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Stability of the West Antarctic ice sheet in a warming world

Abstract

Ice sheets are expected to shrink in size as the world warms, which in turn will raise sea level. The West Antarctic ice sheet is of particular concern, because it was probably much smaller at times during the past million years when temperatures were comparable to levels that might be reached or exceeded within the next few centuries. Much of the grounded ice in West Antarctica lies on a bed that deepens inland and extends well below sea level. Oceanic and atmospheric warming threaten to reduce or eliminate the floating ice shelves that buttress the ice sheet at present. Loss of the ice shelves would accelerate the flow of non-floating ice near the coast. Because of the slope of the sea bed, the consequent thinning could ultimately float much of the ice sheet's interior. In this scenario, global sea level would rise by more than three metres, at an unknown rate. Simplified analyses suggest that much of the ice sheet will survive beyond this century. We do not know how likely or inevitable eventual collapse of the West Antarctic ice sheet is at this stage, but the possibility cannot be discarded. For confident projections of the fate of the ice sheet and the rate of any collapse, further work including the development of well-validated physical models will be required.

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Figure 1: Rates of elevation change along the Amundsen Coast of West Antarctica as determined from ICESAT by Pritchard et al.9.
Figure 2: Map of Antarctica with red-brown colours indicating the bed elevation of the marine portions of the WAIS14.
Figure 3: MODIS image (centre panel) with history of retreat leading up to the collapse of the Larsen B ice shelf98.

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References

  1. Rignot, E. et al. Recent Antarctic ice mass loss from radar interferometry and regional climate modelling. Nature Geosci. 1, 106–110 (2008).

    Article  Google Scholar 

  2. Shepherd, A. & Wingham, D. Recent sea-level contributions of the Antarctic and Greenland ice sheets. Science 315, 1529–1532 (2007).

    Article  Google Scholar 

  3. Velicogna, I. & Wahr, J. Measurements of time-variable gravity show mass loss in Antarctica. Science 311, 1754–1756 (2006).

    Google Scholar 

  4. Rignot, E., Velicogna, I., van den Broeke, M. R., Monaghan, A. & Lenaerts, J. Acceleration of the contribution of the Greenland and Antarctic ice sheets to sea level rise. Geophys. Res. Lett. 38, L05503 (2011).

    Google Scholar 

  5. Mercer, J. H. Antarctic ice and Sangamon sea level rise. IAHS Publ. 179, 217–225 (1968).

    Google Scholar 

  6. Helsen, M. M. et al. Elevation changes in Antarctica mainly determined by accumulation variability. Science 320, 1626–1629 (2008).

    Google Scholar 

  7. Joughin, I. & Bamber, J. L. Thickening of the ice stream catchments feeding the Filchner-Ronne Ice Shelf, Antarctica. Geophys. Res. Lett. 32, L17503 (2005).

    Google Scholar 

  8. Joughin, I. & Tulaczyk, S. Positive mass balance of the Ross Ice Streams, West Antarctica. Science 295, 476–480 (2002).

    Google Scholar 

  9. Pritchard, H. D., Arthern, R. J., Vaughan, D. G. & Edwards, L. A. Extensive dynamic thinning on the margins of the Greenland and Antarctic ice sheets. Nature 461, 971–975 (2009).

    Google Scholar 

  10. Hughes, T. J. The weak underbelley of the West Antarctic Ice-Sheet. J. Glaciol. 27, 518–525 (1981).

    Google Scholar 

  11. Wilson, G. S., Harwood, D. M., Askin, R. A. & Levy, R. H. Late Neogene Sirius Group strata in Reedy Valley, Antarctica: A multiple-resolution record of climate, ice-sheet and sea-level events. J. Glaciol. 44, 437–447 (1998).

    Google Scholar 

  12. Mercer, J. H. Antarctic ice and interglacial high sea levels. Science 168, 1605–1606 (1970).

    Google Scholar 

  13. Kopp, R. E., Simons, F. J., Mitrovica, J. X., Maloof, A. C. & Oppenheimer, M. Probabilistic assessment of sea level during the last interglacial stage. Nature 462, 863–867 (2009).

