SEATTLE - New research on the distribution and formation of gas hydrates, a potential fossil fuel source, is changing ideas on how much hydrate is present in marine sediments and providing clues about how to find concentrated deposits, scientists said this weekend at the annual meeting of the American Association for the Advancement of Science.
Researchers have long known about the existence of large reservoirs of gas hydrate in sediments along the margins of continents, but quantifying this potential resource has been difficult because gas hydrates are not stable at the sea surface.
Gas hydrates are essentially water molecules frozen in a cage-like structure around gas molecules. When samples are recovered from the deep sea, they decompose into water and methane - ice that burns - and most of the gas hydrate that exists at the seafloor is lost.
As a result of research by Anne Trehu, a professor of oceanic and atmospheric sciences at Oregon State University, and colleagues at OSU and elsewhere, there is now a better understanding of how much gas hydrate is present in the seafloor and the geologic situations that control where it forms. This information is needed to identify likely targets for future extraction of methane from gas hydrates.
It should be possible to mine hydrates as fuel in the near future, researchers say.
Trehu and her colleagues have found that some widely cited previous models estimating the total mass of methane trapped in marine sediments are probably too high. On the other hand, some local concentrated deposits may be larger than previously thought.
"There is still a lot of methane out there, even if the models were wrong," Trehu said. "Part of our research involves developing more accurate models for the formation and distribution of methane hydrate deposits. Concentrated deposits have the potential to contribute to fossil fuel resources in about 20 years or so."
Although methane is considered to be a more environmentally friendly fossil fuel than most, Trehu says "we also need to take a much broader look at the energy picture and start moving away from our fossil fuel base."
Another reason why it is important to know how much methane is present in submarine gas hydrates is that methane is a powerful greenhouse gas that can trap heat 10-20 times as effectively as carbon dioxide. If released in large enough quantities, it could contribute to global warming.
"There is pretty strong isotopic evidence that global warming has been associated with massive hydrate dissociation in the past," said Trehu, "and a global change in sea level or temperature could trigger destabilization on a global scale. Earthquakes and other disturbances may trigger destabilization on a more regional scale."
Massive and simultaneous release of gas hydrate reservoirs is suspected as the cause of a global warming event about 55 million years ago, know as the Paleocene Eocene thermal maximum, although the mechanism of the release is still being debated. Researchers have suggested that this sudden change in climate may have been responsible for dramatic shifts in dominant plankton species, particularly through the extinction of species that could only survive in cold waters.
Trehu's recent research is part the Ocean Drilling Program, supported by the National Science Foundation and other national and international partners. COAS associate professor Marta Torres, doctoral student Joel Johnson, and masters student Johanna Chevallier are also involved in this research program. Her presentation was made at the annual meeting of the AAAS, one of the largest general science conferences in America.
Future research plans include establishing an observatory on the seafloor to see how the hydrate system evolves with time.