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STEFFEN, KONRAD  CIRES, Univ. of Colorado.
Cullen, Nicolas  CIRES, Univ. of Colorado.
Huff, Russel  CIRES, Univ. of Colorado.
Stewart, Craig  British Antarctic Survey.
Rignot, Erioc  JPL/NASA.

Petermann Gletscher is the largest and most influential outlet glacier in central northern Greenland. Located at 81 N, 60 W, it drains an area of 71,580 km2, with a discharge of 12 cubic km of ice per year into the Arctic Ocean. The dominant form of mass loss (55%) at the Petermann Gletscher floating ice tongue has been attributed to basal melting, with the never before measured surface ablation thought to account for about 2-3 m/yr. The extensive field campaign during 2002 and 2003 allows surface ablation to be described for the first time.

A MALÅ GeoScience RAMAC/GPR unit was used to measure the thickness of the floating glacier tongue along profiles of several hundred meters. The control unit (32-bit processor) keeps track of current position and time, connected to transmitter and receiver with fiber optic cable. The unit was installed on a sledge with 25 MHz and 50 MHz antennas. We used a sampling frequency of 1 sec with 8 stacks and a 4100 ns time window. Geolocation of the measured profile was obtained with differential GPS measurements (Trimble Pathfinder), with reference stations at the Camp, and at Thule AFB. Large sub-glacial melt channels on the floating ice tongue were discovered running along the flow direction. Some of these melt channels are up to 200 m deep.

A step frequency radar based on a vector network analyzer (VNA) with a center frequency of 305 MHz at 1260 MHz bandwidth was used to measure the bottom melt of the floating Petermann glacier tongue with resolution of 2.3 mm in thickness change over only a couple of hours to days. Maximum bottom melt values of up to 50 m/y were measured. These multi-phase radar point measurements revealed interesting results of bottom melt rates, which exceed all previous estimates. It is worth mentioned that the largest bottom melt rates were not found at the grounding line, which is common on ice shelves in the Antarctica. In addition, GPS tidal motion has been measured over one lunar cycle at the flex zone and on the free floating ice tongue and the result will be compared to historic measurements made at the beginning of last century.

A peculiar surface feature resembling an “ice worm” was found some 5-km from the orographic left margin of the floating ice tongue. The vertical extension of this “ice worm” is approximately 50 m and it can be identified on Landsat imagery running for several tens of kilometers.

Figure 1. Ground Penetration Radar (MALÅ GeoScience RAMAC/GPR) on Petermann Gletscher with 100 MHz antenna.

Figure 2. Base Camp on Petermann Gletscher with Step Frequency Radar based on a Vector Network Analyzer (VNA). Transmitting and receiving antennae are shown separated by approximately 10 m.

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