Community of organisms found at bottom of Mariana Trench

Life thrives at lowest depths


Scientists said Sunday that they had discovered an unexpectedly large and active community of single-celled organisms living on the Pacific seafloor at the deepest site on Earth.

The “surprisingly active” community of microbes exists in the Challenger Deep, about 11 km below sea level in the Mariana Trench. One of the world’s most inaccessible places, it lies about 350 km southwest of Guam.

Surprisingly, researchers found the trench housed almost 10 times more bacteria than a nearby 6-km-deep site, living on organic waste from dead sea animals, algae and microbes that settle on the ocean floor.

Many scientists had thought that the deeper a floor lies below sea level, the more deprived it would be of food, which has to sink all the way from the oxygen-rich surface to the bottom of the ocean.

In fact, the team found the Mariana Trench was unexpectedly rich in organic matter.

“Their analysis documents that a highly active bacteria community exists in the sediment of the trench, even though the environment is under extreme pressure almost 1,100 times higher than at sea level,” said a press statement.

The Mariana Trench made headlines a year ago when Hollywood director James Cameron made history’s first solo trip by submarine to the bottom.

Before Cameron, the trench had been briefly visited only once, by a two-man crew in 1960.

He described a “desolate” and “alien” environment.

Because of its extreme depth, the Mariana Trench is cloaked in perpetual darkness with temperatures just a few degrees above freezing.

The water pressure at the bottom is a crushing 1.2 tons per square centimeter — about a thousand times the standard atmospheric pressure at sea level.

For the latest study, an international research team used a specially designed underwater robot with ultrathin sensors to probe the seabed for oxygen consumption in a 2010 expedition.

Scientists cannot remove samples to study in the laboratory, as many of the microorganisms specially adapted to life at these extreme conditions will die due to changes in temperature and pressure.

The team also made videos of the bottom of the trench and confirmed there were very few large creatures at these depths.

“Rather, we find a world dominated by microbes that are adapted to function effectively at conditions highly inhospitable to most higher organisms,” said team leader Ronnie Glud from the University of Southern Denmark’s Nordic Center for Earth Evolution.

The Mariana Trench is a crescent-shaped scar in the Earth’s crust, more than 2,550 km long and 69 km wide on average.