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Mass Balance and Velocity Data for Greenland's Ice Sheets at High Elevations

Goal

Estimation of mass balance of the Greenland Ice Sheet at higher elevations by using a mass budget method

Procedure & Methodology

Mass balance was computed as the difference between the estimated annual total snow accumulation and ice discharge

Outgoing flux is estimated from ice sheet velocity and ice thickness measured around the central part of the Greenland Ice Sheet

• Ice velocity and thickness measurements at 161 stations located 30 km apart, at 2000 m elevation that circumnavigates Greenland
• Stations are numbered counter-clockwise starting in the northwest corner
• Ice velocities were determined from repeat, differential carrier-phase GPS data collected in 1-2 years intervals between 1993 to 1997
• Ice thickness was measured by using ice-penetrating radar

Annual snow accumulation is estimated from an observational analysis of ice core and pit data

Results are presented as mass balance estimates in single gates:

• Data from two adjacent stations were combined to form 161 single gate

Mass balance estimates at medium-sized regions:

• Adjacent single gates were combined to form 130 medium gates each with a minimum area of 30,000 km2.
• The gates were grouped by shifting one traverse station at a time.

Mass balance estimates at large regions:

• The single gates were combined to form 12 large gates (A-L) with an average area of approximately 100,000 km2 each.
• The maximum numbers of single gates were in gate D with 23 single gates, from station F069 to F096.
• The minimum numbers of single gates were in gate C with 6 single gates, from station F096 to F101.

Results

• Overall the ice sheets in Greenland are in balance within 10mm/yr; thickening and thinning in different regions.
• In the northwest the ice sheet thinned 5 cm/yr, and thickened 2 cm/yr in the northeast.
• In the southwest the ice sheet thickened 21 cm/yr, and thinned 30 cm/yr in the southeast

References

• Thomas, R., T. Akins, B. Csatho, M. Fahnestock, P. Gogineni, C. Kim, and J. Sonntag. 2000. Mass balance of the Greenland Ice Sheet at high elevations. Science 289: 426-427.
• Thomas, R., B. Csatho, C. Davis, C. Kim, W. Krabill, S. Manizade, J. McConnell and J. Sonntag. 2001. Mass balance of higher-elevation parts of the Greenland Ice Sheet. Journal of Geophysical Research - Atmosphere 106 (D24) (December): 33707-33716.
• Thomas, R., B. Csatho, S. Gogineni, K. Jezek, and K. Kuivinen. 1998. Thickening of the western part of the Greenland Ice Sheet. Journal of Glaciology 44: 653-658.

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