‘It Really Is Otherworldly’: What It’s Like to Visit the Hot Springs of the Deep Sea

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Thousands of feet below the ocean’s surface, boiling hot plumes of seawater shoot like geysers into the abyss. There, some of the strangest life on Earth thrives. Thousands of white crabs with spindly legs creep along the seafloor. Eight-foot-long worms with bright red, mouthless heads poke out of white PVC-looking tubes. Massive golden octopuses float silently through the dark water.

This may sound like the last place on Earth you’d want to go, but what happens in this bizarre ecosystem can have huge implications for the biological makeup of the rest of the ocean. So a team of scientists with the Sylvan Geomicrobiology Lab traveled to the ocean’s bottom last year to check them out.

“It really is otherworldly,” Jason Sylvan, principle investigator on Sylvan Geomicrobiology Lab’s Hot2Cold Vents exploration project and microbiologist at Texas A&M University, told Earther. “You feel like you’re on another planet.”

The deep sea is one of Earth’s least understood environments—just one-fifth of the seafloor is mapped. On their cruise to the seafloor of East Pacific Rise, off the coast of Mexico, Sylvan and his team wanted to see what’s up with these weird plumes of water known as hydrothermal vents for themselves.

The vents form in the spaces where tectonic plates spread apart. There, hot magma rises and cools to form new seafloor. When cold ocean water seeps into these mid-ocean ridges, it gets heated up by that magma. As the seawater gets heated, pressure builds and sets off chemical reactions that pull in minerals from the rocks. Eventually, that sends the hot mineral-laden water shooting up through the seafloor. As the minerals cool down, they solidify and form giant chimneys through which mineral-rich hot water—reaching an average of 700 degrees Fahrenheit (371 degrees Celsius)—pours out.

To reach the vents, the researchers boarded a submarine and went nearly a mile underwater into the vast deep sea, remaining there in six hour spurts. Their vessel, called Alvin, was equipped with temperature probes, data collection devices, and a high quality 4K video camera. Sylvan has previously done this kind of exploration remotely by sending robotic vehicles to the seafloor to collect footage and data. But this time, he got a feel for what the vents are like in person by taking a journey to the bottom of the ocean.

“You just don’t have as good a perspective of what the system looks like,” he said. “I was blown away with just how much different it is actually being there and looking out a window and seeing the site right in front of you.”

Sylvan’s team was particularly interested in what happens to hydrothermal vents when they stop shooting out hot water. Inactive vents are even more poorly understood than active ones. Researchers think that inactive vents are less likely to contain “unique biology,” Sylvan said, “but the truth is we just haven’t studied them very much at all.”

But the way the ecosystems change when venting stops could have important implications for the biological makeup of the rest of the ocean, including release iron that could fertilize the ocean. It’s unclear whether that would benefit the deep sea or harm it, so Sylvan’s team took samples of the minerals and animals there to better understand how the ecosystems function.

The scientists found that the areas around the vents are filled with fish, mussels, and bright-white crabs. Some of the creatures they saw were downright bizarre, like an orange octopus with glassy blue eyes, and six-foot long tubeworms whose feathery red plumes act like gills, absorbing the seawater’s oxygen and the vent fluid’s hydrogen sulfide.

“You will never see anything like this on the surface,” said Sylvan. “It’s just the weirdest ecosystem that I know of.”

Because all vents will eventually become inactive, learning about the process of becoming dormant can help scientists understand how those changes impacts life in the ecosystems and beyond them. The research could have important consequences for public policy. Civic leaders and corporations have expressed interest in mining inactive vents for minerals, but scientists don’t yet understand what ecological effects that could have and how resilient the chimneys would be to those disturbances.

There’s barely been any research on these dormant ecosystems—just a handful of studies. But Sylvan and his team, who plan to take another submarine journey to the seafloor, are hoping to help change that, one spooky venture to the deep sea at a time.