The West Antarctic Ice Sheet Helena Sykes

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The West Antarctic Ice SheetHelena Sykes

• Leeds Glaciology Group Presentation
• 17th February 2005

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Weddell Sea
Antarctic Peninsula
East Antarctic Ice Sheet (EAIS)
West Antarctic Ice Sheet (WAIS)
Transantarctic Mountains
Amundsen Sea
Ross Sea
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Ice streams

• Rapidly moving, channelled ice radiating out
  from the interiors of ice sheets and ice caps
  Benn and Evans (1998, p.16)
• Ice flow is driven by gravity (driving stress)
  and is resisted by basal and lateral drag and
  gradients in the longitudinal stress - Joughin
  et al. (2002, p.3-7)
• Driving stress (td)
• td ?gHsina
• where ? is the average column density, g the
  gravitational acceleration, H the ice thickness
  and a the surface slope
• However, the role of ice streams is not yet
  properly understood - Doake et al. (in Alley and
  Bindschadler 2001, p.221)

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Ross SeaSector
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Ice Stream B (Whillans Ice Stream)

• Archetypal example of an ice stream - Whillans
  et al. (in Alley and Bindschadler 2001, p.257)
• Currently decelerating, thinning and widening
  would become stagnant in 50 to 100 years if this
  continues
• Driving stress 15 kPa, velocity up to 865 m a-1
• Deceleration may be due to decrease in meltwater
  caused by lower geothermal heat flux

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Ice Stream C (Kamb Ice Stream)

• Lower section shut down 150 years ago
• Lots of hypotheses
• Piracy ice from tributary ISC0 diverted into
  tributary WIS2 (ice stream B)
• Water piracy subglacial water needed to
  lubricate the bed diverted into ice stream B
• Thermal model sticky spots at the bed holding
  back the lower section of the ice stream
• Some or all of these processes may be operating
  together evidence for and against each one

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AmundsenSeaSector
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Pine Island Glacier

• Some characteristics of an outlet glacier, some
  of an ice stream
• The part of the West Antarctic ice sheet most
  prone to substantial retreat on human timescales
  - Vaughan et al. (in Alley and Bindschadler 2001,
  p.237)
• Grounding line and hinge line retreating, glacier
  thinning
• Ice front shifting around a mean position
• Drains 10 of the WAIS, velocities up to 1.5 km
  a-1 so discharges lots of ice in little time when
  mass balance is negative

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Thwaites Glacier

• Similar story to Pine Island Glacier
• Warm ocean water causing increased basal melting
• Weertman (1974) suggested removal of buttressing
  ice shelves may cause glaciers behind to speed up
• Pine Island and Thwaites unbuttressed
• This occurred for glaciers on the Antarctic
  Peninsula following the collapse of the Larsen B
  ice shelf

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WeddellSeaSector
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Carlson Inlet

• Former ice stream, now in a stagnant phase like
  the lower section of ice stream C
• May be reactivated by an increase in basal water,
  e.g. from increased melting of Rutford
• Oscillation between catchments, like ice streams
  B and C
• Surge cycle - deceleration, stagnation, and
  reactivation

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Rutford Ice Stream

• Study area due to other projects in the region
• Velocity 200 ma-1 at onset, up to 400 ma-1
• Bed down to 2000m below sea level, 7km vertical
  relief in a 40km distance
• Diurnal period with double velocity not tidally
  related

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Conclusions

• Ice streams may be the first areas to react to
  change, or the first areas where changes are
  shown
• Rutford Ice Stream should be viewed in the
  context of the stability of the WAIS as a whole

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References

• Alley, R.B. and Bindschadler, R.A. (Eds) 2001 The
  West Antarctic Ice Sheet. Washington D.C.
  American Geophysical Union
• Bindschadler, R.A., King, M.A., Alley, R.B.,
  Anandakrishnan, S. and Padman, L. 2003 Tidally
  controlled stick-slip discharge of a West
  Antarctic ice stream. Science, 301, 1087-1089
• Joughin, I., Tulaczyk, S., Bindschadler, R. and
  Price, S.F. 2002 Changes in West Antarctic ice
  stream velocities Observation and analysis.
  Journal of Geophysical Research, 107, article
  number 2289
• Rignot, E., Cassassa, G., Gogineni, P., Krabill,
  W., Rivera, A. and Thomas, R. 2004 Accelerated
  discharge from the Antarctic Peninsula following
  the collapse of Larsen B ice shelf. Geophysical
  Research Letters, 31, L18401
• Vaughan, D.G. and Spouge, J.R. 2002 Risk
  estimation of collapse of the West Antarctic ice
  sheet. Climatic Change, 52, 65-91