STAR-EX (EN)

Project lead: Sophie Sepulcre

Contributors: Laëtitia LICARI (CEREGE, Aix-Marseille Université), Franck BASSINOT (LSCE), Meryem MOJTAHID (Université d’Angers), Frédéric HAURINE (GEOPS), Rosella PINNA (GEOPS), Arnaud BUCH (Centrale Supelec)

Funding: INSU-LEFE-CYBER

Reconstructing past changes in the carbon cycle (CC) is crucial not only for understanding natural climate variability but also for projecting the future of anthropogenic carbon. Observations across all current ocean basins already highlight a change in the ocean carbon cycle (OCC) unequivocally attributable to human activities, with quantifiable consequences for ecosystems (and in particular, calcifying organisms). Therefore, better constraining past changes in the carbon cycle, and notably the fluxes between the ocean and the atmosphere, can help to better anticipate future changes. Variations in atmospheric CO₂ are directly measurable in ice cores, and past changes in OCC are accessible through paleoceanographic tracers such as B/Ca, U/Ca or Sr/Ca (element ratios). Nevertheless, i) contradictory results have been obtained across different studies, often involving several possible environmental factors to explain the observed variations, ii) technical difficulties may be encountered in their analysis (particularly for B/Ca), and iii) diagenesis can alter the original signal. It is therefore necessary to continue efforts to optimise these tracers. This project aims to focus specifically on the Sr/Ca ratio measured in benthic foraminifera. Indeed, this tracer offers several advantages, such as: i) a wealth of data available in the literature, enabling the creation of a robust initial database covering numerous environments; ii) well-established measurement methods, allowing for the preparation and analysis of samples without difficulty; and iii) a moderate impact of diagenesis. Previous studies suggest a relationship between the Sr/Ca ratio and variations in CO₂ concentration, but it is necessary to re-examine existing data to standardise interpretations. This three-year project will assess the potential of Sr/Ca measured in benthic foraminifera as a tracer of changes in CO₂ concentration. It will rely on the creation of a robust database of published Sr/Ca results and associated environmental parameters. The strategy will focus in particular on: 1/ areas under-represented in terms of data and depth, and 2/ species of interest in paleoceanography. This project also includes an analytical development component through the comparison of analyses conducted on several mass spectrometers: comparisons of data from the literature often suffer from issues relating to differences in analytical procedures, preventing a clear interpretation when comparing data. Sr/Ca measurements will be carried out at the LSCE, GEOPS and LGPM to verify the reproducibility of the instrumental approaches. As the analytical method allows for the simultaneous measurement of several elements, the Sr/Ca data will be compared with the B/Ca and U/Ca ratios, thereby strengthening the interpretation of these tracers and enabling the deconvolution of the various possible sources of influence.