How Much of the Ocean Is Unexplored?

Advances in ocean exploration technology allow us to see most of the seafloor.

A robot exploring an underwater reef with headlights. A cord hangs from the robot.

S_Bachstroem / Getty Images

The oceans make up around 70% of planet Earth, yet over 80% of the world's ocean remains unexplored. Since the global boom of ocean exploration technology began in the 1960s, deep-sea exploration has faced a number of barriers. Today, with fewer barriers in place than ever before, international efforts are underway to continue the exploration of the deep ocean.

Barriers to Ocean Exploration

Exploring the ocean is both expensive and technologically challenging—for reasons that are not so surprising. Robots created for deep-sea ocean exploration must be able to withstand the high pressure that comes with depth, operate without the need for maintenance for thousands of hours at a time, and be able to resist the corrosive effects of seawater.

Extreme Pressure

On average, the ocean is about 12,100 feet deep. At this depth, the pressure inflicted by the weight of the seawater above is over 300-times greater than the pressure we experience at the ocean's surface. At the deepest part of the ocean, about 36,000 feet below the surface, the pressure is over 1,000-times greater than the pressure at the ocean's surface.

Devices used for underwater exploration must be designed to withstand the intense pressure of the deep ocean. Submersibles designed to carry people aboard must also have the capacity to maintain an internal pressure compatible with what the human body can withstand. Typically, these manned submersibles use pressure hulls to control internal pressure.

However, these hulls can account for nearly a third of the total weight of the submersible, limiting the machine's capabilities. Until recently, the intense pressure in the deep ocean has been one hurdle preventing people from exploring the abyss directly.

Long Dives

It can take many hours for a submersible to get down to a target depth, let alone explore the environment. Given the substantial amount of time a submersible must remain underwater, all underwater robots must be built to be self-sufficient in a variety of circumstances.

There are three main types of robots used to explore the deep ocean: human-operated vehicles (HOVs), remotely-operated vehicles (ROVs), and autonomous underwater vehicles (AUVs). HOVs are submersibles designed to have people on board, whereas ROVs are operated by people remotely, typically from a ship at the surface. AUVs, on the other hand, are designed to be completely autonomous, exploring the ocean through pre-programmed missions. Once each mission is completed, the AUV returns to the surface for retrieval, at which point scientists get to process the data the AUV collected during its journey.

A robot being lowered into the ocean by a ship.
The U.S. Navy deploying their ROV Scorpio Two in February 2001. U.S. Navy / Getty Images

While HOVs allow scientists to explore the deep ocean directly, they are the most limited of the three types of ocean exploring robots when it comes to time underwater. Most HOVs can only dive for about five hours, whereas ROVs can easily stay down twice as long.

To make the most of the limited time people can spend at depth in an HOV, research institutes will sometimes deploy an ROV to explore an area before sending an HOV. The initial information collected by the ROV informs the HOV's mission, enhancing the potential for discovery during the HOV's narrow dive window.

Corrosive Seawater

Seawater's chemical properties result in electrochemical reactions that can degrade metals. In addition to considering extreme pressure and long dive times, deep-sea robots must be capable of withstanding seawater's corrosive properties. To combat corrosion, most submersibles today use polymers to create a protective barrier between the submersible's metal structure and the seawater.

Recent Progress

Advancements in deep-sea ocean exploration technology have accelerated since the turn of the century, particularly when it comes to transporting people to the deep ocean.

Deep-Sea HOVs

An old photo of a submersible surfacing from the ocean with two people in wetsuits standing on top and a ship in the background.
The Woods Hole Oceanographic Institution's HOV Alvin returning from a dive. CORBIS / Getty Images

First unveiled in the 1960s, the Woods Hole Oceanographic Institute's premier HOV Alvin continues to receive upgrades that maintain the famous robot's status as a piece of "cutting edge" technology. The famous submersible has been used to locate a lost hydrogen bomb in the Mediterranean Sea, allow the first direct human observations of deep-sea hydrothermal vents, and even explore the wreckage of the Titanic. The upgrades currently underway will expand Alvin's depth capabilities from 4,500 meters (14,700 feet) to 6,500 meters (21,300 feet). Upon completion, Alvin will be able to give scientists direct access to about 98% of the ocean floor.

In addition to Alvin, the U.S. operates two other HOVs through the University of Hawaii: the Pisces IV and Pisces V. Each of the Pisces submersibles is built to dive up to 2,000 meters (6,500 feet) deep.

Additional deep-diving HOVs are operated around the world. France's Nautile and Russia's Mir 1 and Mir 2 can each carry people down to 6,000 meters (19,600 feet) deep. Meanwhile, Japan operates the Shinkai 6500, an HOV aptly named for its 6,500-meter (21,000-foot) depth limit. China's HOV, Jiaolong, is capable of diving down to 7,000 meters (23,000 feet).

Deep-Sea ROVs

Despite recent advancements in HOV technologically, expanding people's direct access to the deep, remotely operated ROVs remain simpler to operate and safer to use than HOVs.

The U.S. National Oceanographic and Atmospheric Administration operates the Deep Discoverer, or D2, to explore the deep. The D2 can dive up to 6,000 meters (19,600 feet) deep and is equipped with advanced camera equipment capable of capturing high-definition video of tiny animals from 10 feet away. The D2 also has two mechanical arms for collecting samples from the deep.

The U.S. Navy also recently developed the CURV 21—an ROV capable of down to 20,000 feet. The Navy plans to use the CURV 21 's 4,000-pound lift capacity for deep-sea salvage missions.

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