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PhD Defense

Marion Peral (LSCE)

Title : Calibration of the clumped-isotope thermometer in foraminifera and its application to paleoclimatic reconstructions of the mid-Pleistocene in the Gulf of Taranto

Date and time : The 19-10-2018 at 14h00

Type : thèse

Université qui délivre le diplôme : UVSQ

Location : LSCE vallée, à la bibliothèque au bâtiment 12
Members of jury :

Cedric John, Rapporteur

Nele Meckler, Rapporteur

Thibault De Garidel-Thoron, Examinateur

Bruno Malaizé, Examinateur

Giuseppe Siani, Examinateur

Dominique Blamart, Directeur de thèse

Franck Bassinot, Co-Directeur de thèse

Mathieu Daëron, Co-Encadrant de thèse

Summary :

The quantification of past oceanic temperature changes is a critical requirement for understanding the mechanisms which regulate climate variations. Classical methods of paleothermometry could suffer from well-known limitations related to ecology and/or to physico-chemical biases (sea water salinity, acidity…). This work focuses on clumped-isotope carbonate thermometry (∆47). It aims to establish a calibration of ∆47 foraminifera and use it to study past climatic variations through the Mid-Pleistocene Transition (MPT). Our ∆47 calibration in planktonic and benthic foraminifera collected from modern marine sediment covers a temperature range of -2 to 25 °C. The clumped-isotope compositions of 9 species of foraminifera show a robust correlation with the calcification temperature, estimated from the measurements of oxygen-18. These results confirm the absence of bias linked to foraminifer ecology (species-specific and foraminifer size effects) and provide evidence that salinity does not affect the ∆47 thermometer.  This study constitutes significant methodological progress for future paleoceanographic applications in foraminifera. The MPT is a climatic transition characterized by a shift in the frequencies of glacial-interglacial cycles (from 41 000 to 100 000 years). Understanding the MPT is a major scientific objective, which underlies our effort to study the establishment of our present climate. Our ∆47 calibration was used to quantify temperature changes through the MPT in the Mediterranea Sea (Montalbano Jonico section, south of Italy), and in particular the marine isotopic stages 31 and 19, which may be described as Holocene analogues. We find that (1) ∆47 temperatures are in good agreement with temperatures reconstructed from other paleothermometers, (2) these results allow reconstructing changes in past oceanographic and hydrologic regime, and (3) ∆47 measurement are a promising component of multi-proxy paleoceanographic studies.

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