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PhD Defense

Nicolas Duprey (LOCEAN)

Title : Variabilité climatique de deux périodes clés de l’Holocène, c. 7000-6000 et 3500-2500 années BP, dans le Pacifique Sud-Ouest à partir de l’analyse d’archives biocarbonatées

Date and time : The 25-10-2012 at 14h00

Type : thèse

Université qui délivre le diplôme : UPMC

Location : Institut Océanographique
Members of jury :

C.E. Lazareth : co-directrice
M. Elliot : Rapporteur
Y-M. Paulet : Rapporteur
T. Corrège : examinateur
A. Juillet-Leclerc : examinateur
A. Saliot : examinateur

Summary :

This study aims to document the climate for two key periods of the Holocene from biocarbonated archives.

The giant clamTridacna maximawas validated as a paleoclimatic archive. Fossil specimens of this species were used to document the climatic variability in the Southwest Pacific during the early mid- Holocene – 7.0-6.0 ka BP – and during the Lapita migration over Remote Oceania – 3.5-2.5 ka BP – in addition to δ18O records from fossils specimens of giant clamsT. gigas,Hippopus hippopusand fossils massive coralPorites sp.Records of Sr/Ca fromPorites sp.corals also provided paleo-SST records.

The post glacial SST rise was completed at 7.0-6.0 ka BP and the southeastern edge of the WPWP was located in its current location. At that time the seasonal influence of the SPCZ over the SW Pacific was weaker than it is today as a result of the more northerly location of this structure. The El Niño Southern Oscillation (ENSO) variability was 25-30% weaker than today.

The period when the Lapita culture at 3.6-3.4 ka BP, was characterized by a La Niña-like climatic mean state in the SW Pacific. The Lapita migration-phase at 3.2-2.7 ka BP is coincidental with a strong ENSO variability supporting that the climate had a significant role in the Lapita migration. Indeed, unstable climate may have triggered and/or promoted the development and the expansion of nomad foraging population based on marine resources as the Lapita were.

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