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Is mechanical heterogeneity controlling the stability of the Larsen C ice shelf?

Is mechanical heterogeneity controlling the stability of the Larsen C ice shelf?. Bernd Kulessa 1 , Daniela Jansen 1 , Edward King 2 , Adrian Luckman 1 , Peter Sammonds 3. 1School of the Environment and Society, Swansea University, UK, b.kulessa@swansea.ac.uk

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Is mechanical heterogeneity controlling the stability of the Larsen C ice shelf?

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  1. Is mechanical heterogeneity controllingthe stability of the Larsen C ice shelf? Bernd Kulessa1, Daniela Jansen1, Edward King2, Adrian Luckman1, Peter Sammonds3 1School of the Environment and Society, Swansea University, UK, b.kulessa@swansea.ac.uk 2British Antarctic Survey, High Cross, Cambridge, UK 4Department of Earth Sciences, University College London, UK

  2. What we want to do (SOLIS Project) • Assess present + model the future stability of the Larsen C ice shelf • Identify regions of crevasse opening using 2-D fracture criterion • (Rist et al., 1999; updated for ice shelf mechanical heterogeneities) • + Constraints on the future evolution of these parameters

  3. Ice thickness based on combined ICESat and Bedmap ‘Combined’ minus ‘Bedmap only’ Difference to Bedmap: mainly thinner ice front How does this compare with Griggs and Bamber, GRL, in press?

  4. In-situ density Mean density of overlying ice column Firn / ice densities based on seismic data (from 2008/09 season) Transition from firn to consolidated ice (915 kg/m³) at ~ 80 m depth Mean density of upper layer: 770 kg /m³ Firn density correction here + in Griggs and Bamber, GRL, in press?

  5. m/a Updated velocity map (RAMP + feature tracking) • Preliminary velocity map partly noisy • More filtering could smooth out real velocity gradients • No predictive capability y (km) Velocity inversion for strain/stress not good enough for fracture criterion x (km)

  6. Modelled vs. measured velocities m a-1 m a-1 ~ 5% difference to GPS derived velocities (2008/09)

  7. Deviations in regions with major rifts

  8. Fracture mechanics: regions of potential crevasse opening Stress intensity factor (Fracturing > ~ 50) kPa/m0.5 D. Jansen, B. Kulessa et al., Fracturing of Larsen C and implications for ice-shelf stability, J. Glaciol., shortly in review

  9. Ice Flow ~ 505 m a-1 Solberg Inlet Trail Inlet 10 km Next: model improvements - structural / mechanical heterogeneities Glasser, N., B. Kulessa, A. Luckman, E. C. King, P. R. Sammonds, T. Scambos, K. Jeczek. 2009. The structural glaciology and inferred ice mechanical properties of the Larsen C ice shelf. Journal of Glaciology, 55(191), 400-410.

  10. View Ice Flow • 50 MHz Common-Offset GPR • (0.8 ns SI, 8 stacks) • 1 trace ~ every 3 m incl. GPS position +/- 5m ~ 320 m

  11. Comparison with modelling reveals characteristic two-lobe structure Holland, P. R. et al. (2009), Marine ice in Larsen Ice Shelf Geophys. Res. Lett., 36, L11604 doi:10.1029/2009GL038162. N ~ 5 km

  12. Better defined englacial reflectors parallel than orthogonal to flow N View Englacial debris ‘stringers’ by analogy with Filchner-Ronne ice shelf?

  13. High-quality seismic and GPR CMP data to estimate mechanical properties of firn, meteoric and marine ice

  14. Synthesis and modelling of future scenarios • Can do a pretty job reproducing current observations, know what the problems / weaknesses are (eliminate them) • Estimate and implement ice structural / mechanical heterogeneities (if / as they matter) • Thinner future ice shelf (due to basal or surface melting) • Increasing local / regional stresses due to surface ponding • Altered density / temperature profiles (surface melting, melt water percolation and refreezing) • Different temperature profiles for the flow lines, e.g. marine ice, warmer (?) • Different environmental conditions (waves, wind, etc.)

  15. Footnote 1: significant temporal changes in firn density? King&Jarvis 1989

  16. CMP1-North Footnote 2: significant differences in seismic vs. GPR derived densities CMP2-South

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