Methane-ingesting microbes inhabit deep sea: Sink for greenhouse gases?


Methane seeps deep under the world's oceans may provide a previously-unrecognized sink for greenhouse gases, according to a new study. The greenhouse gas leaks from seafloors in these regions, leading to the buildup of rocks that were long considered dead.

Carbonate rocks on the seafloor provide a home for vast varieties of microbes which consume some of the gases contributing to worldwide climate change.

Many microbes in seafloor sediments are capable of ingesting methane, a powerful contributor to global warming. This effect is especially pronounced in layers where sulphate ions are being pulled in from water. The process helps fuel the metabolisms of the tiny creatures, according to researchers.

These biological actions raise the pH of surrounding water, and the alkaline environment causes carbonate ions to form calcium carbonate, commonly known as chalk. New research on methane seeps in waters near California, Oregon and Costa Rica shows biological material in these deposits. Samples were collected from more than 2,000 feet beneath the surface of the water, utilizing both robotic and human-operated submersibles.

The carbonate mounds under water provide a base for sponges and corals that make their homes on the rock. These can soon become populated by fish, crabs, clams and other aquatic lifeforms.

Carbonate deposits were bathed in water containing methane including carbon-14, a radioactive form of the element. Researchers discovered the substance was taken up by the samples, suggesting microorganisms within the rock were still alive.

Global warming studies have, so far, largely failed to account for uptake of greenhouse gases by these microscopic creatures, the study reports. Climatologists were long aware that these deposits acted as a sink for carbon, but the new study reveals these deposits likely have a greater effect on climate change than previously estimated.

"These [pieces of] data are very believable. Maybe we've been underestimating the amount of methane oxidation going on in the sea-floor setting," John Pohlman, a biogeochemist from the U.S. Geological Survey in Woods Hole, Massachusetts, said.

Researchers also discovered a wide range of other microorganisms within the carbonate deposits that do not consume methane. This could help investigators studying rocks buried beneath the surface of the Earth.

"Methane is a much more powerful greenhouse gas than carbon dioxide, so tracing its flow through the environment is really a priority for climate models and for understanding the carbon cycle," Victoria Orphan, professor of geobiology at Caltech, said.

Discovery of the role played by methane-ingesting microorganisms in ocean floor sediment on global climate change was profiled in the journal Nature Communications

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