Climate of the Past Discussions www.clim-past-discuss.net 1814-9340 1814-9359 2 6 2006 10.5194/cpd-2-1187-2006 http://www.clim-past-discuss.net/2/1187/2006/ http://www.clim-past-discuss.net/2/1187/2006/cpd-2-1187-2006.html http://www.clim-past-discuss.net/2/1187/2006/cpd-2-1187-2006.pdf 1187 1219 2006-11-20 Change of the ice rheology with climatic transitions – implication on ice flow modelling and dating of the EPICA Dome C core G. Durand gd@gfy.ku.dk F. Gillet-Chaulet A. Svensson O. Gagliardini S. Kipfstuhl J. Meyssonnier F. Parrenin P. Duval D. Dahl-Jensen Niels Bohr Institute, University of Copenhagen, Copenhagen, Denmark Laboratoire de Glaciologie et de Géophysique de l'Environnement, Saint Martin d'Hères, France Alfred Wegener Institute, Bremerhaven, Germany The study of the distribution of the crystallographic orientations (the fabric) along ice cores supplies information on the past and current ice flows of ice-sheets. Beside the usually observed formation of a vertical single maximum fabric, the EPICA Dome Concordia ice core (EDC) shows an abrupt and unexpected strenghtening of its fabric during termination II around 1750 m depth. Such strengthenings were already observed for sites located on an ice-sheet. This suggests that horizontal shear could occur along the EDC core. Moreover, the change in the fabric leads to a modification of the viscosity between neighbouring ice layers. Through the use of an anisotropic ice flow model, we quantify the change in viscosity and investigate its implication on ice flow and dating. Alley, R. B.: Fabrics in polar ice sheets: development and prediction, Science, 240, 493–495, 1988. Alley, R. B.: Flow-law hypotheses for ice-sheet modeling, J. Glaciol, 38, 245–256, 1992. Azuma, N., Wang, Y., Mori, K., Narita, H., Hondoh, T., Shoji, H., and Watanabe, O.: Textures and fabrics in the Dome F (Antarctica) ice core, Ann. Glaciol., 29, 163–168, 1999. Castelnau, O., Duval, P., Lebensohn, R. A., and Canova, G.: Viscoplastic modeling of texture development in polycrystalline ice with a self-consistent approach : Comparison with bound estimates, J. Geophys. Res., 101, 13 851–13 868, 1996a. Castelnau, O., Thorsteinsson, T., Kipfstuhl, J., Duval, P., and Canova, G. R.: Modelling fabric development along the GRIP ice core, central Greenland, Ann. Glaciol., 23, 194–201, 1996b. Castelnau, O., Shoji, H., Mangeney, A., Milsch, H., Duval, P., Miyamoto, A., Kawada, K., and Watanabe, O.: Anisotropic Behavior of GRIP Ices and Flow in Central Greenland, Earth Planet. Sci. Lett., 154, 307–322, 1998. Chung, D. H. and Kwon, T. H.: Invariant-based optimal fitting closure approximation for the numerical prediction of flow-induced fiber orientation, J. Rheol., 46, 169–194, 2002. Cuffey, K. M., Thorsteinsson, T., and Waddington, E. D.: A renewed argument for crystal size control of ice sheet strain rates, J. Geophys. Res., 105, 27 889–27 894, 2000. Diprinzio, C. L., Wilen, L. A., Alley, R. B., Fitzpatrick, J. J., Spencer, M. K., and Gow, A. J.: Fabric and texture at Siple Dome, Antarctica, J. Glaciol., 51, 281–290, 2005. Doake, C. S. M. and Wolff, E. W.: Flow law in polar ice sheets, Nature, 314, 255–257, 1985. Dome-F Deep Coring Group: Deep ice-core drilling at Dome Fuji and glaciological studies in East Dronning Maud Land, Antarctica, Ann. Glaciol., 27, 333–337, 1998. Durand, G., Graner, F., and Weiss, J.: Deformation of grain boundaries in polar ice, Eur. Phys. Lett., 67, 1038–1044, \doi10.1209/epl/i2004-10139-0, 2004. Durand, G., Gagliardini, O., Throsteinsson, T., Svensson, A., Kipfstuhl, J., and Dahl-Jensen, D.: Ice microstructure and fabric: an up to date approach to measure textures, J. Glaciol, in press, 2006a. Durand, G., Weiss, J., Lipenkov, V., Barnola, J. M., Krinner, G., Parrenin, F., Delmonte, B., Ritz, C., Duval, P., Roethsliberger, R., and Bigler, M.: Effect of impurities on grain growth in cold ice sheets, J. Geophys. Res., 111, F01015, \doi10.1029/2005JF000320., 2006b. Duval, P. and Castelnau, O.: Dynamic recrystallization of ice in polar ice sheets, Journal de physique, 5, 197–205, 1995. Duval, P., Ashby, M. F., and Anderman, I.: Rate controlling processes in the creep of polycrystalline ice, J. Phys. Chem., 87, 4066–4074, 1983. EPICA Community members: Eight glacial cycles from an Antarctic ice core, Nature, 429, 623–628, 2004. Gagliardini, O. and Meyssonnier, J.: Simulation of Anisotropic Ice Flow and Fabric Evolution Along the GRIP-GISP2 Flow Line (Central Greenland), Ann. Glaciol., 30, 217–223, 2000. Gagliardini, O. and Meyssonnier, J.: Lateral boundary conditions for a local anisotropic ice flow model, Ann. Glaciol., 35, 503–509, 2002. Gillet-Chaulet, F., Gagliardini, O., Meyssonnier, J., Montagnat, M., and Castelnau, O.: A