A new mechanism for the two-step δ18O signal at the Eocene-Oligocene boundary
The most marked step in the global climate transition from "Greenhouse" to "Icehouse" Earth occurred at the Eocene-Oligocene (E-O) boundary, 33.7 Ma. Evidence for climatic changes comes from many sources, including the marine benthic δ 18 O record, showing an increase by 1.2–1.5‰...
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ftcopernicus:oai:publications.copernicus.org:cp8152 2023-05-15T13:36:36+02:00 A new mechanism for the two-step δ18O signal at the Eocene-Oligocene boundary Tigchelaar, M. Heydt, A. S. Dijkstra, H. A. 2018-09-27 application/pdf https://doi.org/10.5194/cp-7-235-2011 https://cp.copernicus.org/articles/7/235/2011/ eng eng doi:10.5194/cp-7-235-2011 https://cp.copernicus.org/articles/7/235/2011/ eISSN: 1814-9332 Text 2018 ftcopernicus https://doi.org/10.5194/cp-7-235-2011 2020-07-20T16:26:11Z The most marked step in the global climate transition from "Greenhouse" to "Icehouse" Earth occurred at the Eocene-Oligocene (E-O) boundary, 33.7 Ma. Evidence for climatic changes comes from many sources, including the marine benthic δ 18 O record, showing an increase by 1.2–1.5‰ at this time. This positive excursion is characterised by two steps, separated by a plateau. The increase in δ 18 O values has been attributed to rapid glaciation of the Antarctic continent, previously ice-free. Simultaneous changes in the δ 13 C record are suggestive of a greenhouse gas control on climate. Previous modelling studies show that a decline in p CO 2 beyond a certain threshold value may have initiated the growth of a Southern Hemispheric ice sheet. These studies were not able to conclusively explain the remarkable two-step profile in δ 18 O. Furthermore, they considered changes in the ocean circulation only regionally, or indirectly through the oceanic heat transport. The potential role of global changes in ocean circulation in the E-O transition has not been addressed yet. Here a new interpretation of the δ 18 O signal is presented, based on model simulations using a simple coupled 8-box-ocean, 4-box-atmosphere model with an added land ice component. The model was forced with a slowly decreasing atmospheric carbon dioxide concentration. It is argued that the first step in the δ 18 O record reflects a shift in meridional overturning circulation from a Southern Ocean to a bipolar source of deep-water formation, which is associated with a cooling of the deep sea. The second step in the δ 18 O profile occurs due to a rapid glaciation of the Antarctic continent. This new mechanism is a robust outcome of our model and is qualitatively in close agreement with proxy data. Text Antarc* Antarctic Ice Sheet Southern Ocean Copernicus Publications: E-Journals Antarctic Southern Ocean The Antarctic Climate of the Past 7 1 235 247 |
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Copernicus Publications: E-Journals |
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ftcopernicus |
language |
English |
description |
The most marked step in the global climate transition from "Greenhouse" to "Icehouse" Earth occurred at the Eocene-Oligocene (E-O) boundary, 33.7 Ma. Evidence for climatic changes comes from many sources, including the marine benthic δ 18 O record, showing an increase by 1.2–1.5‰ at this time. This positive excursion is characterised by two steps, separated by a plateau. The increase in δ 18 O values has been attributed to rapid glaciation of the Antarctic continent, previously ice-free. Simultaneous changes in the δ 13 C record are suggestive of a greenhouse gas control on climate. Previous modelling studies show that a decline in p CO 2 beyond a certain threshold value may have initiated the growth of a Southern Hemispheric ice sheet. These studies were not able to conclusively explain the remarkable two-step profile in δ 18 O. Furthermore, they considered changes in the ocean circulation only regionally, or indirectly through the oceanic heat transport. The potential role of global changes in ocean circulation in the E-O transition has not been addressed yet. Here a new interpretation of the δ 18 O signal is presented, based on model simulations using a simple coupled 8-box-ocean, 4-box-atmosphere model with an added land ice component. The model was forced with a slowly decreasing atmospheric carbon dioxide concentration. It is argued that the first step in the δ 18 O record reflects a shift in meridional overturning circulation from a Southern Ocean to a bipolar source of deep-water formation, which is associated with a cooling of the deep sea. The second step in the δ 18 O profile occurs due to a rapid glaciation of the Antarctic continent. This new mechanism is a robust outcome of our model and is qualitatively in close agreement with proxy data. |
format |
Text |
author |
Tigchelaar, M. Heydt, A. S. Dijkstra, H. A. |
spellingShingle |
Tigchelaar, M. Heydt, A. S. Dijkstra, H. A. A new mechanism for the two-step δ18O signal at the Eocene-Oligocene boundary |
author_facet |
Tigchelaar, M. Heydt, A. S. Dijkstra, H. A. |
author_sort |
Tigchelaar, M. |
title |
A new mechanism for the two-step δ18O signal at the Eocene-Oligocene boundary |
title_short |
A new mechanism for the two-step δ18O signal at the Eocene-Oligocene boundary |
title_full |
A new mechanism for the two-step δ18O signal at the Eocene-Oligocene boundary |
title_fullStr |
A new mechanism for the two-step δ18O signal at the Eocene-Oligocene boundary |
title_full_unstemmed |
A new mechanism for the two-step δ18O signal at the Eocene-Oligocene boundary |
title_sort |
new mechanism for the two-step δ18o signal at the eocene-oligocene boundary |
publishDate |
2018 |
url |
https://doi.org/10.5194/cp-7-235-2011 https://cp.copernicus.org/articles/7/235/2011/ |
geographic |
Antarctic Southern Ocean The Antarctic |
geographic_facet |
Antarctic Southern Ocean The Antarctic |
genre |
Antarc* Antarctic Ice Sheet Southern Ocean |
genre_facet |
Antarc* Antarctic Ice Sheet Southern Ocean |
op_source |
eISSN: 1814-9332 |
op_relation |
doi:10.5194/cp-7-235-2011 https://cp.copernicus.org/articles/7/235/2011/ |
op_doi |
https://doi.org/10.5194/cp-7-235-2011 |
container_title |
Climate of the Past |
container_volume |
7 |
container_issue |
1 |
container_start_page |
235 |
op_container_end_page |
247 |
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1766081332000063488 |