Seas absorb half of carbon dioxide pollution

  • 19:00 15 July 2004
  • news service
  • Maggie McKee
The world's oceans have soaked up half of the carbon dioxide pumped into the air by human activities since the beginning of the industrial age, according to new two studies. The gas is acidifying the seas and may harm marine life, the authors warn.

Atmospheric CO2 has shot up from 280 parts per million (ppm) in 1800 to 380 ppm today. But that figure would be greater than 435 ppm were it not for the oceans.

"The oceans are producing this tremendous service to humankind by reducing the amount of carbon dioxide in the atmosphere, which can lead to global warming," says Chris Sabine, lead author of one study and an oceanographer at the US National Oceanic and Atmospheric Administration (NOAA) in Seattle. "But it's changing the chemistry of the oceans and may have consequences for marine ecosystems."

Sabine, with other researchers from around the world, spent 10 years criss-crossing the globe in ships. They made nearly 10,000 stops along the way, measuring ocean temperatures and salinity, as well as levels of nutrients, carbon, oxygen, and chlorofluorocarbons (CFCs).

Cement manufacturing

They used chemical models and data from a similar ocean survey in the 1970s to subtract natural CO2 levels from their data. They also focused on depths that showed signs of recent contact with the atmosphere, such as CFCs.

The researchers discovered that the oceans have absorbed 48 per cent of all CO2 from fossil-fuel burning and cement manufacturing, which is dissolved in the top 10 per cent of the world's seas.

They also studied the effects of CO2 on sea creatures and plants. When CO2 dissolves in seawater, it forms carbonic acid, which in turn can dissolve the shells and skeletons of marine life.

The snail species Clio pyramidata, scooped up by the researchers during one cruise, had lost the ability to grow their shells, having being exposed to CO2 at levels of 1000 ppm for just 48 hours.

Domino effect

"Although the animals were actively swimming, their shells were clearly dissolving," team member Victoria Fabry, a biologist at California State University in San Marcos, told New Scientist. The animals' survival or reproductive success may be affected, or they may have to move to waters with lower CO2 concentrations, Fabry says.

"We don't really know what kind of domino effects might occur," says colleague Richard Feely, a marine chemist at the NOAA.

The dissolution of the calcium carbonate shells of animals and plankton also plays a key role in ocean chemistry, he says, those effects are "critical to understand how the oceans can absorb CO2 from the atmosphere in the future".

Ken Caldeira, a chemical oceanographer at California's Lawrence Livermore National Laboratory, who was not involved in the research, says the new studies may help inform a debate about whether to actively remove CO2 from the air and store it in the ocean.

"It's clear that putting more CO2 into the ocean would help global warming but there would be some biological cost associated with that," he told New Scientist. "It's not clear whether or not there would be a net benefit."

Journal references: Science (vol 305, p 362, 367)