The Cryosphere Discussions www.the-cryosphere-discuss.net 1994-0432 1994-0440 1 2 2007 10.5194/tcd-1-385-2007 http://www.the-cryosphere-discuss.net/1/385/2007/ http://www.the-cryosphere-discuss.net/1/385/2007/tcd-1-385-2007.html http://www.the-cryosphere-discuss.net/1/385/2007/tcd-1-385-2007.pdf 385 409 2007-11-05 Modelling historical and recent mass loss of McCall Glacier, Alaska, USA C. Delcourt cdelcour@ulb.ac.be F. Pattyn M. Nolan Laboratoire de Glaciologie, Département des Sciences de la Terre et de l'Environnement, Université Libre de Bruxelles, CP 160/03, Avenue F.D. Roosevelt 50, 1050 Brussels, Belgium Inst. of Northern Engineering, 455 Duckering Bldg, University of Alaska Fairbanks, AK, USA Volume loss of valley glaciers is now considered to be a significant contribution to sea level rise. Understanding and identifying the processes involved in accelerated mass loss are necessary to determine their impact on the global system. Here we present results from a series of model experiments with a higher-order thermomechanically coupled flowline model (Pattyn, 2002). Boundary conditions to the model are parameterizations of surface mass balance, geothermal heating, observed surface and 10 m ice depth temperatures. The time-dependent experiments aim at simulating the glacier retreat from its LIA expansion to present according to different scenarios and model parameters. Model output was validated against measurements of ice velocity, ice surface elevation and terminus position at different stages. Results demonstrate that a key factor in determining the glacier retreat history is the importance of internal accumulation (>50%) in the total mass balance. The persistence of a basal temperate zone characteristic for this polythermal glacier depends largely on its contribution. Accelerated glacier retreat since the early nineties seems directly related to the increase in ELA and the sudden reduction in AAR due to the fact that a large lower elevation cirque – previously an important accumulation area – became part of the ablation zone. Blatter, H.: On the Thermal Regime of an Arctic Valley Glacier: a Study of White Glacier, Axel Heiberg Island, N.W.T., Canada, J. Glaciol., 33, 200–211, 1987. Blatter, H. and Hutter, K.: Polythermal Conditions in Arctic Glaciers, J. Glaciol., 37, 261–269, 1991. Huybrechts, P.: The Antarctic Ice Sheet and Environmental Change: a Three-Dimensional Modelling Study, Berichte für Polarforschung, 99, 1–241, 1992. IPCC: Climate Change 2001: The Scientific Basis. Contribution of Working Group I to the Third Assessment Report of the Intergovernmental Panel on Climate Change, Cambridge Univ. Press, Cambridge, 2001. Jóhannesson, T., Raymond, C., and Waddington, E.: Time-Scale for Adjustment of Glaciers to Changes in Mass Balance, J. Glaciol., 35, 355–369, 1989. Nolan, M., Arendt, A., Rabus, B., and Hinzman, L.: Volume change of McCall Glacier, Arctic Alaska, from 1956 to 2003, Ann. Glaciol., 42, 409–416, 2005. Paterson, W.: The Physics of Glaciers, Oxford, Pergamon Press, 3rd edn., 1994. Pattyn, F.: Transient Glacier Response with a Higher-Order Numerical Ice-Flow Model, J. Glaciol., 48, 467–477, 2002. Pattyn, F., Nolan, M., Rabus, B., and Takahashi, S.: Localized basal motion of a polythermal Arctic glacier: McCall Glacier, Alaska, USA, Ann. Glaciol., 40, 47–51, 2005. Rabus, B. and Echelmeyer, K.: The Mass Balance of McCall Glacier, Brooks Range, Alaska, USA; its Regional relevance and Implications for Climate Change in the Arctic, J. Glaciol., 44, 333–351, 1998. Rabus, B. and Echelmeyer, K.: Increase of 10 m Ice Temperature: Climate Warming or Glacier Thinning?, J. Glaciol., 48, 279–286, 2002. Rabus, B., Echelmeyer, K., Trabant, D., and Benson, C.: Recent Changes of McCall Glacier, Alaska, Ann. Glaciol., 21, 231–239, 1995. Schneider, T. and Jansson, P.: Internal Accumulation in Firn and its Significance for the Mass Balance of Storglaciären, Sweden, J. Glaciol., 50, 25–34, 2004. Shapiro, N. and Ritzwoller, M.: Inferring Surface Heat Flux Distributions Guided by a Global Seismic Model: Particular Application to Antarctica, Earth Planet. Sci. Lett., 223, 213–224, 2004. Trabant, D. and Mayo, L.: Estimation and Effects of Internal Accumulation on Five Glaciers in Alaska, Ann. Glaciol., 6, 113–117, 1985.