    Google Scholar 

  14. Bamber, J. L., Riva, R. E. M., Vermeersen, B. L. A. & LeBrocq, A. M. Reassessment of the potential sea-level rise from a collapse of the West Antarctic Ice Sheet. Science 324, 901–903 (2009).

    Google Scholar 

  15. Scherer, R. P. et al. Pleistocene collapse of the West Antarctic Ice Sheet. Science 281, 82–85 (1998).

    Google Scholar 

  16. Barnes, D. K. A. & Hillenbrand, C. D. Faunal evidence for a late quaternary trans-Antarctic seaway. Glob. Change Biol. 16, 3297–3303 (2010).

    Google Scholar 

  17. Naish, T. et al. Obliquity-paced Pliocene West Antarctic Ice Sheet oscillations. Nature 458, 322–328 (2009).

    Google Scholar 

  18. Pollard, D. & DeConto, R. M. Modelling West Antarctic Ice Sheet growth and collapse through the past five million years. Nature 458, 329–332 (2009).

    Google Scholar 

  19. IPCC Climate Change 2007: The Physical Science Basis (eds Solomon, S. et al.) (Cambridge Univ. Press, 2007).

  20. Dowdeswell, J. A., Ottesen, D., Evans, J., Cofaigh, C. O. & Anderson, J. B. Submarine glacial landforms and rates of ice-stream collapse. Geology 36, 819–822 (2008).

    Google Scholar 

  21. Mercer, J. H. West Antarctic Ice Sheet and CO2 greenhouse effect - Threat of disaster. Nature 271, 321–325 (1978).

    Google Scholar 

  22. Vaughan, D. G. & Spouge, J. R. Risk estimation of collapse of the West Antarctic Ice Sheet. Climatic Change 52, 65–91 (2002).

    Google Scholar 

  23. Conway, H., Hall, B. L., Denton, G. H., Gades, A. M. & Waddington, E. D. Past and future grounding-line retreat of the West Antarctic Ice Sheet. Science 286, 280–283 (1999).

    Google Scholar 

  24. Stone, J. O. et al. Holocene deglaciation of Marie Byrd Land, West Antarctica. Science 299, 99–102 (2003).

    Google Scholar 

  25. Retzlaff, R. & Bentley, C. R. Timing of stagnation of Ice Stream-C, West Antarctica, from short-pulse radar studies of buried surface crevasses. J. Glaciol. 39, 553–561 (1993).

    Google Scholar 

  26. Smith, B. E., Lord, N. E. & Bentley, C. R. Crevasse ages on the northern margin of Ice stream C, West Antarctica. Ann. Glaciol. 34, 209–216 (2002).

    Google Scholar 

  27. Nereson, N. A. & Raymond, C. F. The elevation history of ice streams and the spatial accumulation pattern along the Siple Coast of West Antarctica inferred from ground-based radar data from three inter-ice- stream ridges. J. Glaciol. 47, 303–313 (2001).

    Google Scholar 

  28. Conway, H. et al. Switch of flow direction in an Antarctic ice stream. Nature 419, 465–467 (2002).

    Google Scholar 

  29. Joughin, I. et al. Continued deceleration of Whillans Ice Stream, West Antarctica. 32, L22501 (2005).

  30. Fahnestock, M. A., Scambos, T. A., Bindschadler, R. A. & Kvaran, G. A millennium of variable ice flow recorded by the Ross Ice Shelf, Antarctica. J. Glaciol. 46, 652–664 (2000).

    Google Scholar 

  31. Hulbe, C. L. & Fahnestock, M. A. West Antarctic ice-stream discharge variability: Mechanism, controls and pattern of grounding-line retreat. J. Glaciol. 50, 471–484 (2004).

    Google Scholar 

  32. Hulbe, C. & Fahnestock, M. Century-scale discharge stagnation and reactivation of the Ross ice streams, West Antarctica. J. Geophys. Res.-Earth 112, F03S27 (2007).

    Google Scholar 

  33. Hughes, T. Is the West Antarctic Ice-Sheet disintegrating. J. Geophys. Res. 78, 7884–7910 (1973).

    Google Scholar 

  34. Blankenship, D. D., Bentley, C. R., Rooney, S. T. & Alley, R. B. Seismic measurements reveal a saturated porous layer beneath an active Antarctic ice stream. Nature 322, 54–57 (1986).

