The Antarctic ice sheet, its history and response to sea level and climatic changes over the past 100 million years

The development, surface form, flow and erosive activity of the Antarctic ice sheet over the past 100 million years is related to geological evidence that indicates long-term trends of global climate. The glaciological description of the evolution of the ice sheet covers its interactions with the atmosphere and with the ocean. Discussion focuses on changes of the equilibrium line altitude (ELA) with time, of the accumulation rate with global temperature and basal melting of ice shelves by ocean waters. The tendency of global climate to change rapidly or to drift slowly between two near-equilibrium states involves two types of changes. The former that has been widely recognized is reversible. A second type involving ice sheets or ice shelves appears to be almost irreversible since they remain in their changed state unless a much larger reversal of factors driving climate occurs. We refer to any rapid but reversible changes as climatic jumps and to the latter as climate-ice switches. Variability of climate in response to changing radiation with the earth's orbital parameters and other causes is included in our model. Extensive glaciation of East Antarctica commenced after 40 m.y. B.P. with wide fluctuations until shortly after 20 m.y. B.P. A climate-ice switch then prevented any major deglaciation. A further climate-ice switch associated with the ELA falling below sea level occurred soon after 10 m.y. B.P. This led to rapid formation of ice shelves and the marine ice sheet of West Antarctica which advanced as grounded ice to the edge of the continental shelf. After 5 m.y. B.P. the grounded ice started to retreat, extensive ice shelves remained and most glacial debris was then deposited beneath the inner regions of ice shelves. Response to Northern Hemisphere glaciation since 2.4 m.y. B.P. during glacial periods involved extension of the grounded ice area, a large decrease of mass input and decreased melting of outer parts of large ice shelves while the melting rate beneath inner regions was probably similar to the present. Marine core evidence suggests that retreat caused by global cooling has been dominant since 5 m.y. B.P. and that changes in extent due to Northern Hemisphere glaciation since 2.4 m.y. B.P. have had different effects on the major and on smaller northerly ice shelves.