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Accueil > Recherche > Thèses / HDR > Thèses soutenues > 2016

RUAN Jiaoyang

Characterization of Holocene climate variability in Western Europe with stalagmites.

  • Directeurs : Jean-Luc MICHELOT (IDES) & Dominique GENTY (LSCE).
  • Financement : CSC (Chinese Scholarship Council Chine)

The thesis aims to develop well-dated high resolution Holocene climate records in W-Europe and N-Africa by studying stalagmites from France, Belgium, Slovenia and Algeria. As a part of the work, here we present a 14ka record of climate and environment variability in SW-France based on δ18O, δ13C and Mg/Ca ratio analyses of a stalagmite (Vil30) from Villars Cave. The chronology is well constrained by 27 U/Th dates. Replication tests on overlapping stalagmites show significant correlations between contemporary profiles, which demonstrate that Vil30 records are preserving a high climatic signal to site-specific noiseratio. Based on our understanding from long term cave monitoring studyat Villars Mg/Ca, ice volumeadjusted δ18O, and δ13C is primarily interpretedas a proxy of meteoric precipitation, air temperature,and soil respiration rate, respectively.
In general it was drier and colder in the Late-Glacial than the Holocene. A trend of wetting prevailed throughout the Late-Bølling and the Allørod, preceding a drying trend in the Younger Dryas. There wasa regionally coherent climate amelioration throughout the B-Ain the Atlantic facing mid-latitude Europe, Apline, and circum-Mediterranean regions, while in the YD, climates in the regions showed different reponses. During the Holocene, relatively warm and dry conditions prevailed in the earlier half (>6.9ka) while coolerand wetter conditons prevailed after wards. At centennial-scales, wet periods were indentified at round 13.7, 12.6, 9.5, 8.2, 7.4, 6.4, 5.6, 4.8, 1.3ka and the Little Ice Age, comparable with other records derived from glacial, lake sand stalagmites in mid-latitude Europe, which are likely controlled by combination of solar activity, insulation & pro-glacial lake outburst. Particularly during the 8.2ka event (8.0 -8.2ka) it was humid (Mg/Ca decreases by 20%) but probably not cold (growth increases) in SW-France. Abrupt δ18Odepletion during onset of the event can be regarded asa marker of Agassiz outburst at 8200a ±75a. Lastly a fire-associated deforestation event occurredat round 1.0 ka under a drying background since 1.3ka.

Mots clefs : paléoclimats, stalagmite, Holocène, Younger Dryas, événement 8.2ka