The Cryosphere Discussions www.the-cryosphere-discuss.net 1994-0432 1994-0440 3 1 2009 10.5194/tcd-3-223-2009 http://www.the-cryosphere-discuss.net/3/223/2009/ http://www.the-cryosphere-discuss.net/3/223/2009/tcd-3-223-2009.html http://www.the-cryosphere-discuss.net/3/223/2009/tcd-3-223-2009.pdf 223 242 2009-02-24 Increased rate of acceleration on Pine Island Glacier strongly coupled to changes in gravitational driving stress J. B. T. Scott jbts@bas.ac.uk G. H. Gudmundsson A. M. Smith R. G. Bingham H. D. Pritchard D. G. Vaughan British Antarctic Survey, Cambridge, UK Pine Island Glacier, Antarctica, has been undergoing several related changes for at least two decades; these include acceleration, thinning and grounding line retreat. During the first major ground-based study between 2006 and 2008, GPS receivers were used to monitor ice flow from 55 km to 171 km inland, along the central flowline. At four sites both acceleration and thinning rates over the last two years exceeded rates observed at any other time over the last two decades. At the downstream site acceleration was 6.4% over 2007 and thinning was 3.5±0.5 ma^−1. Acceleration and thinning have spread rapidly inland with the acceleration 171 km inland at 4.1% over 2007, greater than any measured annual flow increase along the whole glacier prior to 2006. Increases in surface slope, and hence gravitational driving stress, correlate well with the acceleration and no sustained change in longitudinal stress gradient is needed to explain the force balance. There is no indication that the glacier is approaching a new steady state. Anandakrishnan, S., Voigt, D. E., Alley, R. B., and King, M. A.: Ice stream $D$ flow speed is strongly modulated by the tide beneath the Ross Ice Shelf, Geophys. Res. Lett., 30, 1361, doi:10.1029/2002GL016329, 2003. Bindschadler, R. A., King, M. A., Alley, R. B., Anandakrishnan, S., and Padman, L.: Tidally controlled stick-slip discharge of a West Antarctic ice stream, Science, 301, 1087, doi:10.1126/science.1087231, 2003. Dach, R., Beutler, G., and Gudmundsson, G. H.: Analysis of GPS data from an Antarctic ice stream, in: International Association of Geodesy Symposia, 133, Observing our Changing Earth, edited by: Sideris, M. G., Springer, Berlin Heidelberg, Germany, 569–579, doi:10.1007/978-3-540-85426-5_67, 2008. Gudmundsson, G. H.: Tides and the flow of Rutford Ice Stream, West Antarctica, J. Geophys. Res., 112, F04007, doi:10.1029/2006JF000731, 2007. Joughin, I., Rignot, E., Rosanova, C. E., Lucchitta, B. K., and Bohlander, J.: Timing of recent accelerations of Pine Island Glacier, Antarctica, Geophys. Res. Lett., 30, 1706, doi:10.1029/2003GL017609, 2003. Paterson, W. S. B.: The Physics of Glaciers, Third Edition, Butterworth-Heinemann, Oxford, Great Britain, 1994. Payne, A. J., Vieli. A., Shepherd, A. P., Wingham, D. J., and Rignot, E.: Recent dramatic thinning of largest West Antarctic ice stream triggered by oceans, Geophys. Res. Lett., 31, L23401, doi:10.1029/2004GL021284, 2004. Pawlowicz, R., Beardsley, B., and Lentz, S.: Harmonic analysis including error estimates in MATLAB using T TIDE, Comput. Geosci., 28, 929–937, 2002. Rignot, E.: Fast recession of a West Antarctic Glacier, Science, 281, 549–551, 1998. Rignot, E.: Changes in ice dynamics and mass balance of the Antarctic ice sheet, Phil. Trans. R. Soc. A., 364, 1637–1655, doi:10.1098/rsta.2006.1793, 2006. Rignot, E.: Changes in West Antarctic ice stream dynamics observed with ALOS PALSAR data, Geophys. Res. Lett., 35, L12505, doi:10.1029/2008GL033365, 2008. Rignot, E., Vaughan, D. G., Schmeltz, M., Dupont, T., and MacAyeal, D.: Acceleration of Pine Island and Thwaites Glaciers, West Antarctica, Ann. Glaciol., 34, 189–193, 2002. Shepherd, A., Wingham, D. J., and Mansley, J. A. D.: Inland thinning of the Amundsen Sea sector, West Antarctica, Geophys. Res. Lett., 29, 1364, doi:10.1029/2001GL014183, 2002. Thomas, R., Rignot, E., Kanagaratnam, P., Krabill, W., and Casassa, G.: Force-peturbation analysis of Pine Island Glacier, Antarctica, suggests cause for recent acceleration, Ann. Glaciol., 39, 133–138, 2004a. Thomas, R., Rignot, E., Casassa, G., Kanagaratnam, P., Acuña, C., Akins, T., Brecher, H., Frederick, E., Gogineni, P., Krabill, W., Manizade, S., Ramamoorthy, H., Rivera, A., Russell, R., Sonntag, J., Swift, R., Yungel, J., and Zwally, J.: Accelerated Sea-Level Rise from West Antarctica, Science, 306, 255–258, doi:10.1126/science.1099650, 2004b. Van der Veen, C. J.: Fundamentals of Glacier Dynamics, A. A. Balkema, Rotterdam, Netherlands, 1999. Zwally, H. J., Schutz, R., Bentley, C., Bufton, J., Herring, T., Minster, J., Spinhirne, J., and Thomas, R.: GLAS/ICESat L2 Antarctic and Greenland Ice Sheet altimetry data V028. Boulder, CO: National Snow and Ice Data Centre, Digital media, 2007.