Oxygen isotope disequilibrium in the juvenile portion of oyster shells biases seawater temperature reconstructions

• Published in: Estuarine, coastal and shelf science Vol. 240; p. 106777
• Main Authors: Huyghe, Damien, Emmanuel, Laurent, de Rafelis, Marc, Renard, Maurice, Ropert, Michel, Labourdette, Nathalie, Lartaud, Franck
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 05.08.2020; Elsevier
• Subjects: Earth Sciences; Kinetic isotope effect; Paleoclimatology; Sciences of the Universe; Sclerochronology; Sclerogeochemistry; Stable isotopes; Sclerochronology; Kinetic isotope effect; Paleoclimatology; Sclerogeochemistry; Stable isotopes
• ISSN: 0272-7714; 1096-0015
• DOI: 10.1016/j.ecss.2020.106777

For decades, bivalve shells have constituted one of the most common supports for paleoclimatic archives based on stable isotope approaches. In this work, we conducted chemical marking and recapture techniques to study the fluctuation of δ18O values of oyster shells of the species Magallana gigas reared in natural environment in Normandy (France) for two years. The results were compared to the continuous monitoring of temperature and salinity and monthly records of seawater δ18O. Isotopic measurements were performed on the hinge area that regroups the whole life of the oysters. Here we demonstrate that oysters mineralized their shells with no significant growth breaks during the two-years experiment, even at temperatures below 6 °C. The results confirm that adult oysters (i.e. > 1 yr) mineralized their shells at equilibrium. However, juvenile specimens exhibit a strong isotopic disequilibrium, with a maximum shift of the δ18O values of 3‰ in winter, likely due to kinetic isotope effects. This corresponds to a reconstructed temperature up to 13 °C warmer than expected. This work indicates that although these oyster shells can be used as an accurate archive of (paleo)environmental conditions, the shell portion mineralized during the juvenile stage (i.e. < 1 yr) should be avoided for paleotemperature reconstructions. Given the wide use of bivalve shells as environmental archives, similar studies on others species are required. •We analyze the δ18O composition of oyster shells of Normandy (France).•An isotopic disequilibrium is identified during the juvenile portion of the shell.•Isotopic disequilibrium is related to kinetic effect due to fast growth rate.•Adult oysters mineralize their shells in equilibrium.•Juvenile portion of the shell should be avoided for paleoclimatic reconstructions.