Context:

Planktonic foraminifera have been used since the 1950s to reconstruct the stable isotope composition of the ocean (δ¹⁸O, δ¹³C, δ¹⁵N…) and to provide key information on paleoclimatic variations [1]. More recently, new isotopic systems have emerged to reconstruct past biogeochemical cycles, such as sulfur isotopes measured in Carbonate Associated Sulfate (CAS), incorporated as SO₄²⁻ in the foraminiferal lattice [2]. However, vital effects, i.e. biological influences on geochemical records related to symbiont activity, ontogeny or metabolic processes, are known to strongly affect these isotopic ratios [3, 4]. While these effects are well documented and relatively well constrained for classical stable isotope systems, they remain largely unexplored for sulfur isotopes [5].

Internship subject:

The aim of this internship will be to quantify and characterize vital effects on δ³⁴S in planktonic foraminifera, measured on carbonate-associated sulfate (CAS). The project will focus on samples from core-tops from the LSCE core shack and will target foraminifera species spanning different dwelling depths, several size fractions, and both symbiont-bearing and symbiont-barren species. The project will combine micropaleontology with high-precision geochemistry. Foraminifera will be identified and selected under a binocular microscope before being cleaned in a clean room following previously established protocols [6] (LSCE, Saint-Aubin). Ion chromatography and column chemistry will then be performed to quantify and purify sulfate prior to the measurement of sulfur isotopes by MC-ICP-MS (CRPG, Nancy).

How to Apply? Please send your CV and cover letter to:

• Yanou Crenne (yanou.crenne@mnhn.fr)
• Ana Alves (ana.alves@lsce.ipsl.fr)
• Annachiara Bartolini (annachiara.bartolini@mnhn.fr)
• Guillaume Paris (guillaume.paris@univ-lorraine.fr)

References:

[1] Schiebel, R., & Hemleben, C. (2017). Planktic foraminifers in the modern ocean. In Springer eBooks. https://doi.org/10.1007/978-3-662-50297-6

[2] Paris, G., Fehrenbacher, J. S., Sessions, A. L., Spero, H. J., & Adkins, J. F. (2014). Experimental determination of carbonate-associated sulfate δ34S in planktonic foraminifera shells. Geochemistry Geophysics Geosystems, 15(4), 1452–1461. https://doi.org/10.1002/2014gc005295

[3] Spero, H. J., & Deniro, M. J. (1987). The influence of symbiont photosynthesis on the Δ18O and Δ13C values of planktonic foraminiferal shell calcite. DalSpace (Dalhousie University). http://hdl.handle.net/10222/76974

[4] Duplessy, J., Bé, A., & Blanc, P. (1981). Oxygen and carbon isotopic composition and biogeographic distribution of planktonic foraminifera in the Indian Ocean. Palaeogeography Palaeoclimatology Palaeoecology, 33(1–3), 9–46. https://doi.org/10.1016/0031-0182(81)90031-6

[5] Rennie, V. C. F., Paris, G., Sessions, A. L., Abramovich, S., Turchyn, A. V., & Adkins, J. F. (2018). Cenozoic record of δ34S in foraminiferal calcite implies an early Eocene shift to deep-ocean sulfide burial. Nature Geoscience, 11(10), 761–765. https://doi.org/10.1038/s41561-018-0200-y

[6] Barker, S., Greaves, M., & Elderfield, H. (2003). A study of cleaning procedures used for foraminiferal Mg/Ca paleothermometry. Geochemistry Geophysics Geosystems, 4(9). https://doi.org/10.1029/2003gc000559