Deep Sea Exploration: History and Facts

Here's How We Learn About the Deep Sea

DeepSee deep diving submersible in dark with lights on; Cocos Island, Costa Rica - Pacific Ocean
Diving submersibles make it possible for people to visit the ocean floor. Jeff Rotman / Getty Images

Oceans cover 70 percent of the Earth's surface, yet even today their depths remain largely unexplored. Scientists estimate between 90 and 95 percent of the deep sea remains a mystery. The deep sea is truly the planet's final frontier.

What Is Deep Sea Exploration?

Remote Operated Vehicles (ROVs) are cheaper and safer than human deep sea exploration.
Remote Operated Vehicles (ROVs) are cheaper and safer than human deep sea exploration. Reimphoto / Getty Images

The term "deep sea" doesn't have the same meaning to everyone. To fishermen, the deep sea is any part of the ocean beyond the relatively shallow continental shelf. To scientists, the deep sea is the lowest part of the ocean, below the thermocline (the layer where heating and cooling from sunlight ceases to have an effect) and above the sea floor. This is the part of the ocean deeper than 1,000 fathoms or 1,800 meters.

It's difficult to explore the depths because they are eternally dark, extremely cold (between 0 degrees C and 3 degrees C below 3,000 meters), and under high pressure (15750 psi or over 1,000 times higher than standard atmospheric pressure at sea level). From the time of Pliny until the end of the 19th century, people believed the deep sea was a lifeless wasteland. Modern scientists recognize the deep sea as the largest habitat on the planet. Special tools have been developed to explore this cold, dark, pressurized environment.

Deep sea exploration is a multi-disciplinary endeavor that includes oceanography, biology, geography, archaeology, and engineering.

A Brief History of Deep Sea Exploration

Scientists once thought fish couldn't survive in the deep sea because of the low oxygen content of the water.
Scientists once thought fish couldn't survive in the deep sea because of the low oxygen content of the water. Mark Deeble and Victoria Stone / Getty Images

The history of deep sea exploration begins relatively recently, mainly because advanced technology is needed to explore the depths. Some milestones include:

1521: Ferdinand Magellan attempts to measure the depth of the Pacific Ocean. He uses a 2,400-foot weighted line, but does not touch bottom.

1818: Sir John Ross catches worms and jellyfish at a depth of approximately 2,000 meters (6,550 feet), offering the first evidence of deep sea life.

1842: Despite Ross' discovery, Edward Forbes proposes the Abyssus Theory, which states biodiversity decreases with death and that life cannot exist deeper than 550 meters (1,800 feet).

1850: Michael Sars refutes the Abyssus Theory by discovering a rich ecosystem at 800 meters (2,600 feet).

1872-1876: The HMS Challenger, led by Charles Wyville Thomson, conducts the first deep sea exploration expedition. Challenger's team discovers many new species uniquely adapted to life near the sea floor.

1930: William Beebe and Otis Barton become the first humans to visit the deep sea. Within their steel Bathysphere, they observe shrimp and jellyfish.

1934: Otis Barton sets a new human diving record, reaching 1,370 meters (.85 miles).

1956: Jacques-Yves Cousteu and his team aboard the Calypso release the first full-color, full-length documentary, Le Monde du silence (The Silent World), showing people everywhere the beauty and life of the deep sea.

1960: Jacques Piccard and Don Walsh, with the deep sea vessel Trieste, descend to the bottom of the Challenger Deep in the Mariana Trench (10,740 meters/6.67 miles). They observe fish and other organisms. Fish were not thought to inhabit such deep water.

1977: Ecosystems around hydrothermal vents are discovered. These ecosystems use chemical energy, rather than solar energy.

1995: Geosat satellite radar data is declassified, allowing for global mapping of the sea floor.

2012: James Cameron, with the vessel Deepsea Challenger, completes the first solo dive to the bottom of the Challenger Deep.

Modern studies expand our knowledge of the geography and biodiversity of the deep sea. The Nautilus exploration vehicle and NOAA's Okeanus Explorer continue to discovery new species, unravel man's effects on the pelagic environment, and explore wrecks and artifacts deep beneath the sea surface. The Integrated Ocean Drilling Program (IODP) Chikyu analyzes sediments from the Earth's crust and may become the first ship to drill into the Earth's mantle.

Instrumentation and Technology

Diving helmets couldn't protect divers from the intense pressures of the deep sea.
Diving helmets couldn't protect divers from the intense pressures of the deep sea. Chantalle Fermont / EyeEm / Getty Images

Like space exploration, deep sea exploration requires new instruments and technology. While space is a cold vacuum, the ocean depths are cold, but highly pressurized. The saltwater is corrosive and conductive. It's very dark.

Finding the Bottom

In the 8th century, Vikings dropped lead weights attached to ropes to measure water depth. Beginning in the 19th century, researchers used wire rather than rope to take sounding measurements. In the modern era, acoustic depth measurements are the norm. Basically, these devices produce a loud sound and listen for echoes to gauge distance.

Human Exploration

Once people knew where the sea floor was, they wanted to visit and examine it. Science has progressed way beyond the diving bell, a barrel containing air that could be lowered into the water. The first submarine was built by Cornelius Drebbel in 1623. The first underwater breathing apparatus was patented by Benoit Rouquarol and Auguste Denayrouse in 1865. Jacques Cousteau and Emile Gagnan developed the Aqualung, which was the first true "Scuba" (Self Contained Underwater Breathing Apparatus) system. In 1964, Alvin was tested. Alvin was built by General Mills and operated by the US Navy and Woods Hole Oceanographic Institution. Alvin allowed three people to remain underwater for as long as nine hours and as deep as 14800 feet. Modern submarines can travel as deep as 20000 feet.

Robotic Exploration

While humans have visited the bottom of the Mariana Trench, the trips were expensive and only allowed limited exploration. Modern exploration relies on robotic systems.

Remotely operated vehicles (ROVs) are tethered vehicles that are controlled by researchers on a ship. ROVs typically carry cameras, manipulator arms, sonar equipment, and sample containers.

Autonomous underwater vehicles (AUVs) operate without human control. These vehicles generate maps, measure temperature and chemicals, and take photographs. Some vehicles, such as the Nereus, act as either a ROV or AUV.

Instrumentation

Humans and robots visit locations, but don't remain long enough to collect measurements over time. Undersea instruments monitor whale songs, plankton density, temperature, acidity, oxygenation, and various chemical concentrations. These sensors may be attached to profiling buoys, which drift freely at a depth of about 1000 meters. Anchored observatories house instruments on the sea floor. For example, the Monterey Accelerated Research System (MARS) rests on the floor of the Pacific Ocean at 980 meters to monitor seismic faults.

Deep Sea Exploration Fast Facts

  • The deepest part of the Earth's oceans is the Challenger Deep in the Mariana Trench, at 10,994 meters (36,070 feet or nearly 7 miles) below sea level.
  • Three people have visited the depths of the Challenger Deep. Film director James Cameron reached a record depth of 35,756 feet in a solo submersible dive in 2012.
  • Mount Everest would fit inside the Mariana Trench, with over a mile of extra space above it.
  • Using bomb sounding (throwing TNT into a trench and recording the echo), scientists have found the Mariana Trench, Kermadec, Kuril-Kamchatka, Philippine, and Tonga trenches all exceed 10000 meters in depth.
  • While human exploration still occurs, most modern discoveries are made using data from robots and sensors.

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