HR: 11:50h
AN: C21D-07    [PDF]
TI: Two Decades of Gravity Variations at a Site on the South-central Greenland Ice Sheet
AU: * Jezek, K
EM: jezek.1@osu.edu
AF: Byrd Polar Research Center, 1090 Carmack Road, Columbus, OH 43210 United States
AU: Baumgartner, F
EM: frb@byg.dtu.dk
AF: Arctic Technology Center, Technical University of Denmark, Lyngby, DK-2800 Denmark
AU: Krabill, W
EM: william.b.krabill@nasa.gov
AF: Laboratory for Hydrospheric Processes, Wallops Flight Facility, Wallops Island, VA 23337 United States
AU: Sonntag, J
EM: sonntag@osb1.wff.nasa.gov
AF: Laboratory for Hydrospheric Processes, Wallops Flight Facility, Wallops Island, VA 23337 United States
AB: At the 2002 AGU Fall Meeting, we reported on changes in gravity and surface elevation measured at a site on the South-Central Greenland Ice Sheet. Our goal was, and remains, to understand relationships between changing ice sheet elevation and ice sheet mass. We discussed gravity data collected in 1981, 1993 and 1995 and found a favorable comparison between decreasing trends in the gravity data and the increasing trends in more densely sampled observations of changing elevation. However, our analysis of those data also suggested that while the elevation of the ice sheet was increasing, the magnitude of the change in gravity did not support concluding that there was a comparable increase in mass. This year we report on the analysis of an additional set of gravity and surface elevation measurements collected at the same locations. During June 2003, we measured surface gravity and geodetic positions at six locations separated by about 20 km at a site located on the South-central Greenland Ice Sheet. We used two gravimeters and each was tied to the International Gravity Station Network before and after each set of field observations. A GPS unit operated at each field site and a base station unit recorded data for differential post-processing of the GPS data. The same measurement sites were occupied in 1981 and all were part of a hexagonal network of geodetic and glaciological measurements established by The Ohio State University in 1980. Additional gravity observations were acquired at three of the sites in 1993 and 1995. Gravity data were collected in conjunction with Doppler satellite measurements of position and elevation in 1981 and global positioning system measurements subsequently. The use of satellite navigation techniques permitted reoccupation of the same sites in each year to within a few 10's of meters or better. After detrending the gravity data, making adjustments for tides and removing the residual effects of local spatial gradients in gravity, we observe an average secular decrease in gravity of about 0.01 milligal/year, but with tenths of milligal variations about the mean trend. The trend is consistent with a nearly linear increase in surface elevation of between 7 to 10 cm/yr (depending on location) as measured by repeated airborne laser altimeter, surface Doppler satellite and GPS elevation measurements. We go on to discuss differences between the residual gravity anomalies after free air correction in terms of local mass changes.
DE: 1827 Glaciology (1863)
SC: Cryosphere [C]
MN: 2003 Fall Meeting