The combined influence of temperature and the isotopic composition of the seawater (δ18Ow) often precludes the use of oxygen isotope (δ18O) records, derived from marine carbonates, to reconstruct absolute seawater temperatures, without the application of an independent δ18Ow proxy. Here we investigate the application of carbon isotope records (δ13Cshell), derived from the long-lived marine bivalve Glycymeris glycymeris, as a proxy for δ18Ow variability. Our analyses indicate G. glycymeris δ13Cshell data derived from growth increments >20 years of age contain strong ontogenetic trends (−0.013‰ yr−1, R = 0.98, P < 0.001, N = 51). These analyses demonstrate that, coupled with the ontogenetic trends, 54% of the variability in G. glycymeris δ13Cshell records can be explained by a combination of the marine Suess effect and physical (salinity and riverine input) and biological processes (primary production). The application of these δ13Cshell data in conjunction with co-registered δ18Oshell and growth increment width series, each of which have been shown to be sensitive to seawater temperature and primary productivity respectively, can therefore provide new insights into past environmental variability and help constrain uncertainties on reconstructions of past seawater temperature variability
