POLENET project in Antarctica completes GPS/seismic array
Posted March 9, 2012
Talk to just about any scientist in Antarctica and eventually you’ll hear some variation on this refrain: We just don’t know that much about it. We need more data.
In part, the problem is related to the daunting logistics of doing research in Antarctica —the vast distances, the unpredictable, brutally cold weather. The sort of long-term datasets that give scientists a warm and fuzzy feeling about their conclusions are scarce and relegated to a few, regional locations.
This makes Terry Wilson’s efforts to instrument, in essence, all of West Antarctica in a bid to learn more about its ice sheet and the earth below, just that much more impressive.
Not to mention that much more difficult.
What had been projected to be an initial two-year effort to install an array of GPS and seismometer instruments across roughly a third of the continent is now in its fourth year. Naturally, the last four sites are the most difficult to reach, in a region known as Pine Island Bay, where most of West Antarctica appears to be losing ice, despite being an infamously stormy place.
“It’s been a big frustration,” Wilson said of the missing pieces of the West Antarctic array for the POLENET program. “Weather is the driver if we end up going somewhere.”
A geology professor at The Ohio State University , Wilson is the principal investigator for the National Science Foundation -funded project POLENET, for Polar Earth Observing Network. The project focuses on collecting data from GPS and seismometers at remote, autonomous sites in West Antarctica, as well as Greenland and elsewhere in the Arctic and Antarctic.
Up and down
POLENET has numerous goals; foremost among them is learning about how much ice is disappearing as the world prepares for what appears to be inevitable sea-level rise from shrinking glaciers and ice sheets.
Photo Credit: Seith White/POLENET
Scientists install a GPS station in the Whitmore Mountains during low temperatures and high winds.
But it’s not just about how much polar ice is discharging to the seas today. The scientists are also interested in calculating just how much ice once sat on the poles nearly 20,000 years ago when ice sheets had reached their maximum girth and extent during the last glacial maximum (LGM).
Antarctica’s mighty ice sheets were even more massive then, enough to depress the earth below. The ensuing loss of mass over the millennia has produced a post-glacial rebound, as the ground literally bounces back. Slowly.
That’s where the GPS instruments come in. These instruments can measure with millimeter-level accuracy the rate at which the bedrock of the continent moves vertically. Meanwhile, scientists can use the data from seismometers, which measure the seismic waves produced by earthquakes near and far, to determine the nature of the material that sits below the ice.
“The seismology gives us the earth properties. It tells us what’s under there, including what’s deep under there, which matters with the earth response,” Wilson explained.
“A really interesting part of the seismology is actually sensing the dynamics of the ice,” she added. “We’re finding some solid earth stuff, but it seems the majority of earthquakes that we’re recording are related to ice processes. It’s a different aspect of the project that’s going to be pretty exciting, because we’ve never had sensors in most of these places before.”
A model of exploration
While the nascent network represents one of the biggest efforts to emerge out of the International Polar Year — the 2007-08 global science campaign to study the polar regions in greater detail — the array of instruments isn’t just about monitoring Antarctica, Wilson insisted. It’s also about exploration, she said.
“Here we don’t have any idea of what we’re going to find, because nobody has measured it before,” she said. “We have no idea what the actual patterns and results are going to be. We have some predictions, we have some models, but those models are sometimes models of other models — things we had to resort to because we have no direct observations from these areas.”
Such as the post-glacial rebound effect. Scientists are counting on the POLENET data to fill in big data gaps that will help them create more realistic models of how the polar regions will respond to ice loss today. The data should prove particularly useful to a separate project involving a pair of satellites that measure gravity field changes on Earth.
The Gravity Recovery and Climate Experiment (GRACE) measures changes in gravity by making accurate measurements of the distance between the two satellites, using GPS and a microwave ranging system. GRACE is a collaborative effort between the Center for Space Research at the University of Texas, Austin , NASA’s Jet Propulsion Laboratory , the German Space Agency and Germany’s National Research Center for Geosciences .
Gravity is related to mass, so as mass grows or shrinks, such as with an ice sheet, the satellites can detect the changes. But one variable missing in its calculation is the rebound effect that POLENET measures, which entails mass flow in the solid earth beneath the ice sheets.1 2 3 Next
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