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Rathmann NM, Grinsted A, Mosegaard K, Lilien DA, Westhoff J, Hvidberg CS, Prior DJ, Lutz F, Thomas RE, Dahl-Jensen D. Elastic wave propagation in anisotropic polycrystals: inferring physical properties of glacier ice. Proc Math Phys Eng Sci 2022. [DOI: 10.1098/rspa.2022.0574] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
An optimization problem is proposed for inferring physical properties of polycrystals given ultrasonic (elastic) wave velocity measurements, made across multiple sample orientations. The feasibility of the method is demonstrated by inferring both the effective grain elastic parameters and the grain
c
-axis orientation distribution function (ODF) of ice-core samples from Priestley glacier, Antarctica. The method relies on expanding the ODF in terms of a spherical harmonic series, which allows for a non-parametric estimation of the sample ODF. Moreover, any linear combination of the Voigt (strain) and Reuss (stress) homogenization scheme is allowed, although for glacier ice, the exact choice is found to matter little for bulk elastic behaviour, and thus for inferred physical properties, too. Finally, the accuracy of the inferred grain elastic parameters is discussed, including the well-posedness and shortcomings of the inverse problem, relevant for future adoptions in glaciology, geology and elsewhere.
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Affiliation(s)
| | - Aslak Grinsted
- Niels Bohr Institute, University of Copenhagen, Copenhagen, Denmark
| | - Klaus Mosegaard
- Niels Bohr Institute, University of Copenhagen, Copenhagen, Denmark
| | - David A. Lilien
- Centre for Earth Observation Science, University of Manitoba, Winnipeg, Canada
| | - Julien Westhoff
- Niels Bohr Institute, University of Copenhagen, Copenhagen, Denmark
| | | | - David J. Prior
- Department of Geology, University of Otago, Dunedin, New Zealand
| | - Franz Lutz
- Department of Geology, University of Otago, Dunedin, New Zealand
| | - Rilee E. Thomas
- Department of Geology, University of Otago, Dunedin, New Zealand
| | - Dorthe Dahl-Jensen
- Niels Bohr Institute, University of Copenhagen, Copenhagen, Denmark
- Centre for Earth Observation Science, University of Manitoba, Winnipeg, Canada
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Grinsted A, Hvidberg CS, Lilien DA, Rathmann NM, Karlsson NB, Gerber T, Kjær HA, Vallelonga P, Dahl-Jensen D. Accelerating ice flow at the onset of the Northeast Greenland Ice Stream. Nat Commun 2022; 13:5589. [PMID: 36151072 PMCID: PMC9508143 DOI: 10.1038/s41467-022-32999-2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2021] [Accepted: 08/25/2022] [Indexed: 12/05/2022] Open
Abstract
Mass loss near the ice-sheet margin is evident from remote sensing as frontal retreat and increases in ice velocities. Velocities in the ice sheet interior are orders of magnitude smaller, making it challenging to detect velocity change. Here, we analyze a 35-year record of remotely sensed velocities, and a 6-year record of repeated GPS observations, at the East Greenland Ice-core Project (EastGRIP), located in the middle of the Northeast-Greenland Ice Stream (NEGIS). We find that the shear margins of NEGIS are accelerating, indicating a widening of the ice stream. We demonstrate that the widening of the ice stream is unlikely to be a response to recent changes at the outlets of NEGIS. Modelling indicates that the observed spatial fingerprint of acceleration is more consistent with a softening of the shear margin, e.g. due to evolving fabric or temperature, than a response to external forcing at the surface or bed. A new study finds that the North East Greenland ice stream is not as stable as previously thought and that this will affect its future evolution.
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Affiliation(s)
- Aslak Grinsted
- Niels Bohr Institute, University of Copenhagen, Copenhagen, Denmark.
| | | | - David A Lilien
- Centre for Earth Observation Science, University of Manitoba, Winnipeg, MB, Canada
| | | | | | - Tamara Gerber
- Niels Bohr Institute, University of Copenhagen, Copenhagen, Denmark
| | | | - Paul Vallelonga
- Oceans Graduate School, The University of Western Australia, Perth, Australia
| | - Dorthe Dahl-Jensen
- Niels Bohr Institute, University of Copenhagen, Copenhagen, Denmark.,Centre for Earth Observation Science, University of Manitoba, Winnipeg, MB, Canada
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Abstract
Radar data reveal how sensitive the Greenland Ice Sheet is to long-term climatic changes
[Also see Report by
MacGregor
et al.
