• Introduction • AOGCM results and Eocene/PETM ocean circulation • Hydrate modelling • Conceptual model for hyperthermal orbital pacing A mechanism for the orbital pacing of Eocene hyperthermals Dan Lunt, Andy Ridgwell, Appy Sluijs, Jim Zachos Stephen Hunter, Alan Haywood
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Introduction AOGCM results and Eocene/PETM ocean circulation Hydrate modelling Conceptual model for hyperthermal orbital pacing A mechanism for the orbital.
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• Introduction• AOGCM results and Eocene/PETM ocean circulation• Hydrate modelling• Conceptual model for hyperthermal orbital pacing
A mechanism for the orbital pacing of Eocene hyperthermals
Dan Lunt, Andy Ridgwell, Appy Sluijs, Jim ZachosStephen Hunter, Alan Haywood
Zachos et al, Nature, 2008
Orientation…
Palaeocene-Eocene Thermal Maximum
Dunkley Jones et al, 2010
Causes of PETM have been debated – implications for carbon input and therefore climate sensitivity
Bice and Marotzke, 2004
One hypothesis: release of methane hydrates due to enhanced warming:
• Eocene model shows fairly linear surface temperature response to CO2, but…
• Deep ocean warms non-linearly, associated with reduction in deep water formation and switch in ocean circulation.
• Implications for hydrates: initial forcing (e.g. volcanic) could cause ‘run-away’ positive feedbacks.
• Supported by other modelling work (Winguth et al, 2010)
Lunt et al, Geology, 2010.
Conclusions (1)
Evidence for multiple hyperthermals…
And orbital pacing….
See also Westerhold et al.,
Lourens et al
“Hence, we suggest that the extreme seasonal contrast at both hemispheres during eccentricity maxima increased intermediate seawater temperatures, thereby triggering the release of oceanic methane hydrates.”
6 Additional simulations with orbital pertubations, 1000years in length:
Maximum seasonality: obliquity=0.43 rad, eccentricity=0.054