1. Subglacial conditions of inland West Antarctica from US-ITASE deep radar reflection analysis WAIS Workshop September 30, 2005 Brian Welch, Bob Jacobel and Allison Hagen ‘07 Physics Department, St. Olaf College

2. US-ITASE 4-year program, part of international initiative to study recent climate change 4 traverses in WAIS 11 institutions Radar System 3 MHz center frequency (56 m wavelength) 1500 stacks/trace 12 m/trace

3. Example of processed radar data 2002 US-ITASE Traverse

4. Reflection power Following method of Gades et al. (1998)

5. Changes in reflector strength Attenuation: depth- dependent –Geometric spreading –Internal scattering & absorption Reflector properties –Reflector scattering: roughness –Reflector type: dielectric properties

6. SDM & KIS reflectivity Slope = attenuation Vertical offset due to instrumentation or reflector properties (reflectivity)

7. SDM, KIS, ITASE raw reflectivity

8. SDM, KIS, ITASE WAIS/EAIS raw reflectivity

9. SDM, KIS, ITASE smoothed reflectivity

10. Observations ITASE data shows slope similar to KIS reflectivity data (-32 dB/km) Identical instrumentation in WAIS –Range of reflectivity similar to KIS –EAIS data used different amplifier Use KIS classification boundaries with ITASE data

11. Smoothed reflectivity (WAIS) with classification Note similar slope and range of ITASE and KIS data

12. Initial interpretation Smoother till at bed of ice streams enhances difference between wet and dry bed Hard bedrock inland bed results in a spectrum of reflected power

13. Map of reflectivity and relationship to bed topography

14. Same map with velocity data

15. Basal reflectivity and ice flow

16. Conclusions Radar attenuation vs. depth of inland WAIS is similar to KIS Regions of fast-flowing ice show distinct differences in bed properties Inland WAIS bed shows spectrum of high to low reflectivity –Ice stream tributaries: high reflectivity –Inland WAIS plateau: low reflectivity –Whitmore Mts.: variable reflectivity due to local flow conditions

17. Acknowledgements Mike Helgen ’06 Kieran Cofell-Dwyer ’06 Ian Campbell ’07David Osterhouse ’08 Rickard Pettersson with $$$ from the National Science Foundation Office of Polar Programs Visit us at www.stolaf.edu/other/cegsic Mt. Erebus Photo, Brian C. Welch

19. ITASE bright layer and bed showing dynamic range problem at depth

20. Migration edge effect Migration edge effect

21. Map of reflectivity and Radarsat

22. WAIS vs. EAIS reflectivity EAIS data –different amplifier –Expect a different temperature (attenuation) profile in EAIS Will focus on WAIS data from 2002 traverse for this talk