HR: 11:50h
AN: PP52B-07    [Abstracts]
TI: Stepping into the "Icehouse": Impacts of Orbital Forcing and Atmospheric Carbon Dioxide on Middle Miocene Ice-sheet Expansion
AU: * Holbourn, A E
EM: ah@gpi.uni-kiel.de
AF: Institute of Geosciences, Christian-Albrechts-University, Olshasenstr. 40, Kiel, D-24118 Germany
AU: Kuhnt, W
EM: wk@gpi.uni-kiel.de
AF: Institute of Geosciences, Christian-Albrechts-University, Olshasenstr. 40, Kiel, D-24118 Germany
AU: Schulz, M
EM: mschulz@palmod.uni-bremen.de
AF: Department of Geosciences and Research Center Ocean Margins, University of Bremen, Postfach 330 440, Bremen, D-28334 Germany
AU: Erlenkeuser, H
EM: HErlenkeuser@leibniz.uni-kiel.de
AF: Leibniz Laboratory for Radiometric Dating and Stable Isotope Research, Christian-Albrechts-University, Max-Eyth-Str. 11-13, Kiel, D-24118 Germany
AB: About 13.9 million years ago, the climate on Earth cooled dramatically after an extended period of relative warmth. This key transition, which marked the final stage of stepwise Cenozoic cooling, remains one of the most enigmatic episodes in Cenozoic climate history. Tectonically driven circulation changes and atmospheric CO₂ variations were proposed as driving mechanisms, but testing of these hypotheses has been hampered by the lack of adequately preserved sedimentary successions. We present high resolution (1-5 kyr) middle Miocene (12.7-14.7 Ma) climate proxy records from two complete, non-lithified successions newly recovered from the northwest and southeast subtropical Pacific at ODP Sites 1146 and 1237. We have developed new chronologies for these sections by correlating oxygen isotopic data to the latest astronomical solution. Our results indicate that a conjunction of climatic forcing factors ultimately triggered middle Miocene ice-sheet expansion and global cooling. We suggest that the coincidence of relatively constant low summer insolation over Antarctica and declining atmospheric CO₂ concentration ultimately triggered Southern Hemisphere ice-sheet expansion and global cooling after 13.9 Ma, whereas thermal isolation of Antarctica sustained long-term climatic boundary conditions propitious for ice formation. Our results demonstrate that Antarctic glaciation occurred rapidly within two obliquity cycles, and coincided with a striking transition from obliquity- to eccentricity-driven climate rhythms.
DE: 4870 Stable isotopes (0454, 1041)
DE: 4910 Astronomical forcing
DE: 4930 Greenhouse gases
DE: 9355 Pacific Ocean
DE: 9605 Neogene
SC: Paleoceanography and Paleoclimatology [PP]
MN: Fall Meeting 2005