LATE NEOGENE PALEOENVIRONMENTAL HISTORY OF THE SOUTHERN HIGH LATITUDES: REAFFIRMATION OF DYNAMIC ICE SHEET BEHAVIOR AND ANTARCTIC ICE SHEET RESPONSES TO GLOBAL PLIOCENE WARMTH

Marine microfossils and fossil terrestrial communities in Sirius Group deposits in the Transantarctic Mountains (TAM) initiated a lively debate regarding the Late Neogene glacial and climate history of the Antarctic region. New information bearing on the issue of a ‘stable’ or ‘dynamic’ history of the East Antarctic Ice Sheet comes from diverse disciplines and settings. This paper will (1) review a variety of pertinent geological information that has come to light in recent years, (2) raise compelling questions the Antarctic Earth science community should address, (3) outline research directions where key data are still needed, (4) consider points of agreement between the positions held by proponents of a ‘stable’ Neogene ice sheet and those that support the ‘dynamic’ view; and (5) reaffirm the dynamic behavior of Neogene Antarctic ice sheets. New information from the Pagodroma Group in the Prince Charles Mts. provides a history of prolonged warmer-than-present climate conditions and large (100s of km-scale) ice margin fluctuations. Coastal deposits and drillcores indicate warmer marine and atmospheric temperatures during the Late Neogene, than at present. Reinterpretations of marine deep-sea oxygen isotope records reveal significant ice volume variations into and after the Pliocene. Glacial meltwater pulses in Antarctic fjords, and input of Nothofagus pollen from the TAM into proximal marine sites both reflect warmer-than-present temperatures. Ocean temperature gradients strengthened and relaxed repeatedly through the Late Miocene and Pliocene, and marine temperatures were repeatedly too warm for the presence of sea-ice and large ice shelves. Development and expansion of the sea-ice belt around Antarctica during the late Pliocene and Pleistocene appears to have been one of the most important events, if not the key climatic threshold, that led into the modern cold, polar environment. Future stratigraphic studies and climate model runs should focus attention on the history and influence of the sea-ice record; it provides a critical link between the oceanic, atmospheric, and cryospheric realms. Future drilling targets on the Antarctic shelf through the ANDRILL and SHALDRIL initiatives will address the Antarctic region’s past and future response to, and influence on, global Late Neogene climate events.