99.999% of the Deep Sea Remains Unexplored

Across Earth's deep oceans, explorers have taken a look at an area roughly the size of Rhode Island, which isn't saying much. That works out to about 0.001% of the deep sea, according to a study published Wednesday in Science Advances. In other words, 99.999% of the deep sea, defined as deeper than 200 meters, or 656 feet, remains unexplored. "As we face accelerated threats to the deep ocean—from climate change to potential mining and resource exploitation—this limited exploration of such a vast region becomes a critical problem for both science and policy," lead study author Dr. Katy Croff Bell, president of the Ocean Discovery League, says in a release.

ODL researchers brought together data on 44,000 deep-sea dives in 120 countries since 1958. They found nearly 30% of documented visual observations of the deep sea were completed before 1980 and tended to result in low-resolution black-and-white images. More than 65% have occurred within 200 nautical miles of the US, Japan, and New Zealand. Those three countries, along with France and Germany, have been responsible for 97% of all deep-sea submergence observations, according to the study. That's partly because deep-sea exploration is so expensive. The cost to explore one square kilometer of the deep sea can range from $2 million to $20 million, Bell tells the New York Times.

"This bias in geographic coverage and operator representation has led the oceanographic community to base much of its characterization of the deep ocean ecosystem on this incredibly small and unrepresentative sample," per the release. The study notes that to make assumptions about the deep sea based on observations of 0.001% of it would be like judging Earth by looking only at the Texas city of Houston. Researchers say deep-sea ditches and canyons, like the Mariana Trench and Monterey Canyon, have gotten a lot of attention, while huge areas, including abyssal plains and seamounts, are overlooked. "You can just imagine what's in the rest of the 99.999%," Bell tells the Times. (More deep sea stories.)