Over 99% of the deep ocean seafloor remains a mystery, study finds

Explorers know that the Earth’s oceans are vast – covering about 71% of the surface of the globe. According to a new study, just 0.001% of the deep seafloor has been visually observed. 

The deep ocean seafloor is defined as depths of 200 meters or more below Earth’s surface, where oxygen levels are low and sunlight is virtually nonexistent.

The study, published in Science Advances, equates the area seen by human eyes to being even smaller than the state of Rhode Island.

"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," Katy Croff Bell, Ph.D., president of Ocean Discovery League, National Geographic Explorer and lead author of the study, said in a statement.

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Researchers said they arrived at the surprising figure based on a review of data from approximately 44,000 deep-sea dives conducted since 1958.

While scientists note that not all dive records are publicly accessible, even if their estimates were off by a factor of ten, it would still mean that less than one-hundredth of 1% of the deep ocean floor has ever been visually documented.

Due to the costs and the technology needed to explore at vast depths, only a few countries are equipped to scan the ocean floor. These countries include the United States, Japan, New Zealand, France and Germany.

What's it like down there?

In the deepest trenches, it is void of life, according to scientists. Organisms such as sea spiders and some crustaceans can be found among hydrothermal vents.

Water pressure is so immense that animals unsuited to the punishing environment would be killed. Because of the lack of sunlight, organisms must rely on senses other than sight to get around.

The limited knowledge of the oceans means entire ecosystems may remain undiscovered, and countless species are not well understood.

"There is so much of our ocean that remains a mystery," said Ian Miller, Ph.D., chief science and innovation officer at the National Geographic Society. "Deep-sea exploration led by scientists and local communities is crucial to better understanding the planet’s largest ecosystem. Dr. Bell’s goals to equip global coastal communities with cutting-edge research and technology will ensure a more representative analysis of the deep sea. If we have a better understanding of our ocean, we are better able to conserve and protect it."

Previous studies have suggested that potentially millions of plants and animals remain undiscovered simply due to the sheer size and inaccessibility of the oceans.

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The study’s authors argue that as technology advances and becomes more cost-effective, expanding efforts to explore the vast ecosystem become increasingly feasible and necessary.

By investing in emerging tools and strategies, researchers believe the world can gain a much deeper understanding of Earth’s most critical and least known ecosystem.