TC The Cryosphere TC The Cryosphere 1994-0424 Copernicus Publications Göttingen, Germany 10.5194/tc-9-603-2015 Self-regulation of ice flow varies across the ablation area in south-west Greenland van de Wal R. S. W. 1 Smeets C. J. P. P. 1 Boot W. 1 Stoffelen M. 1 van Kampen R. 1 Doyle S. H. 2 Wilhelms F. 3 van den Broeke M. R. https://orcid.org/0000-0003-4662-7565 1 Reijmer C. H. 1 Oerlemans J. https://orcid.org/0000-0001-5701-4161 1 Hubbard A. 2 Institute for Marine and Atmospheric research Utrecht, Utrecht University, the Netherlands Centre for Glaciology, Department of Geography and Earth Sciences, Aberystwyth University, Aberystwyth, UK Alfred Wegener Institute, Bremerhaven, Germany 01 04 2015 9 2 603 611 Copyright: © 2015 R. S. W. van de Wal et al. 2015 This work is licensed under the Creative Commons Attribution 3.0 Unported License. To view a copy of this licence, visit https://creativecommons.org/licenses/by/3.0/ This article is available from https://tc.copernicus.org/articles/9/603/2015/tc-9-603-2015.html The full text article is available as a PDF file from https://tc.copernicus.org/articles/9/603/2015/tc-9-603-2015.pdf

The concept of a positive feedback between ice flow and enhanced melt rates in a warmer climate fuelled the debate regarding the temporal and spatial controls on seasonal ice acceleration. Here we combine melt, basal water pressure and ice velocity data. Using 20 years of data covering the whole ablation area, we show that there is not a strong positive correlation between annual ice velocities and melt rates. Annual velocities even slightly decreased with increasing melt. Results also indicate that melt variations are most important for velocity variations in the upper ablation zone up to the equilibrium line altitude. During the extreme melt in 2012, a large velocity response near the equilibrium line was observed, highlighting the possibility of meltwater to have an impact even high on the ice sheet. This may lead to an increase of the annual ice velocity in the region above S9 and requires further monitoring.

 References Andreas, E. L.: A theory for scalar roughness and the scalar coefficients over snow and ice, Bound.-Lay. Meteorol., 38, 159–184, 1987. Bartholomaus, T. C., Anderson, R. S., and Anderson, S. P.: Response of glacier basal motion to transient water storage, Nat. Geosci., 1, 33–37, 2008. Bartholomew, I., Nienow, P., Mair, D., Hubbard, A., King, M. A., and Sole, A.: Seasonal evolution of subglacial drainage and acceleration in a Greenland outlet glacier, Nat. Geosci., 3, 408–411, 2010. Bartholomew, I., Nienow, P., Sole, A., Mair, D., Cowton, T., King, M. A., and Palmer, S.: Seasonal variations in Greenland Ice Sheet motion: Inland extent and behaviour at higher elevations, Earth Planet. Sci. Lett. 307, 271–278, 2011. Bartholomew, I., Nienow, P., Sole, a., Mair, D., Cowton, T., King, M. A.: Short-term variability in Greenland Ice Sheet motion forced by time-varying meltwater drainage: implications for the relationship between subglacial drainage system behaviour and ice velocity, J. Geophys. Res., 117, F03002, <a href="http://dx.doi.org/10.1029/2011JF002220">https://doi.org/10.1029/2011JF002220</a>, 2012. Chandler, D. M., Wadham, J. K., Lis, G. P., Cowton, T., Sole, A., Bartholomew, I., Telling, J., Nienow, P., Bagshaw, E. B., Mair, D., Vinen, S. and Hubbard, A.: Evolution of the subglacial drainage system beneath the Greenland ice sheet revealed by tracers, Nat. Geosci., 6, 195–198, 