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Typhoons bury vast amounts of carbon dioxide at sea

Typhoons bury vast amounts of carbon dioxide at sea

  • 18:00 19 October 2008
  • news service
  • Catherine Brahic
In just a few days a single typhoon can dump the same amount of carbon to the bottom of the ocean as an entire year of rain. The storms do this by ripping mud and decaying vegetation off the land, and flushing it down rivers in huge floods and out to sea.

Two studies have recently measured just how much carbon gets moved from land to sea in this way and come to similar conclusions.

The researchers went to some lengths to conduct the study, tying themselves to secure land in the middle of the storms, and shoving bottles to the bottom of rapidly flooding rivers.

Carbon dump

Meng-Chiang Chen, who works at the headquarters of Taroko National Park in Taiwan, did this before, during and after super-typhoon Mindulle, which struck Taiwan in June 2004, and typhoon Aere, a category 2 storm that made landfall in August 2004.

He then sent the samples to Robert Hilton at the University of Cambridge in the UK to carry out the analysis.

Hilton and colleagues' analysis revealed that about 5000 tonnes of organic carbon were stripped from vegetation and soils, and carried down the LiWu river by the typhoon-induced floods. Ninety per cent of it was carried in just 14 hours.

When river and rainwater flows out to sea, it would normally float on top of the denser seawater. But in a typhoon, the floodwater contains so much mud and sediment it does just the opposite and slides beneath to the ocean floor.

This creates ideal conditions for storing carbon inside the sediment, though just how much is stored, and for how long, remains uncertain. "What is clear is that it has a high chance of being preserved if it is washed out to sea by these floods," says Hilton.

No CO2 remedy

The process could be significant because each year, several typhoons hit islands such as the Philippines, Taiwan and Japan, large parts of which are covered in forest.

By dragging huge amounts of soil and other organic matter out to sea typhoons effectively transfer the carbon from a place where it is dynamically exchanged between land and atmosphere to a place where it can be locked away.

However, Hilton warns that typhoons will do little to counter anthropogenic climate change.

"The typhoons store away carbon about 500 to 1000 times more slowly than we emit it by burning fossil fuels," he says.

Hilton says, though, that the figures roughly equate to the amount of carbon released from volcanoes and the weathering of rocks every year.

Steven Goldsmith of Ohio State University and colleagues also sampled rivers during Mindulle and came to similar conclusions (Geology, DOI: 10.1130/G24624A.1).

Journal reference: Nature Geoscience (DOI: 10.1038/ngeo333)

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