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| Titel |
Is there an orbital control on Eocene hyperthermals? |
| VerfasserIn |
Daniel Lunt, Paul Valdes, Andy Ridgwell |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250040802
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| Zusammenfassung |
| Here, we use the UK Met Office coupled atmsphere-ocean GCM, HadCM3(L), to elucidate
the potential mechanisms behind an astronomical pacing of Early Eocene hyperthermal
events.
We carry out extremely long (>3000 years) spinup simulations of the model under
Eocene palaeogeographies and various CO2 simulations. These indicate a threshold in
greenhouse gas forcing which controls the mode of ocean circulation. Above  4*
pre-industrial prescribed CO2 levels, the ocean circulation is characterised by weak
overturning, and deep water formation at relatively low Northern Hemisphere latitudes.
At levels below this threshold, the ocean circulation is vigorous - dominated by a
negatively overturning cell driven by deep water formation in Southern Hemisphere
high latitudes. The switch on ocean circulation is associated with non-linear large
warming in the tropical and sub-tropical Atlantic. This non-linearity is suggested as a
potential mechanisms for hyperthermal events: crossing the threshold could lead to
large warming of hydrate-rich sediments and additional warming due to released
methane.
We then perturb these simulations with idealised extremes in orbital forcing - either
high-eccentricity-high-obliquity or low-eccentriciity-low-obliquity, and again run them
towards equilibrium. We assess whether the resulting changes in ocean circulation and
temperature are sufficient to support the hypothesis that Early Eocene hyperthermals such as
the PETM and ELMO were orbitally paced, as has been inferred from the geological record. |
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