The Exploration of the Deep

In the first century A.D., Roman naturalist and historian Pliny the Elder believed that already the sea was understood, that the definitive list of marine fauna was complete—totaling 176 species—and that, "by Hercules, in the ocean ... nothing exists which is unknown for us." Sailors of his time knew that our blue planet was covered with a skin of seawater over much of its surface, but they could not know the vastness of the volume of water beneath the surface, nor how many different creatures might live there. It wasn't until French mathematician Pierre Simon Laplace calculated the depth of the Atlantic Ocean in the late 1700s that we began to understand what the "deep" in "deep sea" means. At an average depth of 2.2 miles, the deep sea, the largest ecosystem on our planet, has been hidden from our view, inaccessible and unknown, for nearly as long as man has sailed upon it.

The deep sea was long perceived as a lifeless world. In 1858, British naturalist Edward Forbes wrote that life could not exist below 300 fathoms (1/3 mile). Forbes's "azoic theory" was soon thoroughly discredited by Sir Charles Wyville Thomson, who led the first oceanographic circumnavigation of the world: the Challenger Expedition of the 1870s. Over four years, Thomson and his colleagues scraped the seafloor with trawls and dredges at depths of up to nearly five miles and recovered more than 4,000 new species of marine life. The dredged-up animals were often mangled almost beyond recognition, but they were nevertheless precious specimens that revealed hitherto untold tales about the rich diversity of deep-sea fauna. There were limits to what could be inferred from these samples; they often provided little insight into the way life on the seafloor looked, or into how the animals might interact with one another. To paraphrase explorer and humanist Théodore Monod, attempting to understand life in the deep sea using dredges is like aliens trying to understand life on Earth by blindly dangling a hook from space and retrieving a cockroach, a T-shirt, and an iPod. Trawls and dredges allow us to measure the biological diversity found in the deep sea—they are still used today for species counts and other statistics—but they are almost useless for understanding animal behavior in natural settings. To achieve this goal, one needs to observe organisms in their environment.

In the late 19th century, an underwater voyage was the dream of many adventurers inspired by Jules Verne's 20,000 Leagues under the Sea, but it was not until the 1930s that the first explorers descended beyond where light penetrates, into the relentless dark, the veritable deep sea. William Beebe—lanky, literary, lyrical naturalist of the Bronx Zoo—was the leader of these first deep dives, ultimately making a round trip half a mile down. Otis Barton, a young man of large fortune, designed and built the bathysphere, a tethered metal sphere with an inside diameter of less than three feet in which the deep-sea pioneers cramped themselves for several hours during each immersion. In accounts of his dives, Beebe gives attention to the pale green "dancing" lights—the bioluminescent lanterns of creatures unnamed and never seen before by any man—which came into focus before his astonished eyes.

As Beebe explored beneath the surface of the sea in his bathysphere, Swiss scientist Auguste Piccard was making the first flights into the stratosphere, "out far beyond the atmosphere," nearly 10 miles above the ground. To accomplish this feat, Piccard designed a pressurized, spherical gondola suspended beneath a hydrogen-filled balloon. Using the principles of design he learned from its construction, Piccard worked to fulfill his own dream of descending, untethered, into the depths of the sea. He built a small metal sphere that could withstand pressure and coupled it to a buoyant "balloon" filled with gasoline. Dream became reality when, in 1954, Piccard descended to a depth of 4,000 meters in his bathyscaphe, the first untethered class of vehicle to take people into the deep sea. In 1960, the Trieste, a second generation bathyscaphe operated by Piccard's son Jacques and U.S. Navy lieutenant Don Walsh, descended seven miles to the deepest part of the ocean, the Mariana Trench. The Walsh and Piccard dive was more a record breaker than a dive of exploration, but it is a record that remains unmatched today: More men have walked on the moon than have dived to the deepest part of our oceans.

The technological successes of the bathyscaphes inspired a team of U.S. oceanographers led by geologist Al Vine to call for a smaller, more maneuverable submersible that could be used to explore the deep sea. With its gasoline balloon, the Trieste was inherently buoyant; she sank only when loaded with expendable weights. Thus she could descend and ascend, but she could not adjust her depth once her weights were dropped, nor could she move laterally. Alvin, the three-person submersible named for Al Vine, was the first deep-diving submersible to require a pilot who could drive over the seafloor by controlling the angle and speed of a large aft propeller. Alvin made its first dives in 1964, marking the commencement of the true age of ocean exploration.

Alvin, together with the new French submersible, Cyana, demonstrated the merit of submersibles as scientific workhorses during an unprecedented mission of exploration: Project FAMOUS (French-American Mid-Ocean Undersea Study, 1972). Geologists were able to dive up to 2.5 miles below the surface and observe for the first time the Mid-Atlantic Ridge, the long volcanic mountain chain that bisects the Atlantic Ocean. In the mid 1970s, geologists shifted their focus from the Atlantic to the Pacific, diving to 1.5 miles on the Galápagos Rift, where they encountered warm water (20º C or more) flowing out of cracks in the rocky seafloor. Soon after, they discovered spectacular hot springs (350º C) spewing from tall mineral chimneys on the East Pacific Rise, the mountain range that begins in the Gulf of California and extends southward off the coasts of Central and South America.

Geologists had predicted that hot springs, "hydrothermal vents," would exist on the seafloor, but no one anticipated the extraordinary communities of strange animals bathed in the flow of warm water. Reports of six-foot-long red-plumed worms living on chemicals in the water hastened return trips to the dive sites by biologists. The seafloor observations of the late 1970s motivated the development of deep-submergence assets by other nations. Alvin and Cyana were joined by other deep-diving research submersibles operated by French, Canadian, Russian, and Japanese teams.

Since the discovery of hydrothermal vents in 1977, the pace of exploration in the deep sea has steadily increased, fueled by the finding of novel adaptations to extreme environments and by the gain of fundamental insights into how our planet works. Our increasing ability to access the seafloor with new tools and sensors promotes and enhances exploratory activities. Tethered and untethered robots are now the tools of choice for many of the challenges faced by deep-sea explorers. Nevertheless, the construction of two new human-occupied submersibles, one Chinese and the other American, underscores the anticipated need for a human presence on the seafloor for the next half century.

Man has observed less than one percent of the seafloor; the challenge lies before us. During the 20th century, the deep sea became accessible. In this 21st century, the deep sea will become known.

Cindy Lee Van Dover is professor of marine biology at Duke University, director of the university's Marine Laboratory, and chair of its Division of Marine Science and Conservation. She previously taught at the College of William and Mary.

Related Articles

4,000 Meters Below
New Research Reveals the Wonders of the Deep Sea
By Claire Nouvian

The Exploration of the Deep
By Cindy Lee Van Dover

Living Lights in the Sea
By Edith Widder

The Deep Seafloor: A Desert Devoid of Life?
By Craig M. Young

Gas Promotes Mass: Methane Seeps
By Lisa Levin