HR: 12:05h
AN: PP32A-08    [Abstracts]
TI: Early Cenozoic Southern Hemisphere Cooling and Establishment of the Antarctic Circumpolar Current
AU: * Pfuhl, H A
EM: pfuhl@geophysik.uni-muenchen.de
AF: Godwin Lab., Dept. of Earth Sciences, University of Cambridge, now at: Dept. of Earth and Environmental Sciences, Ludwig-Maximilians-University Munich, Theresienstr. 41, Munich, 80333 Germany
AU: McCave, I N
EM: mccave@esc.cam.ac.uk
AF: Godwin Lab., Dept. of Earth Sciences, University of Cambridge, Downing Street, Cambridge, CB2 3EQ United Kingdom
AB: Antarctica's climatic transition from ''greenhouse'' to ''icehouse'' is generally linked to the establishment of the Antarctic Circumpolar Current (ACC). Development of this strong, wind-driven current was dependent on changes in atmospheric circulation patterns largely influenced by progressive isolation of the Antarctic continent due to tectonic opening of Tasman Gateway (TG) south of Australia and Drake Passage (DP) south of America to deep throughflow. Timing of TG deepening from around 35.5 to 30.2 Ma is well constrained and the widespread Marshall Paraconformity of the Australasian region from ~ 33-30 Ma relates to this event. Timing of a deep opening of DP, however, remains contentious, although several recent publications argue that deep throughflow was established around late Eocene/early Oligocene and that subsequent initiation of the ACC drove abrupt climatic cooling at the E/O-boundary. We present data that reveal a far more complex process of climate deterioration in the Southern Hemisphere than previously assumed. Benthic stable isotopic data from all three Southern Ocean basins, show that Maud Rise in the southernmost Atlantic was exceptionally cool, while a warming around 26 Ma at southern Kerguelen Plateau in the Indian Ocean was most likely a regional signal only. Our data from the TG, together with Pacific data from the 1970's show that temperatures post Oi-1 glaciation event developed differently in the southern Pacific from those in the other two basins. Our data suggest that a homogenous bottom water mass in the Southern Ocean was only established at the Oligocene-Miocene boundary and that growth of a permanent East Antarctic Icesheet was delayed by another few million years. Additional data indicating changes in current speed (sortable silt) reveal a single, strong, abrupt increase just prior to the Mi-1 glaciation event in the earliest Miocene. We believe that this increase relates to the onset of ACC-type circulation and is the driving force behind early Miocene cooling. These data contradict some of the evidence cited in support of an earlier deep throughflow.
DE: 1605 Abrupt/rapid climate change (4901, 8408)
DE: 4900 PALEOCEANOGRAPHY (0473, 3344)
DE: 4999 General or miscellaneous
DE: 9310 Antarctica (4207)
DE: 9604 Cenozoic
SC: Paleoceanography and Paleoclimatology [PP]
MN: Fall Meeting 2005