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Emmanuel Guillerme


Engineer-geologist graduated from the ENSG Nancy
PhD from the University of Lyon 1 Claude Bernard
Qualified as a lecturer

"Emmanuel did his thesis between my laboratory, Institut Lumière Matière, and the Laboratory of Geology in Lyon where he was co-supervised by Véronique Gardien. His first paper as first author was accepted in Geostandards and Geoanalytical Research..."




THESIS

Turning Halite Fluid Inclusions into Accurate Paleothermometers with Brillouin Spectroscopy : Development of a New Method and Application to the Last Interglacial in the Dead Sea.

Abstract

Determining past continental temperatures is a key aspect of paleoclimate reconstructions, as continents are more sensitive than oceans to climate variations.Modest global changes may cause a rearrangement of the atmospheric circulation and may thus induce large changes in the distribution of heat and moisture over lands. Therefore, in the perspective of understanding continental climate, it is necessary to investigate a large number of climate archives displaying a dense spatial distribution. Unfortunately, contrary to the oceanic and polar realms, most land masses are lacking such archives. Continuous deposits are rare, and the tools used by paleoclimatologists to decipher the mall have their own biases, which are usually circumvented by means of a multi-proxy approach. Such an approach requires the availability of several proxies. However, a mere glance at the location map of temperature datasets used for the famous Holocene global temperatures tack of Marcott et al. (2013) reminds us that proxies applicable to the continental realm are sorely lacking. Arid environments in particular, where the scarcity of water prevents potential organic archives from thriving and depositing, present as it were, no Rosetta stone to decipher their past temperature fluctuations.With this in mind, halite fluid inclusions (FIs) revealed very promising when Roberts andSpencer (1995), using the microthermometry technique, first showed their potential to hold past saline lakes temperature. Indeed, these micro-droplets of parent brine trapped inside cavities of the salt crystals happen to keep their initial density, and therefore the entrapment temperature, like the density of mercury indicating the temperature in the thermometer. However, Lowenstein et al. (1998) soon showed that FIs undergo damages during the requisite step of vapor phase nucleation in the freezer. Since then, paleoclimate studies using halite FIs have been few. During this thesis, we have developed a new methodology, based on Brillouin spectroscopy (BS), to bypass the limitations of microthermometry. This technique utilizes the inelastic interaction between light and spontaneous (thermal) density fluctuations in the fluid to measure its speed of sound, hence allowing for the determination of its density, ergo entrapment temperature. This non-destructive approach avoids submitting samples to large temperature gaps, as it does not require the presence of a bubble in the FI as a prerequisite. A sour method keeps FIs intact, we have restored their potential as an accurate paleothermometer. We show that BS on halite FIs reveals the entrapment temperature with an accuracy better than ±1 ◦C.
 
Using Brillouin spectroscopy as a mechanical sensor, we were able to measure the empirical temperature beyond which FIs deteriorate, allowing us to propose a quantified size-dependent safety limit to avoid measuring wrong temperatures. To make the calculation of the safety limit possible for a wide range of FI compositions, we have developed a model that applies to the Na-K-Mg-Ca-H2O system. The model, based on the Pitzer formalism and the Young mixing rule, calculates the density of multi-electrolyte brines as a function of temperature, pressure and salinity. Through predicting the elastic mechanical response of the host crystal to the FI density changes, the model then back calculates the FI internal pressure. Knowing the pressure inside FIs then enables us to predict the temperature at which they get damaged. In the future, extending the model to SO4 and (H)CO3 will allow the determination of pressure for all major types of FI compositions.

To illustrate the power of Brillouin thermometry, we sampled several tens of halite intervals from the 450-meters-long core 5017-1 drilled in 2010-2011 in the deepest part of the Dead Sea in Palestine within the framework of the Dead Sea Deep Drilling Project (DSDDP, a project of the International Continental Scientific Drilling Program). The application of Brillouin thermometry to this record provides a unique quantification of temperature changes in this region during the Last Interglacial (LIG,~135,000 to 115,000 years ago). Furthermore, we show that Brillouin spectroscopy allows, at the same time, the quantification of the Dead Sea level and its evolution. Using the reconstructed lake level curve to quantify paleorainfall, we thus propose a complete temperature-precipitation reconstruction that enable us to outline a radically new narrative for the climate of the region during this period. We show that the LIG winter temperatures were mostly lower than today, and precipitation were much higher, albeit on a drying trend. Contrary to previous estimations, the region never experienced extremed rought during the LIG, and only reached conditions as dry as today towards the end of the period. The clear connections with the Mediterranean and the Atlantic exhibited by the record, along with the clear climatic trends observed, lead us to suggest a strong orbital forcing of the atmospheric circulation over this part of the globe. The example of the Dead Sea shows that Brillouin spectroscopy on halite FIs is in position to provide valuable data to test the efficiency of climate models.

Key words

Halite, fluid inclusions, paleothermometer, Brillouin spectroscopy, Dead Sea, Last Interglacial.

H2O'Lyon thesis Director

Frédéric Caupin, Université Lyon 1 Claude Bernard

Thesis Co-Director

Véronique Gardien, Université Lyon1 Claude Bernard

Doctoral School

ED Phast

Laboratory

LGL-TPE (UMR 5276) et ILM (UMR 5306)

Defence date

December 6, 2019

Defence language

English

Thesis Jury Members

David Hodell, University of Cambridge
Tim Lowenstein, Binghamton University
Mouna El Mekki Azouzi, Université de Bizerte
Ina Neugebauer, GFZ Potsdam
Christophe Lécuyer, Université Lyon 1 Claude Bernard
Véronique Gardien, Université Lyon 1 Claude Bernard
Frédéric Caupin, Université Lyon 1 Claude Bernard