2013. Colgan, W., Rajaram, H., Anderson, R. S., Steffen, K., Phillips, T., Joughin, I., Zwally, H. J., and Abdalati, W.: The annual glaciohydrology cycle in the ablation zone of the Greenland Ice Sheet: Part 1 Hydrology, J. Glaciol., 57, 697–709, 2011. Colgan, W., Rajaram, H., Anderson, R. S., Zwally, H. J., Steffen, K., Phillips, T., and Abdalati, W.: The annual glaciohydrology cycle in the ablation zone of the Greenland Ice Sheet: Part 2 Observed and modeled ice flow, J. Glaciol., 58, 51–64, 2012. Cowton, T., Nienow, P., Sole, A., Wadham, J., Lis, G., Bartholomew, I., Mair, D., and Chandler, D.: Evolution of drainage system morphology at a land-terminating Greenlandic outlet glacier, J. Geophys. Res.-Earth, 118, 1–13, 2013. Das, S. B., Joughin, I., Behn, M. D., Howat, I.M., King, M. A., Lizarralde, D., and Bhatia, M. P.: Fracture propagation to the base of the Greenland ice sheet during supraglacial lake drainage, Science, 320, 778–781, 2008. den Ouden, M. A. G., Reijmer, C. H., Pohjola, V., van de Wal, R. S. W., Oerlemans, J., and Boot, W.: Stand-alone single-frequency GPS ice velocity observations on Nordenskiöldbreen, Svalbard, The Cryosphere, 4, 593–604, <a href="http://dx.doi.org/10.5194/tc-4-593-2010">https://doi.org/10.5194/tc-4-593-2010</a>, 2010. Dow, C. F., Hubbard, A., Booth, A. D., Doyle, S. H., Gusmeroli, A., and Kulessa, B.: Seismic evidence of mechanically-weak sediments underlying Russell Glacier, West Greenland. Ann. Glaciol., 54, 135–141, <a href="http://dx.doi.org/10.3189/2013AoG64A032">https://doi.org/10.3189/2013AoG64A032</a>, 2013. Doyle, S. H., Hubbard, A., Fitzpatrick, A. A. W., van As, D., Mikkelsen, A. B., Petterson R., Hubbard, B.: Persistent flow acceleration within the interior of the Greenland Ice Sheet, Geophys. Res. Lett., 41, 899–905, <a href="http://dx.doi.org/10.1002/2013GL058933">https://doi.org/10.1002/2013GL058933</a>, 2014. Fettweis, X.: Reconstruction of the 1979–2006 Greenland ice sheet surface mass balance using the regional climate model MAR, The Cryosphere, 1, 21–40, <a href="http://dx.doi.org/10.5194/tc-1-21-2007">https://doi.org/10.5194/tc-1-21-2007</a>, 2007. Fitzpatrick, A. A. W., Hubbard, A. L., Joughin, I., Quincey, D. J., van As, D., Mikkelsen, A. P. B., and Doyle, S. H.: Ice flow dynamics and surface meltwater flux at the land-terminating margin of the west Greenland Ice Sheet, J Glaciol., 59, 687–696, <a href="http://dx.doi.org/10.3189/2013JoG12J143">https://doi.org/10.3189/2013JoG12J143</a>, 2013. Hoffman, M. J., Catania, G. A., Neuman, T. A., Andrews, L. C., and Rumrill, J. A.: Links between acceleration, melting, and supraglacial lake drainage of the western Greenland ice sheet, J. Geophys. Res., 116, F04035, <a href="http://dx.doi.org/10.1029/2010JF001934">https://doi.org/10.1029/2010JF001934</a>, 2011. Howat, I. M., Joughin, I., and Scambos, T. A.: Rapid changes in ice discharge from Greenland outlet glaciers, Science, 315, 1559–1561, 2007. Howat, I. M., de la Peña, S., van Angelen, J. H., Lenaerts, J. T. M., and van den Broeke, M. R.: Brief Communication "Expansion of meltwater lakes on the Greenland Ice Sheet", The Cryosphere, 7, 201–204, <a href="http://dx.doi.org/10.5194/tc-7-201-2013">https://doi.org/10.5194/tc-7-201-2013</a>, 2013. Iken, A. and Bindschadler, R.: Combined measurements of subglacial water pressure and surface velocity of Findelengletscher, Switzerland: conclusions about the drainage system and sliding mechanism, J. Glaciol., 32, 101–119, 1986. Iken, A., Rothlisberger, H., Flotron, A., and Haeberli, W.: The uplift of Unteraargletscher at the beginning of the melt season – a consequence of water storage at the bed, J. Glaciol., 29, 28–47, 1983. Iken, A., Echelmeyer, K., Harrison, W., and Funk, M.: Mechanisms of fast flow in Jakobshavns Isbræ, West Greenland, I: Measurements of temperature and water level in deep boreholes, J. Glaciol., International Glaciological Society, 39, 15–25, 1993. 