An active subglacial water system in West Antarctica mapped from space

Science

Volumn 315, Issue 5818, 2007, Pages 1544-1548

  Fricker, Helen Amanda ^a   Scambos, Ted ^b   Bindschadler, Robert ^c   Padman, Laurie ^d  

^a UNIVERSITY OF CALIFORNIA   (United States)

^b UNIVERSITY OF COLORADO   (United States)

^c NASA GODDARD SPACE FLIGHT CENTER   (United States)

^d Earth and Space Research   (United States)

Author keywords

[No Author keywords available]

Indexed keywords

ICE; WATER;

DRAINAGE; GLACIAL LAKE; ICE FLOW; IMAGE PROCESSING; LASER; MASS BALANCE; SATELLITE ALTIMETRY; SATELLITE IMAGERY; SUBGLACIAL ENVIRONMENT; VERTICAL MOVEMENT;

ANTARCTICA; ARTICLE; GLACIAL MASS BALANCE; GLACIER; IMAGE ANALYSIS; PRIORITY JOURNAL; SPACE; SURFACE WATER HYDROLOGY; TELECOMMUNICATION; WATER TRANSPORT;

ANTARCTICA; MERCER ICE STREAM; WEST ANTARCTIC ICE SHEET; WEST ANTARCTICA; WHILLANS ICE STREAM;

EID: 33947416043     PISSN: 00368075     EISSN: 10959203     Source Type: Journal    
DOI: 10.1126/science.1136897     Document Type: Article

References (47)

