The climatic consequences of a rare orbital anomaly at the Oligocene/Miocene boundary (23Ma)
Zachos, J.C., Shackleton, N.J., Revenaugh, J.S., Pälike, H. and Flower, B.P. (2001) The climatic consequences of a rare orbital anomaly at the Oligocene/Miocene boundary (23Ma). In, Earth System Processes 2001: GSA/GSL Global Meeting, Edinburgh, 24-28 June 2001, Proceedings with Abstracts. Earth System Processes 2001: GSA/GSL Global Meeting Boulder CO, USA, Geological Society of America, p.94.
The late Oligocene to early Miocene (20-26Ma) is characterized by a complex climate history that includes a stepped transition toward a cooler climate, intermittent partial glaciations of Antarctica, and a transient glaciation, Mi-1, at the Oligocene/Miocene (O/M) boundary. The Mi-1 event is characterized by an anomalous positive oxygen isotope excursion, the magnitude of which suggests the brief appearance of a full-scale ice-sheet on east Antarctica coupled with a few degrees of deep sea cooling. A recent breakthrough in extending the astronomical calibration back to ~30 Ma has provided a unique opportunity to compare the climatic events of the O/M transition relative to Earth’s orbital variations. Here, we present an uninterrupted 5.5 My long high-fidelity chronology of late Oligocene-early Miocene climate and ocean carbon chemistry that is based on a composite in the western equatorial Atlantic. This unique isotope record provides a rare window into how the climate system responded to orbital forcing uncer boundary conditions significantly different from those of the recent past. Time-series analyses reveal climate variance concentrated at all Milankovitch frequencies, but with unusually strong power at the primary eccentricity band periods of 406, 125, and 95-ky. These cycles, which represent in part glacial advances and retreats of Antarctic ice-sheets, show significantly enhanced variability over a 1.6 my period (21.4-23.0 Ma) of suspected low greenhouse gas levels as inferred from the carbon isotope record. Perhaps the most unexpected finding is that of a rare orbital congruence between eccentricity and obliquity that precisely corresponds with the Mi-1 glaciation. This orbital anomaly involves ~four consecutive cycles of low amplitude variance in obliquity (a node) during a period of low eccentricity. The net result is an extended period (~200ky) of low seasonality orbits, which allows for a step-like expansion of an Antarctic ice-sheet.
|Item Type:||Book Section|
|Subjects:||Q Science > QE Geology|
|Divisions:||University Structure - Pre August 2011 > School of Ocean & Earth Science (SOC/SOES)
|Date Deposited:||16 Oct 2006|
|Last Modified:||28 Jun 2012 10:42|
|Contributors:||Zachos, J.C. (Author)
Shackleton, N.J. (Author)
Revenaugh, J.S. (Author)
Pälike, H. (Author)
Flower, B.P. (Author)
|Publisher:||Geological Society of America|
|RDF:||RDF+N-Triples, RDF+N3, RDF+XML, Browse.|
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