Nature advance online publication 13 September 2009 |
doi:10.1038/nature08447; Received 18 May 2009; Accepted 21 August
2009; Published online 13 September 2009
Atmospheric carbon dioxide through the Eocene-Oligocene climate transition
Paul N. Pearson1, Gavin L. Foster2 & Bridget S. Wade3
1. School of Earth and Ocean Sciences, Cardiff
University, Cardiff CF10 3YE, UK
2. Bristol Isotope Group, Department of Earth Sciences,
University of Bristol, Bristol BS8 1RJ, UK
3. Department of Geology and Geophysics, Texas A&M
University, College Station, Texas 77843-3115, USA
Correspondence to: Paul N. Pearson1 Correspondence and requests for
materials should be addressed to P.N.P.
(Email: [email protected]).
Abstract
Geological and geochemical evidence1, 2, 3 indicates that the
Antarctic ice sheet formed during the Eocene-Oligocene transition4,
33.5-34.0 million years ago. Modelling studies5, 6 suggest that such
ice-sheet formation might have been triggered when atmospheric carbon
dioxide levels (pCO2 atm) fell below a critical threshold of
750 p.p.m.v., but the timing and magnitude of pCO2 atm relative to
the evolution of the ice sheet has remained unclear. Here we use the
boron isotope pH proxy7, 8 on exceptionally well-preserved carbonate
microfossils from a recently discovered geological section in
Tanzania9, 10 to estimate pCO2 atm before, during and after the
climate transition. Our data suggest that a reduction in pCO2 atm
occurred before the main phase of ice growth, followed by a sharp
recovery to pre-transition values and then a more gradual decline.
During maximum ice-sheet growth, pCO2 atm was between 450 and
1,500 p.p.m.v., with a central estimate of 760 p.p.m.v. The ice cap
survived the period of pCO2 atm recovery, although possibly with
some reduction in its volume, implying (as models predict11) a
nonlinear response to climate forcing during melting. Overall, our
results confirm the central role of declining pCO2 atm in the
development of the Antarctic ice sheet (in broad agreement with
carbon cycle modelling12) and help to constrain mechanisms and
feedbacks associated with the Earth's biggest climate switch of the
past 65 Myr.
--~--~---------~--~----~------------~-------~--~----~
You received this message because you are subscribed to the Google Groups
"geoengineering" group.
To post to this group, send email to [email protected]
To unsubscribe from this group, send email to
[email protected]
For more options, visit this group at
http://groups.google.com/group/geoengineering?hl=en
-~----------~----~----~----~------~----~------~--~---
