Hobart

Seminar Abstract

Wednesday 8 February 2012, *9.30am* (Tas time)
Shearwater Room, Hobart [Sorry, open to CMAR staff only]

James C Zachos
Earth and Planetary Sciences
University of California
Santa Cruz

Rapid Greenhouse Warming & Climate Sensitivity: Insights from the Paleocene-Eocene Thermal Maximum

The Paleocene-Eocene Thermal Maximum (PETM) was first discovered 20 years ago(1). In the time since, significant progress has been achieved in detailing the primary features of this rapid and extreme global warming event, as well as impacts on marine and terrestrial environments. This includes quantification of the magnitude of global warming, 5 to 6°C, and the mass of carbon released, 4500 to 6000 Pg C. Evidence has also emerged for a dramatic shift in global precipitation patterns and intensity, and a transient reduction in oceanic overturn and deoxygenation. Chronostratigraphic constraints indicate the majority of these changes unfolded in less than 10 k.y., then reversed with recovery taking well over 100 k.y. The one exception is the reduction in oceanic overturn and deoxygenation which was transient (2). The overall impacts of the PETM on biota were substantial as evidenced by major shifts in species diversity and abundances in both marine and terrestrial environments.

Given the differences in boundary conditions (e.g., absence of large ice-sheets and associated feedbacks) and a more gradual rate of perturbation, it is evident that the PETM does not represent an ideal analog for future anthropogenic warming. There are, however, several key features of the PETM that can be used to test theory on greenhouse climate dynamics as well as carbon cycle dynamics. For one, observations of the PETM indicate a temperature sensitivity to CO2 that is at the high end of current sensitivity estimates from models (3,4). Second, the sequestration of carbon released during the PETM required well over 100 k.y., consistent with estimates for the lifetime of anthropogenic carbon. Finally, though the evidence is spatially limited and mostly indirect, particularly for continental settings, it appears the hydrologic cycle intensified during the PETM. Sedimentological and fossil evidence recovered from continental and coastal sections indicate increased precipitation, but with a shift toward seasonal extremes (i.e., brief, but intense wet season, long dry season), resulting in reduced vegetative cover, extreme flood events, and enhanced sediment erosion (2,5).

1 Kennett, J. P. & Stott, L. D., Nature 353, 225-229 (1991).
2 Nicolo, M., Dickens, G. R. & Hollis, C. J., Paleoceanography 25, PA4210, doi:10.1029/2009PA001904 (2010).
3 Panchuk, K., Ridgwell, A. & Kump, L. R., Geology 36, 315-318 (2008).
4 Zeebe, R. E., Zachos, J. C. & Dickens, G. R., Nat Geosci 2, 576-580, doi:10.1038/ngeo578 (2009).
5 Schmitz, B. & Pujalte, V., Geology 35, 215-218 (2007).

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Location:
CSIRO = Marine Laboratories Auditorium, Castray Esplanade, Hobart

For further information, or to schedule a seminar, contact:
Andrew Meijers, (Oceanographic seminars) CSIRO Marine and Atmospheric Research (03) 6232 5335
Natalie Kelly, (Biology/Modelling seminars) CSIRO Marine and Atmospheric Research 0438 452 483
Jillian Enraght-Moony, (seminar administrator) CSIRO Marine and Atmospheric Research (03) 6232 5320
Communications Manager, Antarctic Climate and Ecosystems CRC (03) 6226 7888
Tracey Cochrane, Institute for Marine and Antarctic Studies (IMAS), University of Tasmania (03) 6226 2937

Last updated 17/02/12