Page 3/3 - Posted December 23, 2011
Peaks and valleys
Finally, last year, BAS scientists flew a Twin Otter with their own radar instruments across parts of the ice shelf. The tight grid lines flown by pilots — called “mowing the lawn” — revealed that the bottom of the ice shelf isn’t being cleanly planed off by the warm water. Instead, the bottom more closely resembles corrugated steel, where channels have been carved.
That ocean action affects not just the bottom of the ice shelf, but also the surface, Bindschadler explained. The channeling below creates an inverse effect on top, causing small ridges to form longitudinally between where two channels exist on the bottom of the ice shelf.
Each surface ridge, heavily crevassed by the flexing, is next to a narrow valley that appears free of cracks. Mirroring each surface valley below the ice shelf is one of the channels carved by the warm water.
Photo Credit: NASA
The Pine Island Glacier Ice Shelf, where the team will work about 15 kilometers south (up) from the crack that recently formed.
“It’s really nice that the one place where we can work, which is in the valleys, is sitting right over the top of where that meltwater is being concentrated by the topography of the bottom of the ice shelf,” Bindschadler said. “That’s the water we want to see. We get lucky. That’s where we can work and that’s where we want to work.”
But it’s not a lot of room to work. Each valley is only a few hundred meters wide, but enough to establish the drill camp and all of the associated equipment, which must be moved by helicopter.
The helos will also be used to ferry glaciologist Sridhar Anandakrishnan from Pennsylvania State University around the ice shelf. Anandakrishnan is an expert in using a technique called reflection seismology, which uses seismic waves, or waves of energy generated from something like an earthquake or explosion, to learn about the properties of the Earth’s subsurface. In this case, the technique will reveal the shape of the ocean cavity, the properties of the bedrock under the ice shelf and the layers of ocean sediment draped on that bedrock.
The researchers plan to install three profilers between this year and next. The instruments were developed by co-principal investigator Tim Stanton and his team at the Ocean Turbulence Laboratory in the Oceanography Department at the Naval Postgraduate School . The technology was first used in the Arctic.
Each installation should take a about a week, Bindschadler said, based on a test run of the system two years ago near McMurdo Station on the nearby ice shelf. The team hopes it can deploy two profiler systems this year, but the ongoing transportation delays are jeopardizing that plan.
“The hardest part we always knew would be getting out to PIG,” said Bindschadler, whose patience seems to be matched only by his desire to capture the data that he has been chasing for years.
Time may be short for the expedition. But based on the rates of melting under way in parts of Antarctica and Greenland, the world may be running out of time before catastrophic sea-level rise begins. Many scientists now believe global oceans will likely rise by a meter by the end of the century — but the uncertainties are still too great to predict the future properly.
“Melting ice holds the greatest possibility for change, and that’s why we’re interested in it,” Holland said. “Many cities around the world would be affected by sea-level change.”
NSF-funded research in this story: Robert Bindschadler and Alberto Behar, Goddard Space Flight Center, Award No. 0732906 ; Tim Stanton, Naval Postgraduate School, Award No. 0732926 ; David Holland, New York University, Award No. 0732869 ; Sridhar Anandakrishnan, Penn State University, Award No. 0732844 ; Miles McPhee, McPhee Research Company, Award No. 0732804 ; and Martin Truffer, University of Alaska, Fairbanks, Award No. 0732730 .