    Google Scholar 

  35. Alley, R. B., Blankenship, D. D., Bentley, C. R. & Rooney, S. T. Deformation of till beneath Ice Stream-B, West Antarctica. Nature 322, 57–59 (1986).

    Google Scholar 

  36. Tulaczyk, S., Kamb, W. B. & Engelhardt, H. F. Basal mechanics of Ice Stream B, West Antarctica 1. Till mechanics. J. Geophys. Res.-Solid 105, 463–481 (2000).

    Google Scholar 

  37. Kamb, B. Rheological nonlinearity and flow instability in the deforming bed mechanism of ice stream motion. J. Geophys. Res.-Solid 96, 16585–16595 (1991).

    Google Scholar 

  38. Joughin, I., MacAyeal, D. R. & Tulaczyk, S. Basal shear stress of the Ross ice streams from control method inversions. J. Geophys. Res. 109, B09405 (2004).

    Google Scholar 

  39. MacAyeal, D. R., Bindschadler, R. A. & Scambos, T. A. Basal friction of Ice-Stream-E, West Antarctica. J. Glaciol. 41, 247–262 (1995).

    Google Scholar 

  40. Whillans, I. M. & van der Veen, C. J. Transmission of stress between an ice stream and interstream ridge. J. Glaciol. 47, 433–440 (2001).

    Google Scholar 

  41. Alley, R. B. In search of ice-stream sticky spots. J. Glaciol. 39, 447–454 (1993).

    Google Scholar 

  42. Raymond, C. Shear margins in glaciers and ice sheets. J. Glaciol. 42, 90–102 (1996).

    Google Scholar 

  43. Jacobson, H. P. & Raymond, C. E. Thermal effects on the location of ice stream margins. J. Geophys. Res. 103, 12111–12122 (1998).

    Google Scholar 

  44. Tulaczyk, S., Kamb, W. B. & Engelhardt, H. F. Basal mechanics of Ice Stream B, West Antarctica 2. Undrained plastic bed model. J. Geophys. Res.-Solid 105, 483–494 (2000).

    Google Scholar 

  45. Bougamont, M., Tulaczyk, S. & Joughin, I. Response of subglacial sediments to basal freeze-on - 2. Application in numerical modeling of the recent stoppage of Ice Stream C, West Antarctica. J. Geophys. Res.-Solid 108, 2223 (2003).

    Google Scholar 

  46. Raymond, C. F. Energy balance of ice streams. J. Glaciol. 46, 665–674 (2000).

    Google Scholar 

  47. MacAyeal, D. R. A low-order model of the Heinrich event cycle. Paleoceanography 8, 767–773 (1993).

    Google Scholar 

  48. Hollin, J. T. On the glacial history of Antarctica. J. Glaciol. 4, 172–195 (1962).

    Google Scholar 

  49. Denton, G. H. & Hughes, T. J. Global ice-sheet system interlocked by sea-level. Quat. Res. 26, 3–26 (1986).

    Google Scholar 

  50. Thomas, R. H. & Bentley, C. R. Model for Holocene retreat of West Antarctic Ice Sheet. Quat. Res. 10, 150–170 (1978).

    Google Scholar 

  51. Alley, R. B., Anandakrishnan, S., Dupont, T. K., Parizek, B. R. & Pollard, D. Effect of sedimentation on ice-sheet grounding-line stability. Science 315, 1838–1841 (2007).

    Google Scholar 

  52. Gomez, N., Mitrovica, J. X., Huybers, P. & Clark, P. U. Sea level as a stabilizing factor for marine-ice-sheet grounding lines. Nature Geosci. 3, 850–853 (2010).

    Google Scholar 

  53. Fyke, J. G., Carter, L., Mackintosh, A., Weaver, A. J. & Meissner, K. J. Surface melting over ice shelves and ice sheets as assessed from modeled surface air temperatures. J. Climate 23, 1929–1936 (2010).

