Fast recession of a West Antarctic glacier

Science

Volumn 281, Issue 5376, 1998, Pages 549-551

  Rignot, E J ^a  

^a CALIFORNIA INSTITUTE OF TECHNOLOGY   (United States)

Author keywords

[No Author keywords available]

Indexed keywords

ICE;

GLACIER RETREAT; RADAR INTERFEROMETRY; SATELLITE IMAGERY;

ANTARCTICA; ARTICLE; GEOLOGY; INTERFEROMETRY; MODEL; OCEANIC REGIONS; PHYSICS; PRIORITY JOURNAL; WARMING;

ANTARCTICA;

EID: 0032563302     PISSN: 00368075     EISSN: None     Source Type: Journal    
DOI: 10.1126/science.281.5376.549     Document Type: Article

References (35)

1. A. Jenkins, D. G. Vaughan, S. S. Jacobs, H. H. Hellmer, J. R. Keys, J. Glaciol. 43, 114 (1997).
2. D. Lindstrom and D. Tyler, Antarct. J. U.S. 19, 53 (1984).
3. D. Lindstrom and T. J. Hughes, ibid., p. 56.
4. R. D. Crabtree and C. S. M. Doake, Ann. Glaciol. 3, 65 (1982).
5. B. K. Lucchitta, C. E. Rosanova, K. F. Mullins, ibid. 21, 277 (1995).
6. T. J. Hughes, J. Glaciol. 24, 493 (1979); ibid. 27, 518 (1981); G. H. Denton et al., ibid. 24, 495 (1979); C. S. Lingle and J. A. Clarke, ibid., p. 213; R. H. Thomas, ibid., p. 167.
7. T. J. Hughes, J. Glaciol. 24, 493 (1979); ibid. 27, 518 (1981); G. H. Denton et al., ibid. 24, 495 (1979); C. S. Lingle and J. A. Clarke, ibid., p. 213; R. H. Thomas, ibid., p. 167.
8. T. J. Hughes, J. Glaciol. 24, 493 (1979); ibid. 27, 518 (1981); G. H. Denton et al., ibid. 24, 495 (1979); C. S. Lingle and J. A. Clarke, ibid., p. 213; R. H. Thomas, ibid., p. 167.
9. T. J. Hughes, J. Glaciol. 24, 493 (1979); ibid. 27, 518 (1981); G. H. Denton et al., ibid. 24, 495 (1979); C. S. Lingle and J. A. Clarke, ibid., p. 213; R. H. Thomas, ibid., p. 167.
10. T. J. Hughes, J. Glaciol. 24, 493 (1979); ibid. 27, 518 (1981); G. H. Denton et al., ibid. 24, 495 (1979); C. S. Lingle and J. A. Clarke, ibid., p. 213; R. H. Thomas, ibid., p. 167.
11. M. Stuiver, C. H. Denton, T. J. Hughes, J. L. Fastook, in The Last Great Ice Sheets, G. H. Denton and T. J. Hughes, Eds. (Wiley, New York, 1981), pp. 319-346.
12. J. Weertman, J. Glaciol. 13, 3 (1974); R. H. Thomas and C. R. Bentley, Quat. Res. 10, 150 (1978); R. H. Thomas, T. J. O. Sanderson, K. E. Rose, Nature 277, 355 (1979).
13. J. Weertman, J. Glaciol. 13, 3 (1974); R. H. Thomas and C. R. Bentley, Quat. Res. 10, 150 (1978); R. H. Thomas, T. J. O. Sanderson, K. E. Rose, Nature 277, 355 (1979).
14. J. Weertman, J. Glaciol. 13, 3 (1974); R. H. Thomas and C. R. Bentley, Quat. Res. 10, 150 (1978); R. H. Thomas, T. J. O. Sanderson, K. E. Rose, Nature 277, 355 (1979).
15. R. H. Thomas, in Climate Processes and Climate Sensitivity, J. E. Hansen and T. Takahashi, Eds., vol. 29 of Geophysical Monograph Series, vol. 5 of Maurice Ewing Series (American Geophysical Union, Washington, DC, 1984), pp. 265-274.
16. S. S. Jacobs, H. H. Hellmer, A. Jenkins, Geophys. Res. Lett. 23, 957 (1996).
17. H. H. Hellmer, S. S. Jacobs, A. Jenkins, in Antarctic Research Series, vol. 75 (American Geophysical Union, Washington, DC, in press).
18. E. Rignot, J. Glaciol. 42, 476 (1996); _, S. P. Gogineni, W. B. Krabill, S. Ekholm, Science 276, 934 (1997); E. Rignot, Ann. Glaciol, in press; J. Glaciol., in press.
19. E. Rignot, J. Glaciol. 42, 476 (1996); _, S. P. Gogineni, W. B. Krabill, S. Ekholm, Science 276, 934 (1997); E. Rignot, Ann. Glaciol, in press; J. Glaciol., in press.
20. E. Rignot, J. Glaciol. 42, 476 (1996); _, S. P. Gogineni, W. B. Krabill, S. Ekholm, Science 276, 934 (1997); E. Rignot, Ann. Glaciol, in press; J. Glaciol., in press.
21. E. Rignot, J. Glaciol. 42, 476 (1996); _, S. P. Gogineni, W. B. Krabill, S. Ekholm, Science 276, 934 (1997); E. Rignot, Ann. Glaciol, in press; J. Glaciol., in press.
22. To locate a glacier hinge line with ERS radar interferometry, I formed the difference between two radar interferograms generated with data acquired 1 day apart (1996), 3 days apart (1994), and 6 days apart (1992). Differencing eliminates information common to both interferograms, which is the steady and continuous creep deformation of the glacier, a mostly horizontal motion. After differencing of the two interferograms, I removed the interferometric signal associated with the glacier topography given by an altimetric DEM of Antarctica (16) at a 5-km spacing, interpolated to the 20-m spacing of the radar interferograms. The coarse spatial resolution of the DEM is sufficient to remove the mean glacier surface slope (less than 2%) from the data. The resulting "quadruple" difference interferogram measures the glacier surface displacement along the radar line of sight (23° off vertical) in response to changes in ocean tide, which is a vertical motion. To process the 1992 and 1994 quadruple difference interferograms successfully, I first registered the radar scenes with subpixel precision (15) to follow the glacier motion (which exceeds 20 m in 3 days) and then generated radar interferograms at the finest spatial resolution before differencing.
