1. Data source: I. Joughin, JPL G. Catania, H. Conway, C. Raymond and T. Scambos * Earth and Space Sciences, University of Washington, Seattle WA, 98195 * National Snow & Ice Data Center, University of Colorado, Boulder CO, 80309 Many thanks to: NSF support (OPP #9909518) Raytheon Polar Services A. Gades, M. Conway & E. Waddington Ungrounded Conditions in the Mouth of Kamb Ice Stream?

2. Identification of boundaries and terrains Siple Dome Engelhardt Ridge Kamb Ice Stream Whillans Stream Ice

3. Siple Dome Engelhardt Ridge Kamb Ice Stream Whillans Stream Ice Identification of boundaries and terrains

4. Siple Dome Engelhardt Ridge Identification of boundaries and terrains Kamb Ice Stream Whillans Stream Ice

5. Siple Dome Engelhardt Ridge Identification of boundaries and terrains Kamb Ice Stream Whillans Stream Ice

6. Siple Dome Engelhardt Ridge Identification of boundaries and terrains Kamb Ice Stream Whillans Stream Ice

7. Siple Dome Engelhardt Ridge Identification of boundaries and terrains Kamb Ice Stream Whillans Stream Ice

8. Siple Dome Engelhardt Ridge Identification of boundaries and terrains Kamb Ice Stream Whillans Stream Ice

9. Terrain on both sides of KIS Diffractors have uniform depth Diffractors are line-type No near-surface diffractors Flat-ice terrain Identification of other features Syncline feature Ice Stream Terrain

10. Syncline feature Syncline amplitude grows with depth. Deep layers are truncated by the bed. Synclines are narrow in width. No change in layer thickness across dip. Identification of other features Flat-ice Terrain Ice Stream Terrain

11. Localized Basal Melt Causes of layer downwarping

12. Localized Basal Melt Causes of layer downwarping How long did it melt for?

13. Localized Basal Melt Causes of layer downwarping How long did it melt for? Melting lasted for ~10-130 years

14. Localized Basal Melt Causes of layer downwarping Melting lasted for ~10-130 years Short-lived melting Spatially focussed melting Deep diffractors Syncline features wrap around ridges How long did it melt for?

15. Ice Stream Margin? Pros:  melting is spatially focussed  melting is short-lived Cons:  no explanation of deep line-diffractors  synclines wrap around ridges Localized Basal Melting

16. Ice Stream Margin? Pros:  melting is spatially focussed  melting is short-lived Cons:  no explanation of deep line-diffractors  synclines wrap around ridges Geothermal Source? Pros:  synclines wrap around ridges Cons:  no explanation of deep line-diffractors  source must be extremely shallow  melting is short-lived Localized Basal Melting

17. Ice Stream Margin? Pros:  melting is spatially focussed  melting is short-lived Cons:  no explanation of deep line-diffractors  synclines wrap around ridges Geothermal Source? Pros:  synclines wrap around ridges Cons:  no explanation of deep line-diffractors  source must be extremely shallow  melting is short-lived Grounding Line Melt? Pros:  explains deep line-diffractors  melting is short-lived  synclines wrap around ridges Cons:  not currently floating  melting is spatially focussed Localized Basal Melting

18. When did it float? Relict Grounding Line Positions BEDMAP Siple Dome Engelhardt Ridge Kamb Ice Stream Whillans Stream Ice  not floating now (50-100 m above)  sea level is steady so floatation due to thickness changes  thickness changes indicate it could have grounded ~350 years ago  Accumulation  Compression  became floating ~480 years ago

19. Flow history of Kamb Ice Stream ~700 y.b.p Siple Dome Engelhardt Ridge CIR Wide trunk, fast flow permits thinning

20. Flow history of Kamb Ice Stream ~500 y.b.p Siple Dome Engelhardt Ridge CIR Thinning  floatation Shift in flow direction of WIS

21. Flow history of Kamb Ice Stream ~450 y.b.p Siple Dome Engelhardt Ridge CIR Ice/water piracy  shutdown of SIS

22. Flow history of Kamb Ice Stream ~350 y.b.p Siple Dome Engelhardt Ridge CIR SIR Re-advance (b/c of WIS?) Narrowing of KIS Destruction of water system?

23. Flow history of Kamb Ice Stream ~250 y.b.p Siple Dome Engelhardt Ridge CIR SIR Ice/water piracy  shutdown of KIS0

24. Flow history of Kamb Ice Stream ~150 y.b.p Siple Dome Engelhardt Ridge CIR SIR Stagnation of KIS Continued flow in tributaries

25. Syncline features/flat-ice terrain identified:  Strongly downwarped isochrones bound flat-ice terrains  Likely caused by basal melting for 130 years  Melting is a result of grounding line melt?  Associated deep diffractors caused by past floatation events  Floating occurred between 500 years ago and ended ~350 years ago Ice flow history of KIS:  Grounding line retreat in the mouth of KIS prior to stoppage  Sudden floatation and regrounding could destroy the subglacial drainage network  This might permit freezing to occur as upstream water is unable to reach the trunk SUMMARY: Flow history of Kamb Ice Stream