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Seafloor microbes hoover up methane, keeping global warming in check

Microbes (as seen via a microscope) found on the Port Dume seep off the coast of Southern California. Image by Jeffrey Marlow.

  • A new study found that carbonate rock mounds on the ocean floor host communities of microbes that actively consume methane, a greenhouse gas that is particularly potent if released into the atmosphere.
  • The researchers found that rock-inhabiting microbes consumed methane 50 times faster than microbes that live in sediment.
  • These microbes therefore play a crucial role in regulating the Earth’s temperature by consuming methane before it travels up into the water column and into the atmosphere.

Jeffrey Marlow says we should be thinking more about microbes — those teensy, tiny organisms that inhabit just about every part of the biosphere, but are only visible under the lens of a microscope.

“Microbes really matter in the environment,” Marlow, an assistant professor of biology at Boston University, told Mongabay in an interview. “They’re often out of sight, out of mind — but they are the first line of defense often in terms of climate change.”

Marlow is the lead author of a new study published in the Proceedings of the National Academy of Sciences that looks at microbes that live in carbonate rock mounds and their interactions with methane, the chemical compound that naturally seeps out of the seafloor. By collecting samples at seven different seafloor seeps around North America, Marlow and his colleagues figured out that rock-inhabiting microbes were actually consuming methane inside the rocks.

“That was surprising to me because we’ve often viewed these rocks as old repositories of ancient life, or past geochemical signals of what had happened in many years past, but the fact that they host these active microbes is pretty remarkable to me,” Marlow said.

What’s more, these microbes appeared to consume methane 50 times faster than microbes in sediment, the study found.

“We often see that some sediment microbes from methane-rich mud volcanoes, for example, may be five to ten times faster at eating methane, but 50 times faster is a whole new thing,” co-author Peter Girguis, a biologist and professor at Harvard University, said in a statement. “Moreover, these rates are among the highest, if not the highest, we’ve measured anywhere.”

A sensor being deployed above one of the Point Dume carbonate chimneys to measure the composition of the fluids being emitted. Image by Ocean Exploration Trust.

At a methane seep off the coast of Malibu, California, known as the Point Dume site, microbes were found to consume methane at rates five times higher than other prolific methane sites, according to the study. Marlow says they are still trying to pin down the exact reason why methane is consumed at various rates across the different sites.

Methane is a hydrocarbon that is the primary component of natural gas, the energy source used to power some kitchen stoves, heat our homes, or fuel city buses. It’s also a greenhouse gas that is 80 times more potent than carbon dioxide during its first 20 years in the atmosphere, causing warming at a faster rate. Yet microbial communities, including those inside carbonate rock mounds, prevent methane from moving up into the water column and into the atmosphere. So in this sense, methane-eating microbes also play a crucial role in regulating the Earth’s temperature.

“The microbes in these carbonate rocks are acting like a methane bio filter consuming it all before it leaves the ocean,” Girguis said.

The researchers identified 1,025 different microbial species across the seven sites they studied. Across the entire span of the Earth, there are an estimated 1 trillion microbial species.

Marlow says this study sheds light on the fact that methane-consuming microbes don’t just live in sediment, but also live inside of carbonate rock mounds. But he says there is still plenty to learn.

“How deep does it go into these rock mounds?” he said. “[That’s] another question. How far does it go into other geological settings? We’ve only started studying these sites around North America, but there are methane seeps all over the world.”

Citations:

Locey, K. J., & Lennon, J. T. (2016). Scaling laws predict global microbial diversity. Proceedings of the National Academy of Sciences, 113(21). doi:10.1073/pnas.1521291113

Marlow, J. J., Hoer, D., Jungbluth, S. P., Reynard, L. M., Gartman, A., Chavez, M. S., … Girguis, P. R. (2021). Carbonate-hosted microbial communities are prolific and pervasive methane oxidizers at geologically diverse marine methane seep sites. Proceedings of the National Academy of Sciences, 118(25). doi:10.1073/pnas.2006857118

Elizabeth Claire Alberts is a staff writer for Mongabay. Follow her on Twitter @ECAlberts.

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