Effect of the Ordovician paleogeography on the (in)stability of the climate
The Ordovician Period (485–443 Ma) is characterized by abundant evidence for continental-sized ice sheets. Modeling studies published so far require a sharp CO<sub>2</sub> drawdown to initiate this glaciation. They mostly used non-dynamic slab mixed-layer ocean models. Here, we us...
| Main Authors: | , , , , |
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| Format: | Article |
| Language: | English |
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Copernicus Publications
2014-11-01
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| Series: | Climate of the Past |
| Online Access: | http://www.clim-past.net/10/2053/2014/cp-10-2053-2014.pdf |
| _version_ | 1828420238511702016 |
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| author | A. Pohl Y. Donnadieu G. Le Hir J.-F. Buoncristiani E. Vennin |
| author_facet | A. Pohl Y. Donnadieu G. Le Hir J.-F. Buoncristiani E. Vennin |
| author_sort | A. Pohl |
| collection | DOAJ |
| description | The Ordovician Period (485–443 Ma) is characterized by abundant evidence for continental-sized
ice sheets. Modeling studies published so far require a sharp
CO<sub>2</sub> 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
CO<sub>2</sub> and paleogeography. We conduct experiments for a wide
range of CO<sub>2</sub> (from 16 to 2 times the preindustrial
atmospheric CO<sub>2</sub> 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-CO<sub>2</sub> relationship is highly non-linear when ocean
dynamics are taken into account. Two climatic modes are simulated as
radiative forcing decreases. For high CO<sub>2</sub> 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 CO<sub>2</sub> 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 CO<sub>2</sub> 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 CO<sub>2</sub> drawdown. |
| first_indexed | 2024-12-10T15:08:31Z |
| format | Article |
| id | doaj.art-2b0112eaa8444af79c00d2ab05a5e69c |
| institution | Directory Open Access Journal |
| issn | 1814-9324 1814-9332 |
| language | English |
| last_indexed | 2024-12-10T15:08:31Z |
| publishDate | 2014-11-01 |
| publisher | Copernicus Publications |
| record_format | Article |
| series | Climate of the Past |
| spelling | doaj.art-2b0112eaa8444af79c00d2ab05a5e69c2022-12-22T01:43:59ZengCopernicus PublicationsClimate of the Past1814-93241814-93322014-11-011062053206610.5194/cp-10-2053-2014Effect of the Ordovician paleogeography on the (in)stability of the climateA. Pohl0Y. Donnadieu1G. Le Hir2J.-F. Buoncristiani3E. Vennin4LSCE – Laboratoire des Sciences du Climat et de l'Environnement, UMR8212 – CNRS-CEA-UVSQ, CEA Saclay, Orme des Merisiers, 91191 Gif-sur-Yvette Cedex, FranceLSCE – Laboratoire des Sciences du Climat et de l'Environnement, UMR8212 – CNRS-CEA-UVSQ, CEA Saclay, Orme des Merisiers, 91191 Gif-sur-Yvette Cedex, FranceIPGP – Institut de Physique du Globe de Paris, Université Paris7-Denis Diderot, 1 rue Jussieu, 75005 Paris, FranceLaboratoire Biogéosciences, UMR/CNRS 6282, Université de Bourgogne, 6 Bd Gabriel, 21000 Dijon, FranceLaboratoire Biogéosciences, UMR/CNRS 6282, Université de Bourgogne, 6 Bd Gabriel, 21000 Dijon, FranceThe Ordovician Period (485–443 Ma) is characterized by abundant evidence for continental-sized ice sheets. Modeling studies published so far require a sharp CO<sub>2</sub> 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 CO<sub>2</sub> and paleogeography. We conduct experiments for a wide range of CO<sub>2</sub> (from 16 to 2 times the preindustrial atmospheric CO<sub>2</sub> 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-CO<sub>2</sub> relationship is highly non-linear when ocean dynamics are taken into account. Two climatic modes are simulated as radiative forcing decreases. For high CO<sub>2</sub> 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 CO<sub>2</sub> 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 CO<sub>2</sub> 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 CO<sub>2</sub> drawdown.http://www.clim-past.net/10/2053/2014/cp-10-2053-2014.pdf |
| spellingShingle | A. Pohl Y. Donnadieu G. Le Hir J.-F. Buoncristiani E. Vennin Effect of the Ordovician paleogeography on the (in)stability of the climate Climate of the Past |
| title | Effect of the Ordovician paleogeography on the (in)stability of the climate |
| title_full | Effect of the Ordovician paleogeography on the (in)stability of the climate |
| title_fullStr | Effect of the Ordovician paleogeography on the (in)stability of the climate |
| title_full_unstemmed | Effect of the Ordovician paleogeography on the (in)stability of the climate |
| title_short | Effect of the Ordovician paleogeography on the (in)stability of the climate |
| title_sort | effect of the ordovician paleogeography on the in stability of the climate |
| url | http://www.clim-past.net/10/2053/2014/cp-10-2053-2014.pdf |
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