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| 02/16/08 10:23 PM |
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Antarctica's Largest Glacial Stream - Pine Island
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Ice streams of the Antarctic
In 2001 scientists at the Scott Polar Research Center were able to demonstrate that the Antarctic icecap is slowly flowing into the sea via enormous ice streams flowing out of the icecap.
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Giant rivers of ice thread their way across the Antarctic Ice Sheet to the sea. The rivers, termed by scientists "streams", are the largest flows of ice in the world. Some streams are over 2 kilometers thick, 30 km wide and travel at speeds up to 1 km per year. Radar observations by polar orbiting, European ERS satellites have been used by CPOM scientists to map in detail the geography of the streams, many of which were hitherto unknown.
The ice velocity observed is mapped in the image below"
Pine Island Glacier
A particularly interesting stream of ice is named the 'Pine Island Glacier' (PIG). Pine Island Glacier is one of several glaciers draining the West Antarctic Ice Sheet. The Pine Island Glacier transports an enormous volume of ice from the West Antarctic Ice Sheet to the sea. It is both the largest transporter of ice in Antarctica and also the Antarctic's fastest moving glacier. It is currently thinning and retreating which is of concern since it's flow velocity and ice volume is accelerating.
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The West Antarctic Ice Sheet (WAIS) contains enough water to raise global sea level by ~5 m (1) if the ice were to melt into the ocean. The Pine Island Glacier (PIG) (Fig. 1) has the largest discharge (75 Gt year-1) of all WAIS ice streams .. Satellite radar interferometry observations (12) have shown that the PIG grounding line retreated 5 km inland between 1992 and 1996.
The observations can be found in the paper here: Acceleration of Pine Island Glacierflow. The image below shows the glacier grounding lines and flow velocity in 1996.
Calving of B21 in 2001
In 2001 the Pine Island Glacier calved an enormous iceberg dubbed B21 42 km by 17 km. The calving has been captured by the NASA/Goddard Space Flight Center Scientific Visualization Studio
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The Pine Island Glacier is the largest discharger of ice in Antarctica and the continent's fastest moving glacier. Even so, when a large crack formed across the glacier in mid 2000, it was surprising how fast the crack expanded, 15 meters per day, and how soon the resulting iceberg broke off, mid-November, 2001. This iceberg, called B-21, is 42 kilometers by 17 kilometers and contains seven years of glacier outflow released to the sea in a single event. This series of images from the MISR instrument on the Terra satellite not only shows the crack expanding and the iceberg breakoff, but the seaward moving glacial flow in the parts of the Pine Island Glacier upstream of the crack.
Calving of Pine Island in 2007
In 2007 Pine Island calved agai this time observed by the Envisat Advanced Synthetic Aperture Radar (ASAR) instrument
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Envisat captures the birth of a giant iceberg that has broken off from the Pine Island Glacier in West Antarctica. Spanning 34 km in length by 20 km in width, the new iceberg covers an area nearly half the size of Greater London.
The attached .kmz file includes the animation as a time series. A large remnant of B21 is may still visible in the Google Earth imagery.
An enormous iceberg (right) breaks off the Knox Coast in the Australian Antarctic Territory - Photograph: Torsten Blackwood/Getty Image
Antarctic Ice Loss
A recent 2007 article in Science by Shepard documents the loss of significant ice on the West Antarctic Ice Sheet as well as Greenland.
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"The thinning is 10 times greater than the rate of snowfall in the basin," said Shepherd. "The speed of the glacier means that much more mass is going out [through melting and breaking off of icebergs] than is coming in.'' ... Shepherd said if the present rate of change continues, the main stem of the Pine Island Glacier will be undercut by the sea and lifted up in about 600 years. When the glacier floats, it would cause a dramatic shift in sea level, he said.
Accelerating Antarctic Ice loss in 2008
In a new study, a team lead by Eric Rignot of NASA's Jet Propulsion Laboratory has documented that
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Ice loss in Antarctica increased by 75 percent in the last 10 years due to a speed-up in the flow of its glaciers and is now nearly as great as that observed in Greenland ...
Rignot said the losses, which were primarily concentrated in West Antarctica's Pine Island Bay sector and the northern tip of the Antarctic Peninsula, are caused by ongoing and past acceleration of glaciers into the sea. This is mostly a result of warmer ocean waters, which bathe the buttressing floating sections of glaciers, causing them to thin or collapse. "Changes in Antarctic glacier flow are having a significant, if not dominant, impact on the mass balance of the Antarctic ice sheet,"
The Antarctic ice loss between 1996 and 2006 is shown in the graphic below. The colors indicate the speed of the ice loss. Purple/red is fast. Green is slow. From NASA/MODIS. The results of the study are published in February's issue of Nature Geoscience.
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The team found that the net loss of ice mass from Antarctica increased from 112 (plus or minus 91) gigatonnes a year in 1996 to 196 (plus or minus 92) gigatonnes a year in 2006. A gigatonne is one billion metric tons, or more than 2.2 trillion pounds. ...Rignot says the increased contribution of Antarctica to global sea level rise indicated by the study warrants closer monitoring.