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In the deep sea, subsurface microbes are plentiful and hungry

Researcher Elizabeth Trembath-Reichert is pictured operating the winch for the CTD water sampler, which was used to pump fluids back up to the research vessel from the Atlantic seafloor. Photo by Ben Tully
Researcher Elizabeth Trembath-Reichert is pictured operating the winch for the CTD water sampler, which was used to pump fluids back up to the research vessel from the Atlantic seafloor. Photo by Ben Tully

April 28 (UPI) -- Boreholes drilled deep into the floor of the Atlantic are offering scientists new insights into the microbial communities found thousands of feet beneath the surface of the ocean.

Scientists knew there were microbes living beneath the ocean floor, but until now, little was known about their energy requirements.

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For the study -- the results of which were published Wednesday in the journal Science Advances -- scientists sent a smorgasbord of snacking options down boreholes drilled into North Pond, a section of the western flank of the mid-Atlantic Ridge.

The experiments not only revealed the types of microbes living been beneath the ocean floor, but also the kinds of food they like to eat.

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"Our experiments use specialized tracers that can only be observed if a microorganism eats something on the buffet of options we provide," lead author Elizabeth Trembath-Reichert said in a press release.

"If we see these tracers in the microbes, then we know they must have been active and eating during our experiments and we get an idea of what food sources they can use to survive," said Trembath-Reichert, a geobiologist and assistant professor at Arizona State University.

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After retrieving the sample trays from the boreholes, which were drilled in 2010 as part of the International Ocean Discovery Program, researchers used a Nanoscale secondary ion mass spectrometer, or NanoSIMS, to identify the chemical signatures of different microbe species.

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Biomass and carbon levels within subseafloor environs are limited, but the latest research suggests that rocks and sediments buried beneath the ocean floor are covered in active, hungry microbes.

"The microbes we studied are extremely adaptable and are able to make a living in what seems like a really harsh environment to surface dwellers, like ourselves," said Trembath-Reichert.

The research suggests subseafloor microbes use a unique metabolic technique to consume carbon dioxide.

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Scientists hypothesized that microbes trap CO2 much the way plants do, "fixing" or converting it into more digestible forms of carbon, but the latest investigation provided little evidence of such.

"Our theory is that these microbes are being resourceful and using the carbon dioxide directly as a building block without having to convert it into a food source first," said Trembath-Reichert. "And this could have major implications for the deep ocean carbon cycle."

Scientists said they plan to conduct followup studies to better understand exactly how different microbe communities at the bottom of the ocean are utilizing what little CO2 is found 14,500 feet below the surface of the ocean.

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