By Lee Anna Sherman
The colossal clamshells caught the young scientist’s eye soon after he arrived at Oregon State University in the late 1970s. Giant bivalves the size of footballs were piled in the corners of offices and cradled in the arms of researchers walking the halls of the School of Oceanography.
“I realized pretty quickly that they weren’t left over from a clambake,” marine geologist Erwin Suess recalls wryly.
Far from being beach-party cuisine, the mega-shellfish evidenced one of the most stunning discoveries ever made in ocean science. Superheated water seeping from deep-sea volcanic rifts, discovered near the Galapagos Islands during a 1977 expedition led by OSU oceanographer Jack Corliss, jolted the fields of marine chemistry and geology. The implications for scientists’ understanding of heat exchange and geochemical balance across the planet were profound. Even more startling was the host of outlandish creatures found thriving in the sulfurous, sunless depths.
These mysterious species – the gargantuan clams, red-tipped tube worms, ghostly crabs and other weird residents of the ocean’s hydrothermal vents – rocked biology to its core. Animals subsisting on gasses instead of sunlight had never been imagined, let alone witnessed from the portal of a manned submersible. These “chemosynthetic” organisms, scientists realized, could hold clues to life’s very origins in Earth’s ancient chemical soup.
“Here were animals living in the dark, in warm and chemical-laden water streaming out of the earth. It was as if these organisms had been left behind as the rest of the planet evolved toward the sun.”
— Joseph Cone,
Fire Under the Sea
On Their Shoulders
These discoveries underpin the work of a whole new generation of researchers in the College of Earth, Ocean, and Atmospheric Sciences (CEOAS). When Ph.D. candidate Brandon Briggs, for instance, hunkers over his microscope to study methane-making and methane-consuming microbes from the ocean’s subsurface biosphere, he is carrying on the legacy of Corliss, Suess and dozens of other marine geologists, physicists, chemists and biologists who, over the program’s 50-year history, have elevated COAS into one of the nation’s top-three oceanographic research institutions (along with Scripps and Woods Hole).
“I was drawn to the interdisciplinary nature of the research here,” says Briggs, whose passion for environmental microbiology took hold in his home state of Idaho. “You have to understand math, physics, chemistry and geology along with the microbiology. You have to be able to converse with people in all the different disciplines.”
Briggs’ research is anchored in a COAS discovery closely related to hydrothermal vents: ocean floor “cold seeps.” First located in 1984 at the Cascadia Subduction Zone by Suess and Professor LaVern Kulm, the cold-water vent systems leak methane and other carbon-rich fluids from decaying life forms buried in subsurface sediments. The seeps support their own unique collections of “extremophiles” – organisms that exist in ecosystems devoid of light or oxygen. The gasses not only feed such oddities as the “seep tubeworm” (which can live 250 years) but also play a role in another deep-sea anomaly being studied by Briggs under the advisement of geomicrobiologist Rick Colwell: gas hydrates.
Caged in Ice
Methane in ocean sediments can, under certain conditions of temperature and pressure, become locked into a lattice of water molecules to form ice-like structures. Once thought to exist naturally only on Saturn’s moons, hydrates have been found not only in ocean deposits around the globe but also in polar permafrost.
As a potential energy source, hydrates have gotten the attention of the U.S. Department of Energy, the agency funding Briggs’ and Colwell’s research. But the researchers warn that exploiting this resource must be approached with great caution. That’s because methane is a potent greenhouse gas and hydrates are highly unstable; their gaseous “guest” molecules escape rapidly when the “host” latticework melts. This poses serious worries for environmental science, Briggs says. A runaway greenhouse effect could be triggered if hydrate fields were disturbed by earthquakes, rising ocean temperatures, changing sea levels, deep-sea oil drilling, melting permafrost or ocean-floor mining, releasing massive amounts of trapped methane, the researcher explains.
“When temperatures rise, hydrates release their methane,” he adds. “There’s evidence that methane from hydrates may have been released into the atmosphere the last time Earth was really hot, about 55 million years ago during the Paleocene-Eocene Thermal Maximum.”
Examining core samples from Hydrate Ridge off the coast of Newport, Oregon, as well as from Canada’s Vancouver Island and India’s Bay of Bengal, Briggs is documenting microbial distribution using DNA analysis and studying biochemical pathways of microbes living in and around hydrates. Of special interest is the balance between microbes that make methane and those that use methane, the latter providing a brake on the accumulation of this gas in the environment. One central question is: If the rate of methane production were to speed up because of, say, rising temperatures, could the methane users keep up, or would they become overwhelmed and lose their buffering function?
“We’re interested in the amount of methane produced in deep marine sediments, what controls the rate of methanogenesis, and how that biogenic methane factors into the global carbon cycle,” says Colwell, a member of OSU’s Subsurface Biosphere Initiative who came to the university in 2006 from the Idaho National Laboratory.
The answers may help scientists predict harmful off-gassing from melting hydrates. They may also guide decisions about carbon sequestration and energy exploitation in the ocean.
“I’m motivated to find answers to the pressing questions of global climate change,” says Briggs.
Already, his research into the microbes’ biochemical pathways is yielding intriguing findings. He has, for instance, identified microorganisms living in “biofilms” – “slimy, pinkish-orange” coatings of bacteria – feeding on methane 60 feet deep in Indian Ocean sediments. “To have that amount of biomass that deep in ocean sediments is surprising,” Briggs says. “This hasn’t been reported anywhere else.”
On the Web: Exploring extreme deep-sea habitats has become a passion for Brandon Briggs and other students in Rick Colwell’s lab. Learn more here