One of the most interesting scientific developments in recent years has been the discovery of life in some of the most extreme conditions on the planet.
From the waters surrounding deep-sea thermal vents and soils beneath the driest deserts, to deep within rock beneath the ocean floor and the frigid troposphere high above, microorganisms have shown a remarkable ability to survive in the unlikeliest of places.
Now, thanks to an international team of scientists and a specialized underwater robot, we can add the crushing pressures at the bottom of the Mariana Trench to those places where life has been found to thrive.
Located in the western Pacific, the Mariana Trench is nearly 11 km beneath the surface and the deepest known spot on Earth. There, pressures run as high as 15,750 psi, or roughly 1,100 times the standard atmospheric pressure at sea level.
Despite such an inhospitable environment, researchers found a “highly active bacteria community” living in sediments at the bottom of the trench. In fact, these sediments contain nearly 10 times more bacteria than sediments from the surrounding plain at a depth of only 5-6 km.
Deep sea trenches act as hot spots for microbial activity because they receive an unusually high flux of organic matter, made up of dead animals, algae and other microbes, sourced from the surrounding much shallower sea-bottom. It is likely that some of this material becomes dislodged from the shallower depths during earthquakes, which are common in the area. So, even though deep sea trenches like the Mariana Trench only amount to about two percent of the World Ocean area, they have a relatively larger impact on marine carbon balance — and thus on the global carbon cycle, according to lead author Professor Ronnie Glud of the Nordic Center for Earth Evolution at the University of Southern Denmark.
In order to detect the rates of microbial activity at such depths, a specially-designed robot measured the distribution of oxygen in sediments at the sea floor — a challenging but necessary approach since microorganisms that have adapted to such extreme conditions would likely die if brought to the surface for study.
The expedition to the Mariana Trench took place in 2010, and the research appeared online at Nature Geoscience, March 17.
A subsequent expedition has explored the bottom of the Japan Trench (9 km deep), and later this year the team is planning a dive in the world’s second deepest trench — the 10.8 km Kermadec-Tonga Trench near Fiji in the Pacific.
“The deep sea trenches are some of the last remaining ‘white spots’ on the world map. We know very little about what is going on down there or which impact the deep sea trenches have on the global carbon cycle as well as climate regulation. Furthermore, we are very interested in describing and understanding the unique bacterial communities that thrive in these exceptional environments. Data from multiple deep sea trenches will allow us to find out how the general conditions are at extreme depths, but also the specific conditions for each particular trench – that may experience very different deposition regimes. This will contribute to our general understanding of Earth and its development,” says Glud.