Could frozen methane (called methane hydrate) trapped in the ocean floor be the answer to the world's energy problems? Even conservative estimates of the potential for this untapped resource are tantalizing, so researchers are trying to develop realistic models of hydrate distribution and rate of formation in seafloor sediments. In the lab, INEEL microbiologist Rick Colwell and his team are literally starving the methane-producing microbes called methanogens trying to get some answers.
Through the research, the INEEL is putting science to work to meet the nation's grand challenge of developing new energy resources.
The INEEL team is experimenting with a biomass recycle bioreactor to sustain methanogens at the near dormancy levels of their submarine home 300 meters below the seafloor. The reactor attempts to stabilize the stage when cellular processes are just on the border between survival and disintegration, and reproduction is none or minimal. Because the microbial activity is so minimal, it's a trial of patiently waiting for the data to slowly roll in, however. Colwell will present the team's results to date on Feb. 14, 2003, at the American Association for the Advancement of Science annual meeting in Denver. His presentation is part of the Environmental and Biological Diversity Symposium on Microbes Beneath the Earth's Surface.
The journey to study methanogens has brought some unexpected surprises along the way. When the team extracted microbial DNA from the marine sediment cores, they discovered more biomass and biodiversity much deeper in the seafloor than they expected. INEEL's collaborator, Dave Boone at Portland State University, has already identified what he believes to be a new species of methanogen, and has published a family tree of unique DNA sequences from the hydrate microorganisms to show other researchers the relationships of the cells from hydrated sediments to many other microbes.
This is particularly interesting because "the boundaries between different species, particularly in the diverse family of bacteria, can be hazy," said INEEL microbiologist Mark Delwiche.
Another surprise is that the methanogens seem happiest producing methane at 35 degrees Celsius (95 degrees Fahrenheit). "Since we found the methanogens living within a cool range of 8 to 16 degrees Celsius (50 to 60 degrees Fahrenheit), it's odd that they are clearly adapted to living in warmer temperatures-temperatures we wouldn't think they'd have been exposed to," said Delwiche.
"This makes us wonder if the microbes originated farther down in the earth where it's warmer, and then slowly migrated upwards," said Colwell.
One thing is becoming clear, however. "The true rates of methane production in deep sediments are likely much lower than values obtained in the lab," said Colwell.
"The team has detected methane production from a variety of food sources in all their lab experiments, within a wide range of incubation temperatures. But from what researchers know about the methanogens' native sediment dungeons, the microbes would need 300 times more food than we know is available there to be able to replicate the lab methane production rates," Colwell said. "It's difficult to create a harsh enough environment in the lab for these microbes, but we're starting to get a good feel for what conditions the methanogens really live in."
Aside from the potential as an energy source, it's important to learn more about hydrates because they help solidify seafloor sediments. When the overlying blanket of water changes temperature or pressure, hydrates can destabilize and release their cache of methane. When that happens on a small scale, the movement of the sediments can wreck subsea structures like drill rigs or pipelines that carry oil and gas. On a large-scale, hydrate destabilization may cause tsunamis and force climate change.
The team will continue its microbiological investigations of hydrate sediments using molecular methods to determine the biomass of the methanogenic microbes responsible for making the methane. The researchers plan to compare the methanogenic biomass in hydrate samples that came from offshore Oregon to the biomass present in hydrated sediments from deep beneath permafrost in the Canadian Arctic. By combining estimates of biomass to methanogenic activity in the reactors, they hope to provide data needed for the mathematical models that predict hydrate distribution and abundance.
INEEL microbiologists are part of a handful of researchers who have gotten access to hydrate-bearing sediment cores. Staff has participated in offshore drilling in 1999 and 2002, and drilling in the Canadian Arctic in 1998 and 2002.
Colwell noted, "We wish to thank the Department of Energy Office of Fossil Energy, Ocean Drilling Program, the National Science Foundation, the Japanese National Petroleum Exploration Company, and the Canadian Geological Survey for their generous support."
The INEEL is a science-based, applied engineering national laboratory dedicated to supporting the U.S. Department of Energy's missions in energy, national security, science and environment. The INEEL is operated for the DOE by Bechtel BWXT Idaho, LLC.
Technical contact: Rick Colwell, 208-526-0097, fxc@inel.gov. At the meeting: Holiday Inn Denver, 303-573-1450.
Media contact: Deborah Hill, 208-526-4723, dahill@nasw.org. At the meeting: 208-313-1251.
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