WHOI Robot Implodes In Deep-Sea Trench

The ocean exploration vehicle Nereus, seen here in Woods Hole during an early dock testing deployment. Nereus was a unique hybrid in the word of ocean submersibles: it operated as both a remotely operated vehicle via an optical fiber tether and as a free-swimming autonomous vehicle. It imploded in the South Pacific last week.
PHOTO COURTESY CHRIS GRINER/WHOI - The ocean exploration vehicle Nereus, seen here in Woods Hole during an early dock testing deployment. Nereus was a unique hybrid in the word of ocean submersibles: it operated as both a remotely operated vehicle via an optical fiber tether and as a free-swimming autonomous vehicle. It imploded in the South Pacific last week.

An unmanned deep-sea exploration vehicle built by the Woods Hole Oceanographic Institution (WHOI) imploded six miles below the ocean’s surface last Friday.

Named Nereus, the vehicle was exploring the Kermadec Trench in the South Pacific when the video feed from the robot suddenly went blank.

“We had a basket full of push cores [sediment samples], and had just picked the vehicle off the seafloor and started moving again, when all video went blank all at once,” WHOI engineer Daniel Gomez-Ibanez said. (Mr. Gomez-Ibanez, who is still on the research ship that was carrying Nereus, spoke to the Enterprise via a satellite phone on Wednesday evening, which was Thursday morning in the Western South Pacific.)

There was an “audible gasp” from the crowd watching the video feed. However, communication disruptions with Nereus were common, Mr. Gomez-Ibanez said. The vehicle talked to the ship via a 10,000-meter fiber optic cable that was vulnerable to any number of technical difficulties when spooled out that far—catastrophic failure was not the immediate assumption.

Nereus was programmed to drop its weights and ascend in the event of a communication failure. Once at the surface it would flash a light and send a radio signal to the ship.

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“We assumed it would be on its way back up,” Mr. Gomez-Ibanez said. But after the customary six hours, there was no sign of Nereus. “After six hours, we started to get nervous.”

There was then a scramble to communicate back to engineers in Woods Hole and assemble alternate locating devices.

After 14 hours, “Some of the deck hands started to see bits of white stuff” floating near the boat, Mr. Gomez-Ibanez said. The science crew came out and decided the white stuff was probably pumice, floating volcanic rock. They then “rushed back” to continue hunting for the vehicle, he said.

But one hour after that, another object surfaced: “It was unmistakably a piece of plastic,” Mr. Gomez-Ibanez said.

More and more bits of plastic from Nereus surfaced. The vehicle was made of many different materials, including ceramic floatation spheres built to withstand pressures of 16,000 PSI, but, Mr. Gomez-Ibanez said, “Plastic is the only part of the vehicle that can float” once broken up.

The ship’s net was out of commission and so three crew members deployed in a small boat and began scooping up the pieces with a milk crate. They filled three mesh bags the size of shopping bags with the debris before the “wind and waves began to kick up” and the captain ordered the small boat back in, Mr. Gomez-Ibanez said. The pieces may hold clues as to what caused the vehicle to fail.

The chief scientist on the Nereus cruise is WHOI biologist Timothy M. Shank of Falmouth. Dr. Shank recently launched HADES (Hadal Ecosystem Studies), a multi-million dollar global initiative to explore and coordinate knowledge about the world’s ocean trenches, funded by the National Science Foundation.

“This was our first cruise of the program,” Dr. Shank said, also speaking via satellite phone from the expedition’s ship, R/V Thomas G. Thompson. “It’s devastating,” he said of the loss of Nereus, which was the only vehicle in the world capable of collecting samples and sending video from the deep ocean.

That said, he added, “You don’t do deep ocean work without a lot of challenges. Nereus proved it can be done. We know it can be done, we just need to get another one built, and we’ll push for that.” Nereus was completed in 2008, and went on many successful dives, including to the bottom of the Mariana Trench, before imploding last week.

If the United States can send a rover 55 million kilometers to Mars, it should be able “to go 10 kilometers in our own ocean,” Dr. Shank said. “If that’s valuable to us, we should do it, we should have 10 Nereuses—we have another world on our own planet.”

On this most recent cruise, Nereus enabled Dr. Shank to “see habitat and trenches we’ve never seen before.” It brought up a dozen unidentified species from the depths, he said. One of the animals resembles an anemone, “But the back end looks like a sea cucumber, and the arms and tip look like coral—we’ve been staring at it, we’re perplexed.”

After the accident last Friday, the crew mobilized additional “free falling landers” and baited fish traps capable of reaching the bottom of ocean trenches and doing some basic sampling. “But these are static landers, they don’t move across the seafloor, like Nereus,” Dr. Shank said. Not wanting to waste valuable “ship time,” the crew continued to collect data for another week, he said. The expedition began April 11; science operations ended yesterday.

The loss of Nereus “is not the end of everything” said Mr. Gomez-Ibanez, who designed the vehicle’s thrusters and lithium-ion battery pack. “But it’s a big adjustment, not just for this cruise” but for several other cruises already planned that were depending on the vehicle, he said.

Nereus’s empty “cradle” on the ship deck is a constant reminder of the loss, he said. “Every time we walk past it, it’s not there,” he said.

But Mr. Gomez-Ibanez did have a hopeful moment the other day when he packed up Nereus’s spare set of thrusters. “I tested them, and cleaned them, and packed them up carefully so maybe they can be used again,” he said. The thrusters, he noted with pride, were “the only thrusters that have been successful in trenches.”

At the end of the conversation, Dr. Shank shared that he bought two silver bracelets in New Zealand for his daughters back home in Falmouth. He had affixed the bracelets to the side of Nereus on its final dive. (It is common for oceanographers to send objects down to the seafloor with their gear and bring them back up as mementos.)

“And those bracelets are on the seafloor,” Dr. Shank said. “So now I’m trying to figure out how long silver lasts in the deep oceans.” He and Mr. Gomez-Ibanez consulted on that point briefly, then he said, “Well, nothing lasts forever.”

Nereus was insured at a replacement value of $3.1 million, according to WHOI engineer Andrew D. Bowen.

To learn more about deep-ocean science, and read WHOI writer Kenneth D. Kostel’s blog posts from the Nereus cruise and the vehicle disaster, go to www.whoi.edu/hades

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