The deep sea is one of the hardest areas on Earth to study. The crushing pressure created by gravity, along with absolute darkness, make it hard to reach and navigate safely.<\/p>\n
\u201cWe know more about the dark side of the moon than we do about this, the deep seafloor,\u201d Kenneth Macdonald, a marine geophysicist and professor emeritus at University of California Santa Barbara who was not involved in the study, told Mongabay.<\/p>\n
Researchers have used seafloor mapping, which involves the use of sonar, more than imaging, largely because the former is more practical: Sound waves travel farther than light waves. More than a quarter of the seafloor has been mapped, thanks largely to a major international project called Seabed 2023 that is currently underway.<\/p>\n
Seafloor imaging, which began in 1958, is a slower undertaking: Many of the remote operating vehicles (ROVs) that are used to capture imagery move at below 1 mile per hour and have a visual field just 10 meters (33 feet) wide. Not surprisingly, it\u2019s also very expensive. The ROVs cost millions of dollars each and often require big research vessels to bring them out to sea, where it can then cost roughly $100,000 a day to run seafloor operations, Bell said.<\/p>\n
Given the logistical challenges, it\u2019s no surprise that seafloor imaging has been limited. But until now, just how limited hasn\u2019t been known. Data on observations were spread out at institutions all over the world, and no one had ever collected and analyzed them globally.<\/p>\n
\u201cNobody had ever done the math before,\u201d Bell said.<\/p>\n
Bell and her team didn\u2019t collect the photos and videos of the seafloor \u2014 building such a central repository or archive would be a separate project \u2014 but rather the data on those observations: where they were taken, how many dives and types of vehicles used.<\/p>\n
From that database, they used two complementary methods to determine the percentage of the deep seafloor that had been imaged. One was a dive-based method: They estimated the size of area covered per dive for each type of ROV and extrapolated. They found that a maximum of 2,130 square kilometers (822 square miles) had been covered \u2014 well under 0.001% of the deep seafloor.<\/p>\n The authors\u2019 more conservative 0.001% estimate in fact comes from the second method, which was based on the total time in the water and at the seafloor (\u201cbottom time\u201d), taking into account ROVs\u2019 speed and the width of their visual fields. Using this method, they calculated that total seafloor coverage since 1958 has been 3,823 square kilometers (1,476 square miles). That\u2019s about 0.001% of the deep seafloor, which covers two-thirds of the Earth\u2019s surface. (They define the deep seafloor as that found more than 200 m, or 656 ft, beneath the surface.)<\/p>\n Bell said there are surely seafloor observations that didn\u2019t make into the database, but she and her team made efforts to counter that by overestimating the visual coverage figures. In any case, even if their finding was off by an order of magnitude, it would still be powerful, she said.<\/p>\n Larry Mayer, a geophysicist at the University of New Hampshire who is one of the leaders of the Seafloor 2023 mapping project, and who wasn\u2019t involved with the new study, told Mongabay that it was a \u201creminder to people about how big the ocean is and how little we know about it.\u201d<\/p>\n Mayer said that imaging is a way to \u201cgroundtruth\u201d other techniques: Photo and video offer fine-grained details that mapping can\u2019t.<\/p>\n Matt Gianni, co-founder of the Deep Sea Conservation Coalition, an umbrella group of NGOs, agreed with Mayer about the importance of visual observation, saying that it offers key data on \u201clife history characteristics, community structures and the connectivity of both species and ecosystems.\u201d<\/p>\n Gianni emphasized that it\u2019s important for scientists to explain to regulators and policymakers that which isn\u2019t known. In such cases, decision-makers are sometimes legally bound to take a more precautionary approach when assessing the impacts of human activities, he said. The U.N. Fish Stocks Agreement, for example, requires member states to \u201cbe more cautious when information is uncertain, unreliable or inadequate. The absence of adequate scientific information shall not be used as a reason for postponing or failing to take conservation and management measures.\u201d<\/p>\n Lisa Levin, a biological oceanographer and marine ecologist emeritus with the Scripps Institution of Oceanography at the University of California San Diego, told Mongabay that a wide range of international institutions should bear the new study\u2019s findings in mind, including the regional fisheries management organizations that manage deep-sea fishing, the parties to the London Convention and Protocol that govern, among other activities, the potential use of marine carbon dioxide sequestration systems, and the parties to the Convention on Biological Diversity, which is implementing a \u201c30\u00d730\u201d initiative that aims to safeguard 30% of the planet\u2019s land and sea with official protections by 2030.<\/p>\n The study comes in the middle of international debate over deep-sea mining, which is governed by the International Seabed Authority (ISA), though U.S. President Donald Trump recently moved to circumvent that body and issue deep-sea mining permits unilaterally. (A spokesperson for the U.S. State Department told Mongabay that \u201cPresident Trump is prioritizing the revitalization of domestic maritime industries \u2026 and establishing the United States as a global leader in responsible seabed mineral exploration and processing.\u201d) Several experts told Mongabay that the ISA and U.S. authorities need to consider the lack of research that\u2019s been done before issuing permits. Likewise, Bell said Ocean Discovery League\u2019s position on activities like deep-sea mining is that more research needs to be done first; she said the group\u2019s focus is research, not advocacy, however.<\/p>\n Bell said the second major takeaway from their research was the high level of geographic bias in the results. Certain dive sites have gotten a disproportionate amount of research attention. Monterey Canyon on the U.S. West Coast was surveyed 3,530 times, nearly as much as all other canyons in the world combined. The U.S., Japan and New Zealand not only were home to most of the deep-sea dives but also, along with France and Germany, led the vast majority of the research: 97.2%. And the remaining 2.8% was also mostly done by high-income countries.<\/p>\n Deep-sea research dominance by high-income countries is slowly changing: A \u201cdiversity of operators\u201d is starting to emerge, the study says. That could lead to a wider range of areas and geological features surveyed.<\/p>\n \u201cPart of that is because of right now we\u2019re seeing [an increase in] lower cost, more accessible technologies to be able to study the deep sea, so that\u2019s going to hopefully decrease some of the biases that we see and enable more people in more places to explore,\u201d Bell said.<\/p>\n Bell, K. L., Johannes, K. N., Kennedy, B. R., & Poulton, S. E. (2025). How little we\u2019ve seen: A visual coverage estimate of the deep seafloor. Science Advances, 11(19). doi:10.1126\/sciadv.adp8602<\/p>\nCitation:<\/h2>\n