second on delaying tactics in the face of these urgent warnings from nature.

“The planet is now facing a new quality of change, increasingly difficult to adapt to and soon impossible to reverse.

“Governments in Poznan must agree to peak and decline global emissions well before 2020 to give people reasonable hope that global warming can still be kept within limits that prevent the worst.

“In addition to constructive discussions in Poznan we need to see signals for immediate action.”

The CO2 storage capacity of oceans and land surface – the Earth’s natural sinks – has been decreasing by 5 per cent over the last 50 years. At the same time, manmade CO2 emissions from fossil fuels have been increasing – four times faster in this decade than in the previous decade.

WWF is urging governments to use the Poznan talks for an immediate U-turn away from the fatal direction the world is heading in.

“We are at the point where our climate system is starting to spin out of control,” said Carstensen. “A single year is left to agree a new global treaty that can protect the climate, but the UN talks next year in Copenhagen can only deliver this treaty if the meeting in Poznan this year develops a strong negotiation text.”

Article copyright WWF