1. M. Siegert, S. Carter, I. Tabacco, S. Popov, D. Blankenship, Antarct. Sci. 17, 453 (2005).
2. L. Gray et al., Geophys. Res. Lett. 32, L03501 (2005).
3. D. J. Wingham, M. L. Siegert, A. Shepherd, A. S. Muir, Nature 440, 1033 (2006).
4. I. Goodwin, J. Glaciol. 34, 95 (1988).
5. B. Kamb, Antarct. Res. Ser. 77, 157 (2001).
6. R. E. Bell, M. Studinger, C. A. Shuman, M. A. Fahnestock, I. Joughin, Nature 445, 904 (2007).
7. M. Siegert, J. Bamber, J. Glaciol. 46, 703 (2000).
8. R. B. Alley, S. Anandakrishnan, C. R. Bentley, N. Lord, Ann. Glaciol. 20, 187 (1994).
9. A. Iken, R. A. Bindschadler, J. Glaciol. 32, 101 (1986).
10. The three-dimensional InSAR technique requires ascending and descending passes, which only exist in a few areas of Antarctica. InSAR data for Antarctica are mainly derived from the tandem mission of European Remote-sensing Satellite-1 (ERS-1) and ERS-2 (18 months in 1995-1996). RADARSAT provided InSAR data as far as the South Pole, but only for 3 months in 1997 (9).
11. K. C. Jezek, Ann. Glaciol. 29, 286 (1999).
12. U.S. Navy's GEOSAT operated to 72°S during 1985 to 1989 in a 17-day orbit; the European Space Agency has flown three radar altimeters (RAs) in a 35-day orbit to 81.5°S: ERS-1 (1991 to 2000); ERS-2 (1995 to 2003); and Envisat (2002 to present). All four of these satellites miss much of the dynamic West Antarctic ice streams. The RA has a large footprint (∼2 to 3 km over flat ice for ERS). Steep slopes on the ice streams cause tracking problems for the RA, limiting its vertical accuracy.
13. C. A. Shuman et al., Geophys. Res. Lett. 33, L07501 (2006).
14. H. A. Fricker, L. Padman, Geophys. Res. Lett. 33, L15S02 (2006).
15. ICESat data were filtered for clouds by use of the gain and energy parameters. Elevation anomalies for each segment were calculated by resampling the remaining repeat-track data onto common latitude values and calculating the difference between each elevation profile and the mean. At each point, the elevation range was also calculated.
16. T. A. Scambos, G. Kvaran, M. Fahnestock, Remote Sens. Environ. 69, 56 (1999).
17. R. A. Bindschadler, P. L. Vornberger, Ann. Glaciol. 20, 327 (1994).
18. T. A. Scambos, M. A. Fahnestock, J. Glaciol. 44, 97 (1998).
19. Materials and methods are available as supporting material on Science Online.
20. A. M. Smith et al., Geology 35, 127 (2007).
21. S. Shabtaie, C. R. Bentley, Ann. Glaciol. 11, 126 (1988).
22. J. DiMarzio, J. Zwally, A. Brenner, B. Schutz, Boulder, Colorado, USA: National Snow and Ice Data Center. Digital media (2007).
23. S. W. Vogel et al., Geophys. Res. Lett. 32, L14502 (2005).
24. S. R. Atre, C. R. Bentley, Ann. Glaciol. 20, 177 (1994).
25. D. D. Blankenship, C. R. Bentley, S. T. Rooney, R. B. Alley, J. Geophys. Res. 92, 8903 (1987).
26. C. R. Bentley, R. Retzlaff, N. Lord, A. N. Novick, Antarct. J. U.S. 26, 62 (1991).
27. In satellite altimetry data, crossover analysis is a powerful means to validate elevation along any single track (45) and is the method previously used to detect subglacial water movement in ERS RA data (3).
28. G. W. Evatt, A. C. Fowler, C. D. Clark, N. R. J. Hulton, Philos. Trans. R. Soc A 364, 1769 (2006).
29. The latest ICESat data shown in Fig. 4 (Laser 3f data; May to June 2006) suggest that minor uplift occurred, but at levels close to the ICESat detection limit. Initial examination of data from the most recent operations period (Laser 3g, November to December 2006) suggests that this filling has continued, but since those data are still uncalibrated for precise pointing, we cannot yet confidently assert that the signal is real.
30. T. A. Scambos, T. Haran, M. A. Fahnestock, T. Painter, J. Bohlander, Remote Sens. Inviron., in press.
31. This estimate is in part affected by some surface lowering that had already taken place at the epoch of ICESat's Laser 2a data, which were used to create the digital elevation model
32. M. J. Roberts, Rev. Geophys. 43, RG1002 (2005).
33. A pressure of 100 kPa corresponds to a 10-m vertical difference in water-column height.
34. From the MODIS imagery (Figs. 2 and 4), we observe that the shortest length for a channel connecting the lake to the ocean is ∼7 km long. ICESat data along Track 221 show a depression ∼2 km wide, which gives an upper bound to the width of the outlet channel.
35. H. Rothlisberger, J. Glaciol. 11, 177 (1972).
36. G. E. Flowers, H. Bjornsson, F. Palsson, G. K. C. Clarke, Geophys. Res. Lett. 31, L05401 (2004).
37. The discharge curve we observe is similar to that for Lake L1 in (3). The drop in elevation is ∼9 m for Lake Engelhardt compared to ∼3.5 m for Lake L1, and the time scale is 26 months for Lake Engelhardt compared to 16 months for Lake L1.
38. The dimensions of Subglacial Lake Engelhardt are ∼30 km by ∼10 km, i.e., 14 to 40 times the ice thickness (∼700 m), so the central ice cannot be supported at the lake margins. The flat surface profiles in the center of the lake confirm this.
39. R. Bindschadler, P. Vornberger, Science 279, 689 (1998).
40. Errors in the surface-elevation and ice-thickness fields used for subglacial pressure mapping could modify the subglacial water catchments and allow some exchange of water between them. These issues were examined by adding ±5-m and ±50-m random errors to the surface and bed elevations, respectively. The major features discussed here did not change.
41. I. Joughin, S. Tulaczyk, D. R. MacAyeal, H. Englehardt, J. Glaciol. 50, 96 (2004).
42. R. A. Bindschadler, M. King, R. A. Alley, S. Anandakrishnan, L. Padman, Science 301, 1087 (2003).
43. R. Bindschadler, P. Vornberger, L. Gray, J. Glaciol. 51, 620 (2005).
44. I. Joughin et al., Geophys. Res. Lett. 32, L22501 (2005).
45. H. J. Zwally, R. A. Bindschadler, A. C. Brenner, T. V. Martin, R. H. Thomas, J. Geophys. Res. 88, 1589 (1983).
46. ICESat data release numbers are of the form YXX. Y refers to the amount of orbit and attitude calibration applied (a good indicator of quality), where 1 is the lowest and 4 is the highest XX refers to the software version used to process the data.
47. We thank K. Yanagimachi, C. Bentley, D. Blankenship, J. Bohlander, G. Clarke, N. Lord, B. Smith, and D. Young for their contributions to this work. Thanks to J. Zwally, B. Schutz, and NASA's ICESat project. Thanks also to two anonymous referees for helpful comments on this manuscript. This work was supported by NASA. This is ESR contribution number 86.