Life thrives at nearly 10,000 meters in the depths of the Kamchatka Sea.

The seas surrounding the Kamchatka Peninsula hide two of the deepest and longest marine trenches on the planet. They are the orographic expression of the plate tectonics behind the powerful earthquake that just occurred there this Wednesday in the far east of Russia. A scientific mission has now discovered that they are also home to the deepest ecosystems on Earth. The results of some thirty submersible dives, published this Wednesday in Nature , show how several complex living beings live in an environment rich in methane and hydrogen sulfide, poor in oxygen, and, of course, where not even a ray of light reaches.

Off Kamchatka, far out at sea, lies the Kuril-Kamchatka Trench, a 2,100-kilometer-long chasm that extends south from Japan. Forming almost a 45° angle, it meets the western part of the Aleutian Trench, which extends from Alaska, forming a fissure in the earth that stretches another 2,900 km. Here are some of the deepest areas on the planet after the Mermaid Deep in the Mariana Trench .

Its origin lies in the fact that up to six different tectonic plates meet in this region. The Kuril-Kamchatka Trench, for example, is the result of the Pacific Plate colliding with the Okhotsk Plate under the northern pressure of the North American Plate. This subduction is believed to be behind the magnitude 8.8 earthquake this Wednesday. This dynamic creates holes in the Earth's crust that reach as deep as 9,578 meters. Down there, without light or oxygen, one wouldn't expect life, but they've discovered that it exists; and it's very complex, abundant, and diverse.

“We found mollusks and siboglinids across a wide range of depths,” says researcher Vladimir Mordukhovich of the AV Zhirmunsky National Scientific Center for Marine Biology (Russia) and co-author of the study published in Nature in an email. Siboglinids are little-known animals that live in tubes on the seafloor. They were found in the so-called Sweet Winter Valley—the largest part of the two trenches had never been explored until now and is unnamed—at a depth of 9,533 meters. In another area, which the researchers have named the Cotton Field because of their striking resemblance, they found an even deeper concentration (9,566 meters) of these creatures with up to 5,813 siboglinids per square meter.

At somewhat higher elevations, they recorded several species of bivalves that would resemble white mussels, if it weren't for the fact that mussels don't exist at 8,764 meters below sea level. Furthermore, these newly discovered creatures are chemosymbiotrophic: "They receive organic carbon from symbiotic microorganisms capable of assimilating methane or utilizing reduced compounds, particularly sulfur," explains Mordukhovich. They also found various species of gastropods and, much higher up, the first deep-sea fish.

Megan Du, from the Institute of Deep-Sea Science and Engineering (IDSSE) of the Chinese Academy of Sciences and first author of the research, explains how these creatures survive thanks to the action of other microscopic organisms: “The symbiotic microbes within these animals use the energy obtained from the oxidation of hydrogen sulfide or methane to synthesize organic compounds,” explains Du. CO₂ reaches the seafloor in the form of organic matter. “The methane present in sediments is the result of microbial reduction of CO₂ derived from sedimentary organic matter, while hydrogen sulfide originates from the oxidation of methane and the reduction of sulfates,” explains the researcher.

So these are ecosystems based on methanogenesis, the deepest found so far. This work is based on 30 dives by the Fendouzhe , the IDSSE submersible and a symbol of China's burgeoning ocean exploration. But that means they've explored only a few kilometers of the more than 5,000 kilometers that the two trenches cover combined. Researchers believe there must be much more life down there, much more chemosynthetic fauna that has managed to thrive in such extreme conditions.

Life in the “death zone”

The discovery has significant implications for our understanding of the deep carbon cycle. Isotopic analyses indicate that methane in these environments is produced by microbial activity deep within sedimentary layers, which could sequester substantial amounts of the element, forming methane deposits, possibly in the form of gas hydrates. A note from the Chinese Academy of Sciences argues that this finding challenges the conventional view that the deepest ocean ecosystems are sustained primarily by particulate organic matter derived from the surface. The new results suggest, instead, that they may be sustained by "a carbon source from the deep subsurface," the note states.

From the Scripps Institution of Oceanography, University of California, San Diego (USA) professor Douglas Bartlett considers this work “shocking.” He argues: “Because it reports on an enormous distribution—across 2,500 km!—of chemosynthetic communities in the Kuril-Kamchatka Trench, one of the least studied trenches on Earth, and because the communities have been found to be very deep.” Bartlett, a microbiologist, participated in the Deepsea Challenge mission , which took film director and oceanographer James Cameron in March 2012 to the third deepest point on Earth—the Mermaid Deep, in the Marianas. There, they found traces of bacterial mats. But nothing like the ecosystems found now, which live in the hadal depths. This term to refer to the deepest marine ecosystems comes from the French hadal , zone of death, which refers to the Greek god of the underworld, Hades.

“They have acquired robust geochemical and isotopic data that support the widespread presence of methane-generating microbes and microbes capable of anaerobic [in the absence of oxygen] methane oxidation in syntrophic association [that feed off the metabolism of other organisms] with sulfate-reducing bacteria,” Bartlett notes. This particular form of methanogenesis is highly relevant to the American scientist, who was not involved in the new research: “The article also points to the distinctive phases of methane present at hadal depths and postulates that hadal cold emanations could form by a different mechanism than those present at shallower depths.” If confirmed, we would then be looking at an alternative way of sustaining life in what is etymologically called “the death zone.”