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| Titel |
Effect of the Ordovician paleogeography on the (in)stability of the climate |
| VerfasserIn |
A. Pohl, Y. Donnadieu, G. Le Hir, J.-F. Buoncristiani, E. Vennin |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1814-9324
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| Digitales Dokument |
URL |
| Erschienen |
In: Climate of the Past ; 10, no. 6 ; Nr. 10, no. 6 (2014-11-26), S.2053-2066 |
| Datensatznummer |
250117078
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| Publikation (Nr.) |
 copernicus.org/cp-10-2053-2014.pdf |
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| Zusammenfassung |
| The Ordovician Period (485–443 Ma) is characterized by abundant evidence for continental-sized
ice sheets. Modeling studies published so far require a sharp
CO2 drawdown to initiate this glaciation. They mostly used
non-dynamic slab mixed-layer ocean models. Here, we use a general
circulation model with coupled components for ocean, atmosphere, and
sea ice to examine the response of Ordovician climate to changes in
CO2 and paleogeography. We conduct experiments for a wide
range of CO2 (from 16 to 2 times the preindustrial
atmospheric CO2 level (PAL)) and for two continental
configurations (at 470 and at 450 Ma) mimicking
the Middle and the Late Ordovician conditions. We find that the
temperature-CO2 relationship is highly non-linear when ocean
dynamics are taken into account. Two climatic modes are simulated as
radiative forcing decreases. For high CO2 concentrations
(≥ 12 PAL at 470 Ma and ≥ 8 PAL at 450 Ma),
a relative hot climate with no sea ice characterizes the warm
mode. When CO2 is decreased to 8 PAL and 6 PAL at 470 and
450 Ma, a tipping point is crossed and climate abruptly
enters a runaway icehouse leading to a cold mode marked by the
extension of the sea ice cover down to the mid-latitudes. At
450 Ma, the transition from the warm to the cold mode is
reached for a decrease in atmospheric CO2 from 8 to 6 PAL
and induces a ~9 °C global cooling. We show that the
tipping point is due to the existence of a 95% oceanic Northern
Hemisphere, which in turn induces a minimum in oceanic heat
transport located around 40° N. The latter allows sea ice to
stabilize at these latitudes, explaining the
potential existence of the warm and of the cold climatic modes. This
major climatic instability potentially brings a new explanation to
the sudden Late Ordovician Hirnantian glacial pulse that does not
require any large CO2 drawdown. |
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