Tokyo

Japanese researchers are beginning to make public the first data from a project that could allow waste carbon dioxide to be dumped in the ocean. The tests are aimed at finding what concentrations of carbon dioxide can be tolerated by worms and bacteria living in the muddy sea floor.

But critics of the scheme say that even the ‘safe’ limits determined by the project could still be harmful in the long term.

Researchers and industry are interested in pumping waste CO2 down to the sea floor to reduce atmospheric levels of the greenhouse gas. But the idea is controversial. Recent tests have shown that the rise in oceanic CO2 levels from natural absorption from the air over the next century could have a detrimental effect on sea creatures’ ability to make shells (R. A. Feely et al. Science 305, 362–366; 2004). Higher concentrations from dumped CO2 could have an even greater impact.

In the project, conducted by the Research Institute of Innovative Technology for the Earth (RITE) in Kyoto and the research arm of the Kansai Electric Power Company in Osaka, plastic containers were placed on the sea floor off the coast of Japan. Carbon dioxide was then pumped into the containers.

Extremely high concentrations of 20,000 and 5,000 parts per million caused most visible creatures, such as nematodes, to die, the team says, although the abundance of smaller creatures and bacteria was barely affected. Shigeo Murai, the ocean chemist who heads the project, says that RITE is working on technologies to dilute CO2 to concentrations tens of thousands of times lower than those used in the experiments before introducing it to the sea floor. This means it should have no effect on marine life, he says.

But Kenji Kato, a microbial ecologist at Shizuoka University, says that low concentrations could also have an effect in the long term. Even if the number of bacteria stays the same, he says, the species of bacteria present could be changing: “An entirely new community could grow in a few months.”

It is also unclear how the CO2 would disperse once it is on the sea floor. Experiments to assess this have been blocked in the past by environmental protesters (see Nature 419, 6; 200210.1038/419006b). Murai plans to look at a natural outlet of CO2 seeping into the ocean floor around Okinawa to study its dispersion.