He recently discovered that blue sharks use warm water ocean tunnels, or eddies, to dive to the ocean twilight zone, where they forage in nutrient-rich waters hundreds of meters down. Born in New Zealand, Simon received his B. With much of his work in the South Pacific and Caribbean, Simon has been on many cruises, logging 1, hours of scuba diving and hours in tropical environs.
He has been a scientist at Woods Hole Oceanographic Institution since Gregory Skomal is an accomplished marine biologist, underwater explorer, photographer, and author. He has been a fisheries scientist with the Massachusetts Division of Marine Fisheries since and currently heads up the Massachusetts Shark Research Program.
For more than 30 years, Greg has been actively involved in the study of life history, ecology, and physiology of sharks. His shark research has spanned the globe from the frigid waters of the Arctic Circle to coral reefs in the tropical Central Pacific. Much of his current research centers on the use of acoustic telemetry and satellite-based tagging technology to study the ecology and behavior of sharks.
He has written dozens of scientific research papers and has appeared in a number of film and television documentaries, including programs for National Geographic, Discovery Channel, BBC, and numerous television networks.
His most recent book, The Shark Handbook, is a must buy for all shark enthusiasts. Robert D. He served in the U. Navy for more than 30 years and continues to work with the Office of Naval Research. A pioneer in the development of deep-sea submersibles and remotely operated vehicle systems, he has taken part in more than deep-sea expeditions. In , he discovered the RMS Titanic , and has succeeded in tracking down numerous other significant shipwrecks, including the German battleship Bismarck , the lost fleet of Guadalcanal, the U.
The newest, thinnest crust on Earth is located near the center of mid-ocean ridge—the actual site of seafloor spreading. The age, density, and thickness of oceanic crust increases with distance from the mid-ocean ridge.
The magnetism of mid-ocean ridges helped scientists first identify the process of seafloor spreading in the early 20th century.
Basalt, the once- molten rock that makes up most new oceanic crust , is a fairly magnetic substance, and scientists began using magnetometer s to measure the magnetism of the ocean floor in the s.
Scientists determined that the same process formed the perfectly symmetrical stripes on both side of a mid-ocean ridge. The continual process of seafloor spreading separated the stripes in an orderly pattern. Oceanic crust slowly moves away from mid-ocean ridges and sites of seafloor spreading.
As it moves, it becomes cooler, more dense, and more thick. Eventually, older oceanic crust encounters a tectonic boundary with continental crust. In some cases, oceanic crust encounters an active plate margin. An active plate margin is an actual plate boundary, where oceanic crust and continental crust crash into each other. Active plate margins are often the site of earthquake s and volcano es. Oceanic crust created by seafloor spreading in the East Pacific Rise, for instance, may become part of the Ring of Fire , the horseshoe-shaped pattern of volcanoes and earthquake zones around the Pacific ocean basin.
In other cases, oceanic crust encounters a passive plate margin. Passive margins are not plate boundaries, but areas where a single tectonic plate transition s from oceanic lithosphere to continental lithosphere. Passive margins are not sites of fault s or subduction zone s.
Thick layers of sediment overlay the transitional crust of a passive margin. The oceanic crust of the Mid-Atlantic Ridge, for instance, will either become part of the passive margin on the North American plate on the east coast of North America or the Eurasian plate on the west coast of Europe.
New geographic features can be created through seafloor spreading. The Red Sea, for example, was created as the African plate and the Arabian plate tore away from each other. Eventually, geologist s predict, seafloor spreading will completely separate the two continent s—and join the Red and Mediterranean Seas. Mid-ocean ridges and seafloor spreading can also influence sea level s. As oceanic crust moves away from the shallow mid-ocean ridges, it cools and sinks as it becomes more dense.
This increases the volume of the ocean basin and decreases the sea level. For instance, a mid-ocean ridge system in Panthalassa—an ancient ocean that surrounded the supercontinent Pangaea —contributed to shallower oceans and higher sea levels in the Paleozoic era. Panthalassa was an early form of the Pacific Ocean, which today experiences less seafloor spreading and has a much less extensive mid-ocean ridge system.
Scientists believe that it is most likely related to the strength of the ocean crust at these different sites and how cold and brittle the upper part of the plate is. Because the plate under the ridge crest is hotter scientists think that the plate responds to the divergent spreading process more fluidly.
The Mid-Atlantic Ridge runs down the center of the Atlantic Ocean, slowly spreading at a rate of 2 to 5 centimeters 0. In contrast, the East Pacific Rise spreads fast, at rates of 6 to 16 centimeters 3 to 6 inches per year.
Due to the fast spreading rates, there is no rift valley in the Pacific, just a smooth volcanic summit with a crack along the crest that is much smaller than the Atlantic rift valley.
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