A global system | Dynamic ice streams | Rapid changes | The past is the key to the present | Reconstructing ancient ice sheets | A large jigsaw with many pieces | Further Reading | References | Comments |
A global system
Why should we study Antarctic glaciers? What can we learn from them? Antarctica plays a vital role in the global oceanic and climatic systems. Cold water is formed in Antarctica. Because freshwater ice at the surface freezes onto icebergs, this water is not only cold, it is salty. This cold, dense, salty water sinks to the sea floor, and drives the global ocean currents, being replaced with warmer surface waters from the equatorial regions. This is the global thermohaline circulation, and these ocean currents keep Britain warm, and drive the earth’s climatic system.
Water from melting glaciers in Antarctica also has the potential to raise global sea levels. How likely this is to happen, and at what rate, is an important research question that scientists are now trying to answer.
Dynamic ice streams
The Antarctic continent is drained by numerous large ice streams. They have considerable variability at short (sub-decadal) timescales, with recent observations of thinning, acceleration, deceleration, lateral migration and stagnation. The mechanisms controlling these variations and advance and recession of grounding lines include a number of potential forcings, such as oceanic temperatures, sea level changes, air temperatures, ocean tides, subglacial bathymetry, geomorphological features, subglacial meltwater, thermodynamics, and the size of the drainage basin.
Around the Antarctic Peninsula, a number of ice shelves have recently dramatically collapsed[2-4], resulting in glacier acceleration, thinning and grounding line retreat[5-7]. In fact, Antarctic ice shelves appear crucial to the stability of their tributary glaciers, and melting ice shelves could have catastrophic consequences for many glaciers. This is particularly concerning for the West Antarctic Ice Sheet, which is largely grounded below sea level, and removal of this could raise sea levels by 3.3 m[10, 11]. Grounding line recession here could be irreversible, leading to rapid glacier thinning and recession, and sea level rise – see Marine Ice Sheet Instability.
The past is the key to the present
Although the Antarctic Peninsula is currently warming rapidly[12-14], the duration of instrumental observations in Antarctica (ca. 100 years) means that it is difficult to differentiate between natural cycles and occurrences, and dynamic behaviour that is beyond the norm. Are ice-shelf collapses a normal part of ice-sheet behaviour, or are they something more sinister? Glaciers in Antarctica are largely currently receding and shrinking (see Antarctic Peninsula Glacier Change), but is this a reaction to long-term climate change and natural climatic cycles during the Holocene, or is the rate of shrinkage and recession faster than ever before?
In order to answer these questions, we must look at the palaeo record – how the Antarctic ice sheet, ice shelves and ice streams have behaved over the last few thousand years (see Ice Sheet Evolution). It is vital to determine what thresholds control ice-sheet behaviour, and whether these have been crossed in the past. By gaining a deeper understanding of past processes, rates of change, rates of ice sheet thinning, and previous temperatures and environmental conditions, we will be better placed to understand how the Antarctic continent as a whole will behave in the future.
Reconstructing ancient ice sheets
We have many tools with which to do this. Terrestrial glacial geologists (such as ourselves) can gain information of past glacial behaviour from mapping and dating former ice sheet extents, and determining the rates at which they receded and thinned, [e.g., 16, 17-19]. Marine geologists do much the same thing on the continental shelf, but use different tools, such as swath bathymetry and marine sediment cores, dated using radiocarbon dating, palaeo-magnetism and other methods, [e.g., 20, 21-24]. Quaternary scientists can use micro-organisms preserved in marine muds and onshore in lakes[25-27] to reconstruct past temperatures, ocean currents, rates of environmental change and previous ice shelf collapses[29-31]. Other researchers look at raised beaches  and palaeo lakes to record previous rates of isostatic uplift and rates of sea level rise[33, 34]; this can help constrain previous ice volumes and rates of ice loss.
A large jigsaw with many pieces
Working with the geologists are numerical modellers, who use the data to test, train and tune numerical models and simulations[35-37]. Through these models, we can make better predictions of future ice sheet behaviour and rates of sea level rise, and ultimately provide policy makers with improved estimates of future change. For an example of some recent modelling work on the former British-Irish Ice Sheet, see the BritIce Modelling Project.
1. Livingstone, S.J., C. O Cofaigh, C.R. Stokes, C.-D. Hillenbrand, A. Vieli, and S.S.R. Jamieson, 2012. Antarctic palaeo-ice streams. Earth-Science Reviews, 111(1-2): 90-128.
2. Scambos, T., H.A. Fricker, C.-C. Liu, J. Bohlander, J. Fastook, A. Sargent, R. Massom, and A.-M. Wu, 2009. Ice shelf disintegration by plate bending and hydro-fracture: Satellite observations and model results of the 2008 Wilkins ice shelf break-ups. Earth and Planetary Science Letters, 280(1â€“4): 51-60.
3. Glasser, N.F. and T.A. Scambos, 2008. A structural glaciological analysis of the 2002 Larsen B ice shelf collapse. Journal of Glaciology, 54(184): 3-16.
