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Methane Munching Microbes

Assessing the Southern Ocean’s Lines of Defense Against a Potent Greenhouse Gas

The aquarium in McMurdo Station's Crary Laboratory was full of some seriously odorous dirt recently.

The orange dive hut next to the Cinder Cones a short drive from the station was the team’s primary dive site to investigate the large mat of methane-eating microbes discovered below
Photo Credit: Mike Lucibella
The orange dive hut next to the Cinder Cones a short drive from the station was the team’s primary dive site to investigate the large mat of methane-eating microbes discovered below.
Researcher Andrew Thurber dons his dry suit as he prepares to dive under the sea ice
Photo Credit: Mike Lucibella
Researcher Andrew Thurber dons his dry suit as he prepares to dive under the sea ice.

“If they smell horrible, that means it’s a very successful sediment sample,” said Andrew Thurber, an ecosystems ecologist at Oregon State University. As the unmistakable smell of rotten eggs seeped out of the mud in their collection tubes, he and his team studied the methane-eating microbes living inside.

“It’s not the methane that smells, it’s the sulfide,” Thurber said, referencing the white by-product of these microorganisms’ digestive process.

He and his team extracted dirt full of these microbes from the seafloor near McMurdo Station. Five years ago, a plume of natural methane started seeping out of the seafloor near the station, providing researchers an unprecedented chance to study the formation and development of colonies of microorganisms that rely on methane for nourishment.

“It’s the first time we’re able to have this opportunity to compare this environment to other seep environments that we’ve seen around the world,” said Sarah Seabrook, a graduate student at Oregon State University. “We’re really fortunate that we’re able to see it with our own eyes when we go down there.”

The team’s aim is to better understand how these microbial colonies grow and evolve as methane first starts seeping out of the seabed. The research was funded by the National Science Foundation, which manages the U.S. Antarctic Program.

“These microbial mats can be a composed of a diversity of different organisms and one of the things that we’re trying to figure out is what they are and what they are doing,” Thurber said. “We don’t know anything about microbes that eat methane in the Southern Ocean, so there is a great opportunity to better understand how the microbial processes in Antarctica may influence our global climate.”

Methane gas can be produced either as organic matter decomposes, or through high-temperature, high-pressure geologic processes deep inside the Earth’s crust. It’s not entirely clear yet what the source of this methane is, and that is part of what Thurber is looking for.

Sarah Seabrook (foreground) and Andrew Thurber adjust their dry suits before a sample-collecting dive
Photo Credit: Mike Lucibella
Sarah Seabrook (foreground) and Andrew Thurber adjust their dry suits before a sample-collecting dive.

However, it’s the microbial colonies that eat methane which are his primary focus because understanding how they grow and thrive has major implications for the future of climate change.

“Methane is a greenhouse gas. [It’s] very efficient at warming our atmosphere, about 25 times more efficient than CO2,” Thurber said. “Thankfully there is a lot of biological activity that eats the methane before it can be released from the ocean into the atmosphere.”

Whenever a methane seep starts, these microbes, called methanotrophs, form large colonies around the source. They’re so efficient at consuming methane and converting it to carbon dioxide that very little actually makes it to the atmosphere as methane gas.

It’s a stable system for now, but climate change could dramatically disrupt this existing methane cycle. As the climate warms and ice sheets melt, methane will start to be released from the newly exposed seafloor.

Sarah Seabrook leaps into a dive hole drilled into the sea ice
Photo Credit: Mike Lucibella
Sarah Seabrook leaps into a dive hole drilled into the sea ice to collect microbe samples off the seafloor.

“The amount of methane that is potentially going to be released from the Antarctic as it warms… is equivalent to that of all of the arctic permafrost, so it’s a huge amount of methane,” Thurber said.

Whether these microbes that live around the Southern Ocean can stay ahead of this deluge of new methane is an open question. Most colonies like these form in deep, nearly inaccessible parts of the ocean, and no one has ever been able to observe one just as it starts out.

If it turns out that the microbes can’t keep up, it could mean that researchers might have to go back and reassess some of their climate change models for the worse.

“You’re still going to have this big amount of CO2 released, but if it’s not eaten by the microbes, for every molecule of methane released, that’s the equivalent of 25 molecules of CO2,” Thurber said. “So it’s really not good to have methane released.”

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Curator: Michael Lucibella, Antarctic Support Contract | NSF Official: Peter West, Office of Polar Programs