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Senin, 29 Agustus 2011

Discovering Giant Seamounts in the South Atlantic Ocean

Discovering Giant Seamounts
in the South Atlantic Ocean
Republished from a March, 2011 press release by the Scripps Institution of Oceanography / University of California, San Diego

Using multibeam sonar, Scripps R/V Melville is charting giant undersea mountains. 
Image by Scripps Institution of Oceanography.

Mapping Seamounts in the South Atlantic
In the latest evidence of the vastness remaining to be explored in the world's oceans, scientists aboard Scripps Institution of Oceanography at UC San Diego's research vessel Melville are mapping a series of colossal and previously uncharted undersea mountains in remote areas of the South Atlantic Ocean.

Over 14,700 Feet High and 87 Miles Across
With the largest seamount rising more than 14,700 feet from the seafloor —- higher than California's Mount Whitney, the tallest mountain in the contiguous United States -— the mountains had been known from satellite data but never before charted at sea.
Because of the exploratory nature of the ship's navigation, R/V Melville Captain Chris Curl and geophysicist J.J. Becker, who received his Ph.D. from Scripps in 2008, are working side-by-side to navigate over the gigantic mountains, the largest of which spans some 140 kilometers (87 miles) across (the approximate distance from San Diego to Long Beach, Calif.)

Some of the Seafloor's Steepest Features
"These particular seamounts are so steep that it was nerve-wracking to go from 3,000 meters (9,840 feet) of water to less than 500 meters (1,640 feet) in 15 or 20 minutes!" said Becker.

David Sandwell, a Scripps professor of geophysics, has been providing guidance to the ship from his office on the Scripps campus as the vessel transits from South Africa to Chile. The researchers are employing a new survey tool based on Google Earth software called "Seamount Discovery Tool" to aid in the exploration.

"There are still 4,000-meter-tall undersea mountains that have never been charted by anyone," said Sandwell, of Scripps' Cecil H. and Ida M. Green Institute of Geophysics and Planetary Physics. "These are really huge seamounts that are somewhat known from satellite altimetry, so the ship data confirm their size and provide accurate measurements."
The seamounts, mapped by Melville's multibeam sonar, are located in the South Atlantic Ocean approximately 1,200 miles southwest of Cape Town, South Africa. (latitude 42°S, longitude 00°E).

Serendipity and South Atlantic Guyots
Prior to Melville's departure, Sandwell provided a proposed trackline where the ship might explore uncharted undersea features. Foul weather in the South Atlantic (persistent in the Southern Ocean) required the scientists to modify their exploration path almost immediately after leaving port. The alternate track, however, has revealed the presence of surprising numbers of large, flat-topped underwater mountains with extremely steep sides, called "guyots."

"This is a great example of how serendipity and skill are involved in successful exploration and discovery," said Bruce Appelgate, associate director for Ship Operations and Marine Technical Support at Scripps. "Dave Sandwell used the satellite data to create a great precruise plan, but the seas forced us to abandon that for a different path. Good oceanographers that they are, he and J.J. Becker were ready with contingency plans that have yielded spectacular results."

Significance of Large Seamounts
Seamounts, especially massive seamounts like these, are important for many reasons, said Appelgate. The chemistry of the volcanic rock they are made from provides information about the underlying mantle where the seamounts formed.

"They are so big they actually deform the lithosphere they sit on, and they have a profound effect on the physical oceanography and biological ecosystems around them," said Appelgate. "Satellite altimetry has detected about 13,000 seamounts, but the total number of seamounts taller than one kilometer probably exceeds 100,000. So clearly these are important, and you need ships like Melville, and scientists like Sandwell and Becker, to go find them."

Becker and Sandwell noted that such discoveries can be made by diverting from the traditional "Great Circle" route of sea transit. The Great Circle is the shortest distance between two ports but significant discoveries can be made by increasing the path by just three percent. Considering uncertainties in weather, a longer path can save time and fuel so it is important for the ship's captain to be involved in mapping decisions.

Physics of the Air-Sea Interface
Scripps' R/V Melville is currently being repositioned from the South Atlantic to the South Pacific in order to support major research programs funded by the National Science Foundation. Scripps' policy is to use every opportunity at sea to collect meaningful data, so rather than simply transit across the ocean, Scripps provided funding through its UC Ship Funds Program to enable a diverse group of scientists to join the research vessel in Cape Town and acquire data.
The cruise is led by Scripps Chief Scientist Robert Frouin, who along with his research team is making observations about the physics of the air-sea interface in areas of extreme wind. These data will be used to improve scientists' ability to interpret data collected globally by satellites. Other Scripps scientists on board are deploying autonomous ocean drifters and building new software tools for shipboard data processing.

Earthquake Deformation of the Ocean Floor
Melville will continue to cross the South Atlantic, pass through the Strait of Magellan and cruise up the west coast of Chile to its destination at Valparaiso, Chile. From there, Melville will continue its expedition of discovery by resuming an investigation of the deformation of the ocean floor caused by the magnitude-8.8 Chile earthquake of February 2010. Last year the ship performed the first-ever detailed seafloor mapping of a major subduction zone earthquake as part of the Scripps rapid scientific response to the Chilean earthquake. The additional data will shed new light on how the crust responds in the wake of giant earthquakes.

Scripps Oceanography Research Vessels
Owned by the U.S. Navy and operated by Scripps Oceanography, the 279-foot R/V Melville is a global-class ship that conducts long-duration science missions. Last year, the U.S. Office of Naval Research selected Scripps as the operator of a new Ocean Class scientific research vessel, which is currently being designed with input from Scripps oceanographers. The U.S. Navy is providing more than $88 million to construct the vessel, which is anticipated to be ready for Scripps to operate by 2015.

From its home port at the Nimitz Marine Facility in Point Loma, Scripps operates a fleet of four oceanographic research vessels and the research platform FLIP.

About Scripps Institution of Oceanography
Scripps Institution of Oceanography at University of California, San Diego, is one of the oldest, largest and most important centers for global science research and education in the world. Now in its second century of discovery, the scientific scope of the institution has grown to include biological, physical, chemical, geological, geophysical and atmospheric studies of the earth as a system. Hundreds of research programs covering a wide range of scientific areas are under way today in 65 countries.

The institution has a staff of about 1,400, and annual expenditures of approximately $170 million from federal, state and private sources. Scripps operates robotic networks, and one of the largest U.S. academic fleets with four oceanographic research ships and one research platform for worldwide exploration. Birch Aquarium at Scripps serves as the interpretive center of the institution and showcases Scripps research and a diverse array of marine life through exhibits and programming for more than 415,000 visitors each year. Learn more at scripps.ucsd.edu.


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