4. Cook, A.J. and D.G. Vaughan, 2010. Overview of areal changes of the ice shelves on the Antarctic Peninsula over the past 50 years. The Cryosphere, 4(1): 77-98.
5. Pritchard, H.D. and D.G. Vaughan, 2007. Widespread acceleration of tidewater glaciers on the Antarctic Peninsula. Journal of Geophysical Research-Earth Surface, 112(F3): F03S29, 1-10.
6. Scambos, T.A., J.A. Bohlander, C.A. Shuman, and P. Skvarca, 2004. Glacier acceleration and thinning after ice shelf collapse in the Larsen B embayment, Antarctica. Geophysical Research Letters, 31: L18402.
7. Rignot, E., G. Casassa, P. Gogineni, W. Krabill, A. Rivera, and R. Thomas, 2004. Accelerated ice discharge from the Antarctic Peninsula following the collapse of Larsen B ice shelf. Geophysical Research Letters, 31(18): L18401.
8. Pritchard, H.D., S.R.M. Ligtenberg, H.A. Fricker, D.G. Vaughan, M.R. van den Broeke, and L. Padman, 2012. Antarctic ice-sheet loss driven by basal melting of ice shelves. Nature, 484(7395): 502-505.
9. Lythe, M.B., D.G. Vaughan, and the BEDMAP Consortium, 2001. BEDMAP: a new ice thickness and subglacial topographical model of Antarctica. Journal of Geophysical Research, 106(B6): 11335-11351.
10. Bamber, J.L., R.E.M. Riva, B.L.A. Vermeersen, and A.M. Le Brocq, 2009. Reassessment of the potential sea-level rise from a collapse of the West Antarctic Ice Sheet. Science, 324(5929): 901-903.
11. Mercer, J.H., 1978. West Antarctic Ice Sheet and CO2 Greenhouse effect – threat of disaster. Nature, 271(5643): 321-325.
12. Vaughan, D.G., G.J. Marshall, W.M. Connelly, C. Parkinson, R. Mulvaney, D.A. Hodgson, J.C. King, C.J. Pudsey, and J. Turner, 2003. Recent rapid regional climate warming on the Antarctic Peninsula. Climatic Change, 60: 243-274.
13. Vaughan, D.G., G.J. Marshall, W.M. Connelly, J.C. King, and R. Mulvaney, 2001. Devil in the detail. Science, 293(5536): 1777-1779.
14. Turner, J., S.R. Colwell, G.J. Marshall, T.A. Lachlan-Cope, A.M. Carelton, P.D. Jones, V. Lagun, P.A. Reid, and S. Iagovkina, 2005. Antarctic climate change during the last 50 years. International Journal of Climatology, 25: 279-294.
15. Cook, A.J., A.J. Fox, D.G. Vaughan, and J.G. Ferrigno, 2005. Retreating glacier fronts on the Antarctic Peninsula over the past half-century. Science, 308(5721): 541-544.
16. Bentley, M.J., D.J.A. Evans, C.J. Fogwill, J.D. Hansom, D.E. Sugden, and P.W. Kubik, 2007. Glacial geomorphology and chronology of deglaciation, South Georgia, sub-Antarctic. Quaternary Science Reviews, 26(5-6): 644-677.
17. Bentley, M.J., C.J. Fogwill, P.W. Kubnik, and D.E. Sugden, 2006. Geomorphological evidence and cosmogenic 10Be/26AL exposure ages for the Last Glacial Maximum and deglaciation of the Antarctic Peninsula Ice Sheet. GSA Bulletin, 118(9/10): 1149-1159.
18. Fogwill, C.J., M.J. Bentley, D.E. Sugden, A.R. Kerr, and P.W. Kubik, 2004. Cosmogenic nuclides 10Be and 26Al imply limited Antarctic Ice Sheet thickening and low erosion in the Shackleton Range for > 1 m.y. Geology, 32(3): 265-268.
19. Mackintosh, A., D. White, D. Fink, D.B. Gore, J. Pickard, and P.C. Fanning, 2007. Exposure ages from mountain dipsticks in Mac. Robertson Land, East Antarctica, indicate little change in ice-sheet thickness since the Last Glacial Maximum. Geology, 35(6): 551-554.
20. Hillenbrand, C.-D., R.D. Larter, J.A. Dowdeswell, W. Ehrmann, C. Ó Cofaigh, S. Benetti, A.G.C. Graham, and H. Grobe, 2010. The sedimentary legacy of a palaeo-ice stream on the shelf of the southern Bellingshausen Sea: Clues to West Antarctic glacial history during the Late Quaternary. Quaternary Science Reviews, 29(19-20): 2741-2763.
21. Graham, A.G.C., R.D. Larter, K. Gohl, J.A. Dowdeswell, C.-D. Hillenbrand, J.A. Smith, J. Evans, G. Kuhn, and T. Deen, 2010. Flow and retreat of the Late Quaternary Pine Island-Thwaites palaeo-ice stream, West Antarctica. Journal of Geophysical Research-Earth Surface, 115: F03025.
