| The Magazine of the CALIFORNIA ACADEMY OF SCIENCES |
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| Horizons Fire in Ice After enduring an extremely expensive winter, Californians are bracing themselves for a still costlier summer. With energy prices shooting through the roof, PG&E in bankruptcy, and the state's deregulated energy system in utter disarray, lights in the state may stay dim for some time to come. The importance of developing alternative energy sources has never been clearer. Oceanographers are already busy investigating one promising solution to humanity's wattage woes: a substance that bears a bizarre resemblance to dirty snow. Brought up from vast deposits at the bottom of the sea, a sand-stained chunk of this queer stuff will bubble and fizz like a dissolving Alka-Seltzer tablet. Touch a lit match to it, and it blossoms into a brilliant ball of flame. Although made from water, the ice actually encases flammable methane gas in a kind of molecular cage. Called methane hydrate, it could be an almost inexhaustible source of energy for the 21st century and beyond. There's certainly plenty of it. By some estimates, global methane hydrate deposits could contain as much as 60 million trillion cubic feet (tcf) of gas-more than 730,000 times the amount of natural gas the world consumed in 1998. Between five and twelve million tcf lies beneath the permafrost in Alaska, Canada, and Siberia near conventional gas and petroleum pockets. But the real mother lode-up to 50,000 million tcf-lies beneath the ocean, along the coastal margins of every continent. People still don't know much about methane hydrates, partly because they are stable only in environments that can't support human life. The requisite conditions range from a chilly -15¼°C to a little over 0¼°C, and the crushing pressures found between 500 meters and 1,000 meters below sea level. Turn up the thermostat, or ease up on the pressure, and the bars of this molecular cage melt to liberate molecules of methane. Chemists Michael Faraday and Humphry Davy first discovered the phenomenon of hydrates in the 1820s. But it wasn't until the 1970s that people first encountered natural hydrates with the help of submersibles and modern drilling technology. Some methane hydrates are essentially the frozen scraps of natural gas seeps on the ocean floor. Many of these have been found in the petroleum-rich Gulf of Mexico. But most of the methane in the world's hydrate deposits has been burped out by the bacteria that live 1,000 meters or more below the seafloor. "Bacteriologists are starting to understand that bacteria can operate at much higher temperatures and pressures than previously assumed," says William Dillon, head of the United States Geological Survey's methane hydrates research program. Like the microbial equivalent of lazy college students, these subterranean bacteria probably live off food delivered to their doorsteps. Sediments flowing from the land into the ocean bring with them decayed plant and animal matter. These wash onto coastal seabeds and are quickly buried and preserved beneath newly arriving sediments. Heat from the planet's molten interior cooks them into a form bacteria can consume. Instead of carbon dioxide, these deep biosphere bacteria make methane as a metabolic byproduct. Obeying gravity, the lighter-than-air methane bubbles travel slowly upward through the sediment. The farther they rise, the colder the methane becomes, until it freezes within the soils adjacent to the cold ocean bottom. "You wind up with something like concrete," says oceanographer Jean Whelan with the Woods Hole Oceanographic Institute. When the institute's Alvin submersible goes down to get samples, Whelan says, controllers use its robotic arms to pound in wedges just to pry up a few laboratory specimens. Research by William Durham of Lawrence Livermore Laboratories has shown that under some conditions, pure methane hydrate is up to 30 times stronger than ice. And as if these collection conditions weren't difficult enough, the Styrofoam-like chunks, once loosened, will promptly float to the surface. The billion-dollar question, of course, is how to exploit this peculiar substance for fuel. If someone can invent an extraction technology that's cheap and efficient, it could eventually overturn the current geopolitical apple cart. So just about any country with deepwater oceanfront property could become energy independent. Japan, which imports more than 95 percent of its fuel, has already hit pay dirt in its methane hydrate explorations. Just last year, engineers found gas hydrate in ideal conditions for extraction in the Japan Sea about 100 kilometers from Tokyo. The United States hasn't been left behind. Since 1998, Congress has committed millions of dollars to transform these buried