    Google Scholar 

  54. Jacobs, S. S., Helmer, H. H., Doake, C. S. M., Jenkins, A. & Frolich, R. M. Melting of ice shelves and the mass balance of Antarctica. J. Glaciol. 38, 375–387 (1992).

    Google Scholar 

  55. Thomas, R. H., Sanderson, T. J. O. & Rose, K. E. Effect of climatic warming on the West Antarctic Ice Sheet. Nature 277, 355–358 (1979).

    Google Scholar 

  56. Dupont, T. K. & Alley, R. B. Assessment of the importance of ice-shelf buttressing to ice-sheet flow. Geophys. Res. Lett. 32, L04503 (2005).

    Google Scholar 

  57. Nicholls, K. W., Osterhus, S., Makinson, K., Gammelsrod, T. & Fahrbach, E. Ice-ocean processes over the continental shelf of the southern Weddell Sea, Antarctica: A review. Rev. Geophys. 47, RG3003 (2009).

    Google Scholar 

  58. Thyssen, F., Bombosch, A. & Sandhäger, H. Elevation, ice thickness and structure mark maps of the central part of Filchner-Ronne Ice Shelf. Polarforschung 62, 17–26 (1993).

    Google Scholar 

  59. Jenkins, A. & Doake, C. S. M. Ice-ocean interaction on Ronne Ice Shelf, Antarctica. J. Geophys. Res.-Oceans 96, 791–813 (1991).

    Google Scholar 

  60. Joughin, I. & Padman, L. Melting and freezing beneath Filchner-Ronne Ice Shelf, Antarctica. Geophys. Res. Lett. 30, 1477 (2003).

    Google Scholar 

  61. Horgan, H. J., Walker, R. T., Anandakrishnan, S. & Alley, R. B. Surface elevation changes at the front of the Ross Ice Shelf: Implications for basal melting. J. Geophys. Res. 116, C02005 (2011).

    Google Scholar 

  62. Rignot, E. & Jacobs, S. S. Rapid bottom melting widespread near Antarctic ice sheet grounding lines. Science 296, 2020–2023 (2002).

    Google Scholar 

  63. Nicholls, K. W. Predicted reduction in basal melt rates of an Antarctic ice shelf in a warmer climate. Nature 388, 460–462 (1997).

    Google Scholar 

  64. Walker, R. T., Dupont, T. K., Parizek, B. R. & Alley, R. B. Effects of basal-melting distribution on the retreat of ice-shelf grounding lines. Geophys. Res. Lett. 35, L17503 (2008).

    Google Scholar 

  65. Payne, A. J. et al. Numerical modeling of ocean-ice interactions under Pine Island Bay's ice shelf. J. Geophys. Res.-Oceans 112, C10019 (2007).

    Google Scholar 

  66. Joughin, I., Smith, B. E. & Holland, D. M. Sensitivity of 21st century sea level to ocean-induced thinning of Pine Island Glacier, Antarctica. Geophys. Res. Lett. 37, L20502 (2010).

    Google Scholar 

  67. Jacobs, S. S., Jenkins, A., Giulivi, C. F. & Dutrieux, P. Stronger ocean circulation and increased melting under Pine Island Glacier ice shelf. Nature Geosci. 10.1038/ngeo1188 (2011).

  68. Thoma, M., Jenkins, A., Holland, D. & Jacobs, S. Modelling Circumpolar Deep Water intrusions on the Amundsen Sea continental shelf, Antarctica. Geophys. Res. Lett. 35, L18602 (2008).

    Google Scholar 

  69. Shepherd, A., Wingham, D. & Rignot, E. Warm ocean is eroding West Antarctic Ice Sheet. Geophys. Res. Lett. 31, L23402 (2004).

    Google Scholar 

  70. Rignot, E. Changes in West Antarctic ice stream dynamics observed with ALOS PALSAR data. Geophys. Res. Lett. 35, L12505 (2008).

    Google Scholar 

  71. Jacobs, S. S., Giulivi, C. F. & Mele, P. A. Freshening of the Ross Sea during the late 20th century. Science 297, 386–389 (2002).

