Microscopic image of a group of multi-celled methane-oxidizing microbes found in deep-sea methane seeps in Hydrate Ridge, Oregon. (S. McGlynn, Caltech)
Microscopic image of methane-oxidizing microbes recovered from deep-sea methane seep sediments. Methane-oxidizing Archaea are stained with DNA probe in green, associated symbiotic bacteria are stained in blue. The orange-yellow materials are sediment particles. (S. McGlynn, Caltech)
Using the manipulator arm of the submersible Alvin to collect carbonate and associated animals from an active methane seep off the coast of Costa Rica. (L. Levin, SIO)
Manipulator arm of Alvin submersible collecting piece of carbonate from the ledge of the methane seep, Costa Rica Margin, 1,000 meters deep. (V. Orphan)
Carbonate slab collected from Costa Rica Margin seep, with associated worms, snails and limpets. (G. Rouse)
A piece of deep-sea carbonate ledge in the manipulator claw with attached white sulfide oxidizing bacterial filaments and anemone, from the Eel River Basin, off the California coast, 550 meters deep. (V. Orphan)
Submersible Alvin about to be launched from the back deck of the R/V Atlantis, Costa Rica Margin. (V. Orphan)
View of R/V Atlantis ship from inside Alvin after a successful dive to the methane seeps off of Hydrate Ridge, Oregon. (V. Orphan)
Sponges colonizing carbonates from a dormant methane seep site, Eel River Basin, California. (V. Orphan)
View from inside Alvin of carbonate pavement and boulders in an area of methane seepage from Hydrate Ridge, Oregon, 700 meters deep. (V. Orphan)
Mussels nestled within exposed carbonate mound in an active methane seep. Costa Rica Margin, 1,000 meter water depth. (V. Orphan)
California Institute of Technology geobiology class on a field trip to a paleo-methane seep outcrop in Panoche Hills, California. These ancient seep carbonates are Cretaceous-aged (~100-66 million years ago), extend nearly 20 kilometers and are approximately 200 meters thick in some areas. (V. Orphan)
The gas methane has been linked to rising temperatures on Earth. But methane does not stay in the atmosphere as long as another “greenhouse gas” -- carbon dioxide. Scientists say both gases trap heat from the sun. They prevent heat from escaping into outer space.
Methane can come from wetlands, as a byproduct of raising farm animals, and from human activities, such as leakage from natural gas systems. Methane is also plentiful in the ocean. It can be found in ice, but also rises from deep within the earth through small cracks, or holes, in the ocean floor.
Little of that methane reaches the atmosphere, thanks to methane-eating organisms that live in sea bed sediments – materials that sink to the sea floor. Now, an American scientist says other deep sea microorganisms are also attacking the gas. These organisms live in an unlikely place – inside rock on the ocean floor!
Victoria Orphan is with the California Institute of Technology. She studies microorganisms that live in sediment near methane vents in the ocean. These vents release methane trapped inside the earth. Ms. Orphan says the organisms have changed to survive in this extreme environment.
“These organisms would be able to extract energy from methane using sulfate found in sea water rather than oxygen. And as an end product, they would produce hydrogen sulfide, sort of that rotten egg smell. And also as another by-product, these organisms would produce carbonate, sort of like the pavement you see on the sidewalk.”
Over time, that calcium carbonate forms tall, rocky seamounts around the methane vents. Victoria Orphan suspected that these rocky areas served as a shelter for sea life. So she found a submersible -- a small vehicle like a submarine -- and went down 800 meters to the sea floor to prove it.
Ms. Orphan made four such trips between 2006 and 2011. As part of her studies, she collected sediments and seamount particles from the near-freezing water. She says the rocks she collected confirmed her theory.
“These are not just simply end products of methane oxidation, but they actually maintain a viable community of microorganisms living inside the pore spaces of the rock that turns out are still capable of consuming methane.”
However, her research showed the seamount microbes attacked the gas at a slower rate than the methane-eating organisms in the sediment. That is because not as much methane reaches the small holes in the rock.
“But considering that the volume of rock that’s available to colonize down in these deep-sea environments, it still can be a significant potential source of methane consumption. So instead of just considering this a process that is going on in sediments, we now have this whole other expansive habitat to look at as a sink for methane over time.”
The journal Nature Communications published her findings. She says the large number of small organisms – both in the sediment and in rock – explains how the microbes can limit the amount of methane in the world’s oceans. As a result, the gas has trouble reaching the atmosphere. And she notes that the worms, crabs and other creatures living around the rocks eating the microbes may show evidence of an ecosystem formerly unknown to scientists.
I’m Anne Ball.
*This report was based on a story from VOA Roseanne Skirble. George Grow wrote it for Learning English. The editor was Ashley Thompson.
Words in this Story
gas – n. any substance that is not solid or liquid
byproduct – n. a secondary product made in the manufacture of something else
atmosphere – n. the gases surrounding any star or planet
trap – v. to catch or be caught by being tricked; to be unable to move or escape
deep – adj. going far down; a long way from top to bottom
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