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Long-term and millennial-scale climate variability in northwestern France during the last 8850 years

UMR-CNRS EPOC 5805, Bordeaux 1 University, France, f.naughton{at}epoc.u-bordeaux1.fr, Departamento de Geologia, Lisbon University, Portugal

Jean-François Bourillet

IFREMER, Département Géosciences Marines, Laboratoire Environnements Sédimentaires, Plouzané, France

Maria Fernanda Sánchez Goñi

EPHE, UMR-CNRS EPOC 5805, Bordeaux 1 University, France

Jean-Louis Turon

UMR-CNRS EPOC 5805, Bordeaux 1 University, France

Jean-Marie Jouanneau

UMR-CNRS EPOC 5805, Bordeaux 1 University, France

Vegetation and quantitative climate reconstructions from a northwestern France shelf core (VK03-58Bis) show orbital and suborbital climate variability for the last 8850 years in this region. A long-term cooling trend in summer temperatures, marked by gradual temperate and humid forest decline, parallels cooling in Greenland and the decrease of mid-latitude summer insolation reduction until at least 2000 cal. yr BP. At the long-term scale, the lowering in seasonal contrast revealed by vegetation changes follows the increase of precession. Corylus woodlands spread at the expense of deciduous Quercus forest, between 8740 and 8390 cal. yr BP, linked with the high seasonality conditions that, counterbalancing the long-term astronomical forcing trend, were amplified by the north Atlantic high-latitudes winter sea-ice expansion. High seasonality conditions resulted from the Agassiz and Ojibway final outburst episodes and consequent gradual reduction of the Meridional Overturning Circulation (MOC). Between 8390—8060 cal. yr BP, a sudden Corylus woodland decline marks the 8.2 kyr cold event in northwestern France probably triggered by the severe MOC reduction leading to the additional drop in winter temperature over Europe and Greenland. Nonetheless, seasonality remains high during this interval. The high seasonality conditions detected in `VK03-58Bis' between 8740 and 8060 cal. yr BP reflects the multicentennial-scale climate cooling 8.6—8.0 kyr episode of the North Atlantic. Following the Agassiz and Ojibway final outburst episodes, climate became more stable. However, millennial-scale climate cooling episodes are recorded in `VK03-Bis' and are characterized by weak winter cooling and increases in precipitation. Furthermore, dinocyst analysis and benthic gastropod Turritella communis occurrences indicate regional changes such as the southward migration of the Boreal biogeographical zone between 8740 and 8480 cal. yr BP and the subsequent opening of the English Channel at around 8480—8390 cal. yr BP.

Key Words: Holocene • long-term cooling • millennial-scale climate variability • 8.2 kyr event • Corylus • marine core • vegetation • Europe • France • Bay of Biscay.

The Holocene, Vol. 17, No. 7, 939-953 (2007)
DOI: 10.1177/0959683607082410


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