Below the depth that can be safely reached by divers, exploration is possible in submersibles where air can be breathed at normal pressure. Such vehicles must

'Formica' board
^-> Pencil

Figure 3.29 (a) Divers using slates and cameras to record habitats and species; (b) diver's slate.

be of great strength to withstand the enormous water pressures encountered in the deeps and must be provided with lighting equipment to illuminate the surroundings. In recent years, the development of the offshore oil industry has led to the design of a number of manned submersibles and unmanned remotely operated vehicles (ROVs). In addition to the vehicle itself, surface support vessels, handling gear, logistic and maintenance support are needed.

Early deep-sea exploration had of necessity to concentrate primarily on the logistics of the exercise and only limited observations were possible. Between

1930 and 1934, William Beebe and Otis Barton broke all previous records for descent into the deep sea. Their bathyshere was a spherical observation cabin, 1.5 m in diameter, which was lowered and raised on a cable from a winch on a surface vessel. This device was the first to reach the deep-sea bottom at a depth of nearly 1000 m, the limit of length of cable then available. They were the first to see many deep-sea fish previously only known from trawled-up, damaged specimens. In 1950, in a later version known as the Benthoscope, Barton made a deeper descent to 1300 m.

The next development after the bathysphere was the bathyscape, invented by Professor Auguste Piccard and able to operate without cables. The design combined an observation cabin or gondola with an underwater float, which may be likened to an underwater balloon. The small spherical, pressure-resisting cabin with portholes was suspended beneath the large, lightly built float filled not with gas but with aviation fuel. Being much lighter than water and virtually incompressible, the fuel provided adequate buoyancy to support the heavy cabin, and the float did not need to be constructed to withstand great pressure. The bathyscape carried iron-shot ballast and sank freely under its own weight. To ascend, sufficient ballast was shed for the vehicle to float up to the surface. In some models, electrically driven propellers provided a limited amount of horizontal movement when submerged.

Piccard called his bathyscape the Trieste and made the first manned dives in it in 1953 funded largely by the Italian government. In 1958 the Trieste was bought by the the US Navy and on 23 January 1960, Auguste Piccard's son Jaques and Donald Walsh embarked on one of the most perilous underwater journeys ever undertaken. On that day, they made a successful return voyage from nearly 11 000 m in the Challenger Deep of the Marianas Trench, only about 122 m short of the deepest known part of the ocean floor.

At the moment there is only one vessel, the Japanese 'Kaiko', able to reach the bottom of the Marianas Trench. It is unmanned and operated via a 12-km-long cable. An American prototype manned 'Deep Flight' submarine is currently being developed to enable it to reach 11 000 m. The one-person submarine will 'fly' on inverted wings rather than simply sinking under its own weight (Mullins, 1995).

A variety of small, manoeuvrable submersibles, both manned and unmanned, are now in use, mainly for underwater engineering projects or geophysical research. Unmanned submersibles (remote-operated vehicles or ROVs) can reach 6000 m and carry a wide array of instruments and cameras. An example is the ROV Jason operated by the US Woods Hole Oceanographic Institution. It carries cameras and sonar and is connected to the support vessel by a 10-km-long fibre-optic cable which allows the operator to 'see' and steer the vehicle. Untethered ROVs that operate under their own power without connecting cables are also coming into increasing use.

Manned Research Submersible

Manned research vessels have greater depth restrictions than ROVs and there are presently only six in the world, capable of reaching depths of between 4000 m and 6000 m or so. The Alvin, commissioned by the US Navy in 1964, is one of the most widely used. Only 7.6 m long, it has now made more than 1700 dives. It was from this submersible that new forms of life around deep-sea vents were first discovered (see Section 6.4.4). The Alvin was also used in 1986 to view the remains of the infamous ocean liner, the Titanic, which sank to a depth of 3810 m after a collision with an iceberg on its maiden voyage in 1912. The United States also has Sea Cliff. Other well-known submersibles include the Russian Mir I and Mir II carrying two crew and a scientist; the French Nautile; and the Japanese Shinkai 6500.

Other manned submersibles operate down to only 1000 m or so. An example is the US Johnson Sealink which has an acrylic dome allowing excellent viewing, and carries two crew and two scientists (Figure 3.30).

The chief advantage of manned submersibles is in enabling direct visual observations to be made at great depths. Submersibles have various applications in biological work, and have been used for benthic surveys and photography of the sea bottom and of mesopelagic and bathypelagic organisms. Actual collection of small organisms by submersible can be done with a 'slurp gun', a form of suction pump with a flexible hose gripped by the submersible's manipulator arm. Organisms can be gently sucked into the nozzle of the hose and thence into a cannister. Fragile animals such as radiolaria, medusae, siphonophores, ctenophores, amphiphods, mysids and small fish have been collected in this way

50 m

400 m

500 m

Scuba diver

Deep Flight I oé4

1000 m ift Deep Rover

2000 m

3000 m

4000 m

5000 m

Al vin

Shinkai 6500

Newt WASP suit

Johnson Sealink

Sea Cliff f

Jim suit

Jason (robot)

11,000 m f Kaiko (robot)

Figure 3.31 Diagram illustrating depth capabilities of various submersible craft and suits.

in excellent condition, which when collected by deep-water nets are usually severely damaged.

Unmanned submersibles do not need a pressure sphere to accommodate crew and since they draw power from the surface via a tether, are not limited by battery power. These systems continue to be developed, and in the future unmanned submersibles with sophisticated robotic capabilities will undoubtedly allow extensive sampling, visualization and experimentation in the deep sea. Already sophisticated camera equipment allows stereo viewing and virtual reality technology can be used to control manipulator arms with great accuracy.

Recent years have seen the development of a variety of one- and two-man submersibles for use in shallow water down to several hundred metres, and mainly developed in connection with the offshore oil and gas industry. Armoured diving suits operate in a similar manner to submersibles but are 'submarines you can wear'. The diver's limbs are encased in tubes, with hands of claws or claspers appropriate to the work to be undertaken. The suit contains a life support system, with a duration of about 70-90 hours, and can operate down to several hundred metres. Examples are the Jim, Wasp, Newt and Spider suits (Sisman, 1982). In general they are too clumsy and expensive for scientific use.

Currently, simple, easy-to-use and cheap submersibles are being developed for use by scientists and even sports divers, to depths of about 100 m. Further development of these will enable scientists and laymen alike to observe and record without the restrictions imposed by diving.

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