In the northern Pacific Ocean, undersea slopes leading to the Aleutian Trench are believed to teem with worms, clams, anemones, and countless microbes thriving on methane bubbling up from the sediment. “People know they’re there,” Lisa Levin says of the deep-sea creatures. “But nobody’s had a good look.” One reason: Alvin, the iconic U.S. research submersible, could not dive deep enough.
Now, Levin, a University of California San Diego marine ecologist and biological oceanographer, is finally coming face to face with the otherworldly deep-sea ecosystem, thanks to a $50 million upgrade that will allow Alvin to dive up to 6500 meters deep. Levin’s mission, a survey of methane seeps off the coast of Alaska that embarked on 16 May, will mark the first crewed U.S. research expedition below 4500 meters, the submersible’s previous depth limit.
That limit allowed Alvin to reach about 68% of the ocean floor. But with its thicker titanium hull and stronger seals, Alvin can now reach about 99% of the ocean bottom—an expansion roughly equivalent to the combined areas of Asia, Africa, Europe, Australia, and North America—and match deeper diving submersibles operated by other nations.
The greater depth will give scientists a look at novel organisms and ecosystems, says Shana Goffredi, an Occidental College marine biologist on the Alaska expedition. Goffredi has studied life around shallower methane seeps, such as worms endowed with symbiotic microbes capable of converting methane into energy. Now, she wants to see whether the more extreme conditions at depths of about 5000 meters near the Aleutian Trench translate into different biological adaptations. “That’s one of the most exciting things about this expedition,” she says.
As Alvin is deployed elsewhere, the deeper range will also put sites such as abyssal plains in reach, says Jeffrey Marlow, an environmental microbiologist at Boston University. These vast stretches of flat, sediment-covered ocean bottom—as much as 6000 meters down—are in some places speckled with potato-size rocks rich in valuable minerals, making them a prime target for mining companies. But little is known about organisms that might be at risk. “There’s a lot going on beneath the surface, and we want to investigate that further,” says Marlow, lead author of a 2022 paper outlining research opportunities with a deeper diving Alvin.
Alvin’s new capability comes 60 years after the three-person vessel, owned by the U.S. Navy, revolutionized ocean research. Initially capable of carrying scientists nearly 2000 meters below the sea surface, it played a pivotal role in pioneering discoveries, such as the ecosystems clustered around underwater vents spewing chemical-rich hot water. But it last received a major upgrade in the 1970s, and in recent decades, other countries’ research submersibles began to surpass its capabilities.
Starting in the 1980s, France, Russia, Japan, and China built submersibles that could bring scientists to depths of 6500 meters. In 2020, China unveiled Fendouzhe (Striver), capable of carrying three people to the very deepest parts of the ocean, below 10,000 meters. Privately owned subs began to perform similar feats. In 2012, Titanic filmmaker James Cameron piloted the cramped one-person Deepsea Challenger to 10,898 meters, the deepest known spot on Earth. More recently, businessman Victor Vescovo took a custom-built two-person submersible to the deepest places in the world’s five oceans.
The United States struggled to catch up. The current upgrade was authorized in 2004 by the National Science Foundation, the Alvin program’s main funder. The original plan to replace it with an entirely new $22 million vessel by 2007 fell flat because of cost overruns and technical difficulties. “Let’s just say it was not our greatest hour,” says Will Kohnen, an engineer and founder of the company Hydrospace Group who served for nearly a decade on a committee overseeing the project.
The sub’s managers switched to overhauling the existing machine, but that proceeded slowly. Meanwhile, U.S. efforts to expand its deep-sea research capabilities suffered another setback in 2014, when its new $8 million robotic vehicle Nereus imploded while diving to 10,000 meters.
Now, the U.S. is finally rejoining the club of deep-diving nations. In addition to the newly fortified hull, today’s upgraded Alvin features a more spacious interior, updated cameras to give scientists a better view, and a sample basket twice the size of the old one.
Alvin won’t be able to go everywhere. The 1% of ocean beyond its reach might not sound like a lot, but it represents nearly half of the ocean’s total depth. To extend scientists’ reach further, U.S. agencies have opted for robots. On the Alaska expedition, Alvin will be accompanied by two new autonomous vehicles (AUVs) capable of reaching the ocean’s lowest points: Orpheus and Eurydice, named after the lovers in Greek myth who descended to the underworld.
Built in the wake of the Nereus disaster, the new devices are designed to be relatively cheap to replace, much like small “cube satellites” now orbiting Earth by the hundreds, explains Tim Shank, a deep-sea biologist at the Woods Hole Oceanographic Institution, which operates Alvin for the U.S. Navy.
Alongside the Aleutian Trench, Shank says, the two AUVs will voyage to the bottom at night to map the area and identify the best spots for Alvin to visit during the day. The machines are also capable of research of their own, extracting sediment cores, taking high-resolution photos, and carrying ocean chemistry sensors.
This iteration of Alvin may prove to be the last. As robotic vehicles become more advanced, with improved camera and video capability, there may be little scientific reason to send humans to the bottom of the ocean, says Weicheng Cui, a deep-ocean vessel expert at Westlake University in China. “From my personal point of view, this is the end of the manned submersible,” says Cui, chief designer of China’s Jiaolong submersible, able to reach 7000 meters. “That game is over.”
But Levin relishes the prospect of getting up close to ecosystems that have fascinated her for years. She has taken more than 50 trips to the deep in Alvin, and has learned that seeing things with her own eyes brings insights that can get lost through a camera lens. “The deep ocean is inches from you,” she says. “If you watch somebody’s slide show or watch somebody’s movie of a place, it’s not the same as going. It’s better to be there.”
More: https://www.science.org/content/article/em-alvin-em-iconic-research-submersible-plunges-deeper-ever
