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NATURE

Ocean studied for carbon dioxide storage

Researchers are studying the feasibility of storing liquid carbon dioxide deep in the oceans   

May 10, 1999
Web posted at: 12:00 PM EDT





Researchers at the Monterey Bay Aquarium Research Institute are studying the possibility of storing excess carbon dioxide from the burning of fossil fuels in the cold, high-pressure environment of the deep sea.

Carbon levels in the Earth's atmosphere have gone up about 25 percent since the Industrial Revolution primarily due to the burning of oil, coal and natural gas to supply about 80 percent of the world's energy needs.

These increased emissions of carbon are believed responsible for a one degree Fahrenheit increase in the global average temperature and if nothing is done to reduce the excess carbon, the Earth will continue to warm, resulting in a host of environmentally damaging consequences, according to some scientists.

Since scientists already know that the oceans naturally absorb carbon dioxide, they believe that one cost-effective way to mitigate global warming is to store the excess carbon dioxide in a liquid form in the depths of the ocean.

Ocean chemist Peter Brewer and his colleagues at the Monterey Bay Aquarium Research Institute and Stanford University designed and executed some of the first experiments to test theoretical predictions about the behavior of liquid carbon dioxide in the depths of the ocean.

Under cool temperatures and high pressures, carbon dioxide and other greenhouse gases react with water to form a solid ice-like compound called clathrate hydrate.

At shallow depths liquid carbon dioxide will rise to the surface. But based on laboratory experiments with carbon dioxide hydrates, researchers imagined that liquid carbon dioxide put deep in the ocean would form a stable layer on the seafloor with a skin of solid hydrate as a boundary, like a pond covered by ice in winter.

Brewer and his colleagues generated carbon dioxide hydrate from gas and liquid at depths ranging from 350 meters to 1,000 meters in Monterey Bay. At these shallow depths, they discovered that liquid carbon dioxide with a skin of hydrate is indeed less dense than seawater and will rise toward the surface and back into the atmosphere.

Brewer's most recent work, conducted last summer, concentrated on the behavior of liquid carbon dioxide at much greater depths where it is denser than seawater. In these experiments, the researchers injected several liters of liquid carbon dioxide into a glass beaker at a depth of 3,600 meters.

A video camera aboard the remotely operated vehicle that deployed the beaker relayed surprising information back to the researchers -- the liquid carbon dioxide was highly reactive with the surrounding seawater, significantly increasing in volume within the first hour of the experiment.

As water molecules combined with carbon dioxide molecules, gas hydrate formed and accumulated at the bottom of the beaker. The expanding volume of hydrate plus remaining liquid carbon dioxide caused globules of liquid carbon dioxide to spill over the top of the beaker, where they bounced to the seafloor and were carried easily away by the currents.

"Nothing like this was predicted," said Brewer.

Brewer and colleagues will conduct subsequent experiments this summer to test new hypotheses generated from previous results. They also have begun collaborations with ecologists from the institute to study the possible effects of liquid carbon dioxide on deep-sea organisms.

Ocean disposal for excess atmospheric carbon dioxide is gaining interest internationally with the recent adoption of the 1997 Kyoto Protocols to the United Nations Framework Convention on Climate Change. The enormous natural carbon buffering system of the ocean suggests that the deep ocean could absorb the amount of carbon that would cause a doubling in atmospheric concentrations and change its concentration by only two percent.

Brewer is optimistic that ocean disposal, while expensive, is a safe and viable option for deterring the harmful buildup of atmospheric carbon dioxide. "It's imperative to conduct research that will help us understand the fundamental science, the risks and the opportunities," he said.

An article on this research was published in the May 7 issue of the journal Science.

Copyright 1999, Environmental News Network, All Rights Reserved



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