Reconstruction of annual and seasonal variations in water temperature in the Haute-Dronne River of southwest France based on δ18O records of freshwater pearl mussel shells (M. margaritifera), and its palaeoenvironmental implications

The aragonitic shells of freshwater pearl mussels (Margaritifera margaritifera) contain annual growth increments, whose composition reflect the geochemistry of the river water and bivalve metabolism. The wide geographic distribution and the long lifespan of M. margaritifera coupled with a previously established relationship between the δ¹⁸O values of their shells and river temperature means this taxon is a potentially important environmental archive; such freshwater proxies are currently limited in both space and time. In this paper, we investigate the relationship between δ¹⁸O values and both in situ and modeled river temperature (2007–2015) for a population of M. margaritifera living in the Haute-Dronne River (southwest France). Our δ¹⁸O data permit the reconstruction of seasonal temperature variations in the river. Sclerochronology reveals that shells also record seasonal patterns and produce winter growth increments, contrary to other investigations carried out on the same mussel species from northern Europe where low winter temperatures (below 5 °C) interrupt shell growth. The presented calibration for M. margaritifera and host river temperature offers the potential for reconstructing palaeoenvironmental conditions based on fossil specimens of the same species. Such reconstructions may improve our understanding of past continental climate and help calibrate regional palaeoclimate models.