Methane-breathing undersea microbes that live on rocky mounds could be helping to remove greenhouse gas from the environment.
The microbes could be preventing greenhouse gas from entering the ocean and escaping into the atmosphere, Caltech reported. The findings could help researchers gain insight into where greenhouse gas is being consumed on the seafloor.
"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," said Professor of Geobiology Victoria Orphan, who led the study.
The microbes survive without oxygen, and primarily live off sulfate ions present in the seawater. Researchers recently discovered two different types of microorganisms work in a symbiotic relationship. One of these bacteria, dubbed "ANME," is related to the ancient single-celled creature archaea and works with bacteria to consume methane.
"Without this biological process, much of that methane would enter the water column, and the escape rates into the atmosphere would probably be quite a bit higher," said study first author Jeffrey Marlow, a geobiology graduate student in Orphan's lab.
This study observed ANME and their bacterial partners oxidizing methane inside carbonate mounds (rocky structures up to hundreds of feet above the seafloor) for the first time.
The researchers detected methane-breathing microbes within carbonate rocks from three cold seeps across the globe: "one at a tectonic plate boundary near Costa Rica; another in the Eel River basin off the coast of northwestern California; and at Hydrate Ridge, off the Oregon coast. The team used manned and robotic submersibles to collect the rock samples from depths ranging from 2,000 feet to nearly half a mile below the surface."
Looking at the recently collected carbonate rocks through a microscope, the researchers observed ANME and sulfate-reducing bacterial cells within the samples. The team used radiolabeled 14C-methane tracer gas to determine the amount of methane consumption in the carbonate rocks and sediment. They found rock-dwelling methanotrophs consumed methane at a slower rate than sediment-dwelling bacteria.
"The carbonate-based microbes breathed methane at roughly one-third the rate of those gathered from sediments near active seep sites," Marlow said. "However, because there are likely many more microbes living in carbonate mounds than in sediments, their contributions to methane removal from the environment may be more significant."
The finding suggests marine microorganisms effectively oxidize methane and remove it from the environment.
The study was published Oct, 14 in the journal Nature Communications.
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