We found a match
Your institution may have access to this item. Find your institution then sign in to continue.
- Title
A new interpretation of the two-step δ<sup>18</sup>O signal at the Eocene-Oligocene boundary.
- Authors
Tigchelaar, M.; von der Heydt, A. S.; Dijkstra, H. A.
- Abstract
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 δ18O 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 δ18O values has been attributed to rapid glaciation of the Antarctic continent, previously ice-free. Simultaneous changes in the δ13C record are indicative of a greenhouse gas control on climate. Previous studies show that a decline in pCO2 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 δ18O. Furthermore, they did not address the potential role of changes in ocean circulation in the E-O transition. Here a new interpretation of the δ18O 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 δ18O represents 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. This shift can be initiated by a small density perturbation in the model, although there is also a parameter regime for which the shift occurs spontaneously. The second step in the δ18O profile occurs due to a rapid glaciation of the Antarctic continent. This new interpretation is a robust outcome of our model and is in good agreement with proxy data.
- Subjects
ANTARCTIC Ocean; EOCENE-Oligocene boundary; CLIMATE in greenhouses; ICEHOUSES; CLIMATE change; GREENHOUSE gases; ICE sheets; OCEAN circulation
- Publication
Climate of the Past Discussions, 2010, Vol 6, Issue 4, p1391
- ISSN
1814-9324
- Publication type
Article
- DOI
10.5194/cpd-6-1391-2010