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Because of the tremendous pressure, the depth to which a diver
can descend without special equipment is severely limited.
The deepest recorded dive by a skin diver is now 171 meters (561 ft), set on October 30, 2004, by Loic Leferme. The deepest recorded dive by a scuba diver is 313 meters (1,027 feet), made by British diver Mark Ellyatt.
Revolutionary
new diving suits, such as the "Jim suit" shown
below, enable divers to reach depths up to about 600
meters (2,000 ft). Some suits feature thruster packs
that can boost a diver to different locations underwater.
Courtesy of NOAA
To
visit even greater depths, deep-sea explorers must
rely on specially constructed steel chambers to protect
them. In 1934, American oceanographer William Beebe and
engineer Otis Barton were lowered to about 1,000 meters (3,280 ft) in a round steel chamber called a bathysphere, which
was attached to a ship on the surface by a long cable.
During the dive, Beebe peered out of a porthole and reported
his observations by telephone to a colleague, Miss Hollister,
on the surface.
In
1948, Swiss physicist Auguste Piccard began testing a
much deeper-diving vessel he invented called the bathyscaphe. (This
word is derived from the Greek words bathos — "deep" and scaphos — "ship.")
On an unpiloted dive in the Cape Verde Islands, his invention,
named FNRS 2, successfully withstood the pressure
on it at 1,402 meters (4,600 ft), but its float was severely
damaged by heavy waves after the dive.
In
the 1950s, Jacques Piccard joined his father in building
new and improved bathyscaphes including Trieste, which
dived to 3,139 meters (10,300 ft) in field trials. The
U.S. Navy acquired Trieste in 1958 and equipped
it with a new cabin to enable it to reach deep ocean
trenches. In 1960, Jacques Piccard and Navy Lieutenant
Donald Walsh descended in Trieste to the deepest
known point on Earth — the Challenger Deep in the
Mariana Trench. The two men made the deepest manned dive
in history: 10,915 meters (35,810 ft).
Today,
scientists are making exciting discoveries about the
ocean floor, thanks to deep-sea submersibles such as Alvin. Operated
by the Woods Hole Oceanographic Institution in Massachusetts,
this three-person sub made its first dive in 1964. Since
then, Alvin has made more than 4,000 dives to
an average depth of 2,079 meters (6,820 ft).
Alvin has
conducted a wide variety of research missions, from discovering
giant tubeworms on the Pacific Ocean floor near the Galápagos
Islands, to surveying the wreck of HMS Titanic in
the Atlantic Ocean.
Alvin has
met some amazing life on its travels, but so far it has
not encountered one of the deep sea's most mysterious
inhabitants — the elusive giant squid. However, Alvin once
was attacked by a swordfish, which became trapped between
two pieces of the sub's fiberglass skin. The fish was
brought back to the surface and cooked for dinner!
Plans
now are under way for a new Alvin. The new sub, slated
for completion in 2008, will reach more than 99% of the
seafloor, diving to depths of 6,500 meters (21,320 feet).
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| Inventor
Salim Joseph Peress's diving suit, "Tritonia," with
its reticulated joints (left), explored the wreck of the
Lusitania in 1937. The novel diving gear was the forerunner
of the "Jim suit." Photo courtesy of NOAA. |
Throughout
history, scientists have relied on a number of specialized
tools to measure, map, and view the ocean's depths. These are
a few highlights.
One
of the first instruments used to investigate the sea bottom
was the sounding weight. Viking sailors took measurements
of ocean depth and sampled seafloor sediments with this device,
which consisted of a lead weight with a hollow bottom attached
to a line. Once the weight reached the ocean bottom and collected
a sample of the seabed, the line was hauled back on board ship
and measured in the distance between a sailor's outstretched
arms — a 1.83-meter (6 ft) unit called a fathom. This
term is still used today for nautical depth.
Cornelius
van Drebel, a Dutch inventor, is credited by many historians
with building the first submarine. His underwater vessel consisted
of a wooden frame sheathed in leather. Oars extending out the
sides propelled the craft through the water, at depths up to
4.6 meters (15 ft). The oar openings were sealed with tight-fitting
leather flaps. Drebel tested the sub in the Thames River in
England between 1620 and 1624. King James I is said to have
taken a short ride in the craft.
From
1872 to 1876, a landmark ocean study was undertaken by British
scientists aboard HMS Challenger, a sailing vessel that
was redesigned into a laboratory ship. The Challenger expedition
covered 127,653 kilometers (68,890 nautical miles) and is credited
with providing the first real view of major seafloor features
such as the deep ocean basins. The researchers used wire-line
soundings to determine depths and collected hundreds of water,
sediment, and biological samples from all the oceans except
the Arctic. They discovered more than 4,700 new species of
marine life, including deep-sea organisms.
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This
is how Atlantis launches the submersible Alvin.
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Deep-sea
exploration advanced dramatically in the 1900s with a series
of inventions, ranging from sonar — a system for detecting
the presence of objects underwater through the use of sound — to
manned deep-diving submersibles such as Alvin.
Owned
by the U.S. Navy and operated by the Woods Hole Oceanographic
Institution, Alvin can carry a crew of three to depths
of 4,500 meters (14,764 ft). The sub is equipped with lights,
cameras, computers, and highly maneuverable arms for collecting
samples in the darkness of the ocean's depths.
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| The
sub Alvin, with a crew of two sicientist and
a pilot, begins its descent to the seafloor. |
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In the future, with the expanded use of fiber optics, high-tech sensors, and robotics, marine scientists hope to observe and monitor well-defined marine systems from the lab versus a porthole.
Currently,
a team of researchers from several U.S. and Canadian institutes
is developing the NEPTUNE project, a plan for installing 3,000
kilometers (1,864 miles) of fiber-optic cable on Juan de Fuca
Plate, a tectonic plate in the northeast Pacific. Between 30
and 50 experimental sites will be established at nodes along
the cable. They will provide real-time ocean data and imagery
to shore-based Internet sites, as well as interactive control
over robotic vehicles on site. The system is expected to be
in operation by 2007.
On
a national level, the ocean research community is working to
develop a national ocean observing system or "National Weather
Service for the sea." Composed of a series of connected regional
ocean observing hubs along the U.S. coastline, the system is designed
to advance a host of applications, from improving weather forecasting
to aiding resource managers in predicting and addressing problems
such as harmful algal blooms and oil spills.
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