Posted on 05/10/2002 10:22:57 AM PDT by cogitator
Breakaway Bergs Disrupt Arctic Ecosystem
WASHINGTON, DC, May 9, 2002 (ENS) - Another large iceberg has newly calved from the Ross Ice Shelf, the National Ice Center has confirmed. Iceberg C-18 is the latest in a series of bergs to break away from the warming Antarctic ice mass.
National Ice Center analyst Judy Shaffier spotted the new iceberg Sunday while performing a weekly satellite image analysis of the Ross Sea using an image from the Defense Meteorological Satellite Program. The Ross Ice Shelf is a large sheet of glacial ice and snow extending from the Antarctic mainland into the southern Ross Sea.
(Photo courtesy National Ice Center)
Named Iceberg C-18 to show its location in the Western Ross Sea, the new floating ice mass is roughly 41 nautical miles long and four nautical miles wide. It covers an area of about 164 square nautical miles.
Warming temperatures appear to be responsible for the continuous calving of enormous icebergs over the past three years. In March, scientists reported two huge pieces of ice on separate sides of the Antarctic continent shattered and broke off.
On the Antarctic Peninsula, a piece broke away from the Larsen B ice shelf in the largest single event in a 30 year series of ice shelf retreats, reducing the shelf to a size not seen for some 12,000 years.
Also in March, on the coast of West Antarctica, another monster iceberg broke off the Thwaites Glacier, increasing concerns such events may lead to much bigger losses of stored ice.
Two years ago, in March 2000, one of the largest icebergs ever observed broke off the Ross Ice Shelf near Roosevelt Island. Designated B-15, its 4,250 square mile (11,007 square kilometer) area is almost as large as the state of Connecticut.
Using data from three orbiting satellites, researchers have been monitoring B-15 since it broke away. Within a few months, they observed, B-15 had fractured into smaller bergs that formed dams along the coast, preventing thousands of square miles of pack ice from drifting out of the Ross Sea.
"This is the first time that satellite imagery has been used to document the potential for large icebergs to substantially alter the dynamics of a marine ecosystem,” said Kevin Arrigo, assistant professor of geophysics at Stanford and lead author of the Antarctica satellite study.
Arrigo and his colleagues published their results in the April 6 issue of "Geophysical Research Letters," a publication of the American Geophysical Union.
Grounded iceberg at Cape Washington in the Ross Sea, February 1997 (Two photos by Michael Van Woert courtesy NOAA)
Massive icebergs break off from the Ross Ice Shelf about every 10 years. While increased iceberg calving is an important indicator of climate change, Arrigo says the jury is still out with respect to climate change in the Ross Sea, but not in other parts of Antarctica.
“On a thousand-year time scale, there’s good evidence that calving from the Ross Ice Shelf has increased,” he said. “However, in the last 150 years – the period of the Industrial Revolution when human activity produced high levels of greenhouse gas – there is not much evidence that calving in the Ross Sea has increased. That’s not true in other parts of Antarctica, where average temperatures have increased several degrees, causing ice sheets to rapidly melt.”
The new icebergs have changed the Antarctic ecosystem, scientists say, blocking sunlight needed for growth of the microscopic plants called phytoplankton that form the underpinning of the entire food web. They are a primary food source for miniscule shrimp-like krill, which in turn are consumed by fish, seals, whales and penguins.
“B-15 broke into smaller pieces that prevented the normal movement of sea ice out of the region,” Arrigo explained. “Sea ice is very effective at blocking light, so the phytoplankton couldn’t grow – there was just too much ice around.“
The lives of penguins in the Ross Sea were disrupted by the enormous bergs. The Ross Sea is home to 25 percent of the world population of Emperor penguins and 30 percent of Adélie penguins.
“We know for certain that penguins suffered breeding losses because of the icebergs in this region,” said Arrigo. “There was a lot less food nearby for penguins to get to, so they had to go much farther to feed,” he added. “In doing so, they left their nests exposed for longer periods of time than they normally would. That made them vulnerable to predators such as the skua – a large gull that feeds on chicks and the eggs. So penguin breeding success was much lower last year.”
