~ P Pergamon 0277-3791(95)00002-X Quaternary Science Reviews, gol. 14, pp. 101-123, 1995. Copyright © 1995 Elsevier Science Ltd. Printed in Great Britain. All rights reserved. 0277-3791/95 $29.00 THE NEOGENE EAST ANTARCTIC ICE SHEET: A DYNAMIC OR STABLE FEATURE? GARY S. WILSON Byrd Polar Research Center, The Ohio State University, Columbus, OH 43210, U.S.A. Abstract -- This paper is a review of the history and behaviour of the East Antarctic ice sheet dur- ing the late Neogene and is a response to the publication of Sugden et al. (1993a), 'The Case for a Stable East Antarctic Ice Sheet', in Geografiska Annaler, 75A(4). The Antarctic ice sheet is a criti- cal factor in the global climate and oceanographic system. Knowledge of its historical development is critical to understanding global palaeoceanographic and palaeoclimatic systems and their devel- opment. The 'Webb-Harwood hypothesis' proposes that the ice sheet, while being present in Antarctica for more than 40 Ma, was, until recently (ca. 2.5 Ma), a dynamic feature, waxing and waning under a more temperate climatic and glaciologic regime. The 'stabilistic hypothesis' pro- poses that the current ice sheet has existed in its present cold and polar form for at least the last 14 Ma. 'The Case for a Stable East Antarctic Ice Sheet' is the clearest statement of the stabilistic argu- ment to date. The authors find support for their viewpoint by presenting evidence, from several geologic data bases, that does not support their own null 'meltdown hypothesis', which they deem to be equivalent to the 'Webb-Harwood hypothesis', thereby they conclude supporting the 'sta- bilistic hypothesis'. However, their conclusions are weakened by: failure to reject their null hypothesis, conflict between the 'meltdown' and 'Webb-Harwood' hypotheses, infraction of geo- logical laws, and poor application of stratigraphic principles. Several issues are highlighted here as important for direction of future research and discussion concerning Late Cenozoic Antarctic glacio-climatic history. QSR INTRODUCTION The present day Antarctic ice sheet is a major geo- graphical and historical global feature, containing 30 mil- lion km ~ of ice (Drewry et al., 1982). To the west (with respect to the Greenwich Meridian) of the Transantarctic Mountains (Fig. 1), the ice sheet is currently dynamic, largely marine based, and discharges through large ice stream systems. It contains approximately 3 million km 3 of ice that, should it melt, would contribute a volume of water to the world's oceans equivalent to a rise in global sea level of 6 m (Denton et al., 1991). To the east of the Transantarctic Mountains, the current ice sheet is stable, predominantly terrestrial, and has limited discharge; into surrounding ice shelves and by surface ablation. It con- tains more than 26 million km 3 of ice that if melted would cause a further global sea level rise of some 60 m (Denton et al., 1991). Sugden et al. (1993a) suggested that, even with the current threat of global warming, such a catastrophic meltdown of the major East Antarctic ice sheet is less than unlikely, because, they suggested, it has existed close to its current stable configuration for at least the last 14 Ma. This includes the Pliocene Epoch, a time when global climates were known to be warmer than pre- sent (Gammon et al., 1985). The implications of these claims, if correct, bear not only on the direct response of the current Antarctic ice sheet to predicted global warm- ing, but also on our understanding of the development of the Antarctic psychrosphere (Kennett, 1982) and its role in climatic and oceanic systems and their development. This, in turn, may help scientists understand how it may influence or stabilise the global system as it responds to future warming. This recent volume by Sugden et al. (1993a) is the lat- est contribution to a 10 year old debate on the history of the Antarctic ice sheets and their importance in the devel- opment (both responsive and causative) of global climat- ic, oceanographic and tectonic evolution. Sugden et al. (1993a), and consequently this review also, address only the current impasse of either a stable glaciated or dynam- ic deglaciated East Antarctic ice sheet in the late Neogene. The proponents of the two different viewpoints have become affectionately referred to as the 'stabilists' and the 'dynamicists', with Sugden et al. (1993a) pre- senting the most recent stabilistic argument. However, the two viewpoints seem predestined to remain at odds, not only because of their mutually exclusive data sets but also because of their inherently different approaches to the problem. The 'dynamicists' base their model on inter- pretations of stratigraphy, events, datums, and correla- tions of continent-wide terrestrial and ocean margin stra- ta. Whereas, the 'stabilists' base their model on interpretations of both the geomorphology of the Dry Valleys region of southern Victoria Land and indirect proxy records from the deep ocean. Sugden (1992, p. 776) suggested that "the impasse will only be solved by careful scrutiny of the assumptions underlying the alter- native hypotheses". This review is written with this in mind and also with careful analysis of the fundamental basis for the observations of each data set and its inter- pretation. Other issues such as the initial glaciation of Antarctica, its nature, timing, and extent, and the evolu- 101