Attempt to reconstitute last interglacial stage sea surface temperatures from the study of Giant Clam of New Caledonia and derived issues

The study of climatic variability in tropics at some determined key-past period is needed to better understand the current climatic dynamic. One of those periods corresponds to the last interglacial; MIS 5e. West Pacific tropical region is a rich biocarbonate archive of past climate variability and a particularly interesting region since it lies under the influence of the Intertropical Convergence Zone and the Indo-Pacific Warm Pool from which ENSO phenomenon emerges. In this study, we analyzed the biocarbonate archive of a MIS 5e New Caledonian giant clam fossil, by spectrometry along growth axis, determining its variation in trace elements (Ba/Ca, Sr/Ca, U/Ca and Mg/Ca) and isotopes ratio (δ13C and δ18O). This should provide us with information on environmental and climatic conditions and allow us to reconstitute paleo-SST. However, the results were not as clear. Broadly, we observed that reconstituted temperatures in New Caledonia at MIS 5e were similar but a little colder than today. The warm pool may have been moved forward. Ba/Ca was not very conclusive as upwelling or rainfall indicator. We observed a sudden high i) increase of Sr/Ca, Mg/Ca, δ13C ii) decrease of U/Ca and a slight decrease of δ18O around the 12th year of growth, which corresponds to maturity setting. This change in isotopic and trace elements behavior added to the positive correlation found between δ13C and δ18O let one suggest the presence of a vital effect and more precisely and particularly a kinetic effect. Besides, there could also be a metabolic effect. This may be combined to diagenesis processes in other areas than those that we validated with MEB and X-ray analyses. The lack of clear cycles could also be due to the lack of resolution of our sampling device.

ISCED Categories

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0532 - Physical and chemical oceanography", "0511 - Biology