Hint: it’s less than 1% — a lot less

It is a common refrain that we know more about the surface of Mars than the bottom of the oceans. Now, oceanographer Katherine Bell and her collaborators have quantified just how little of the deep seafloor scientists have actually explored: less than 0.001%, an area equivalent to about one-tenth the size of Belgium. The findings were published on 7 May in Science Advances¹.

The team collected data from about 44,000 deep-sea dives performed either by crewed deep-sea vessels or by remotely operated or autonomous submersibles. Their map shows how dives have focused heavily on waters near a few countries — especially the United States, Japan and New Zealand. Moreover, data from many of those dives are owned by private companies and unavailable to researchers. Vast expanses of the seafloor remain where the only information available comes from rough mapping tools such as sonar, Bell says. “The Indian Ocean is one of the least explored areas.”

This map shows the locations of deep-sea dives carried out between 1958 and 2024. Expeditions have focussed on a small number of places, primarily around the United States, Japan and New Zealand.Credit: Ocean Discovery League

Bell is the founding director of the Ocean Discovery League in Saunderstown, Rhode Island, a nonprofit organization that is helping to develop affordable remotely operated vehicles and leading an effort to compile a list of 10,000 potential deep-dive sites that could begin to sample a representative portion of the unexplored abyss.