treasures into usable fuel. Research has already turned up rich deposits along every coast and in Alaskan permafrost. In 2000, an experimental well sponsored by the United States, Japan, Canada, India, and Germany was drilled into Canada's Mackenzie Delta. Cores from the site are rich in gas, and are helping scientists understand how strong and stable sediments impregnated with gas hydrate can be. Petroleum producers live in fear of melting hydrate banks while installing or drilling with oil rigs, because the sudden expansion of gas could suddenly transform the solid ground supporting a drill rig into quicksand. The most efficient method to harvest this fuel would probably involve melting the ice and then collecting the methane that bubbled up. The science is simple: heat it, or lessen the pressure around the hydrate. However, no one has yet worked out an economically feasible way to extract the gas for commercial production. More attractive targets for energy explorers may be the pockets of free methane gas trapped beneath some methane hydrate deposits. These may have bubbled up but were prevented from traveling closer to the chilly ocean by the hydrate above them. A means to harvest methane hydrate could also benefit the world's air quality. While burning fossil fuels belch out the sulfur that causes smog and acid rain, lung-choking particulates, and toxic heavy metals, methane hydrate releases only water, hydrogen, and carbon dioxide. "So from an environmental point of view, it's got some big advantages," Dillon says. But carbon dioxide is a greenhouse gas that prevents heat from escaping the atmosphere and warms the planet. Since hydrates are so abundant, releasing their vast stores of carbon into the atmosphere through combustion could conceivably nudge the global temperature gauge well into the tropical range. "The picture many people have had, that hydrates are geochemical fossils that will stay inert for a long time, is not so," says Peter Brewer, an ocean chemist with the Monterey Bay Aquarium Research Institute. Because methane dissolves readily into seawater, even small changes in the ocean's temperature could melt the world's hydrate deposits en masse. Luckily for us, that's not likely to happen immediately. "It will take tens of decades for warm surface water to circulate down to the depths, and then you'll only break down gas hydrate at its shallowest feather edge," Dillon says. On a longer timescale, methane hydrate may actually have stabilized Earth's climate. During the last Ice Age, spreading glaciers locked much of the world's water up in vast ice sheets. The resulting drop in sea level and water pressure melted the lowest layers of hydrate along vast stretches of coastline, possibly triggering mammoth landslides and tsunamis off the eastern seaboard of the United States about 15,000 years ago. The sudden addition of so much greenhouse gas could have been enough to push the climatic pendulum back into a warming cycle. "Methane hydrate may be a real important reservoir for modulating the way our Earth works now," says Kevin Kvenvolden, a hydrates expert at the United States Geological Survey in Menlo Park. "If it's an important control on our climate, we shouldn't be messing with it. There could be a ratio we could use without affecting that, but no one knows what that is right now." Climate issues aside, exploiting hydrates on an industrial scale could have the immediate effect of destroying the unique marine oases clustered around hydrate deposits on the ocean floor. The deposits' rich carbon content fuels whole communities of unusual deepwater clams and mussels, worms, and examples of the most ancient life forms known, the archaebacteria. Among the unique species that have been found in places such as the Gulf of Mexico and the Cascadia Margin are fearsome-looking, four-centimeter-long "ice worms" (Hesiocaeca methanicola) that defend their shallow burrows dug into the hydrate formations. Annihilating these ecosystems to obtain a few extra BTUs would be unethical, says Michael Whiticar, professor of geochemistry at the University of Victoria in British Columbia, Canada. "These life forms are in a different system than we're used to seeing and often represent very ancient life that may be like what we might find on Mars. To lose that genetic information and diversity would be quite critical." Whiticar, for one, isn't rooting for methane hydrate to become a staple of the world's energy economy. He's hoping nonpolluting energy sources such as solar will attain mass market availability first. "If it takes 10 to 15 years before we have the capability [to harvest methane hydrate], we may run out of time. In a good sense." Kathleen Wong is Senior Editor of California Wild. |
Summer 2001
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