Scientists diving to astounding depths in two oceanic trenches in the northwest Pacific have discovered thriving communities of marine creatures that get their sustenance not by eating organic matter like most animals but by turning chemicals into energy.
They found these chemosynthesis-based animal communities - dominated by tube worms and clams - during a series of dives aboard a crewed submersible to the bottom of the Kuril-Kamchatka and Aleutian trenches. These creatures are nourished by fluids rich in hydrogen sulfide and methane seeping from the seafloor in this dark and frigid realm beyond the reach of sunlight.
These ecosystems were discovered at depths greater than the height of Mount Everest, Earth's tallest peak. The deepest one was 9,533 meters (31,276 feet) below the ocean surface in the Kuril-Kamchatka Trench. This was almost 25% deeper than such animals had previously been documented anywhere.
"What makes our discovery groundbreaking is not just its greater depth - it's the astonishing abundance and diversity of chemosynthetic life we observed," said marine geochemist Mengran Du of the Institute of Deep-sea Science and Engineering, or IDSSE, part of the Chinese Academy of Sciences, one of the authors of the research published on Wednesday in the journal Nature.
"Unlike isolated pockets of organisms, this community thrives like a vibrant oasis in the vast desert of the deep sea," Du added.
While some marine animals have been documented at even greater depths, nearly 11,000 meters (36,000 feet) below the surface in the Pacific's Mariana Trench, Du said, those were not chemical eaters.
In the new research, the scientists used their submersible, called the Fendouzhe, to journey down to what is called the hadal zone. The hadal zone is where one of the continent-sized plates that make up Earth's crust slides under a neighboring plate in a process called subduction.
"The ocean environment down there is characterized by cold, total darkness and active tectonic activities," said IDSSE marine geologist and study co-author Xiaotong Peng, leader of the research program.
This environment, Peng said, was found to harbor "the deepest and the most extensive chemosynthetic communities known to exist on our planet."
The Kuril-Kamchatka Trench runs about 2,900 km (1,800 miles) and is located off the southeastern coast of the Kamchatka Peninsula. The Aleutian Trench runs roughly 3,400 km (2,100 miles) off the southern coastline of Alaska and the Aleutian Islands.
The newly observed ecosystems were dominated by two types of chemical-eating animals - tube worms that were red, gray or white in color and around 20-30 cm (8-12 inches) long and clams that were white in color and up to 23 cm (nine inches) long. Some of these appear to be previously unknown species, Du said.
"Even though living in the harshest environment, these life forms found their way in surviving and thriving," Du said.
Some non-chemical-eating animals, sustained by eating organic matter and dead marine creatures that filter down from above, also were found living in these ecosystems, including sea anemones, spoon worms and sea cucumbers.
Du, the expedition's chief scientist, described what it was like to visit this remote watery sphere.
"Diving in the submersible was an extraordinary experience -like traveling through time. Each descent transported me to a new deep-sea realm, as if unveiling a hidden world and unraveling its mysteries," Du said, while expressing amazement at the remarkable resilience and beauty of the creatures the scientists witnessed.
The study illustrates how life can flourish in some of the most extreme conditions on Earth - and potentially beyond.
"These findings extend the depth limit of chemosynthetic communities on Earth. Future works should focus on how these creatures adapt to such an extreme depth," Peng said.
"We suggest that similar chemosynthetic communities may also exist in extraterrestrial oceans, as chemical species like methane and hydrogen are common there," Peng added.