Current satellite images show that a large iceberg remains wedged against Ross Island – site of several large penguin rookeries.
Emperor penguin colony at Cape Washington in the Ross Sea, February 1997. [Note: Mt. Erebus in the background. Doesn't look like much of a colony to me!]
“Now the penguins have another obstacle they have to get around,” Arrigo said. “Not only do they have to go farther to find food, but they have to swim around this enormously large iceberg that has found its way in their path. Some rookeries have been abandoned altogether.”
Soon after B-15 broke away, satellite images show it fractured into smaller bergs that formed dams along the coast, preventing thousands of square miles of pack ice from drifting out of the Ross Sea.
As a result, large stretches of normally open ocean were covered with ice from November 2000 to March 2001. During these crucial spring and summer months, the Ross Sea usually teems with life, as tons of phytoplankton, go through their reproductive blooming cycles.
Phytoplankton need open water and sunlight to reproduce, but satellite data showed that last season’s high levels of pack ice caused a 40 percent decline in plankton productivity.
To determine the amount of phytoplankton production in the Ross Sea, researchers collected data from SeaWIFS – NASA’s Sea-viewing Wide Field-of-view Sensor satellite.
“SeaWIFS measures the amount of light coming out of the ocean at different wavelengths,” Arrigo said. “Phytoplankton are plant-like organisms that contain green chlorophyll, and with SeaWIFS, you can measure the intensity of the greenness of the water. The greener the water is, the more phytoplankton there are.”
Recent observations show that most of the Ross Sea pack ice has drifted away, and that phytoplankton levels are returning to normal. Researchers plan to continue monitoring the region and to assess the ecological impact of icebergs in other parts of the continent.
“Antarctica is a very expensive place to work,” Arrigo said. “Satellite technology gives us an extraordinarily powerful tool. A single satellite image can teach us more than years of on-site monitoring.”
Other co-authors of the GRL study were Gert van Dijken, a Stanford science and engineering associate; David Ainley of H.T. Harvey & Associates in San Jose, California; Mark Fahnestock of the University of Maryland; and Thorsten Markus of the NASA Goddard Space Flight Center.
Funding for the satellite research was provided by NASA, the National Science Foundation Office of Polar Programs and the New Zealand Foundation for Research, Science and Technology.
While earth's northern hemisphere has warmed about one degree Celsius since the Industrial Revolution began, there is equally compelling satellite data suggesting that the rest of the world is actually cooling.Satellite measurements of temperatures in the troposphere, and independent measurements from balloons, show no evidence of significant global warming over the past 22 years, according to John Christy, the director of the Earth System Science Centre at the University of Alabama. .
Alaska, where the Columbia Glacier is rapidly retreating, has been warmer in recent decades. But Greenland, where the ice edge also is thinning, has been colder, said ice expert Joe McConnell, at the Desert Research Institute, Nevada.In the same way, the Antarctic Peninsula has been warming steadily. But on the other side of the continent, Antarctica's Dry Valleys - the polar region's only ice-free areas - have been getting colder. At the South Pole, temperatures recently have dropped as low as minus 77 degrees, the coldest there in 40 years.
Try watching a little less Dan Rather, chum.
--Psalms, 89:48
Yes, it's easy to forget how big Antarctica is. We wouldn't expect climate processes to be the same on the East and West Coasts of the United States, either.
The 24-hour sunlight during the winter months could have huge implications for certain manufacturing industries, not to mention agriculture and tourism. Imagine round-the-clock skiing, sailing, amusement parks. The possibilities are endless.
(Is it FRiday yet?)
FMCDH
Agreed!...I started the day I was born.
BWAHAHAHA!!!
FMCDH
Slowly - very slowly we are killing ouselves.
Should take each of us about 80 years, give or take 20.
Oh really? Some person saw the shelf 12,000 years ago and noted its size? I stopped reading the article when I was saw this. Sounds like more global baloney, American civilizaton is detroying the earth hysteria.
Man I hate typos! ".... American civilization is destroying the earth hysteria." Now, all corrected.
Agreed!...I started the day I was born.
Yeah, and I'm still going !
Where does it say in my contract that I get to live forever? Outside my religious beliefs, that is.
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