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Paradigm Shifts - GSAC

Summary of paradigm shifts and key references from BAS research programme Global Science in an Antarctic Context (GSAC):

  1. Anthropogenic climate change responsible for the collapse of East Antarctic Peninsula ice shelves
  2. Atmosphere-ocean-ice interaction in the Amundsen Sea — a potential “fast track” to increased melting of the West Antarctic Ice Sheet
  3. Influence of the Panamanian gateway on Greenland ice sheet development.
  4. How animals search for food
  5. Terrestrial life in Antarctica alter the continent’s established glacial history

1. Anthropogenic climate change responsible for the collapse of East Antarctic Peninsula ice shelves

Since the mid-1990s, ice shelves on the eastern side of the Antarctic Peninsula have retreated rapidly and, in some cases, disappeared altogether. Glaciers draining the Peninsula ice sheet have consequently accelerated, leading to a loss of grounded ice that will contribute to sea-level rise.

Analysis of climate data and studies using high-resolution numerical models have shown that summer temperatures in this region (which control the rate of surface melting on the ice shelves) have risen rapidly as a result of interaction of strengthening westerly winds with the steep topography of the Peninsula. Since the recent strengthening of the westerly winds has already been confidently attributed to anthropogenic effects (ozone depletion and greenhouse warming), this work reveals, for the first time, a direct link between anthropogenic climate change and regional environmental change in the Antarctic. These studies provide a much more substantial basis for making predictions of future environmental change in this region.

Publications

  • Marshall, G.J., Orr, A., van Lipzig, N.P.M., and King, J.C., 2006.
    The impact of a changing Southern Hemisphere Annular Mode on Antarctic Peninsula summer temperatures.
    Journal of Climate, 19, 5388-5404.
  • van Lipzig, N.P.M., Marshall, G.J., Orr, A., and King, J.C., 2008.
    The relationship between the Southern Hemisphere Annular Mode and Antarctic Peninsula summer temperatures: Analysis of a high-resolution model climatology.
    Journal of Climate, 21, 1649-1668.
  • Orr, A., Marshall, G.J., Hunt, J.C.R., Sommeria, J., Wang, C.-G. van Lipzig, N., Cresswell, D., and King, J.C., 2008.
    Characteristics of summer airflow over the Antarctic Peninsula in response to recent strengthening of westerly circumpolar winds.
    Journal of Atmospheric Science, 65, 1396-1413.
  • King, J.C., Lachlan-Cope, T.A., Ladkin, R.S. and Weiss, A., 2008.
    Airborne measurements in the stable boundary layer over the Larsen Ice Shelf, Antarctica.
    Boundary Layer Meteorology, 127(3), 413-428.

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2. Atmosphere-ocean-ice interaction in the Amundsen Sea — a potential “fast track” to increased melting of the West Antarctic Ice Sheet

Observations reveal that the ice streams feeding the ice shelves in the Amundsen Sea sector of Antarctica have accelerated and thinned in recent years, probably as a result of increased melting of the ice shelves. A coupled ice-ocean model was used to study the delivery of warm Circumpolar Deep Water (CDW) to the Amundsen Sea continental shelf, where it drives rapid melting at the base of the floating ice shelves.

Our model results showed that the inflow of CDW is strongly controlled by variations in wind forcing at the continental shelf edge. The winds in this sector are subject to considerable interannual variability which leads to a period of low CDW inflow during the late 1980s and early 1990s, a period in which the flow of at least one of the region’s ice streams was steady. During the warmer periods before and after, the flow of the ice stream accelerated, suggesting a direct link between the wind-driven ocean circulation and the mass balance of the ice sheet. This study challenged the view that changes in ocean-driven melting would be driven by warming of the CDW (which can only occur slowly) and presented a new paradigm where melting responds to changes in the rate of inflow of CDW, which can occur relatively rapidly in response to atmospheric circulation changes.

Publications

  • Thoma, M., Jenkins, A., Holland, D., and Jacobs, S., 2008.
    Modelling Circumpolar Deep Water intrusions on the Amundsen Sea continental shelf, Antarctica.
    Geophysical Research Letters, 35, 6.

