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No extreme bipolar glaciation during the main Eocene calcite compensation shift

No extreme bipolar glaciation during the main Eocene calcite compensation shift
No extreme bipolar glaciation during the main Eocene calcite compensation shift
Major ice sheets were permanently established on Antarctica approximately 34 million years ago1,2,3, close to the Eocene/Oligocene boundary, at the same time as a permanent deepening of the calcite compensation depth in the world’s oceans4. Until recently, it was thought that Northern Hemisphere glaciation began much later, between 11 and 5 million years ago1,2,3,5. This view has been challenged, however, by records of ice rafting at high northern latitudes during the Eocene epoch6,7 and by estimates of global ice volume that exceed the storage capacity of Antarctica8 at the same time as a temporary deepening of the calcite compensation depth ∼41.6 million years ago9. Here we test the hypothesis that large ice sheets were present in both hemispheres ∼41.6 million years ago using marine sediment records of oxygen and carbon isotope values and of calcium carbonate content from the equatorial Atlantic Ocean. These records allow, at most, an ice budget that can easily be accommodated on Antarctica, indicating that large ice sheets were not present in the Northern Hemisphere. The records also reveal a brief interval shortly before the temporary deepening of the calcite compensation depth during which the calcite compensation depth shoaled, ocean temperatures increased and carbon isotope values decreased in the equatorial Atlantic. The nature of these changes around 41.6 million years ago implies common links, in terms of carbon cycling, with events at the Eocene/Oligocene boundary4 and with the ‘hyperthermals’ of the Early Eocene climate optimum3,10,11. Our findings help to resolve the apparent discrepancy between the geological records of Northern Hemisphere glaciation6,7,8 and model results12,13 that indicate that the threshold for continental glaciation was crossed earlier in the Southern Hemisphere than in the Northern Hemisphere.
0028-0836
908–911
Edgar, Kirsty M
15a6f655-0ec8-431c-b181-2050bacce584
Wilson, Paul
f940a9f0-fa5a-4a64-9061-f0794bfbf7c6
Sexton, Philip F.
8f381c3d-6181-4027-bc35-258780a1f383
Suganuma, Yusuke
592c8211-bd4c-4578-bb30-a62f4da5e17a
Edgar, Kirsty M
15a6f655-0ec8-431c-b181-2050bacce584
Wilson, Paul
f940a9f0-fa5a-4a64-9061-f0794bfbf7c6
Sexton, Philip F.
8f381c3d-6181-4027-bc35-258780a1f383
Suganuma, Yusuke
592c8211-bd4c-4578-bb30-a62f4da5e17a

Edgar, Kirsty M, Wilson, Paul, Sexton, Philip F. and Suganuma, Yusuke (2007) No extreme bipolar glaciation during the main Eocene calcite compensation shift. Nature, 448, 908–911. (doi:10.1038/nature06053).

Record type: Article

Abstract

Major ice sheets were permanently established on Antarctica approximately 34 million years ago1,2,3, close to the Eocene/Oligocene boundary, at the same time as a permanent deepening of the calcite compensation depth in the world’s oceans4. Until recently, it was thought that Northern Hemisphere glaciation began much later, between 11 and 5 million years ago1,2,3,5. This view has been challenged, however, by records of ice rafting at high northern latitudes during the Eocene epoch6,7 and by estimates of global ice volume that exceed the storage capacity of Antarctica8 at the same time as a temporary deepening of the calcite compensation depth ∼41.6 million years ago9. Here we test the hypothesis that large ice sheets were present in both hemispheres ∼41.6 million years ago using marine sediment records of oxygen and carbon isotope values and of calcium carbonate content from the equatorial Atlantic Ocean. These records allow, at most, an ice budget that can easily be accommodated on Antarctica, indicating that large ice sheets were not present in the Northern Hemisphere. The records also reveal a brief interval shortly before the temporary deepening of the calcite compensation depth during which the calcite compensation depth shoaled, ocean temperatures increased and carbon isotope values decreased in the equatorial Atlantic. The nature of these changes around 41.6 million years ago implies common links, in terms of carbon cycling, with events at the Eocene/Oligocene boundary4 and with the ‘hyperthermals’ of the Early Eocene climate optimum3,10,11. Our findings help to resolve the apparent discrepancy between the geological records of Northern Hemisphere glaciation6,7,8 and model results12,13 that indicate that the threshold for continental glaciation was crossed earlier in the Southern Hemisphere than in the Northern Hemisphere.

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More information

Published date: 23 August 2007
Additional Information: Copyright © 2007, Nature Publishing Group

Identifiers

Local EPrints ID: 46734
URI: http://eprints.soton.ac.uk/id/eprint/46734
ISSN: 0028-0836
PURE UUID: 7f1de6bf-e54c-4248-866a-504c6bace18b
ORCID for Paul Wilson: ORCID iD orcid.org/0000-0001-6425-8906

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Date deposited: 16 Jul 2007
Last modified: 16 Mar 2024 03:13

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Contributors

Author: Kirsty M Edgar
Author: Paul Wilson ORCID iD
Author: Philip F. Sexton
Author: Yusuke Suganuma

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