Stepping into the "Icehouse": Impacts of Orbital Forcing and Atmospheric Carbon Dioxide on Middle Miocene Ice-sheet Expansion

Details Stepping into the "Icehouse": Impacts of Orbital Forcing and Atmospheric Carbon Dioxide on Middle Miocene Ice-sheet Expansion Stepping into the "Icehouse": Impacts of Orbital Forcing and Atmospheric Carbon Dioxide on Middle Miocene Ice-sheet Expansion

Dec 2005

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005agufmpp52b..07h&link_type=abstract

American Geophysical Union, Fall Meeting 2005, abstract #PP52B-07

Astronomy and Astrophysics

Astronomy

4870 Stable Isotopes (0454, 1041), 4910 Astronomical Forcing, 4930 Greenhouse Gases, 9355 Pacific Ocean, 9605 Neogene

Scientific paper

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.

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