23. The hinge line, or limit of tidal flexing, detected with radar interferometry is a surface proxy for the grounding line. The hinge-line position is mapped automatically by fitting (in the least squares sense) an elastic beam model of tidal flexure (12) through individual tidal displacement profiles extracted from difference interferograms across the zone of tidal flexure, in a direction perpendicular to the iso-contours of vertical displacement of the glacier. The mapping precision is highest (80 m) in areas of high signal-to-noise ratio, large tidal motion, and large radius of curvature of the hinge line; it degrades along the glacier side margins where the signal is limited by the resolution of the ERS radar imaging system. On average, the mapping precision is better than ±200 m.
24. -1 for the 6-day pairs. The across-track displacements are five times less precise (spatial resolution is 20 m across track compared with 4 m along track) and affected by tide (3 m of tide compared with 13 m of creep flow in 6 days along the radar line of sight). Two independent estimates of the glacier motion were obtained for the 1992 and 1994 data to increase the measurement precision. The 1996 ice fluxes were calculated with only the along-track displacements with cross-glacier profiles oriented in the across-track direction.
25. J. Bamber and R A. Bindschadler, Ann. Glaciol. 25, 439 (1998).
26. -1 based on a ±30-m uncertainty in ice thickness.
27. -1 w.e. accumulation, which is close to my estimate obtained from more accurate elevation data.
28. -1 at a location 12 km upstream of my inferred hinge line but using ice thickness data of uncertain positional accuracy (1). My analysis uses complete cross-glacier profiles of thickness and velocity at the precise location of the grounding line.
29. Multiyear ERS data from ascending and descending tracks were registered independently to reference scenes acquired in 1996 (ERS-1 orbit 23,627 for ascending tracks and ERS-1 orbit 23,616 for descending tracks) with the cross-correlation of the signal intensity over nonmoving parts of the scene. The precision of registration is better than ±40 m in the along-and across-track directions. Topographic information was required to register ascending and descending tracks together. I projected all data onto a common polar stereographic grid at 50-m spacing using surface elevation from the altimetric DEM of Antarctica. The two geocoded reference scenes for ascending and descending tracks (which were acquired 1 day apart) were subsequently coregistered to within ±50 m with the cross-correlation of the signal intensity over the entire area (glacial motion is less than 7 m in 1 day). This final coregistration provides the framework for comparing ascending and descending data of any year with ±60 m, which is two orders of magnitude less than the detected hinge-line migration.
30. -1.
31. T. B. Kellog, D. E. Kellog, T. J. Hughes, Antarct. J. U.S. 20, 79 (1985).
32. Increased basal melting should increase the glacier velocity to compensate for mass loss and back pressure reduction from the floating tongue. The ice-front velocity of Pine Island Glacier has remained stable at the 10% level since the 1970s (1). I found no change in ice velocity between 1992 and 1996 at the 1% level. Hence, the grounding line was probably already retreating at the earliest times of observation.
33. J. H. Swift, Int. WOCE Newsl. 18, 15 (1995).
34. T. B. Kellog and D. E. Kellog, J. Geophys. Res. 92, 8859 (1987).
35. I thank the European Space Agency for providing ERS data; S. Jacobs, A. Jenkins, H. Hellmer, and D. Vaughan for discussions; J. Bamber for providing a DEM of Antarctica; G. Peltzer, P. Rosen, and three anonymous reviewers for comments; and M. Schmeltz, G. Buscarlet, and C. Werner for assistance. This work was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the Polar Program of NASA.