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, 2008. Joughin, I., Das, S. B., Flowers, G. E., Behn, M. D., Alley, R. B., King, M. A., Smith, B. E., Bamber, J. L., van den Broeke, M. R., and van Angelen, J. H.: Influence of ice-sheet geometry and supraglacial lakes on seasonal ice-flow variability, The Cryosphere, 7, 1185–1192, <a href="http://dx.doi.org/10.5194/tc-7-1185-2013">https://doi.org/10.5194/tc-7-1185-2013</a>, 2013. Meierbachtol, T., Harper, J., and Humphrey, N.: Basal drainage system response to increasing surface melt on the Greenland ice sheet, Science, 341, 777–779, <a href="http://dx.doi.org/10.1126/science.1235905">https://doi.org/10.1126/science.1235905</a>, 2013. Nghiem, S., Hall, D. K., Mote, T. L., Tedesco, M., Albert, M. R., Keegan, K., Shuman, C. A., DiGiolamo, N. E., and Neumann, G.: The extreme melt across the Greenland ice sheet in 2012, Geophys. Res. Lett., 39, L20502, <a href="http://dx.doi.org/10.1029/2012GL053611">https://doi.org/10.1029/2012GL053611</a>, 2012. Nick, F. M., Vieli, A., Andersen, M. L., Joughin, I., Payne, A., Edwards, T. L., Pattyn, F., and Van de Wal, R. S. W.: Future sea-level rise from Greenland's main outlet glaciers in a warming climate, Nature, 497, 235–237, 2013. Palmer, S., Shepherd, A., Nienow, P., and Joughin, I.: Seasonal speedup of the Greenland Ice Sheet linked to routing of surface water, Earth Planet. Sci. Lett., 302, 3–4, 2011. Parizek, B. R.: Sliding to sea, Nat. Geosci., 3, 385–386, <a href="http://dx.doi.org/10.1038/ngeo879">https://doi.org/10.1038/ngeo879</a>, 2010. 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. Philips, T., Rajaram, H., and Steffen, K.: Cryo-Hydrologic warming: a potential mechanism for rapid thermal response of ice sheets, Geophys. Res. Lett., 37, L20503, <a href="http://dx.doi.org/10.1029/2010GL044397">https://doi.org/10.1029/2010GL044397</a>, 2010. Price, S., Payne, A., Catania, G., and Neumann, T.: Seasonal acceleration of inland ice via longitudinal coupling to marginal ice, J. Glaciol., 54, 213–219, 2008. Pritchard, H. D., Arthern, R., Vaughan, D., and Edwards, L. A.: Extensive dynamic thinning on the margins of the Greenland and Antarctic ice sheets, Nature, 461, 971–975, 2009. Rignot, E. and Kanagaratnam, P.: Changes in the velocity structure of the Greenland ice sheet, Science, 311, 986–990, 2006. Schoof, C.: Ice-sheet acceleration driven by melt supply variability, Nature, 468, 803–806, <a href="http://dx.doi.org/10.1038/nature09618">https://doi.org/10.1038/nature09618</a>, 2010. Shannon, S., Payne, A. J., Bartholomew, I. D., Van den Broeke, M. R., Edwards, T. L., Fettweis, X., Gagliardini, O., Gillet-Chaulet, F., Goelzer, H., Hoffman, M. J., Huybrechts, P., Mair, D. W. F., Nienow, P. W., Perego, M., Price, S. F., Smeets, C. J. P. P., Sole, A. J., Van de Wal, R. S. W., and Zwinger, T.: Enhanced basal lubrication and the contribution of the Greenland ice sheet to future sea level rise, P. Natl. A. Sci., 110, 14156–14161, <a href="http://dx.doi.org/10.1073/pnas.1212647110">https://doi.org/10.1073/pnas.1212647110</a>, 