• Main Authors: Ian Joughin, Richard B. Alley
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Subjects: Amundsen Sea; Transantarctic Mountains; Mercer; Buttress; Ice Sheet; Ice Shelves
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.1029.4511; http://www.ccpo.odu.edu/%7Eklinck/Reprints/PDF/joughinNatGeo11.pdf

with the rate growing over at least the past two decades1–4. These observations intensify concerns about the ice sheet’s stability that were first raised more than four decades ago5. Although early atten-tion focused on the ice stream drainages feeding the large Ross and Filchner–Ronne ice shelves (Box 1), at present these areas are thickening at moderate rates (several centimetres per year) or are near balance6–9. Instead, net WAIS losses result predominately from the strong thinning (tens to hundreds of centimetres per year) of the glaciers draining the ice sheet’s Amundsen Sea sector (Fig. 1), which in the 1980s was presciently described as the “weak under-belly ” of the WAIS10. Although the large changes in the Amundsen Sea region have recently shifted focus from the Ross and Filchner– Ronne drainages, all sectors of the WAIS are subject to potential instabilities, although varied sensitivities to ice–ocean–atmosphere forcings may produce regional losses with differing onset times and durations. WAIS history as a possible prelude to the future Mercer5 first raised concern over a possible future WAIS collapse by suggesting that the ice sheet was not present for an extended period during the last interglacial, corresponding to Marine Isotope Stage 5e (MIS 5e). This conclusion was largely based on geologic evi-dence of ice-marginal lakes that he assigned to MIS 5e at elevations (1,400 m) in the Transantarctic Mountains where present tempera-tures produce only negligible summer melt, but that remain poorly dated to this day11,12. From this finding he concluded that tempera-tures were at least 7 °C warmer than present. He argued that such warming was sufficient to eliminate the floating ice shelves needed to buttress the WAIS (see Box 2), resulting in the nearly total loss of the ice sheet and a consequent sea-level rise of several metres12. A further argument by Mercer for a past WAIS collapse was that it would have raised sea level by an amount consistent with palaeo-sea-level records5. Relative to the ...