Environmental versus biological controls on multi-proxy records from bivalve shell carbonate

Field experiments on different bivalve species have been conducted in the Dutch Wadden Sea near the Netherlands Institute for Sea Research (NIOZ) to investigate the environmental and biological controls on the fractionation pattern of different stable isotope systems (¹⁸O/¹⁶O, ²⁶Mg/²⁴Mg, ⁴⁴Ca/⁴²Ca) and elemental/calcium ratios, and their reliability as geochemical proxies for high- resolution palaeoclimate reconstructions. Our study includes various individuals of the blue mussel, Mytilus edulis and juveniles of the ocean quahog, Arctica islandica. Our study is completed using samples from growth experiments on young Arcitca's which were also performed at the NIOZ laboratory. These individuals were cultured in five temperature controlled basins, ranging from 1 to 12° Celcius. The third sample set analysed was collected at several sites in the Baltic Sea characterised by salinities lower than 15 permil. Our data shows that both species deposit their shells in isotopic equilibrium with ambient seawater. Trace element ratios in Mytilus edulis further indicate that Mg/Ca may indeed provide a reliable palaeothermometer. In contrast, Calcium and magnesium isotope fractionation is obviously controlled by biological processes. However, environmental signals (e.g. temperature, salinity) are well recorded in the shells. Therefore, the combined approach could give new insights into biomineralization processes. This is a contribution to EuroCLIMATE project 04 ECLIM FP08 CASIOPEIA.