BELISSIMA: BELgian Ice Sheet- Shelf Ice Measurements in Antarctica

Transcription

1 BELISSIMA: BELgian Ice Sheet- Shelf Ice Measurements in Antarctica Frank PATTYN 1, Jean-Louis TISON 1, Denis SAMYN 1, Kenichi MATSUOKA², Howard CONWAY², Bryn HUBBARD³ (1)Laboratoire de Glaciologie, DSTE, Université Libre de Bruxelles, Brussels, Belgium ( (2)Earth and Space Sciences, University of Washington, Seattle, USA (3)Institute of Geography and Earth Sciences, University of Wales, Aberystwyth, UK

2 Hypothesis I Conventional view Emerging evidence East Antarctic regions remained mostly invariable since the Last Glacial Maximum, about ka ago (Anderson et al., 2002). WAIS contribution to sea-level rise since LGM was much smaller than sea-level rise predicted by continental ice-sheet models DML might in fact be a missing source of the fresh water (Huybrechts, 2002) Pag. 2

3 Hypothesis II IPCC predicted future sea-level rise: poor understanding in ice-sheet dynamics prevents to make quantitative assessments (IPCC, 2007). Antarctic ice sheet has lost its mass for the last decade and the continental-scale mass balance is mostly governed by dynamics of less than a dozen of regions that directly drain ice into the ocean (Rignot et al., 2008). Observed rapid increases of ice-flow speeds after the collapse of downstream ice shelves demonstrate that ice shelves play a key role to stabilize the upstream ice sheet (Rott et al., 1996; De Angelis and Skvarca, 2003). (Rignot et al., 2008) Pag. 3

4 (van de Berg et al., 2006) (IPCC,2007) (Bamber et al., 2000) H t = vh -M ice thickness change (imbalance) ice flux divergence local accumulation rate Pag. 4

5 PHYSICS OF THE ICE SHEET ICE SHELF TRANSITION Grounded sheet: Spreads under its own weight Stress: shears in the vertical Transition zone: Stress: longitudinal stretching and vertical shear Floating shelf: Buoyant, wants to spread like a drop of oil on water Stress: longitudinal stretching Schoof, Pag. 5

6 PREVIOUS WORK Balance fluxes in and around the Sør Rondane Mountains Sør Rondane (Pattyn et al., 2005) Pag. 6

7 ICE RISES = PINNING POINTS Grounding line Pag. 7

8 QUESTION 1 Is the ice flow in DML stable for a sustained period? Do ice rises have a local flow pattern? Can Raymond bumps be observed? ANSWER Ice-penetrating radar survey across pinning points (ice rises) Analysis of isochrones with ice flow model (a) Stratigraphy within the ice, and surface and bed topography detected by ice-penetrating radar and GPS at Roosevelt Island, Ross Embayment. (b) Magnitudes of the bump beneath the divide revealed by radar (dots) and by ice-flow models (solid lines) with various timings of the divide-flow initiation. After Conway et al. (1999) Pag. 8

9 QUESTION 2 How do ice shelves in these embayments stabilize ice flow? What is the role of marine ice in bottom crevasses and rifts? ANSWER Ice core drilling Deformation experiments in laboratory to define flow law of (marine) ice Model experiments to match flow field/viscosity Radar survey to determine thickness of meteoric ice layer Optimized ice rheology for Larsen B ice shelf (Vieli et al., 2007) Pag. 9

10 NOVO BELISSIMA PES Romnoesfjellet Pag. 10

11 PROPOSED WORK Drilling? Radar saddle Grounding line Pag. 11

12 DETAIL OF THE SADDLE AREA Estimated flow direction of local dome and saddle area to be determined with differential GPS Pag. 12

13 (a) Longitudinal transaction from the grounded ice sheet to floating ice shelf. Accreted ice fills subglacial crevasses near the grounding zone and more coherently distributes beneath the ice shelf. (b) Crosssectional view of a longitudinal transaction crossing over the ice rise. Ice-penetrating radar detects accreted ice, diagnoses bed conditions, and illustrate isochrones (gray dots in panel b). Isochrones can be used to decipher accumulation and ice-flow histories Pag. 13