Proposition de Postdoc – LSCE/Chrono-Environnement

Un postdoc de 18 mois est proposé à partir du 1er septembre 2012 au Laboratoire des Sciences du Climat (LSCE, Gif-sur-Yvette) et au Laboratoire Chrono-Environnement (Besançon) sur le sujet suivant : « Isotopic composition of oxygen in chironomid chitin: analytical protocol setup and application to Annecy lake (France) and Igaliku lake (Greenland) ».

Contact : Valérie Daux

Descriptif en anglais


Laboratoire des Sciences du Climat et de l’Environnement, L’Orme des Merisiers,
91191 Gif-sur-Yvette, France (≈ 2/3 of the time), and Laboratoire Chrono-environnement – La Bouloie – UFR Sciences et Techniques, 16 route de Gray, 25030 Besançon cedex – France (≈ 1/3 of the time)

Description of the project
The post-doc is part of the multi-disciplinary ANR-Green Greenland project which aims at documenting past Greenland climate variability, investigating the large scale drivers of past and future Greenland climate changes and assessing the impacts of Greenland climate variability on vegetation, glaciers and human activities, with a focus on South Greenland.
In order to complement information provided by ice core from central greenland, a key challenge lies in the reconstruction of coastal temperatures. In these areas, lake sediments offer the potential for high resolution paleoenvironmental and paleoclimatic records (Massa et al., in press). In suitable lakes, the water d18O is controlled by the d18O of precipitation, which is itself strongly controlled by fluctuations in the mean annual temperature (MAT) at these high latitudes. Methods have been developed to reconstruct past lake water d18O using ostracod calcite d18O (e.g. Von Grafenstein 1999, 2000). However, in most arctic lakes, waters are too acidic for calcite preservation. Chironomid larvae have a worldwide distribution and their subfossil remains (chitineous head capsules) preserve in lake sediments. Recent studies have revealed the potential of stable isotopes (dD and d18O) from chironomid chitin to reconstruct past lake water d18O (e.g. Wang et al., 2008; 2009).
This postdoctoral fellowship will therefore be built on a two-pronged approach: analytical development and  the assessment of the relevance of d18O from chironomid chitin as a proxy for lake water d18O in an a  well-studied context (Lake Annecy), (ii) application of this method to a sediment record from South-west Greenland (Lake Igaliku, Massa et al., in press). The benchmarking site of Annecy Lake (SE France) was chosen because 1) the chironomid distribution in its surface sediments is well known (Frossard et al.,  2011), 2) past variations of the d18O of Annecy lake water were reconstructed from the d18O of ostracode calcite and shown to be related to MAT (Danis et al.,  2003). We therefore have the guarantee to get enough well characterized chironomid material in Annecy sediments and we have at our disposal a reference curve of water d18O variation. We propose therefore to analyse the d18O of chironomid chitin along some portions of a core from Annecy lake already sampled and analysed for ostracode d18O and to compare the results obtained by both methods.
After this validation step, the method will be applied to the sediment record of lake Igaliku. A sediment core covering the last 1400 years was retrieved in 2011 from the deepest part of the lake basin. A robust chronology was built from a combination of radiocarbon dates and radionuclides (137Cs and 210Pb). Multiproxy analyses including sedimentology, diatoms and chironomid community have been carried out at high resolution (i.e. chironomids were studied in 104 samples covering the last 1400 years). A summer temperature reconstruction has been inferred from chironomid communities (Millet et al., in prep). The Igaliku chironomid record provides then a unique opportunity to compare community-inferred versus d18O derived climate reconstructions.

The successful candidate will have to set up the analytical protocol using existing EA-IRMS facilities (LSCE). He/she will identify and collect chironomid head capsules (Besançon) and perform the chironomid chitin extraction and analyses from the lakes sediments.

Institution/Lab description
The candidate will work mainly with Valérie Daux (isotope geochemistry, LSCE), and Laurent Millet (chironomid, Chrono-Environnement Lab.). He will interact with the ANR-Green Greenland team (Valérie Masson-Delmotte, PI, Vincent Bichet (sedimentology),Emilie Gauthier, PI of the lake part of the project, Uli von Grafenstein, lake ostracod).

Educational Background
Applicants should have a PhD degree in Geology-Geochemistry and have a background in isotope  geochemistry. Experience with mass spectrometer is mandatory. Experience in chitin analysis would be highly appreciated.

Application must be sent to Valérie Daux. It should include a clear statement of your interest and background for this position, Curriculum Vitae and the contact details of two academic referees in electronic form.

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