The Cryosphere Discussions www.the-cryosphere-discuss.net 1994-0432 1994-0440 2 4 2008 10.5194/tcd-2-711-2008 http://www.the-cryosphere-discuss.net/2/711/2008/ http://www.the-cryosphere-discuss.net/2/711/2008/tcd-2-711-2008.html http://www.the-cryosphere-discuss.net/2/711/2008/tcd-2-711-2008.pdf 711 736 2008-08-21 Partitioning of melt energy and meltwater fluxes in the ablation zone of the west Greenland ice sheet M. Van den Broeke broeke@phys.uu.nl P. Smeets J. Ettema C. Van der Veen R. Van de Wal J. Oerlemans Utrecht University, Institute for Marine and Atmospheric research (IMAU) P. O. Box 80005, 3508 TA Utrecht, The Netherlands We present four years of surface mass balance data from the ablation zone of the west Greenland ice sheet along the 67° N latitude circle. Sonic height rangers and automatic weather stations continuously measured accumulation/ablation and near-surface climate at distances of 6, 38 and 88 km from the ice sheet margin at elevations of 490, 1020 and 1520 m a.s.l. Using a melt model and reasonable assumptions about snow density and percolation characteristics, these data are used to quantify the partitioning of energy and mass fluxes during melt episodes. The lowest site receives very little winter accumulation, and ice melting is nearly continuous in June, July and August. Due to the lack of snow accumulation, little refreezing occurs and virtually all melt energy is invested in runoff. Higher up the ice sheet, the ice sheet surface freezes up during the night, making summer melting intermittent. At the intermediate site, refreezing in snow consumes about 10% of the melt energy, increasing to 40% at the highest site. The sum of these effects is that total melt and runoff increase exponentially towards the ice sheet margin, each time doubling between the stations. At the two lower sites, we estimate that radiation penetration causes 20–30% of the ice melt to occur below the surface. Anderson, E. A.: A point energy and mass balance model of a snow cover, NOAA Technical Report, 19, US Dept. of Commerce, Silver Spring, MD, 150 pp., 1976. Andreas, E. L.: A theory for the scalar roughness and the scalar transfer coefficients over snow and sea ice, Bound.-Lay. Meteorol., 38, 159–184, 1987. Bamber, J. L., Ekholm, S., and Krabill, W. B.: A new, high-resolution digital elevation model of Greenland fully validated with airborne altimeter data, J. Geophys. Res., 106, 6733–6745, 2001. Bøggild, C. E., Reeh, N., and Oerter, H.: Modelling ablation and mass-balance sensitivity to climate change of Storstrømmen, northeast Greenland, Global Planet. Change, 9, 79–90, 1994. Bougamont, M., Bamber, J. L., and Greuell, W.: A surface mass balance model for the Greenland Ice Sheet, J. Geophys. Res., 110, F04018, doi:10.1029/2005JF000348, 2005. Bougamont, M., Bamber, J. L., Ridley, J. K., Gladstone, R. M., Greuell, W., Hanna, E., Payne, A. J., and Rutt, I.: Impact of model physics on estimating the surface mass balance of the Greenland ice sheet, Geophys. Res. Lett., 34, L17501, doi:10.1029/2007GL030700, 2007. Box, J. E., Bromwich, D. H., Veenhuis, B. A., Bai, L.-S., Stroeve, J. C., Rogers, J. C., Steffen, K., Haran, T., and Wang, S.-H.: Greenland ice sheet surface mass balance variability (1988–2004) from calibrated Polar MM5 output, J. Climate, 19, 2783–2800, 2006. Braithwaite, R. J.: Positive degree-day factors for ablation on the Greenland ice sheet studied by energy balance modelling, J. Glaciol., 41, 153–160, 1995. Brandt, R. E. and Warren, S. G.: Solar heating rates and temperature profiles in Antarctic snow and ice, J. Glaciol., 39, 99–110, 1993. Cassano, J. J., Box, J. E., Bromwich, D. H., Li, L., and Steffen, K.: Evaluation of Polar MM5 simulations of Greenland's atmospheric circulation, J. Geophys. Res., 106, 33 867–33 890, 2001. Cazenave, A.: How fast are the ice sheets melting?, Science, 314, 1250–1252, 2006. Dethloff, K., Schwager, M., Christensen, J. H., Kiilsholm, S., Rinke, A., Dorn, W., Jung-Rothenhäusler, F., Fischer, H., Kipfstuhl, S., and Miller, H.: Recent Greenland accumulation estimated from regional climate model simulations and ice core analysis, J. Climate, 15, 2821–2832, 2002. Fettweis, X.: Reconstruction of the 1979–2006 