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3. Influence of the Panamanian gateway on Greenland ice sheet development.

The formation of the first Northern Hemisphere ice sheets over Greenland was thought to be triggered by the opening of the Panama Isthmus, 3–5 million years ago during the warm Pliocene. This scenario involves the creation of the Gulf Stream, which brought wetter weather to the polar regions, which fell as snow over Greenland and allowed the build up of the ice sheet we observe today.

BAS used a fully coupled atmosphere–ocean general circulation model and an ice-sheet model to assess a number of possibilities, and demonstrated that changes in carbon dioxide concentration in the atmosphere in combination with orbital variations were more likely to trigger the formation of the Greenland ice sheet than any other mechanism.

Publications

  • Lunt, D.J., Foster, G.L., Haywood, A.M., and Stone, E.J., 2008.
    Late Pliocene Greenland glaciation controlled by a decline in atmospheric CO2 levels.
    Nature, 454, 1102-1105.
  • King, J.C., Lachlan-Cope, T.A., Ladkin, R.S., and Weiss, A., 2008.
    Airborne measurements in the stable boundary layer over the Larsen Ice Shelf, Antarctica.
    Boundary Layer Meteorology, 127(3), 413-428.

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4. How animals search for food

How animals search for food is of great practical ecological importance. It is also part of a much wider problem of how best to find things. One possible search strategy is the Lévy flight, which is a random journey whose stages have no typical size. Eleven years ago, a study concluded that wandering albatrosses perform Lévy flights when searching for prey on the ocean surface. This widely reported finding was followed by similar ones concerning deer, bumblebees, reindeer, microzooplankton, grey seals, spider monkeys and fishing boats.

Scientists at BAS, in Brazil and in the USA re-visited this problem using new, high-resolution data on the movements of wandering albatrosses. We found no evidence for Lévy flight behaviour. Using a new method, no evidence of Lévy flights was found in the deer and bumblebee data either. The results question whether the Lévy flight paradigm is a suitable model of ecological search behaviour.

Publications

  • Edwards, A.M., Phillips, R.A., Watkins, N.W., Freeman, M.P., Murphy, E., Afanasyev, V., Buldyrev, S.V., da Luz, M.G.E., Raposo, E.P., Stanley, H.E., and Viswanathan, G.M., 2007.
    Revisiting Lévy flight search patterns of wandering albatrosses, bumblebees and deer.
    Nature, 449 (7165). 1044-1048.

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5. Terrestrial life in Antarctica alter the continent’s established glacial history

A BAS study of life on Antarctica’s frozen wastes has questioned current understanding of Antarctic glacial history and millions of years of biological development. There is clear evidence that, as recently as the Last Glacial Maximum (LGM) (~20,000 years ago), Antarctic ice sheets were thicker and more extensive than they are now. Ice-sheet modelling of the LGM and previous ice maxima shows that most, if not all, ground that is currently ice-free would have previously been covered. This has led to a widely held perception that all Mesozoic (pre-glacial) terrestrial life on Antarctica was wiped out by successive and more extensive glacial events.

Such widespread destruction implies that most, possibly all, terrestrial life found on the continent today has colonised Antarctica during the recent glacial retreat. Emerging insights suggest that Antarctic terrestrial organisms have been continuously isolated in situ on a multi-million year timescale, even before the final phases of the break-up of the Gondwana supercontinent (more than 40 million years ago). The findings mean we must adopt a new biological paradigm for Antarctica and directly challenge current understanding of Antarctic glacial history.

Publications

  • Convey, P., Gibson, J., Hillenbrand, C.-D., Hodgson, D.A., Pugh, P.J.A., Smellie, J.L., and Stevens, M.I., 2008.
    Antarctic terrestrial life — challenging the history of the frozen continent?
    Biological Reviews, 83, 103-117.
  • Convey, P., and Stevens, M.I., 2007.
    Antarctic Biodiversity.
    Science, 317, 1877-1878.

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