More than 99% of the Deep Sea Still Remains a Mystery

The Trump Administration signed an executive order late last month aiming to fast-track approval for seabed mining critical minerals found in the deep sea. The move has faced international condemnation, particularly from experts who say that more research needs to be done into the impacts the practice might have on deep sea ecosystems, the majority of which remain unexplored.

A new study published today in Science Advances shows just how little we know about the deep sea. According to the research, humans have observed less than 0.001% of the deep seafloor—an area roughly the size of Rhode Island. 

The deep sea refers to the part of the ocean below 200 meters (656 ft.), at which light begins to disappear. Despite making up more than 90% of the Earth’s marine environment, much of the deep-sea ecosystems is still a question mark for researchers.

But the area is critical for maintaining our climate—absorbing about 90% of the excess heat and about 30% of the carbon dioxide that’s been released into the atmosphere by human activities. “If all of that had stayed into the atmosphere, it would make life on Earth practically impossible,” says Katy Croff Bell, president of Ocean Discovery League, National Geographic Explorer, and lead author of the study.

Read more: What to Know About Trump’s Push to Boost Deep-Sea Mining

The area humans have explored is vastly limited—and heavily biased towards certain regions. Over 65% of visual observations have occurred within 200 nautical miles of three countries: the United States, Japan, and New Zealand, meaning that much of our assumptions about the deep sea are based on a minuscule sample size.

“It’s like if we were to make all assumptions about terrestrial ecosystems from observations of 0.001% of land area, that would equate to smaller than the land area of Houston, Texas,” says Bell. 

To determine the amount of the seafloor we have explored, the team drew on data from approximately 44,000 deep-sea dives with observations conducted since 1958. The 0.001% also includes assumptions about the number of private dive records that are not publicly recorded.

Read more: A Climate Solution Lies Deep Under the Ocean—But Accessing It Could Have Huge Environmental Costs

Because so little is still known about this ecosystem, many experts fear deep-sea mining could come with too great a risk to the environment. Thirty-two countries have called for a moratorium on the practice, and Bell hopes the study shows the need for further research before countries begin extractive—and potentially irreparable—mining practices in the deep sea.

“[We need to know] what kind of impacts are we going to have on the deep sea, and will the deep sea recover from those activities?” Bell says. “That’s a big open question right now. What we don’t want to do is do irreparable harm to the deep ocean. So we really need this baseline information about the deep sea.”