Greenland ice sheet surface mass balance using the regional climate model MAR, The Cryosphere, 1, 21–40, 2007. Gregory, J. M., Huybrechts, P., and Raper, S.: Threatened loss of the Greenland ice sheet, Nature, 428, 6983, doi:10.1038/428616a, 2004. Greuell, W. G. and Konzelmann, T.: Numerical modelling of the energy balance and the englacial temperature of the Greenland Ice Sheet, Calculations for the ETH-Camp location (West Greenland, 1155 m~a.s.l.), Global Planet. Change, 9, 91–114, 1994. Hanna, E., McConnell, J., Das, S., Cappelen, J., and Stephens, A.: Observed and modeled Greenland ice sheet snow accumulation, 1958–2003, and links with regional climate forcing, J. Climate, 19, 344–358, 2006. Henneken, E. A. C., Bink, N. J., Vugts, H. F., Cannemeijer, F., and Meesters, A. G. C. A.: A case study of the daily energy balance near the equilibrium line on the Greenland ice sheet, Global Planet. Change, 9, 69–78, 1994. Janssens, I. and Huybrechts, P.: The treatment of meltwater retention in mass-balance parameterizations of the Greenland ice sheet, Ann. Glaciol., 31, 133–140, 2001. Joughin, I., Das, S. B., King, M. A., Smith, B. E., Howat, I. M., and Moon, T.: Seasonal speedup along the western flank of the Greenland ice sheet, Science, 320, 781–783, 2004. Krabill, W., Hanna, E., Huybrechts, P., Abdalati, W., Cappelen, J., Csatho, B., Frederick, E., Manizade, S., Martin, C., Sonntag, J., Swift, R., Thomas, R., and Yungel, J.: Greenland Ice Sheet: Increased coastal thinning, Geophys. Res. Lett., 31, L24402, doi:10.1029/2004GL021533, 2004. Lemke, P., Ren, J., Alley, R. B., Allison, I., Carrasco, J., Flato, G., Fujii, Y., Kaser, G., Mote, P., Thomas, R. H., and Zhang, T.: Observations: Changes in Snow, Ice and Frozen Ground, in: Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, edited by: Solomon, S., Qin, D., Manning, M., Chen, Z., Marquis, M., Averyt, K. B., Tignor, M., and Miller, H. L., Cambridge University Press, UK and New York, USA, 337–383, 2007. Oerlemans, J. and Vugts, H. F.: A Meteorological Experiment in the Melting Zone of the Greenland Ice Sheet, B. Am. Meteorol. Soc., 74, 355–365, 1993. Parizek, B. R. and Alley, R. B.: Implications of increased Greenland surface melt under global-warming scenarios: Ice-sheet simulations, Quaternary Sci. Rev., 23, 1013–1027, 2004. Schlatter, T. W.: The local surface energy balance and subsurface temperature regime in Antarctica, J. Appl. Meteorol., 11, 1048–1062, 1972. Smeets, C. J. P. P. and Van den Broeke, M. R.: Temporal and spatial variation of momentum roughness length in the ablation zone of the Greenland ice sheet, Bound.-Lay. Meteorol., 128, 315–338, doi:10.1007/s10546-008-9291-0, 2008a. Smeets, C. J. P. P. and Van den Broeke, M. R.: Parameterizing scalar roughness over smooth and rough ice surfaces, Bound.-Lay. Meteorol., 128, 339–355, doi:10.1007/s10546-008-9292-z, 2008b. Steffen, K. and Box, J. E.: Surface climatology of the Greenland ice sheet: Greenland Climate Network 1995–1999, J. Geophys. Res., 106, D24, 33 951–33 964, 2001. Van de Wal, R. S. W. and Oerlemans, J.: Modelling the short-term response of the Greenland ice sheet to global warming, Clim. Dynam., 13, 733–744, 1997. Van de Wal, R. S. W., Greuell, W., Van den Broeke, M. R., Boot, W., Snellen, H., Reijmer, C. H., and Oerlemans, J.: Mass balance measurements along a transect in West-Greenland over the period 1990–2003, Ann. Glaciol., 42, 311–316, 2005. Van den Broeke, M. R.: Characteristics of the lower ablation zone of the west Greenland ice sheet for energy-balance modelling, Ann. Glaciol., 23, 160–166, 1996. Van den Broeke, M. R., Smeets, C. J. P. P., Ettema, J., and Kuipers-Munneke, P.: Surface radiation balance in the ablation zone of the west Greenland ice sheet, J. Geophys. Res., 113, D13105, doi:10.1029/2007JD009283, 2008a. Wild, M., Calanca, P., Scherrer, S. C., and Ohmura, A.: Effects of polar ice sheets on global sea level in high-resolution greenhouse scenarios, J. Geophys. Res., 108, 4165, doi:10.1029/2002JD002451, 2003. Zwally, H. J., Abdalati, W., Herring, T., Larson, K., Saba, J., and Steffen, K.: Surface melt-induced acceleration of Greenland ice-sheet flow, Science, 297, 5597, doi:10.1126/science.1072708, 2002.