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Antarctica: Siple Coast Ice Streams Balance velocities Measured - - PowerPoint PPT Presentation
Antarctica: Siple Coast Ice Streams Balance velocities Measured - - PowerPoint PPT Presentation
Antarctica: Siple Coast Ice Streams Balance velocities Measured velocities One is missing! Balance velocities indicate that there should be ice streams A, B, C, D, E und F. Ice Stream C is missing today, it stagnates since 200 years 1 Siple
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Siple Coast Ice Streams: Ice Flow und grounding lines
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Thomas (2013)
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Antarctic Ice Stream Geometries: Longitudial Sections and Stresses
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Whillans Whillans Whillans
Bennet (2003)
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Geothermal Heat Flux as Source of Melt Water?
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Winsborrow (2010) Talalay (2020)
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Extremely Soft Subglacial Sediments
Properties of sediments
- extremely low strength τf
(yield stress)
- sediments are water-saturated
→ high porosity
- high water pressure pw
→ low effective pressure N = po − pw
- τf = µN + c0
τf = 0.443N + 1.3 kPa
- for comparison: pressure of a human
100 kg·9.81 m s−2 0.05 m2
≃ 20 kPa
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Tulaczyk (2001)
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Whillans: Flow Velocities
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Haselhoff (2019)
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Whillans: Shear Margins
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Meyer (2018)
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Crevassing in Marginal Shear Zones
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- C. Larson
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High Ice Deformation in Marginal Shear Zones
Marginal shear zones
- velocity changes rapidly across
marginal shear zones
- in models the ice has to be 10 times
softer (enhancement E)
- effect of crevasses and strain heating
- feedback: faster motion leads to
softer ice
- sideways migration of shear margins is
possible
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- K. Echelmeyer
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Whillans: Thermal Softening in Shear Margins
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Perol (2015)
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Whillans: Thermal Softening in Shear Margins
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Haselhoff (2019)
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Whillans (Ice Stream B): Stick-Slip Motion
Stick-slip motion
- the Ice-Plain (∼ half Switzerland) moves
- nly episodically
- usually two motion events per day
- motion distance about 40 cm
- clear influence of ocean tides
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Bindschadler (2003)
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Whillans: Stick-Slip Events
Timing of events
- triggering of slip-events by ocean
tides
- usually two events per tidal cycle
- 14-day cycle like tides
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Winberry (2008)
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Whillans: Stick-Slip Motion Event: Animation
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Wiens (2008) Winberry (2009)
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Whillans: Stick-Slip Motion Events
- episodic motion controlled by tides
- mostly at rising or falling tide level
- similar repetitions
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Winberry (2013)
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Whillans: Explanation of Stick-Slip Motion
- ice stream is compressing the "stick-slip region" in longitudinal direction
- the elastic stress ¯
τupstream is increasing
- tides modulate the stress ¯
τtide (right)
- if stress ¯
τb is larger than a critical value → motion event
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Winberry (2013)
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Whillans: Stick-Slip Motion Events
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Winberry (2014)
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Whillans: Stick-Slip Slow-Down
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Winberry (2014)
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Whillans: Ice Flow Velocities
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Thomas (2013)
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Whillans: Slow-Down Measurements
- marked slow-down of ice streams A and B (Mercer/Whillans)
- stagnation of ice stream C (Kamb)
- unclear for ice streams D and E (Bindschadler/MacAyeal)
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Thomas (2013)
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Whillans: Slow-Down Measurements
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Thomas (2013)
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Whillans: Slow-Down Measurements
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Beem (2014)
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Siple Coast: Water Fluxes and Subglacial Lakes
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Carter (2013)
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Siple Coast: Basal Topography
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Catania (2012)
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Siple Coast: Changing Ice Fluxes
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Catania (2012)
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Siple Coast Ice Streams: Hypotheses
Causes for shutdown of Kamb Ice Stream (C)
- water piracy: Whillans (B) reroutes melt water
- sediment under Kamb consolidates → less deformation
- less heat production → less water → less deformation
Causes for slow-down of Whillans Ice Stream (B)
- melt water is increasingly routed towards Kamb (C)
- potential re-activation of Kamb
- after long time a stagnation of Whillans (B) is possible
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