2013. Shepherd, A., Hubbard, A., Nienow, P., King, M., McMIllan, M., and Joughin, I.: Greenland ice sheet motion coupled with daily melting in late summer, Geophys. Res. Lett., 36, L01501, <a href="http://dx.doi.org/10.1029/2008GL035758">https://doi.org/10.1029/2008GL035758</a>, 2009. Shepherd, A., Ivins, E. R., Geruo A., Barletta, V. R., Bentley, M. J., Bettadpur, S., Briggs, K. H., Bromwich, D. H. Forsberg, R., Galin, N., Horwath, M., Jacobs, S., Joughin, I., King, M. A., Lenaerts, J. T. M., Li, J., Ligtenberg, S. R. M., Luckman, A., Luthcke, S. B., McMillan, M., Meister, R., Milne, G., Mouginot, J., Muir, A., Nicolas, J. P., Paden, J. Payne, A. J., Pritchard, H., Rignot, E., Rott, H., Sandberg Sørensen, L., Scambos, T. A., Scheuchl, B., Schrama, E. J. O., Smith, B., Sundal, A. V., Van Angelen, J. H., Van de Berg, W. J., Van den Broeke, M. R., Vaughan, D. G.,Velicogna, I., Wahr, J., Whitehouse, P. L.,Wingham, D. J., Yi,D., Young, D., Zwally, H. J.: A reconciled estimate of ice-sheet mass balance, Science, 338, 1183–1189, 2012. 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, 2008a. Smeets, C. J. P. P. and Van den Broeke, M. R.: The parameterisation of scalar transfer over rough ice surfaces, Bound.-Lay. Meteorol., 128, 339–335, 2008b. Smeets, C. J. P. P., Boot, W., Hubbard, A., Petterson, R., Wilhelms, F., Van den Broeke, M. R., and Van de Wal, R. S. W.: A wireless subglacial probe for deep ice applications, J. Glaciol., 58, 211, 841–848, 2012. Sole, A., Nienow, P., Bartholomew, I., Mair, D., Cowton, T., Tedstone, A., and King, M. A.: Winter motion mediates dynamic response of the Greenland Ice Sheet to warmer summers, Geophys. Res. Lett., 40, 3940–3944, <a href="http://dx.doi.org/10.1002/grl.50764">https://doi.org/10.1002/grl.50764</a>, 2013. Sundal, A. V., Shepherd, A., Nienow, P., Hanna, E., Palmer, S., Huybrechts, P.: Melt-induced speed-up of Greenland ice sheet offset by efficient subglacial drainage, Nature, 469, 521–524, 2011. Tedstone, A. J., Nienow, P. W., Sole, A. J., Mair, D. W. F., Cowton, T. R., Bartholomew, I. D., and King, M. A.: Greenland ice motion insensitive to exceptional meltwater forcing, P. Natl. A. Sci., 110, 19719–19724, <a href="http://dx.doi.org/10.1073/pnas.1315843110">https://doi.org/10.1073/pnas.1315843110</a>, 2013. van den Broeke, M., Smeets, P., Ettema, J., van der Veen, C., van de Wal, R., and Oerlemans, J.: Partitioning of melt energy and meltwater fluxes in the ablation zone of the west Greenland ice sheet, The Cryosphere, 2, 179–189, <a href="http://dx.doi.org/10.5194/tc-2-179-2008">https://doi.org/10.5194/tc-2-179-2008</a>, 2008. Truffer, M., Harrison, W. D., and March, R.S.: Correspondence, Journal of Glaciology, 51, 663–664, 2005. Van den Broeke, M. R., Bamber, J., Ettema, J., Rignot, E., Schrama, E., Van de Berg, W. J., Meijgaard, E., Velicogna, I., and Wouters, B.: Partitioning recent Greenland mass loss, Science, 326, 984–986, 2009. Van de Wal, R. S. W., Boot, W., Van den Broeke, M. R., Smeets, C. J. P. P., Reijmer, C. H., Donkers, J. J. A., and Oerlemans, J.: Large and rapid melt-induced velocity changes in the ablation zone of the Greenland Ice Sheet, Science, 321, 111–113, 2008. Van de Wal, R. S. W., Boot, Smeets, C. J. P. P., W., Snellen, H., Van den Broeke, M. R., and Oerlemans, J.: Twenty-one years of mass balance observations along the-K-transect, West Greenland, Earth Syst. Sci. Data, 4, 31–35, 2012. 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, 218–222, 2002.