Deepest spot on Earth a hotspot for bacteria, say scientists

At some 36,000 feet below the ocean's surface, the deepest part of the Mariana Trench hosts an oxygen-consuming community of microbes, a new study indicates.

Anni Glud
The central part of the autonomous instrument that was deployed to measure the oxygen dynamics of the sea-bed in the Mariana Trench at a depth of 11 km. Data documented intensified microbial life in the bottom of the trench as compared to conditions at the surrounding abyssal plains at 6 km water depth.

The deepest oceanic trench on Earth is home to a surprisingly active community of bacteria, suggesting other trenches may be hotspots of microbial life, researchers say.

Life in the deep ocean often relies on organic matter snowing down from above. As these particles waft down, their nutrients get degraded by microbes attached to them, so only 1 to 2 percent of the organic matter produced in surface waters is expected to make it to the average ocean depth of about 12,150 feet (3,700 meters). Just how much makes it to the very deepest parts is unknown.

To learn more about life in the dirt at the ocean's depths, scientists used a submersible lander to analyze mud from the surface of Challenger Deep, the deepest spot of the Mariana Trench at the bottom of the central west Pacific Ocean. This 36,000-foot-deep (11,000 m) trench is the deepest known point on Earth's surface.

Natural trap

The researchers analyzed the levels of oxygen consumption within the sediments, which revealed how active the deep-sea microbes were. They discovered unexpectedly high rates of oxygen consumption from the Mariana seafloor, indicating a microbial community twice as active as that of a nearby 19,700-foot (6,000 m) site about 35 miles (60 kilometers) to the south. [Strangest Places Where Life Is Found on Earth]

"In the most remote, inhospitable places, you can actually have higher activity than their surroundings," researcher Ronnie Glud, a biogeochemist at the Southern Danish University in Odense, Denmark, told OurAmazingPlanet.

Sediments from Challenger Deep also had significantly higher levels of microbes and organic compounds than the nearby, more elevated site. The investigators suggest the Mariana Trench acts as a natural trap for sediments from up high. Similar effects are seen in other submarine canyons.

"It acts as a trap just because it's a big hole. If you have a hole in a garden, it just fills up because things blowing over it tend to fall in, and the same is true with the seafloor," Glud said. The trench is also located in a subduction zone where one of the tectonic plates making up the surface of the Earth is diving under another, "and these areas are very unstable, and frequently see earthquakes that can trigger mudslides that transport material into the trench," he added.

Microbes, microbes everywhere

Another team of scientists recently discovered communities of microbes thriving in the oceanic crust. That research looked at rocks up to about 1,150 to 1,900 feet (350 to 580 m) below the seafloor under about 8,500 feet (2,600 m) of water off the coast of the northwestern United States. These microbes apparently live off energy from chemical reactions between water and rock instead of nutrients snowing from above.

"You can find microbes everywhere — they're extremely adaptable to conditions, and survive wherever they are," Glud said.

The researchers are now analyzing other trenches to see what bacterial activity is also relatively high there. They also want to learn more about the genetics of bacteria in the Mariana Trench and other trenches "to see how special these bacteria are compared to other bacteria," Glud said.

The scientists detailed their findings online March 17 in the journal Nature Geoscience.

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