f Robot submersibles enable long explorations to extreme depths that would be impossible, or very costly, for manned craft. This is an Automonous Underwater Vehicle (AUV) programmed to operate underwater without any remote control.
Mount Everest; hot volcanic jets on the seabed, which support their own unique communities of life that survive incredible heat, entirely without creatures that need sunlight; corals that live in cold water thousands of feet below the sea; the body of a colossal squid, the world’s largest invertebrate; fish living more than 7,000 m (23,000 ft) down in the ocean; mats of microbes as big as France on the seafloor. The latter two discoveries have been made in the last ten years. So there is clearly much to learn; in fact, barely 3 percent of the ocean has been explored in detail. mappiNG techNoloGy
The big problem with undersea exploration is seeing through the water. In the 1870s, when HMS Challenger made its pioneering voyage to explore the world’s oceans, all it could use to help it were weights and scoops lowered into the water. That is why the development of sonar has been so crucial. Sonar, which works by beaming sound and using its echo to find objects, was originally developed in World War II to hunt for submarines, but it was soon realized that, with different frequencies, it could be used to map the ocean floor, and even the rocks beneath the seabed. It was with sonar that the first proper maps of the seafloor were made during the 1950s. Multi-beam sonar arrays now provide a much more detailed view.
Even the latest sonar, though, takes a long time to map just a tiny portion of the seabed. That is why the addition of satellite technology has been so crucial. In 1995, the US declassified data from the Navy’s Geosat satellite, which by mapping minute variations in the sea surface height revealed the relief of the seafloor. It works through gravitational differences. The sea surface, for instance, is fractionally raised by the extra gravitational attraction of an undersea mountain’s bulk. This technique, known as satellite altimetry, only works for large objects, but it covers vast areas and has revealed the presence of tens of thousands of previously unsuspected undersea mountains. Meanwhile, other satellites, with their global overview, can show surface currents, sea surface temperatures, salinity, and even biological productivity. Global positioning systems, too, have made it much easier to establish locations accurately. SubmerSibleS
At the same time, just as the last 50 years have seen the
development of spacecraft for exploring the hitherto unreachable realm of space, so submersibles have been developed that have allowed humans to travel to the very deepest parts of the ocean. In 1960, Jacques Piccard and Don Walsh dived 10,915 m (35,810 ft) down in the bathyscaphe Trieste to the very bottom of Challenger Deep in the Mariana Trench, the world’s deepest place (see page 37). Since then, submersibles, such as the Woods
61 h Small sonar devices like this can map the seafloor in detail. This device is being used to scan the seabed for traces of ancient settlements in the Mediterranean off the coast of France.
e A combination of satellite data and a variety of sophisticated
sonar systems have enabled oceanographers to finally map the ocean floor and create 3D computer images like this. Hole Oceanographic Institution’s Alvin, have allowed
explorers to make many voyages into the deep ocean. But manned submersibles are very expensive to construct and are often limited in the places they can reach. Tremendous advances in computer and communications technology have led to the development of numerous Remote Operated Vehicles (ROVs) and there are now hundreds of these in operation, gliding through the deep ocean, operated from the surface by researchers sitting comfortably at a screen rather than peering through a murky porthole. It was the ROVs named Argo and Jason that explored the wreck of the Titanic in the 1980s, relaying back live video images. Simple ROVs called gliders can remain on a mission for up to a year, programmed to follow particular routes and track deep-sea currents, beaming back information all the time. This is how oceanographers have discovered the massive global circulation of ocean water deep down, which is known as the thermohaline circulation. They are also discovering major new currents continually, such as the Kerguelen current, a deep-sea current off the coast of Antarctica with a flow 40 times as big as the Amazon River, discovered in April 2010.
The advances have been massive, and it is clear that we are learning more and more about the oceans all the time. At the Monterey Bay Aquarium Research Institute in California, visitors can watch live videos beamed from the deep seafloor. Online, you can see live webcam footage from the NOAA’s permanent underwater laboratory Aquarius located 20 m (66 ft) down in the Florida Keys. Ships, such as the Okeanos Explorer, are roaming the world mapping the oceans in hitherto unachieved detail.
A network of hundreds of Integrated Ocean Observing Systems (IOOS) is helping to build a comprehensive and continually updated picture. And the combined efforts of the researchers who are working on the Marine Census (see pages 62–63) are building up a remarkably detailed picture of life in the oceans.
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