The deep ocean is a world of crushing pressure, freezing temperatures, and eternal darkness. For most of history, scientists considered the deepest parts of our planet — the hadal trenches, plunging more than 6,000 meters (about 20,000 feet) below the surface — to be desolate, life-starved voids. But a recent expedition has shattered that view.
A team of Chinese researchers embarked on a daring expedition onboard the Striver (Fèndòuzhě) submersible and discovered bustling ecosystems of tubeworms and mollusks not just surviving, but thriving, in the inky blackness of the northwest Pacific Ocean’s deepest trenches. These newly found communities, documented in a study published in Nature, were located at depths reaching a staggering 9,533 meters (over 31,000 feet).
Their location was telling: dense colonies of life clustered around geologic faults in the tectonic plate.
What Lies in the Deep
The vast majority of life on Earth requires sunlight to survive. Generally, you use sunlight to produce nutrients through photosynthesis, eat the plants that produce, or eat the animals that eat the plants. In the deep ocean, that just doesn’t work.
Sunlight generally penetrates the ocean to a depth of about 200 meters (656 feet) in water. After that, things get very dark and very cold.
Before this discovery, it was widely believed that life in the deep, hadal zone was scarce and depended solely on the slow rain of organic debris from above. This is not what researchers found. They came across communities dominated by slender, pale tubeworms known as siboglinid polychaetes and clam-like mollusks called bivalves. These creatures have formed a remarkable partnership with specialized microbes that perform a chemical magic trick. These microbes convert hydrogen sulfide and methane — toxic to most organisms — into energy that sustains the entire community. In essence, the microbes substituted photosynthesis with chemosynthesis, generating nutrients not from sunlight, but from the ocean’s chemistry.
These communities “are confined to areas where fluids rich in hydrogen sulfide and/or methane are released through geological fractures” the researchers state. One such site, teeming with worms and mollulsks, was aptly named “The Deepest,” as it is the deepest known seepage location discovered to date. In another area, dubbed “Wintersweet Valley,” thousands of tubeworms, with their red, plume-like tentacles extended, create an otherworldly garden on the seafloor.
So, where do these life-giving chemicals come from? It comes from everywhere and nowhere in particular. But it gets trapped in tectonically special places.
Communities in the Dark
The research team conducted isotopic analysis on the methane and found that it is produced by microbes in the sediment. These feast on organic matter that has drifted down from the surface waters over millennia. This organic material gets trapped in the deep trenches, and as the Pacific tectonic plate bends and subducts beneath the neighboring plates, it creates faults that act as conduits for the methane-rich fluids to escape.
The researchers suggest that these communities may be more common than previously imagined. “Given geological similarities with other hadal trenches, such chemosynthesis-based communities might be more widespread than previously anticipated,” they write. These findings fundamentally challenge “current models of life at extreme limits and carbon cycling in the deep ocean”.
Ultimately, the discovery opens up a new frontier in deep-sea exploration and forces us to rethink what we thought about the deep ocean. It expands the known habitats for life on our own planet and also provides a tantalizing glimpse into how life might exist in other extreme environments, both on Earth and potentially on other worlds.
For the full details of this groundbreaking research, you can read the original paper here.
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