Strontium/lithium ratio in aragonitic shells of Cerastoderma edule (Bivalvia) - A new potential temperature proxy for brackish environments

- Sr/Li of the common cockle (Bivalvia) serves as a novel temperature proxy.
- Sr/Li-based temperature proxy works in brackish settings.
- Up to 81% of shell Sr/Li variability explained by changes of temperature.
- Uncertainty of shell Sr/Li-based temperature estimates ca. ± 1.5 °C.

Quantitative reconstruction of water temperature from shells of bivalve mollusks is still a very challenging task. For example, in highly variable environments such as intertidal zones, shell oxygen isotope values can only provide reliable temperature estimates if the δ18Owater signature during the time of growth is known. Furthermore, trace element-to-calcium ratios such as Sr/Ca or Mg/Ca often do not serve as reliable paleothermometers, because their incorporation into bivalve shells is known to be strongly biologically controlled. Here, we present a potential novel temperature proxy which is based on the Sr/Lishell ratio of the intertidal bivalve Cerastoderma edule. Up to 81% of the variability in Sr/Lishell is mathematically explained by water temperature. It is suggested that vital effects on the incorporation of Sr and Li into the aragonitic shells are largely eliminated by normalizing Sr/Ca to Li/Ca. Growth rate does not control the incorporation of Sr or Li into the shell of C. edule. By using this new proxy, it was possible to estimate water temperature from C. edule with an uncertainty of ± 1.5 °C. Future studies are required to test if Sr/Lishell also serves as a reliable temperature proxy in other bivalve species and in other environments.