dinsdag 18 juni 2013

Warm Ocean Is Melting Antarctica From The Bottom Up

In another article we informed that the huge 18-mile-long crack that was discovered by NASA's Operation IceBridge during science flight inspections o ver Antarctica.

MessageToEagle.com - A year ago, we informed that very rapid climate changes take place on Antarctica and Antarctic ice shelves are breaking up fast.
Now, researchers say that ocean waters are melting the Antarctic ice shelves from underneath and are responsible for most of the continent's ice shelf mass loss.

Click on image to enlarge
Although Antarctica remains a cold place, this data image illustrates warming across the continent. Red represents areas where temperatures, measured in degrees Celsius per decade, have increased the most during the last 50 years, while dark blue represents areas with a lesser degree of warming. West Antarctica and the Antarctic Peninsula, the craggy finger of land jutting out from the continent, have experienced the most warming. Credit: NASA/GSFC Scientific Visualization Studio

The study conducted by NASA and university researchers has found basal melt accounted for 55 percent of all Antarctic ice shelf mass loss from 2003 to 2008, an amount much higher than previously thought.

"The traditional view on Antarctic mass loss is it is almost entirely controlled by iceberg calving,"
"Our study shows melting from below by the ocean waters is larger, and this should change our perspective on the evolution of the ice sheet in a warming climate," said lead author of the study, Eric Rignot of NASA's Jet Propulsion Laboratory in Pasadena, Calif., and the University of California, Irvine.
In total, Antarctic ice shelves lost 2,921 trillion pounds (1,325 trillion kilograms) of ice per year in 2003 to 2008 through basal melt, while iceberg formation accounted for 2,400 trillion pounds (1,089 trillion kilograms) of mass loss each year.
Antarctica holds about 60 percent of the planet's fresh water locked into its massive ice sheet. Ice shelves support the glaciers behind them, modulating the speed at which these rivers of ice flow into the ocean. During the process known as calving, large chunks of ice break off from the part of the ice shelf facing the sea.

Click on image to enlargeIce Front at Venable Ice Shelf
This photo shows the ice front of Venable Ice Shelf, West Antarctica, in October 2008. It is an example of a small-size ice shelf that is a large melt water producer. The image was taken onboard the Chilean Navy P3 aircraft during the NASA/Centro de Estudios Cientificos, Chile campaign of Fall 2008 in Antarctica. Image credit: NASA/JPL-Caltech/UC Irvine

The study found basal melting is distributed unevenly around the continent and basal melt can have a greater impact on ocean circulation than glacier calving.
The three giant ice shelves of Ross, Filchner and Ronne, which make up two-thirds of the total Antarctic ice shelf area, accounted for only 15 percent of basal melting.
Scientists have studied the rates of basal melt, or the melting of the ice shelves from underneath, of individual ice shelves, the floating extensions of glaciers that empty into the sea, but this is the first comprehensive survey of all Antarctic ice shelves.

Click on image to enlarge
Rates of basal melt of Antarctic ice shelves overlaid on a 2009 mosaic of Antarctica. created from data obtained by MODIS instrument aboard NASA's Terra and Aqua spacecraft. Red shades denote melt rates of less than 5 meters (16.4 feet) per year (freezing conditions), while blue shades represent melt rates of greater than 5 meters (16.4 feet) per year (melting conditions). The perimeters of the ice shelves in 2007-2008, excluding ice rises and ice islands, are shown by thin black lines. Each circular graph is proportional in area to the total ice mass loss measured from each ice shelf, in gigatons per year, with the proportion of ice lost due to the calving of icebergs denoted by hatched lines and the proportion due to basal melting denoted in black. Image credit: NASA/JPL-Caltech/UC Irvine/Columbia University

"Changes in basal melting are helping to change the properties of Antarctic bottom water, which is one component of the ocean's overturning circulation," said author Stan Jacobs, an oceanographer at Columbia University's Lamont-Doherty Earth Observatory in Palisades, N.Y.
"In some areas it also impacts ecosystems by driving coastal upwelling, which brings up micronutrients like iron that fuel persistent plankton blooms in the summer."
"Ice shelf melt doesn't necessarily mean an ice shelf is decaying; it can be compensated by the ice flow from the continent," Rignot said.
"But in a number of places around Antarctica, ice shelves are melting too fast, and a consequence of that is glaciers and the entire continent are changing as well."
The study - based on the results with ice velocity data from satellites, ice shelf thickness measurements from NASA's Operation IceBridge -- a continuing aerial survey of Earth's poles -- and a new map of Antarctica's bedrock - is published in the June 14 issue of the journal Science.

See also:
Ice Melting On The Antarctic Peninsula Has Increased Dramatically
Something Mysteriously Warms Antarctica Ice

Earth's Clouds Are Dropping - Something Important Is Happening

Source: http://www.messagetoeagle.com/warmoceanwaters.php#.UcDaXH1hXMI

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