High Resolution Radar Profiling of the Snow and Ice Stratigraphy beneath the ITASE Traverses, West Antarctic Ice Sheet

My name is Steven Arcone and I work at the U. S. Army Cold Regions Research and Engineering Laboratory in Hanover, New Hampshire. My main research interest is the use of subsurface radar to gain information on the structure of snow and ice. This radar isn't powerful, but it is precise. It sends out very short pulses that enable me to look at the top 330 feet (100 m) of layering with a resolution of about 12 inches (30 cm). This easily covers the last 200 years of snowfall in most parts of West Antarctica. On the ITASE traverse, we obtain ice (or, more properly, firn) cores about every 62 miles (100 km), and we have seventeen already. So how representative will these few cores be for all of the firn in between the core sites? I will be using my high resolution radar to try to answer this question and to solve some other problems.

The main purposes for using radar are:

1. To find a good site for taking a core that represents snow deposition for about the last 200 years. Such a site will have very even layering without big dips and folds. So far in the last three years our sites, except one, have had good layering. However, as we travelled east in November, 2001, the snow layers dipped deeper and it remains to be seen whether or not our 60 m cores will be sufficiently deep to cover the last 200 years.
2. To find how far the even layering extends about any core site. Our results from the last two years showed that some layers can be followed for several hundred kilometers. We may find that their extent could define a local climate regime in West Antarctica. The figure below shows some of these layers around core sites D and E, recorded in December, 2000.



Radar stratigraphy near core sites D and E. The two sections are part of a larger profile that extends 380 kilometers. The layers follow the surface topography. Look real carefully at the layers at 190 km. See how they get steeper with depth?? That is because the snow is subsiding as it is being deposited. This process keeps the surface at the same elevation, year after year.

3. To find crevasses! Radar does a good job of finding crevasses in advance; we just have to slow down our tractors when we see the warning signs! Our antennas not only send radio waves down into the firn, they also send them out along the surface. When they hit a crevasse, or just the snow bridge above the crevasse, they reflect back. Sometimes we can see them 100 feet (30 m) in advance. We don't expect much trouble crossing crevasses when we do find them because they are usually filled with at least 2 m of hard snow. But we will stop and check it all out with probes to make sure. So far, after three years we haven't even seen a hint of a crevasse.

Crevasse detector out in front of our Challenger tractor. The inset shows the small antenna (black box) inside the tire tube. Arrows represent the many directions in which the waves go. If a crevasse is approached, crevasse reflections will start to creep up the radar record, which we look for while watching the profile play out in the tractor cabin.

The crevasse shown in the top picture was imaged by radar before we blew down the snow bridge with dynamite. The upper radar image shows this crevasse. The lower image shows two crevasses which were "en echelon," which means they would appear like a set of overlapping stairs if you could see them from the air.

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