Biomineralisation—the process by which living organisms create minerals—comes in an incredible variety of shapes and patterns. However, the mechanisms behind mineral formation and the reasons driving it remain largely unconstrained.
Under environmental stress, organisms can undergo changes in their biomineralisation, with consequences on the chemical composition of the minerals. For instance, it has been suggested that an increase in the biomineralising rates of coccolithophores can lead these unicellular organisms to incorporate strontium into their shells when calcium availability becomes limited. These changes have important consequences on global biogeochemical cycles, but can also bias the paleoclimate reconstructions that rely on geochemical proxies.
Throughout my career, I have been involved in a number of studies exploring the processes of mineral formation in different key groups of marine organisms, and how these processes affect the chemical signature (or “vital effects”) of these minerals.
References
2022
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Parallel between the isotopic composition of coccolith calcite and carbon levels across Termination II: developing a new paleo-CO_\textrm2 probe
Camille Godbillot, Fabrice Minoletti, Franck Bassinot, and 1 more author
Climate of the Past, Mar 2022
Abstract. Beyond the pCO2 records provided by ice core measurements, the quantification of atmospheric CO2 concentrations and changes thereof relies on proxy data, the development of which represents a foremost challenge in paleoceanography. In the paleoceanographic toolbox, the coccolithophores occupy a notable place, as the magnitude of the carbon isotopic fractionation between ambient CO2 and a type of organic compounds that these photosynthetic microalgae synthesize (the alkenones) represents a relatively robust proxy to reconstruct past atmospheric CO2 concentrations during the Cenozoic. The isotopic composition of coeval calcite biominerals found in the sediments and also produced by the coccolithophores (the coccoliths) have been found to record an ambient CO2 signal through culture and sediment analyses. These studies have, however, not yet formalized a transfer function that quantitatively ties the isotopic composition of coccolith calcite to the concentrations of aqueous CO2 and, ultimately, to atmospheric CO2 levels. Here, we make use of a microseparation protocol to compare the isotopic response of two size-restricted coccolith assemblages from the North Atlantic to changes in surface ocean CO2 during Termination II (ca. 130–140 ka). Performing paired measurements of the isotopic composition (δ13C and δ18O) of relatively large and small coccoliths provides an isotopic offset that can be designated as a “differential vital effect”. We find that the evolution of this offset follows that of aqueous CO2 concentrations computed from the ice core CO2 curve and an independent temperature signal. We interpret this biogeochemical feature to be the result of converging carbon fixation strategies between large and small cells as the degree of carbon limitation for cellular growth decreases across the deglaciation. We are therefore able to outline a first-order trend between the coccolith differential vital effects and aqueous CO2 in the range of Quaternary CO2 concentrations. Although this study would benefit from further constraints on the other controls at play on coccolith geochemistry (growth rate, air–sea gas exchange, etc.), this test of the drivers of coccolith Δδ13C and Δδ18O in natural conditions is a new step in the development of a coccolith paleo-CO2 probe.
2021
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Provenance study of oyster shells by LA-ICP-MS
Vincent Mouchi, Camille Godbillot, Catherine Dupont, and 7 more authors
Journal of Archaeological Science, Aug 2021
2020
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Rare earth elements in oyster shells: Provenance discrimination and potential vital effects
Vincent Mouchi, Camille Godbillot, Vianney Forest, and 5 more authors
Biogeosciences, Aug 2020
Rare earth elements (REEs) and yttrium in seawater originate from atmospheric fallout, continental weathering, and transport from rivers, as well as hydrothermal activity. Previous studies have reported the use of REE and Y measurements in biogenic carbonates as a means to reconstruct these surface processes in ancient times. As coastal seawater REE and Y concentrations partially reflect those of nearby rivers, it may be possible to obtain a regional fingerprint of these concentrations from bivalve shells for seafood traceability and environmental monitoring studies. Here, we present a dataset of 297 measurements of REE and Y abundances by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) from two species (Crassostrea gigas and Ostrea edulis). We measured a total of 49 oyster specimens from six locations in France (Atlantic Ocean and Mediterranean Sea). Our study reports that there is no significant difference in concentrations from shell parts corresponding to winter and summer periods for both species. Moreover, interspecific vital effects are reported from specimens from both species and from the same locality. REE and Y profiles as well as t-distributed stochastic neighbour embedding processing (t-SNE; a discriminant statistical method) indicate that REE and Y measurements from C. gigas shells can be discriminated from one locality to another, but this is not the case for O. edulis, which presents very similar concentrations in all studied localities. Therefore, provenance studies using bivalve shells based on REEs and Y have to first be tested for the species. Other methods have to be investigated to be able to find the provenance of some species, such as O. edulis.