user-friendly anisotropic flow law for ice-sheet modelling, J. Glaciol., 51, 3–14, 2005. Gillet-Chaulet, F., Gagliardini, O., Meyssonnier, J., Zwinger, T., and Ruokolainen, J.: Flow-induced anisotropy in polar ice and related ice-sheet flow modelling, J. Non-Newtonian Fluid Mech., 134, 33–43, 2006. Gow, A. J. and Williamson, T.: Rheological implications of the internal structure and crystal fabrics of the West Antarctic ice sheet as revealed by deep core drilling at Byrd Station, CRREL Report, 76–35, 1976. Gow, A. J., Meese, D. A., Alley, R. B., Fitzpatrick, J. J., Anandakrishnan, S., Woods, G. A., and Elder, B. C.: Physical and structural properties of the Greenland Ice Sheet Project 2 ice core: a review, J. Geophys. Res., 102, 26 559–26 575, 1997. Herron, S. L. and langway, C. C.: A comparison of ice fabrics and textures at Camp Century, Greenland and Byrd station Antarctica, Ann. Glaciol, 3, 118–124, 1982. Hodgkins, R., Siegert, M. J., and Dowdeswell, J. A.: Geophysical investigations of ice-sheet internal layering and deformation in the Dome C region central East Antarctica, J. Glaciol., 46, 161–166, 2000. Jacka, T. H. and Maccagnan, M.: Ice crystallographic and strain rate changes with strain in compression and extension, Cold Reg. Sci. Technol., 8, 269–286, 1984. Johnsen, S. J. and Dansgaard, W.: On flow model dating of stable isotope records from Greenland ice cores, in: The Last Deglaciation: Absolute and Radiocarbon Chronologies, pp. 13–24, NATO ASI Ser. I. Springer-Verlag, New York, edited by: Bard, E. and Broecker, W. S., 1992. Langway, C. C., Shoji, H., and Azuma, N.: Crystal size and orientation patterns in the Wisconsin-age ice from Dye 3, Greenland, Ann. Glaciol., 10, 109–115, 1988. Lipenkov, V. Y., Salamatin, A. N., and Duval, P.: Bubbly-ice densification in ice sheets: II. Applications, J. Glaciol., 43, 397–407, 1997. Lliboutry, L. and Duval, P.: Various isotropic and anisotropic ices found in glacier and polar ice caps and their corresponding rheologies, Ann. Geophys., 3, 207–224, 1985. Mangeney, A., Califano, F., and Hutter, K.: A numerical study of anisotropic, low Reynolds number, free surface flow of ice sheet modeling, J. Geophys. Res., 102, 22 749–22 764, 1997. Meyssonnier, J. and Philip, A.: A model for the tangent viscous behaviour of anisotropic polar ice, Ann. Glaciol., 23, 253–261, 1996. North Greenland Ice Core Project members: High resolution record of northern hemisphere climate extending into the last interglacial period, Nature, 431, 147–151, 2004. Nye, J. F.: Extrusion flow: reply to Mr. J. E. Fisher's comments, J. Glaciol, 2, 52–53, 1952. Nye, J. F.: The topology of ice-sheet centres, J. Glaciol., 37, 220–227, 1991. % %Parrenin, F.: Dating of the EPICA Dome C ice core, Clim. Past, this issue, % in preparation, 2006a. % %Parrenin, F., Dreyfus, G., Durand, G., Fujita, S., Gagliardini, O., Gillet, F., % jouzel, J., Kawamura, K., Lhomme, N., Masson-Delmotte, V., Ritz, C., % Schwander, J., Shoji, H., Uemura, R., Yoshida, N., Watanabe, O., and Wolff, % E.: Ice flow modelling at Dome C and Dome Fuji, East Antarctica, Clim. Past Discuss., % this issue, in preparation, 2006b. Paterson, W. S. B.: Why ice-age is sometimes soft, Cold. Reg. Sci. Technol., 20, 75–98, 1991. Pimienta, P., Duval, P., and Lipenkov, V. Y.: Mechanical behaviour of anisotropic polar ice, In International Association of Hydrological Sciences, Publication 170 (Symposium on The Physical Basis of Ice Sheet Modelling, Vancouver), 57–66, 1987. Rémy, F. and Tabacco, I. E.: Bedrock features and ice flow near the EPICA ice core site (Dome C, Antarctica), Geophys. Res. Lett., 24, 405–408, 2000. Schott Hvidberg, C., Dahl-Jensen, D., and Waddington, E. D.: Ice flow between the GRIP and GISP2 boreholes in Central Greenland, J. Geophys. Res., 102, 26 851–26 859, 1997. Siegert, M. J., Eyers, R. D., and Tabacoo, I. E.: Three-Dimensional ice-sheet structure at Dome C, central East Antarctic: implications for the interpretation of the EPICA ice core, Antarctic Sc., 13, 182–187, 2001. Thorsteinsson, T., Kipfsthul, J., and Miller, H.: Textures and fabrics in the GRIP project, J. Geophys. Res., 102, 26 583–26 599, 1997. Van der Veen, C. J. and Whillans, I. M.: Development of fabric in ice, Cold Reg. Sci. Technol., 22, 171–195, 1994. Vialov, S. S.: Regularities of glacial shields movements and the theory of plastic viscous flow, Physics of the movements of ice IAHS, 47, 266–275, 1958. Wang, Y., Kipfstuhl, S., Azuma, N., Thorsteinsson, T., and Miller, H.: Ice-fabrics study in the upper 1500 m of the Dome C (East Antarctica) deep ice core, Ann. Glaciol., 37, 97–104, 2003. Woodcock, N. H.: Specification of fabric shapes using an eigenvalues method, Geol. Soc. Am. Bull., 88, 1231–1236, 1977.