Scientists Say Deep-Seafloor Rocks Host Life

Researchers have discovered life among lofty rocks at the bottom of the ocean.

Near natural methane (a greenhouse gas) seeps on the seafloor, these rocks are home to methane-eating microbes, recent research finds. On top of that, it appears that the tiny occupants can munch on enough methane to effect global levels of the gas, which can contribute to climate change.

“We’ve recognized for awhile that the deep ocean is a sink for methane, but primarily it has been thought that it was only in the sediment,” said study researcher Jeffrey Marlow, a graduate student at Caltech, to The Christian Science Monitor. “The fact that it appears to be active in the rocks itself sort of redistributes where that methane is going.”

More than a decade ago, Caltech geobiologist Victoria Orphan and team discovered that the mud on the ocean floor near methane seeps was not dead, and that in fact, it’s flourishing with bacteria and nucleus-free organisms called archae. The microbes eat natural methane that comes up from subsurface reservoirs—between six and 22 percent of the planet’s methane is released through these seafloor seeps, while microbes eat about 80 to 90 percent of that.

Towering rocks – hundreds of feet tall and long – are abundant in these deep ocean areas where the archae rest. Marlow notes that the carbonate-rocks had never been studied to see if they, like the seafloor mud, housed life.

Scientists initiated two expeditions that took place at Hydrate Ride, 62 miles off the coast of Oregon, where the undersea formation is dotted with methane vents. More than 2,000 feet deep, in near-freezing waters, the researchers gathered samples of rock near active methane cracks, as well as from patches without methane activity.

Through the use of two devices – Alvin, a manned research submersible, and Jason, a remotely operated submersible – 24 rock samples were brought out to be studied alongside samples from other methane seep areas in the Eel River Basin off northwestern California and the Costa Rica margin. Under microscopes, they found that samples from the rocks adjacent to the methane seeps were replete with microbes. Further DNA analysis uncovered both bacteria and archaea in similar levels as found in the seafloor mud.

To find out that the microbes were doing, the researchers attached certain molecules to methane that they then exposed to the rock-dwelling microbes. Used as tracking devices, the molecules allowed researchers to follow the methane activity, to see where it and its components ended up.

The expedition crew isn’t yet sure how much of the microbial methane-eating activity occurs in rocks versus in seafloor mud.

Additionally, it appears the methane-hungry microbes are likely the basis of an alien ecosystem on the ocean floor, playing the same role that plants play on land.

“There are worms crawling in and around in the rocks, in the sediments, that are very likely eating these clumps of cells,” Marlow said. “So they really are the primary producers in this entire system.”