22. Graham, A.G.C., R.D. Larter, K. Gohl, C.-D. Hillenbrand, J.A. Smith, and G. Kuhn, 2009. Bedform signature of a West Antarctic palaeo-ice stream reveals a multi-temporal record of flow and substrate control. Quaternary Science Reviews, 28(25-26): 2774-2793.
23. Ó Cofaigh, C., R.D. Larter, J.A. Dowdeswel, C.-D. Hillenbrand, C.J. Pudsey, J. Evans, and P. Morris, 2005. Flow of the West Antarctic Ice Sheet on the continental margin of the Bellingshausen Sea at the Last Glacial Maximum. Journal of Geophysical Research, 110: B11103.
24. Hillenbrand, C.-D. and W. Ehrmann, 2005. Late Neogene to Quaternary environmental changes in the Antarctic Peninsula region: evidence from drift sediments. Global and Planetary Change, 45(1-3): 165-191.
25. Björck, S., S. Olsson, C. Ellis-Evans, H. Håkansson, O. Humlum, and J.M. de Lirio, 1996. Late Holocene palaeoclimatic records from lake sediments on James Ross Island, Antarctica. Palaeogeography, Palaeoclimatology, Palaeoecology, 121(3-4): 195-220.
26. Hodgson, D.A., S.J. Roberts, M.J. Bentley, E.L. Carmichael, J.A. Smith, E. Verleyen, W. Vyverman, P. Geissler, M.J. Leng, and D.C.W. Sanderson, 2009. Exploring former subglacial Hodgson Lake, Antarctica. Paper II: palaeolimnology. Quaternary Science Reviews, 28(23-24): 2310-2325.
27. Smith, J.A., D.A. Hodgson, M.J. Bentley, E. Verleyen, M.J. Leng, and S.J. Roberts, 2006. Limnology of two Antarctic epishelf lakes and their potential to record periods of ice shelf loss. Journal of Palaeolimnology, 35: 373-394.
28. Domack, E., A. Leventer, S. Root, J. Ring, E. Williams, D. Carlson, E. Hirshorn, W. Wright, R. Gilbert, and G. Burr, Marine sedimentary record of natural environmental variability and recent warming in the Antarctic Peninsula, in Antarctic Peninsula Climate Variability: Historical and Paleoenvironmental Perspectives, E. Domack, et al., Editors. 2003, American Geophysical Union: Washington. 205-222.
29. Domack, E., D. Duran, A. Leventer, S. Ishman, S. Doane, S. McCallum, D. Amblas, J. Ring, R. Gilbert, and M. Prentice, 2005. Stability of the Larsen B ice shelf on the Antarctic Peninsula during the Holocene epoch. Nature, 436(4): 681-685.
30. Smith, J.A., M.J. Bentley, D.A. Hodgson, S.J. Roberts, M.J. Leng, J.M. Lloyd, M.S. Barrett, C.L. Bryant, and D.E. Sugden, 2007. Oceanic and atmospheric forcing of early Holocene ice shelf retreat, George VI Ice Shelf, Antarctic Peninsula. Quaternary Science Reviews, 26: 500-516.
31. Gilbert, R. and E.W. Domack, 2003. Sedimentary record of disintegrating ice shelves in a warming climate, Antarctic Peninsula. Geochemistry Geophysics Geosystems, 4.
32. Fretwell, P.T., D.A. Hodgson, E.P. Watcham, M.J. Bentley, and S.J. Roberts, 2010. Holocene isostatic uplift of the South Shetland Islands, Antarctic Peninsula, modelled from raised beaches. Quaternary Science Reviews, 29(15-16): 1880-1893.
33. Roberts, S.J., D.A. Hodgson, M. Sterken, P.L. Whitehouse, E. Verleyen, W. Vyverman, K. Sabbe, A. Balbo, M.J. Bentley, and S.G. Moreton, 2011. Geological constraints on glacio-isostatic adjustment models of relative sea-level change during deglaciation of Prince Gustav Channel, Antarctic Peninsula. Quaternary Science Reviews, in press(0).
34. Watcham, E.P., M.J. Bentley, D.A. Hodgson, S.J. Roberts, P.T. Fretwell, J.M. Lloyd, R.D. Larter, P.L. Whitehouse, M.J. Leng, P. Monien, and S.G. Moreton, 2011. A new Holocene relative sea level curve for the South Shetland Islands, Antarctica. Quaternary Science Reviews, 30(21-22): 3152-3170.
35. Le Brocq, A.M., M.J. Bentley, A. Hubbard, C.J. Fogwill, D.E. Sugden, and P.L. Whitehouse, 2011. Reconstructing the Last Glacial Maximum ice sheet in the Weddell Sea embayment, Antarctica, using numerical modelling constrained by field evidence. Quaternary Science Reviews, 30(19-20): 2422-2432.
36. Whitehouse, P.L., M.J. Bentley, and A.M. Le Brocq, 2012. A deglacial model for Antarctica: geological constraints and glaciological modelling as a basis for a new model of Antarctic glacial isostatic adjustment. Quaternary Science Reviews, 32(0): 1-24.
37. Pollard, D. and R.M. DeConto, 2009. Modelling West Antarctic ice sheet growth and collapse through the past five million years. Nature, 458(7236): 329-U89.