Presentation on theme: "A mechanism for the orbital pacing of Eocene hyperthermals Dan Lunt, Andy Ridgwell, Appy Sluijs, Jim Zachos Stephen Hunter, Alan Haywood Introduction."— Presentation transcript:
1 A mechanism for the orbital pacing of Eocene hyperthermals Dan Lunt, Andy Ridgwell, Appy Sluijs, Jim Zachos Stephen Hunter, Alan HaywoodIntroductionAOGCM results and Eocene/PETM ocean circulationHydrate modellingConceptual model for hyperthermal orbital pacing
2 Palaeocene-Eocene Thermal Maximum Orientation…Palaeocene-Eocene Thermal MaximumZachos et al, Nature, 2008
3 Causes of PETM have been debated – implications for carbon input and therefore climate sensitivity Dunkley Jones et al, 2010
4 One hypothesis: release of methane hydrates due to enhanced warming: …and “data”:some evidence from ocean-only modelling.Nunes and Norris, 2006Bice and Marotzke, 2004
5 So, what did we do? – Fully coupled HadCM3(L). (1) PalaeogeographyTopographyVegetation
6 (2) CO2 1680ppmv = 6* 1120ppmv = 4* 560ppmv = 2* Zachos et al, Nature, 2008
7 Runs at 1,2,4,6 * pre-industrial CO2. ~3500 years Global mean temperature vs CO2 forcing
12 Conclusions (1)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.
14 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.”
15 6 Additional simulations with orbital pertubations, 1000years in length: Maximum seasonality: obliquity=0.43 rad, eccentricity=0.054Minimum seasonality: obliquity=0.38 rad, eccentricity=0
16 Mixed layer depth, JJAMinimum seasonalityMaximum SH seasonality1km Temperature difference,Minimum seasonality minus Maximum SH seasonality
17 Time-dependent sediment hydrate model of Davie and Buffett (2001). Simulates hydrate evolution, given a bottom-water temperature forcing, plus other (poorly constrained) variables.Here: depth = 1500m, at ‘bullseye’ of orbitally-induced temperature anomalyResponse:Forcing:CH4 [kg/m2]Millions of years
18 Conceptual ‘threshold’ model for combined CO2 and orbital impacts on circulation, hydrate, and temperature,Informed by GCM and hydrate modelling
19 Conclusions (2)GCM responds in a similar way to orbital forcing as to CO2 forcing.Conceptual model, informed by GCM and hydrate model results, produces results qualitatively in agreement with data.Therefore, we propose a possible mechanism for orbital pacing of hyperthermals, via hydrate destabilisation
20 Warm Climates of the Past – a lesson for the future? October 2011The Royal Society, LondonSpeakers include:Jim Hansen, Bette Otto Bliesner, Jeff Kiehl, Paul Valdes
22 Comparison with data:Temperature ANOMALIES, PETM – ‘backgound’ Eocene
23 Eocene Model Intercomparison Project (‘EoMIP’) results Lunt et al, Geology, 2010Heinemann et al, Climate of the Past, 2009Winguth et al, Journal of Climate, 2010Huber et al, PPP, 2006Roberts et al, EPSL, 2009Panchuk et al, Geology, 2008
24 ppmvWhat are the reasons for the differences between models…? And the differences between models and data…?
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