Peering at hidden Antarctic mountains and lakes
This is the 6th post in Robin Bell’s description of scientific research in Antarctica in late 2008 and early 2009.
At last we are able to mount flights out of AGAP S. With the flat white topography all around us it is hard to visualize a mountain range anywhere near us. Our flight from the South Pole located some minor 100 foot peaks close to camp, but these are not the range we are looking for. Our plan involves surveying beneath the ice to the north with the airborne radar. The data on the flights between South Pole and the camp let us know the systems work well over the thick cold ice. Although we have tested the system, first in Greenland this past summer, and then at McMurdo once in Antarctica, there was a concern that it might not work at this colder environment.
The radar system that makes the data profiles transmits energy from four antennae on the right wing of the aircraft and records the returning echos from the ice on the four antennae on the left wing. While radar systems are widely used in environmental engineering for studying the upper 1-10 meters of the earth surface, radar can be used to map through 4-5 kilometers of ice. The electrical conductivity of ice makes radar a perfect tool. The first echo actually travels straight though the air from one side of the aircraft to another. The second echo is from the surface of the ice sheet. We can use this system to map crevasses, mega dunes and floating ice over lakes, although our laser system will be more accurate.
Within the ice sheet there are changes in electrical conductivity as a result of the changing makeup of the ice – sometimes the result of volcanic dust landing on Antarctica. These chemical changes show up as many layers within the ice sheet, layers reminiscent of a fancy layer cake. The final echo is from the bottom of the ice sheet. Rocks will return a signal, but water at the bottom of the ice sheet will return a really strong signal. The strong reflectivity of water makes lakes easy to spot.
A large lake has emerged under three km of ice, and the mountains are beginning to emerge forming a map of what is underneath the extensive ice sheet. Our survey area is twice as big as the state of California. A large area to cover but despite the setbacks we are finally capturing the images we had hoped for!
Robin Bell is a geophysicist and research scientist at Lamont-Doherty Earth Observatory of Columbia University. She has coordinated seven major aero-geophysical expeditions to Antarctica studying subglacial lakes, ice sheets and the mechanisms of ice sheet movement and collapse, and currently the Gamburtsev Mountains, a large alp sized subglacial mountain range in East Antarctica.