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Digital Extra: Mountains in the Sea |
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 A daily logbook of explorations of an underground range off Cape Cod.
Cruise Log, Day Nine: Rediscovering new zones of life 05.18.2004
Mary Grady
A screen shot of deep-sea life captured by the underwater video camera.
Video Watch live images of the expedition, scheduled to streamed from 9 a.m. to 9 p.m. daily. NOAA will also be broadcasting live programs for an hour a day from the control van, with teachers and scientists interacting live with students on shore What is a seamount? Far to the east of us, in the deepest part of the ocean known as the abyss, an underwater mountain chain runs like a ragged seam down the center of the ocean basin. This is the mid-Atlantic Ridge, and it marks the place where new rock is being created of molten lava from the planet's interior. The hot lava pushes to the surface, forcing the seafloor to spread, and piles up on either side of the fissure in ranges of solid rock that stretch from the Arctic, past Iceland, between South America and Africa, and down to the Antarctic. The force of that spread drives the seafloor away from the ridge toward the East Coast, at a rate of a couple of inches a year. Our New England Seamounts are oriented along that direction of movement, which helps to explain where they came from. The theory goes that now and then, beneath the moving rock seafloor, a hot spot forms. This convection cell brings hot lava near the surface, and as the rock plate slowly moves above it, a chain of volcanoes is formed as magma bursts through the crust. The volcano closest to the ridge is the newest one, and the mounts grow older as they creep toward Cape Cod. Like mountains on land, the seamounts create a vertical gradient that supports a wider range of creatures than would be found on the flat. The mounts stir the currents, they offer canyons and crevices, they create various seabeds at various depths. The altitudnal zones are reversed from those on land -- the coldest regions are at the bottom, and warmer waters bathe the peaks. Rocky ridges provide prime habitat for deep-sea corals -- the creatures need hard rock to hold fast to, and currents stirred up by the topography carry the particles of food they need. Underwater mountain chains also create stepping-stones for shallow-water species that otherwise would be found only on the continental margins. The abyssal plain, much of it covered with soft sediments that provide nothing to hold onto, is a barrier to their dispersal.
'The Zone of Trees'
For years, the conventional wisdom regarding corals has been thus: they are purely tropical creatures, found only in warm waters, at depths shallow enough for light to penetrate. That's what I was taught in college, and students were still being taught that just a few years ago... some are likely still taught that today. Prof. Les Watling, the chief scientist on this mission, told me that the deep-sea corals were well-known by fishermen and naturalists in the 1800s, but then were forgotten by science. He pulled out an antique text, one of many he had dragged on board the ship in milk crates, and showed me the dog-eared monographs with detailed illustrations of deep-sea coral anatomy. "They were caught in fishing nets and that's how the naturalists got their specimens," Watling said. "Fishermen even knew the region where they were likely to find them. It was called The Zone of Trees." The corals, with their trunk-and-branch formations and their hard skeletons, seemed more like plants than animals to the fishermen. Science forgot the corals of the deep sea, while the shallow coral reefs of the tropics got all the attention. Then about five or six years ago, Watling said, a deep-sea coral reef off the coast of Norway made the news when it was being destroyed by trawlers. Nobody even realized it was there, and its destruction focused international attention. That was the beginning of this new and ongoing effort to learn about the lives of corals in the deep cold seas.
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