]
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Affiliation(s)
- Christine S. Hvidberg
- Centre for Ice and Climate, Niels Bohr Institute, University of Copenhagen, 2100 Copenhagen, Denmark
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Fishbaugh KE, Hvidberg CS. Martian north polar layered deposits stratigraphy: Implications for accumulation rates and flow. ACTA ACUST UNITED AC 2006. [DOI: 10.1029/2005je002571] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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Andersen KK, Azuma N, Barnola JM, Bigler M, Biscaye P, Caillon N, Chappellaz J, Clausen HB, Dahl-Jensen D, Fischer H, Flückiger J, Fritzsche D, Fujii Y, Goto-Azuma K, Grønvold K, Gundestrup NS, Hansson M, Huber C, Hvidberg CS, Johnsen SJ, Jonsell U, Jouzel J, Kipfstuhl S, Landais A, Leuenberger M, Lorrain R, Masson-Delmotte V, Miller H, Motoyama H, Narita H, Popp T, Rasmussen SO, Raynaud D, Rothlisberger R, Ruth U, Samyn D, Schwander J, Shoji H, Siggard-Andersen ML, Steffensen JP, Stocker T, Sveinbjörnsdóttir AE, Svensson A, Takata M, Tison JL, Thorsteinsson T, Watanabe O, Wilhelms F, White JWC. High-resolution record of Northern Hemisphere climate extending into the last interglacial period. Nature 2004; 431:147-51. [PMID: 15356621 DOI: 10.1038/nature02805] [Citation(s) in RCA: 313] [Impact Index Per Article: 15.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/05/2004] [Accepted: 06/30/2004] [Indexed: 11/08/2022]
Abstract
Two deep ice cores from central Greenland, drilled in the 1990s, have played a key role in climate reconstructions of the Northern Hemisphere, but the oldest sections of the cores were disturbed in chronology owing to ice folding near the bedrock. Here we present an undisturbed climate record from a North Greenland ice core, which extends back to 123,000 years before the present, within the last interglacial period. The oxygen isotopes in the ice imply that climate was stable during the last interglacial period, with temperatures 5 degrees C warmer than today. We find unexpectedly large temperature differences between our new record from northern Greenland and the undisturbed sections of the cores from central Greenland, suggesting that the extent of ice in the Northern Hemisphere modulated the latitudinal temperature gradients in Greenland. This record shows a slow decline in temperatures that marked the initiation of the last glacial period. Our record reveals a hitherto unrecognized warm period initiated by an abrupt climate warming about 115,000 years ago, before glacial conditions were fully developed. This event does not appear to have an immediate Antarctic counterpart, suggesting that the climate see-saw between the hemispheres (which dominated the last glacial period) was not operating at this time.
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Affiliation(s)
- K K Andersen
- Niels Bohr Institute for Astronomy, Physics and Geophysics, University of Copenhagen, Juliane Maries Vej 30, DK-2100 Copenhagen OE, Denmark
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Johnsen SJ, Clausen HB, Dansgaard W, Gundestrup NS, Hammer CU, Andersen U, Andersen KK, Hvidberg CS, Dahl-Jensen D, Steffensen JP, Shoji H, Sveinbjörnsdóttir ÁE, White J, Jouzel J, Fisher D. The δ18O record along the Greenland Ice Core Project deep ice core and the problem of possible Eemian climatic instability. ACTA ACUST UNITED AC 1997. [DOI: 10.1029/97jc00167] [Citation(s) in RCA: 391] [Impact Index Per Article: 14.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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Clausen HB, Hammer CU, Hvidberg CS, Dahl-Jensen D, Steffensen JP, Kipfstuhl J, Legrand M. A comparison of the volcanic records over the past 4000 years from the Greenland Ice Core Project and Dye 3 Greenland ice cores. ACTA ACUST UNITED AC 1997. [DOI: 10.1029/97jc00587] [Citation(s) in RCA: 145] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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