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A few years ago, film director James Cameron spent hours scouring the world's deepest ocean canyon for any sign of life. He found a few bizarre animals, but it turns out the real action in the Mariana Trench happens beyond the reach of a submersible's camera.
Researchers from Japan have found that bacteria thrive in the canyon called Challenger Deep, which is the lowest point on Earth's ocean floor and the deepest part of the Mariana Trench. They discovered an unusual community of bacteria there called heterotrophs, or microbes that cannot produce their own food and must eat what they find in the water.
The scientists reported their findings on Monday in the Proceedings of the National Academy of Sciences.
Cameron found that larger life forms were scarce, compared to what was found in shallower ocean waters. However, the heterotrophic life in Challenger Deep's waters was relatively abundant, similar to that in untreated well water, said lead study author Takuro Nunoura, a microbiologist with the Japan Agency for Marine-Earth Science and Technology.
The average depth of the ocean floor is about 13,120 feet (4,000 meters); its deepest point is in the western Pacific's Mariana Trench, where the Challenger Deep canyon bottoms out at more than 36,000 feet (nearly 11,000 meters) below sea level. [Infographic: Tallest Mountain to Deepest Ocean Trench]
The heterotrophs probably derive food from sinking particles, such as dissolved fecal pellets or dust, or possibly from geologic processes such as earthquake-triggered landslides, which could send organic-rich sediments tumbling into the canyon's depths, the researchers said.
"These big slope collapses are rare accidents in terms of human life spans, but they happen very frequently on a geologic timescale, and the release of organic compounds could continue for a very long time," Nunoura told LiveScience.
The research team measured the abundance of life and the temperature, salinity and chemistry of seawater from the surface waters above the Mariana Trench to the bottom of the Challenger Deep with a remotely operated vehicle. They used genetic fingerprinting techniques to identify different species of microbes, and found that the ocean's microbial diversity varied with depth.