Descending to the Challenger Deep

SAN FRANCISCO — It’s not every day that scientists get to hobnob with a Hollywood director — especially one famous for bossing around Arnold Schwarzenegger, Leonardo DiCaprio and Zoe Saldana.

But on December 4, Titanic director James Cameron traded movie stars for Teva-sandaled geophysicists. In a packed lunchtime talk at a meeting of the American Geophysical Union, he showed off clips from his recent deep-sea exploration, particularly a record-breaking March 24 dive to the bottom of the Mariana trench. In the Deepsea Challenger submersible his team designed, Cameron plunged solo nearly 11 kilometers down, to the abyss known as the Challenger Deep.

It sounds like a cliché, but the deep ocean is truly the last frontier for natural science. The Challenger Deep has been visited only once before by humans — in the Trieste bathyscaphe in 1960 — and just a handful of times by robotic submersibles. (Even so, the deep ocean is not pristine. The first thing Cameron saw on touching down at the bottom was a pair of skid marks left years earlier by Japan’s unmanned submersible Kaiko.)

“My role is as an enabler of science,” Cameron told the AGU crowd. He geeked out like a little boy, his eyes gleaming with excitement, as he described developing the Deepsea Challenger’s steel pilot sphere, the surrounding composite foam body, and the system of LED lights and high-definition cameras that could survive crushing pressures of 16,000 pounds per square inch. His team of robotics experts and engineers used the same basic design to develop a pair of free-falling landers, which can be sent to the ocean bottom on their own or alongside the piloted submersible.

Together the three deep-sea vehicles have gathered a raft of discoveries, from both the Challenger Deep and during test dives at other nearby deep-sea trenches. The New Britain trench, for instance, turns out to be full of creatures called spoon worms 8.2 kilometers down. “If you’d seen these videos you’d love worms,” said Doug Bartlett, a marine scientist at the Scripps Institution of Oceanography who coordinated the science for Cameron’s expedition.

In a place known as the Sirena Deep, microbial mats blanket outcrops of deep-sea rocks, said astrobiologist Kevin Hand of the Jet Propulsion Laboratory in Pasadena, Calif. Water seeping through the rocks generates chemical reactions that produce methane and hydrogen — aka dinner for microbes. Such reactions, Hand said, may form the basis of life on alien worlds.

In the Challenger Deep itself, shallower dives yielded three main kinds of organisms, Bartlett said. There were sea cucumbers, also known as holothurians, which are the dominant megafauna of the deep sea. There were giant single-celled creatures known as xenophyophores. And there were the shrimp-like creatures known as amphipods — some measuring up to about 17 centimeters long.

Perhaps the most bizarre finding was that some deep-sea amphipods contain the chemical scyllo-inositol, which is being tested in people for treating Alzheimer’s disease. “Who’d have thought that a drug being used in clinical trials for Alzheimer’s would be found in a deep-sea amphipod?” Bartlett asked.

In the deepest dive of all, Cameron burned through his checklist of things to do by 8,000 meters deep. For the last 3,000 meters, he remembered, “I was left with nothing to do but communication checks every 15 minutes, and sit quietly and think about the pressure building up on the outside of the hull.”

As soon as he touched down, Cameron plunged a sampler into the seafloor to pick up some sediment, in case something went wrong and he had to leave right away. Which turned out to be a good idea, because the hydraulics system on the robotic arm was leaking fluid and wasn’t able to gather more samples as planned.

The bottom of the abyss was mostly sterile. Cameron piloted the sub about 200 meters across the seafloor, but the sandy bottom vista didn’t change.

“I personally feel we just barely got started — there’s so much more down there,” Cameron said. “When I was looking out the viewport with my own eyes, I was struck by how much we don’t know, how vast is the unexplored realm down there. These deep trenches are places where life might have emerged on this planet; they’re geologically dynamic places that can spawn tsunamis. What happens in these depths affects all of us.”

For now, though, it’s not clear when science might return to the Challenger Deep. Cameron’s sub is sitting high and dry at his ranch in Santa Barbara, waiting for someone who has the money and interest in turning it again towards science.