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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. Geological Society of America., p.94.

Record type: Conference or Workshop Item (Paper)

Abstract

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.

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More information

Published date: 2001
Venue - Dates: Earth System Processes 2001: GSA/GSL Global Meeting, 2001-06-24 - 2001-06-28

Identifiers

Local EPrints ID: 41870
URI: http://eprints.soton.ac.uk/id/eprint/41870
PURE UUID: 1cedabd6-8425-4218-bc16-3e48ebc5844d

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Date deposited: 16 Oct 2006
Last modified: 17 Jul 2017 15:26

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Contributors

Author: J.C. Zachos
Author: N.J. Shackleton
Author: J.S. Revenaugh
Author: H. Pälike
Author: B.P. Flower

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