Humans have visually documented about 1,470 square miles, or a mere 0.001 percent, of the deep seafloor, according to a new study. That’s a little larger than the size of Rhode Island.
The report, published Wednesday in the journal Science Advances, arrives as nations debate whether to pursue industrial mining of the seabed for critical minerals.
Some scientists argue that so little is known about the undersea world that more research on the deep seafloor is needed to responsibly move forward with extractive activities.
“More information is always beneficial, so we can make more informed and better decisions,” said Katy Croff Bell, a deep ocean explorer who led the study and is the founder of the Ocean Discovery League, a nonprofit group that promotes seafloor exploration.
Learning more about the deep sea is essential for understanding how climate change and human activities are affecting oceans, she said. But the study also highlights the fundamental excitement of exploration that drives many marine scientists.
“You can just imagine what’s in the rest of the 99.999 percent,” Dr. Bell said.
The era of visual documentation included in the study began in 1958, with the deep-sea submersible Trieste. The images collected since then let biologists discover new organisms and observe how they interact with each other and their environments, providing insights into ocean ecosystems.
Bringing deep-sea organisms to the surface to study is challenging. Adapted for high pressures, few animals, if any, survive the journey, so photos and videos are crucial.
“There are some habitats you can’t sample from a ship,” said Craig McClain, a marine biologist at the University of Louisiana who was not involved in the study. “You have to go there in an R.O.V. and do it,” he said, referring to remotely operated vehicles.
Getting seafloor visuals helps geologists, too. Before the advent of remotely operated undersea vehicles and crewed submersibles, researchers had a more limited approach: drop a big bucket off a ship, drag it along, haul it up and see what was inside.
“They’d just have a jumble of rocks and try to sort it out, with no context,” said Emily Chin, a geologist at the Scripps Institution of Oceanography who was not involved in the new study. “It’s like people who study meteorites, trying to understand a process on another planet.”
Seeing seafloor rock outcrops in photos and videos has allowed scientists to learn how fundamental Earth processes work. It also helps companies assess potential sites for mining and oil and gas activities.
But getting to the seafloor is expensive, both in funds and time. Exploring one square kilometer of deep seafloor can cost anywhere from $2 million to $20 million, Dr. Bell estimated. The dives can take years to prepare for, and just hours to go wrong. And once a dive is underway, it progresses slowly. A rover tethered to a ship has a limited radius of exploration, moving at a crawl, and relocating the ship is tedious.
With so many barriers, Dr. Bell wanted to know how much seafloor we’ve seen, and how much is left to explore.
Dr. Bell and her collaborators collected more than 43,000 records of deep-sea dives and assessed the photos and videos that have been collected, estimating how much seafloor area the dives documented.
All together, they estimated that between 2,130 and 3,823 square kilometers of the deep seafloor have been imaged. That works out to about 0.001 percent of the entire deep seafloor.
“I knew it was going to be small, but I’m not sure if I expected it to be quite that small,” Dr. Bell said. “We’ve been doing this for almost 70 years.”
The study excludes proprietary dives where the data are not publicly available, such as from military operations or oil and gas exploration. Even if those increased the documented area by an order of magnitude, Dr. Bell said, “I don’t think it’s enough to move the needle.”
Much of what deep-sea marine biologists know about the seafloor is based on that small fraction. The situation is akin to extrapolating information from an area smaller than Houston to all of Earth’s land surfaces, the authors say.
The study also found that high-income countries led 99.7 percent of all deep dives, with the United States, Japan and New Zealand topping the charts. Most dives were within 200 nautical miles of those three countries. That means that dives are being led by a small group of countries, potentially biasing what is researched and where, the authors said.
“There are many people around the world that have deep sea expertise,” Dr. Bell said. “They just don’t have the tools to be able to do the kind of research and exploration that they want to do.”
Dives tend to be in the same areas, such as the Mariana Trench or Monterey Canyon, or target the same kinds of features of interest, like hydrothermal vents, the study found. And since the 1980s, most deep dives have been in shallower, more coastal waters. That leaves many areas in the deep sea unexplored.
“The study is a good assessment of where we’re at and, quite literally, where we need to go in the deep sea,” Dr. McClain said.