    Google Scholar 

  72. Yin, J. et al. Different magnitudes of projected subsurface ocean warming around Greenland and Antarctica. Nature Geosci. 10.1038/ngeo1189 (2011).

  73. Gillett, N. P., Arora, V. K., Zickfeld, K., Marshall, S. J. & Merryfield, J. Ongoing climate change following a complete cessation of carbon dioxide emissions. Nature Geosci. 4, 83–87 (2011).

    Google Scholar 

  74. Sen Gupta, A. et al. Projected changes to the Southern Hemisphere ocean and sea ice in the IPCC AR4 climate models. J. Climate 22, 3047–3078 (2009).

    Google Scholar 

  75. Hattermann, T. & Levermann, A. Response of Southern Ocean circulation to global warming may enhance basal ice shelf melting around Antarctica. Clim. Dyn. 35, 741–756 (2010).

    Google Scholar 

  76. Thomas, R., Rignot, E., Kanagaratnam, P., Krabill, W. & Casassa, G. Force-perturbation analysis of Pine Island Glacier, Antarctica, suggests cause for recent acceleration. Ann Glaciol. 39, 133–138 (2004).

    Google Scholar 

  77. Schoof, C. Ice sheet grounding line dynamics: Steady states, stability, and hysteresis. J. Geophys. Res.-Earth 112, F03S28 (2007).

    Google Scholar 

  78. Rignot, E. J. Fast recession of a West Antarctic glacier. Science 281, 549–551 (1998).

    Google Scholar 

  79. Payne, A. J., Vieli, A., Shepherd, A. P., Wingham, D. J. & Rignot, E. Recent dramatic thinning of largest West Antarctic ice stream triggered by oceans. Geophys. Res. Lett. 31, L23401 (2004).

    Google Scholar 

  80. Corr, H. F. J., Doake, C. S. M., Jenkins, A. & Vaughan, D. G. Investigations of an “ice plain” in the mouth of Pine Island Glacier, Antarctica. J. Glaciol. 47, 51–57 (2001).

    Google Scholar 

  81. Jenkins, A. et al. Observations beneath Pine Island Glacier in West Antarctica and implications for its retreat. Nature Geosci. 3, 468–472 (2010).

    Google Scholar 

  82. Shepherd, A., Wingham, D. J. & Mansley, J. A. D. Inland thinning of the Amundsen Sea sector, West Antarctica. Geophys. Res. Lett. 29, 1364 (2002).

    Google Scholar 

  83. Wingham, D. J., Wallis, D. W. & Shepherd, A. Spatial and temporal evolution of Pine Island Glacier thinning, 1995–2006. Geophys. Res. Lett. 36, L17501 (2009).

    Google Scholar 

  84. Vaughan, D. G. et al. New boundary conditions for the West Antarctic Ice sheet: Subglacial topography beneath Pine Island Glacier. Geophys. Res. Lett. 33, L09501 (2006).

    Google Scholar 

  85. Holt, J. W. et al. New boundary conditions for the West Antarctic Ice Sheet: Subglacial topography of the Thwaites and Smith glacier catchments. Geophys. Res. Lett. 33, L09502 (2006).

    Google Scholar 

  86. Cook, A. J. & Vaughan, D. G. Overview of areal changes of the ice shelves on the Antarctic Peninsula over the past 50 years. Cryosphere 4, 77–98 (2010).

    Google Scholar 

  87. Vaughan, D. G. & Doake, C. S. M. Recent atmospheric warming and retreat of ice shelves on the Antarctic Peninsula. Nature 379, 328–331 (1996).

    Google Scholar 

  88. Doake, C. S. M., Corr, H. F. J., Rott, H., Skvarca, P. & Young, N. W. Breakup and conditions for stability of the northern Larsen Ice Shelf, Antarctica. Nature 391, 778–780 (1998).

    Google Scholar 

  89. Rott, H., Skvarca, P. & Nagler, T. Rapid collapse of northern Larsen Ice Shelf, Antarctica. Science 271, 788–792 (1996).

    Google Scholar 

  90. MacAyeal, D. R., Scambos, T. A., Hulbe, C. L. & Fahnestock, M. A. Catastrophic ice-shelf break-up by an ice-shelf-fragment-capsize mechanism. J. Glaciol. 49, 22–36 (2003).

