Creatures of the deep see (such as this Rhinochimaera) are adapted to survive in the unique conditions. Photo Source: Flickr.

Creatures of the deep sea (such as this Rhinochimaera) are adapted to survive in the unique conditions. (Source: Flickr)

 What Do We Really Know?

Scientists know more about the surface of the moon than the depths of the oceans. Oceans cover 71 percent of the Earth, but less than five percent of their depths have been explored to date (1). Although it appears that little progress has been made, many new discoveries and inventions were created solely to see what lurks beneath. The curiosity to see the ocean floor led man to build boats to traverse water, develop sonic technology, build submarines, and develop scuba diving gear to see the mysteries of the dark depths for themselves.

The Early Years

It was believed that life could not exist deep in the ocean. At 200 meters (650 feet) below, light scatters and fades. At 4,000 meters (13,000 feet), the temperature drops almost to freezing, and the pressure increases to one nearly unbearable for humans (2). No light means no plant life, which ultimately implies no animal life.

In 1868, Scottish naturalist Sir Charles Wyville Thomson persuaded the Royal Society to support a deep-sea dredging project in the North Atlantic (3). Thomson made use of a tool called the marine biology dredge, a net with a digging apparatus used to scrap the ocean floor and catch forms of life (4). The original dredge, developed by Otto Friedrich Muller in 1830, did not have a closing mechanism, so samples often fell out, fueling the belief that no life existed on or in the ocean floor (4).

Aboard the H.M.S. Lightning, Thomson modified the dredge so that it could close; this adjustment allow him to collect many sponges, crustaceans, mollusks, and other organisms 300 fathoms (548.64 meters) deep in the ocean (3). This discovery increased support for deep sea exploration, and, in 1872, the H.M.S. Challenger was dispatched to begin a three-and-a-half-year oceanographic expedition with Thomson leading the charge (3). The dredges were dropped to deeper and deeper levels, and, by the end of the journey in 1876, 4,417 new species of marine organisms had been discovered, and hundreds of ocean floor and sea water samples had been taken (5). Thomson died before all of the results were compiled. Sir John Murray, another Scottish oceanographer, finished in his place, publishing 50 volumes of the Challenger’s results and discoveries. 

Measuring Depth

In the eighth century, Vikings measured sea depth by dropping lead weights attached to ropes overboard and recording how much rope was underwater when the weight reached the bottom (5). These lengths were measured in fathoms (1.8288 meters per fathom). In 1872, Sir William Thomson replaced the rope with thinner piano wire and invented the Thomson sounding machine (6). The machine still used a lead sinker, but the wire was released by a tension wheel and brake, and a dial registered how much wire was used (7). The Thomson sounding machine provided more accurate measurements of ocean depth and was used for many other expeditions.

The Sigsbee Sounding Machine. Image by Coast and Geodetic Survey - National Oceanic and Atmospheric Administration Central Library,

The Sigsbee Sounding Machine. (Source: Coast and Geodetic Survey – National Oceanic and Atmospheric Administration Central Library)

From 1873 to 1874, Commander George Belknap, aboard the U.S.S. Tuscarora, used a Thomson sounding machine on a telegraph cable to survey the Pacific Ocean. During that time, he discovered the Juan de Fuca Ridge, the Aleutian Trench, and the Japan Trench (6).  In 1874, Commander Charles Sigsbee made the Thomson sounding machine larger and replaced the piano wire with steel wire. This new machine was dubbed the Sigsbee sounding machine and became the basic model for wireline sounding for the next 50 years (6).

After the sinking of the Titanic in 1912, there was an effort to create an acoustic mechanism to detect objects in the water. In 1914, Reginald A. Fessenden developed the Fessenden Oscillator to use a technique called echo ranging, whereby sound and its echoes off objects are used to determine distances in the air (8). The Fessenden Oscillator was a high-powered, underwater loudspeaker that both produced and detected sounds. With his new invention, Fessenden conducted echo-ranging trials and was able to detect a 130-foot high, 450-foot long iceberg two miles away. He could also detect a sea floor 31 fathoms (186 feet) beneath the surface (8).

During World War I, researchers further developed the Fessenden Oscillator to detect underwater submarines. This enhancement paved the way for the current system of Sound Navigation and Ranging (SONAR). Scientists today use of two types of sonar: active and passive (9). Active sonar transducers emit an acoustic signal into the water. The sound then bounces off of any object in its path and returns an “echo” to the transducer, which then measures the strength of the signal (9). It can also calculate the range of the object by determining the time between the sound’s emission and the echo’s reception (9). Passive sonar systems are used to detect noise from marine objects or animals; they detect sound waves coming towards them but do not emit any sound.

Diving into the Deep Blue Sea

After determining how to map out the ocean floor, scientists wanted to see the floor themselves. To achieve this feat, Dutchman Cornelis Drebbel built the first submarine in 1623 (10). His early machine consisted of an outer hull of greased leather over a wooden frame. Oars extending through the sides and sealed with tight-fitting leather flaps provided a means of propulsion. This early craft traveled to depths of 12 to 15 feet (10).

Robert Fulton's Nautilus Design. By Robert Fulton - This image is available from the United States Library of Congress's Prints and Photographs division.

Robert Fulton’s Nautilus Design. (Source: United States Library of Congress’s Prints and Photographs Division, Credit: Robert Fulton)

Since then, more and more improvements in the design have been made. In 1800, Robert Fulton built a submarine called the Nautilus under a grant from Napoleon Bonaparte (10). The hull consisted of copper sheets over iron ribs; the most innovative components of the craft were the ballast tanks. The Nautilus would submerge by taking water into its ballast tanks and releasing water to rise (10). A horizontal rudder was added to help steer. The submarine contained enough air to keep four men alive and two candles burning for three hours (10).

