From University of Texas, Austin via Eurekalert
New ground measurements made by the West Antarctic GPS Network (WAGN) project, composed of researchers from The University of Texas at Austin, The Ohio State University, and The University of Memphis, suggest the rate of ice loss of the West Antarctic ice sheet has been slightly overestimated.
“Our work suggests that while West Antarctica is still losing significant amounts of ice, the loss appears to be slightly slower than some recent estimates,” said Ian Dalziel, lead principal investigator for WAGN. “So the take home message is that Antarctica is contributing to rising sea levels. It is the rate that is unclear.”
In 2006, another team of researchers used data from the Gravity Recovery and Climate Experiment (GRACE) satellites to infer a significant loss of ice mass over West Antarctica from 2002 to 2005. The GRACE satellites do not measure changes in ice loss directly but measure changes in gravity, which can be caused both by ice loss and vertical uplift of the bedrock underlying the ice.
Now, for the first time, researchers have directly measured the vertical motion of the bedrock at sites across West Antarctica using the Global Positioning System (GPS). The results should lead to more accurate estimates of ice mass loss.
Antarctica was once buried under a deeper and more extensive layer of ice during a period known as the Last Glacial Maximum. Starting about 20,000 years ago, the ice began slowly thinning and retreating. As the ice mass decreases, the bedrock immediately below the ice rises, an uplift known as postglacial rebound.
Postglacial rebound causes an increase in the gravitational attraction measured by the GRACE satellites and could explain their inferred measurements of recent, rapid ice loss in West Antarctica. The new GPS measurements show West Antarctica is rebounding more slowly than once thought. This means that the correction to the gravity signal from the rock contribution has been overestimated and the rate of ice loss is slower than previously interpreted.
“The published results are very important because they provide precise, ground-truth GPS observations of the actual rebound of the continent due to the loss of ice mass detected by the GRACE satellite gravity measurements over West Antarctica” said Vladimir Papitashvili, acting director for the Antarctic Earth Sciences Program at the National Science Foundation, which supported the research.
WAGN researchers do not yet know how large the overestimation was. A more definitive correction will be conducted by other researchers who specialize in interpreting GRACE data. Previous estimates of postglacial rebound were made with theoretical models. Assimilation of the direct GPS results into new models will therefore produce significant improvements in estimations of ice mass loss.
The results will appear in “Geodetic Measurements of Vertical Crustal Velocity in West Antarctica and the Implications for Ice Mass Balance” (M. Bevis et al., 2009), published in the electronic journal Geochemistry, Geophysics, Geosystems of the American Geophysical Union and the American Geochemical Society. [View the paper at: http://www.agu.org/journals/gc/gc0910/2009GC002642/ ]
A team from The University of Texas at Austin’s Jackson School of Geosciences (Ian Dalziel, lead principal investigator), The Ohio State University’s School of Earth Sciences (Michael Bevis), and The University of Memphis’ Center for Earthquake Research and Information (Robert Smalley, Jr.) performed the WAGN project.
The network consists of 18 GPS stations installed on bedrock outcrops across West Antarctica. Precise, millimeter level, three-dimensional locations of the stations, which are bolted into the bedrock, were determined during measurements made from 2001 to 2003 and from 2004 to 2006, the two measurements being at least three years apart. The difference in the positions during the two time periods indicates the motion of the bedrock.
The WAGN data were supplemented with data from the first year of the Polar Earth Observing Network (POLENET) project, a project to establish a more sophisticated, continuously recording network of GPS and seismic stations, including the already established WAGN sites. POLENET will further improve our understanding of the interaction between the solid earth and ice sheets at both poles. The lead principal investigator of the U.S. Antarctic contribution to POLENET is Terry Wilson of The Ohio State University.
The West Antarctic GPS Network and the U.S. Antarctic contribution to the Polar Earth Observing Network of the International Polar Year were both funded and logistically supported by the Office of Polar Programs of the National Science Foundation.
Each year, the earth moves 15 centimeters, or 6 inches, further away from the Sun. Thus, assuming the distance by which the radius increases is constant, back in 1 BC, the earth was 1000′ closer to the Sun than it is today, or slightly less than a quarter of a mile (4 NYC blocks).