    Google Scholar 

  91. Scambos, T. A., Hulbe, C., Fahnestock, M. & Bohlander, J. The link between climate warming and break-up of ice shelves in the Antarctic Peninsula. J. Glaciol. 46, 516–530 (2000).

    Google Scholar 

  92. Doake, C. S. M. & Vaughan, D. G. Rapid disintegration of the Wordie Ice Shelf in response to atmospheric warming. Nature 350, 328–330 (1991).

    Google Scholar 

  93. Weertman, J. Can a water filled crevasse reach the bottom surface of a glacier? IAHS Publ. 95, 139–145 (1973).

    Google Scholar 

  94. Das, S. B. et al. Fracture propagation to the base of the Greenland Ice Sheet during supraglacial lake drainage. Science 320, 778–781 (2008).

    Google Scholar 

  95. Alley, R. B., Dupont, T. K., Parizek, B. R. & Anandakrishnan, S. Access of surface meltwater to beds of sub-freezing glaciers: preliminary insights. Ann. Glaciol. 40, 8–14 (2005).

    Google Scholar 

  96. Shepherd, A., Wingham, D., Payne, T. & Skvarca, P. Larsen ice shelf has progressively thinned. Science 302, 856–859 (2003).

    Google Scholar 

  97. Rignot, E. et al. Accelerated ice discharge from the Antarctic Peninsula following the collapse of Larsen B Ice Shelf. Geophys. Res. Lett. 31, L18401 (2004).

    Google Scholar 

  98. Scambos, T. A., Bohlander, J. A., Shuman, C. A. & Skvarca, P. Glacier acceleration and thinning after ice shelf collapse in the Larsen B embayment, Antarctica. Geophys. Res. Lett. 31, L18402 (2004).

    Google Scholar 

  99. Liu, H. X., Wang, L. & Jezek, K. C. Spatiotemporal variations of snowmelt in Antarctica derived from satellite scanning multichannel microwave radiometer and Special Sensor Microwave Imager data (1978–2004). J. Geophys. Res.-Earth 111, F01003 (2006).

    Google Scholar 

  100. Comiso, J. C. Variability and trends in Antarctic surface temperatures from in situ and satellite infrared measurements. J. Clim. 13, 1674–1696 (2000).

    Google Scholar 

  101. Arthern, R. J., Winebrenner, D. P. & Vaughan, D. G. Antarctic snow accumulation mapped using polarization of 4.3-cm wavelength microwave emission. J. Geophys. Res.-Atmos. 111, D06107 (2006).

    Google Scholar 

  102. Alley, R. B., Clark, P. U., Huybrechts, P. & Joughin, I. Ice-sheet and sea-level changes. Science 310, 456–460 (2005).

    Google Scholar 

  103. Pfeffer, W. T., Harper, J. T. & O'Neel, S. Kinematic constraints on glacier contributions to 21st-century sea-level rise. Science 321, 1340–1343 (2008).

    Google Scholar 

  104. Scambos, T. A., Haran, T. M., Fahnestock, M. A., Painter, T. H. & Bohlander, J. MODIS-based Mosaic of Antarctica (MOA) data sets: Continent-wide surface morphology and snow grain size. Remote Sens. Environ. 111, 242–257 (2007).

    Google Scholar 

  105. Weertman, J. Stability of the junction of an ice sheet and an ice shelf. J. Glaciol. 13, 3–11 (1974).

    Google Scholar 

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Acknowledgements

We acknowledge the contributions from the papers cited in this Review, and just as importantly the immense body of WAIS research that could not be cited due to space constraints. Comments by M. Maki improved the manuscript. The US National Science Foundation supported I.J.'s (ANT-0636719 and ANT-0424589) and R.B.A's (ANT-0424589, ANT-0539578, ANT-0944286 and ANT-0909335) effort. Additional support for RBA was provided by NASA (NNX10AI04G).

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Joughin, I., Alley, R. Stability of the West Antarctic ice sheet in a warming world. Nature Geosci 4, 506–513 (2011). https://doi.org/10.1038/ngeo1194

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