Quantitative analyse of trace elements with HR-ICP-MS Element2 : an example of application in calcite shell of the Great Scallop Pecten Maximus.

Carbonate minerals are abundant on the Earth's surface, and they are produced by a number of processes, including precipitation from hydrothermal fluids or synthesis by organisms like coral, foraminifera, molluscs, or bacteria. Consequently, they are found in a large variety of environments. Their isotopic compositions (Sr, C, or O ) and trace element concentrations are widely used to understand or reconstruct biological, geological or biogeochimical processes. A large scientific community define the elemental composition of bivalve shells a promising tool as a recorder of environmental parameters like sea surface temperature, salinity and primary productivity. But we have compile evidences that trace elements variation within shells can be species dependant or change in a complex network of environmental interactions. In this context, a better understanding of the incorporation of elements from seawater into biogenic carbonate is necessary to generalize the use of these proxies. Daily shell growth in the calcitic bivalve Pecten maximus has been extensively measured and these daily growth marks can be used to date each subsequent sample of calcium carbonate. In this study, micro- sampling of carbonate powder along the shell was carried out with a high-resolution inductively coupled plasma-mass spectrometry (HR-ICP-MS, Finnigan Element2). This method led to a quantitative detection of trace element in biocaronates and to the accurate reconstruction of ontogenetic profiles of elemental ratios with a 3-day temporal resolution. Repeated analyses of different growth layers sections on the same valve showed that the trace elements are homogeneously distributed along the shell. Mo concentration was reproducible for several scallop individuals from a same location over different years and from different coastal temperate environments. Each profile was characterised by a background level punctuated by sharp episodic peaks occurring in spring (may). Some hypotheses will be discussed but the most probable is the ingestion of phytoplankton cells grown upon NO3- which have a large concentration of Mo associated to the activity of nitrate reductase.