If the distance between the earth and the Sun increased by 300,000 miles a millennium, as these global warming quacks claim in their article, then in 100,000 years, the earth would be 123,000,000 miles from the Sun, and temperatures would be slightly warmer than those encountered on Mars and we would have long since frozen to death, even if everyone helped prevent global freezing by driving a Hummer.
May not the scientists and others tramping about the polar areas or driving snowcats and setting up permanent camps, along with regular cruise ships visiting with hundreds of humans breathing CO2 all over the ice caps, have something to do with loss of ice? It must have some effect if not switching off a light when leaving a room is soon to be a criminal act.
@Troels Halken. Love it when engineers show up.
My 2001 model Garmin handheld GPS has consistently been accurate to within 1 meter. When I hunt in the mountains of Montana, I stand beside my vehicle, record its location on the GPS, turn off the GPS, throw it in my pack and go. From time to time I record other waypoints. When it’s time to return to the vehicle, usually after dark, I get the GPS a clear view of the sky and tell it to go to the truck. Haven’t missed the truck yet. Haven’t walked off any cliffs either. Don’t try this without also carrying a map and compass. No sense in becoming a statistic.
Dave Middleton (13:41:59) :
“There’s something bugging me about the concept of Post Glacial Rebound (PGR) in Antarctica…
“If Antarctica was once buried under a deeper and more extensive layer of ice during a period known as the Last Glacial Maximum,” several thousand years of ice deposition should be missing from the Votok and other ice cores starting in the Holocene… But there isn’t any missing section.”
Dave, I think you’re missing something here. Just because there’s less ice over Antarctica now than during the Last Glacial Maximum does not mean that an entire layer of ice just melted away. I don’t think ice ever melts in the interior of Antarctica. What happens is, the weight of ice from later years compresses the ice below it and pushes the edges outwards toward the coasts, where it eventually calves off and becomes icebergs. But some portion of the ice from each year remains, buried under tens of thousands of years of additional ice, in the interior of the continent. During the Last Glacial Maximum, the water surrounding Antarctica was cold enough that the ice didn’t calve off as much, so the extent of the ice became greater. But also, the larger extent allowed the ice in the interior to build itself deeper. When the Last Glacial Maximum ended, the ice didn’t just melt away from the interior. Instead, rising water temperatures of the oceans surrounding Antarctica caused more of the coastal ice to melt, and break off. The smaller extent of the ice sheet could no longer support the tremendous weight of ice on top of the continent, and so everything spread out more, which, of course, exposed more ice to the coastal areas, where it too could melt. Eventually, the warming that ended the LGM caused the total extent and depth of ice over Antarctica to decrease significantly, but NOT by melting large volumes of ice in the interior.
Does that make more sense?
Re: Trevor (04:37:57)
Clarification: I was appreciating your humor (in agreement).
Re: tallbloke (20:51:20)
There will be updates to that page (unless some kind of unwelcome interference prevents them…)
jeez (22:04:13) :
Trevor:
From the article linked to by Lucy above.
Water-logged sea ice also may explain why sea ice in the Antarctic is increasing. This occurs when the weight of accumulated snow presses down on a slab of sea ice until it’s nearly submerged. When that happens, waves cause ocean water to spill on top of the ice and into the snow, forming a layer that eventually freezes and becomes “snow ice.”
So, global warming is not only thought responsible for the melting of Arctic ice over the last few decades, but the observed increase in the ice at Antarctica, too.
Anybody have any idea how much snow cover would be necessary to nearly submerge floating sea ice? My impression is that even in coastal areas snowfall annually is in the 2’to3′ range, which at the temperatures of Antarctica would be equivalent to maybe 2 or 3 inches of water or less. This wouldn’t seem to provide enough mass to submerge sea ice.
Since when has GPS been able to measure anything down the the millimeter level? I have no doubt there is a post glacial rebound…I just question the accuracy of the measurements.
The capability has existed for a long time. I worked a surveying project over twenty years ago, establishing baselines at closed landfill sites for MNPCA,that was speced at 5mm+/- 3ppm. We used 4 units which cost about $100K each[ two on known reference points, two on the unknowns ] with 1 hour occupation times and about 2 weeks of post processing of the data. Newer equipment and techniques make it faster, but still require fairly sophisticated and specialized skills to achieve that level of accuracy.
BTW, for those who aren’t that familiar with the technical details of GPS surveying techniques here’s a pretty good basic primer from Trimble, one of the top makers of GPS equipment
http://www.trimble.com/gps/index.shtml