LIPID HYDROGEN ISOTOPE RATIOS FROM MUSSEL SHELLS AND SALINITY IN THE SCHELDT ESTUARY

Most studies in paleoclimatology have been interested in the temperature reconstruction, notably through the use of oxygen isotopes. The salinity is another major parameter to understand the oceanic circulation and the climate. The development of paleosalinity proxies is therefore a major goal in the current paleoclimatology research. The estuarine environment is probably the best choice to study salinity variations. We are looking for isotopic tracers which would make it possible to record these variations. This work focuses on the relationship between the deuterium isotopic composition of the bivalve shells (specific compounds) and the average salinity of the water in which these shells grow. We investigate whether the organic content of shells along the estuarine salinity gradient have a deuterium isotopic composition which reflects the mix between marine and continental water. We have more particularly studied Mytilus edulis specimens sampled at 4 stations located along the Scheldt estuary (The Netherlands). Since for this environment, the fluctuating environmental conditions (salinity, temperature) are well recorded instrumentally, the link between the external condition and the proxy signal in the shell can be easily studied and the possible variability understood. The originality of this study lies in the analysis of the deuterium from lipidic compounds which are very resistant to degradation. Consequently, the technique permits to analyze sediments and fossil shells. The cholesterol and the palmitic acid were the two mainly studied compounds in this work, with regards to their abundance in the shell. Besides, the use of specific compounds may increase the sensibility of the technique - in comparison with the bulk organic - as they come from one specific biosynthetic pathway.