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Data source: I. Joughin, JPL

Ungrounded Conditions in the Mouth of Kamb Ice Stream?. 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:

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Data source: I. Joughin, JPL

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  1. Ungrounded Conditions in the Mouth of Kamb Ice Stream? 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 Data source: I. Joughin, JPL

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

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

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

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

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

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

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

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

  10. Flat-ice Terrain Ice Stream Terrain Identification of other features 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.

  11. Causes of layer downwarping Localized Basal Melt

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

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

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

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

  16. Localized Basal Melting 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

  17. 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 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

  18. Whillans Stream Ice Kamb Ice Stream Relict Grounding Line Positions When did it float? • 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 Engelhardt Ridge Siple Dome BEDMAP

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

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

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

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

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

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

  25. SUMMARY: Flow history of Kamb Ice Stream 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

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