The researchers said on Thursday they used gravity measurements of the seafloor from radar equipment aboard the European Space Agency's CryoSat-2 satellite and NASA's Jason-1 satellite to capture underwater geological features in unprecedented detail.
"The pull of gravity reflects the topography and tectonics of the seafloor," said David Sandwell, a geophysicist at Scripps Institution of Oceanography at the University of California, San Diego who led the study.
University of Sydney geophysicist Dietmar Müller, another of the researchers, said about 71 percent of the Earth's surface is covered by water and roughly 90 percent of the seafloor is uncharted by survey ships that employ acoustic beams to map the depths.
"We know much more about the topography of Mars than we know about Earth's seafloor," Müller said. "The disappearance of Malaysia Airlines flight MH370 earlier this year has heightened global awareness of the poor knowledge of our ocean depths."
The map reveals major seafloor and sub-seafloor structures. They include a mid-ocean ridge beneath the Gulf of Mexico with a length about equal to the width of Texas as well as another ridge under the South Atlantic west of Angola about 500 miles (800 km) long that was formed just after the continent of South America separated from Africa.
Such "spreading ridges" are cracks in the Earth formed where the planet's tectonic plates moved apart and molten material called magma came up to fill them, the researchers said.
"Knowing where and when such ridges existed is essential for deciphering planet Earth's geological past," Müller said.
The new map also provides details on thousands of undersea mountains, or seamounts, rising 1 mile (1.6 km) or more from the seafloor, the researchers said. Some are covered by many miles (km) of sediments, they said.
In addition to the pure scientific value, the new map could have applications for militaries and for oil exploration, Sandwell said.
Müller said the conclusions the researchers made about seabed topography may be less accurate than acoustic beam methods employed by ships.
"But the global coverage is much better and our method is much cheaper, especially as we are mostly using satellite data that were collected for another purpose," added Müller, who estimated that a complete survey of the deep ocean using ships would cost between $2 billion and $3 billion and would take many years.
CryoSat-2 was dedicated to monitoring changes in the thickness of marine ice floating in the polar oceans and variations in the thickness of the vast ice sheets that overlie Greenland and Antarctica. Jason-1 was dedicated to map the change in the topography of the oceans due to ocean currents.
The study was published in the journal Science.- Reuters
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