During World War I, diesel engines were added to submarine designs for propulsion on the surface. Underwater, large batteries powered electric motors that drove the submarines at a high speed of 15 knots for two hours (10). In 1954, the USS Nautilus was commissioned as one of the first nuclear powered submarines, a huge improvement over diesel and electrical engines. Little uranium was needed to power a submarine for days, and the engines were also much quieter (10). Essentially, heat from the uranium would boil either water or metal to produce steam and spin the turbines to propel the submarine forward (10).

The innovation of submarines allowed man to travel deeper into the ocean without being affected by cold temperatures and high pressures. To get up close and personal, however, man had to figure out how to swim underwater for long periods of time. For years humans swam underwater using long reeds as breathing tubes, the idea behind the modern day snorkel (11). The concept of feeding oxygen from the surface to the diver fueled the original designs for underwater diving.

In 1690, Edmund Halley patented a diving bell (chamber) that was connected by a pipe to weighted barrels of air that provided oxygen to the diver (11). Later, in 1788, John Smeaton added a hand-operated pump to efficiently supply oxygen and a non-return valve to prevent air from going back up the hose when the pumping stops (11). A fully functional suit, as opposed to a chamber with arms, came to fruition in 1823 when Charles Anthony Deane patented a smoke helmet. The helmet was originally designed for firefighters but was later repurposed for divers (11). The helmet was weighted and connected to an oxygen hose, but the helmet itself was not connected to the suit and secured only by straps. Thus, the diver could not bend over for risk of drowning (11). Even so, the suit successfully salvaged cannons from the sunken Royal George in 1834-1835 (11).

For the next few decades, scientists worked to create a working oxygen tank that the diver could carry in the water. Frenchmen Benoit Rouquarol and Auguste Denayrouse, a mining engineer and naval lieutenant, respectively, developed and patented an apparatus for underwater breathing in 1865 (11). The tank was horizontal and made of steel and contained 250-350 pounds per square inch (psi) on the diver’s back. A valve and mouthpiece connected the diver to the tank (11).

Known as the “Aerophore,” the device delivered air only when the diver inhaled thanks to a membrane that was sensitive to outside water pressure, (11). A hose that fed the tank oxygen tethered the tank to the surface, but the diver could disconnect the tether and dive with just the tank for a few minutes (11).

Jacques-Yves Cousteau 1972.  By Peters, Hans / Anefo.

Jacques-Yves Cousteau, 1972. (Source: Wikipedia, Credit: Hans Peters, Anefo)

In 1933, French navy captain Yves Le Prieur modified the Rouquayrol-Denayrouse invention by increasing the pressure in the tank to 1,500 psi (11). This increase allowed the diver complete freedom from the tether; to breathe, the diver had to open a tap, and air would come rushing in (11). However, the continuous flow of air actually made it difficult to breathe, restricting dives to short spurts (11). Therefore, in 1942, another French naval officer, Jacques-Yves Cousteau, and Emile Gagnan, an engineer for a Parisian natural gas company, redesigned a car regulator to provide compressed air to the diver only when he inhaled and patented this design as the aqua lung (11). The regulator revolutionized diving, as it allowed the diver to control breathing when carrying large oxygen tanks and ultimately lengthened dive duration (11). A new era of ocean exploration opened now that people could travel to the deep dark depths of the sea to uncover mysteries hidden below.

What Lies Beneath the Surface

Armed with new equipment and technology, humans were able to venture into the deep. It was previously believed that life could not exist in the deep sea due to a lack of light, cold temperatures, and high atmospheric pressures. However, the discovery of thermal vents in 1977 changed that theory (12). These vents, which connected to the magma underneath the Earth’s crust, provide light, heat, and sulfur (12). Organisms such as the green sulfur bacteria thrive around these vents and actually feed off of the sulfur (12). These microorganisms act as the bottom of the food chain; larger organisms such as the giant tube worm feed on these bacteria and, therefore, must stay close to the vents (13).

Deep Sea Anglerfish. By Javontaevious at English Wikipedia, CC BY-SA 3.0.

Deep Sea Anglerfish. (Source: English Wikipedia, Credit: Javontaevious)

Many of the creatures at the bottom of the sea are also bioluminescent, meaning that they produce their own light. One such popular creature is the deep sea anglerfish, which has a long dorsal stalk that contains a light producing organ called a photophore (13). Deep sea anglerfish wave this appendage back and forth to attract prey, which the anglerfish devour with their rows of large teeth.

Another popular creature in the deep sea is the giant squid, which can grow up to 60 feet long. Not much is known about this large animal, as most scientists only ever encounter their corpses (13). Japanese researchers obtained a photograph of a live giant squid in September 2004, and this same team captured a video of a live one in 2006 (13). Stories from World War II have led movies and other forms of media to portray the giant squid as a ship-sinking, man-eating monster. Survivors of sunken ships recounted moments where shipmates were eaten at night and pulled off of boats by. None of these stories have been verified, but a confirmed fact is that the giant squid happens to be the favorite meal of the sperm whale.

Looking Ahead

Man’s curiosity surrounding one subject can spark tangents that prove to be more widely useful as well. The development of sounding equipment and sonar not only allows scientists to map out the ocean floor, but it also allows for the detection of objects in the water. This technology allows submarines to navigate the dark deep waters. In turn, submarines themselves not only provide transportation and visuals of the deep sea, but also are tactical tools. New and improved diving equipment allows humans to experience the beautiful corals in the ocean for themselves and to uncover mysteries of sunken ships that were seemingly lost to history.

Only five percent of the ocean has been explored to date. As time moves on, the technology will only improve, and, eventually, 100 percent of the ocean will be covered. What will humans find next in the deep blue sea?


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By Peter Vo (’18)