A Danish-led team of marine microbiologists looked at sediment samples collected by a robot from the bottom of the Mariana Trench and found evidence of bountiful bacterial activity.

The Mariana Trench, an undersea canyon in the west Pacific, is not a place one would expect to be teeming with life.

Microbes living at the bottom of this underwater fissure survive in near freezing temperatures, with no sunlight and in crushing pressures.

The sediment samples were collected by robot from Challenger Deep, the nadir of the Mariana Trench.

At 36,000 feet beneath the surface, it is the lowest point on the Earth’s surface relative to ocean level. By comparison, Mount Everest is 29,000 feet tall. 

The team analyzed the rate at which oxygen is consumed within the collected sediment samples to determine just how rich the floor of Challenger Deep is with microbial activity.

Counterintuitively, the oxygen consumption rate found at the deepest place on the Earth’s surface was double that of a nearby, much shallower undersea rift.

This curious result is explained by the fact that when dead sea animals and plant matter drift down toward the ocean floor, that organic material is more likely to collect in the very deepest pockets.

“It acts like a trap just because it’s a big hole,” explains Ronnie Glud, a biogeochemist at the Southern Danish University and the lead author of the study, published in Nature Geoscience. “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.” 

The Mariana Trench is formed by the convergence of two tectonic plates and therefore experiences frequent earthquakes. Resulting mudslides, which would bring more organic material to the bottom of the canyon, could also help to explain the surprisingly bacteria-rich environment. 

The discovery suggests that many of the world’s deepest and darkest oceanic canyons might be “hot spots” of microbial life.

Photo: Anni Glud