Going Deep With CO2

Deep exposure. The first sea-floor lab to test the effects of CO2 (top) on deep-sea animals didn't kill these caged eelpouts and an octopus, but sea urchins died and their spines dissolved (bottom, before and after

SAN FRANCISCO--The specter of climate change has prompted radical ideas, such as pumping CO2 into the deep ocean to slow its buildup in the air. Until recently, no one had done the difficult research needed to check how undersea storage might affect marine creatures. Now the first experiments exposing deep-sea animals to the greenhouse gas suggest that carbon dioxide harms life on the sea floor. However, scientists say the tests may have exaggerated the impact by subjecting animals to doses of CO2 far higher than they would sense during careful gas disposal.

Biological oceanographer Jim Barry and his colleagues at the Monterey Bay Aquarium Research Institute (MBARI) in Moss Landing, California, conducted the test this summer near the deep Monterey Canyon. The team collected aquatic organisms from the sea floor and placed them in cages underwater. Then the researchers injected about 50 liters of liquid CO2 into several plastic corrals in the ocean, 3600 meters deep, from a remotely operated vehicle. Other corrals were left empty. When the CO2 hit the seawater, it developed a bizarre icy "hydrate" layer, through which the gas slowly dissolved. This exposed nearby animals to pulses of CO2 and lower pH levels, indicating acidity. Barry's group set up pH meters and a time-lapse camera and left the animals alone for several weeks.

As the team reported here on 12 December at a meeting of the American Geophysical Union, the acidity near the corrals plunged by more than 1.0 pH units, to 6.5 and below--far more extreme than the reduction of 0.1 to 0.3 units forecast for a program of gradual deep-sea CO2 injection. Early results showed that bottom-dwelling creatures such as sea cucumbers and sea urchins died if they were close to a CO2 corral, and organisms in the sediments declined. However, fish and an octopus survived. The team gathered those animals to look for subtle changes in their metabolism or enzyme levels, which might cause harm over time.

Because the CO2 levels were so high, "it's not surprising to see a negative impact, since it's like putting a bird cage near a smokestack," says climate modeler Ken Caldeira of Lawrence Livermore National Laboratory in Livermore, California. "But because this sets the stage for looking at more subtle biological effects [from smaller pH changes], this is incredibly important work."

Related sites

MBARI news release on summer experiments
Greenhouse-gas research by MBARI oceanographer Peter Brewer
Department of Energy research on ocean carbon disposal

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