Isotopic fractionation between seawater and the shell of <i>Scrobicularia plana</i> (Bivalvia) and its application for age validation

This study analyzed the isotopic profiles of four aragonitic shells of Scrobicularia plana in conjunction with measured seawater temperatures and salinities. Comparison of delta O-18(SHELL) with expected values revealed fractionation of delta O-18 in near equilibrium with the ambient environment. Growth cessation occurred between November and March. Carbonate deposition stopped when temperatures were >12 degrees C. Analysis of delta C-13(SHELL) values suggested that carbon in the shell does not reflect the DIC in ambient water, likely due to the incorporation of metabolic carbon. An ontogenetic trend of increasing delta C-13 values over time was observed, likely related to changes in metabolic activity. Annual growth patterns were inferred from delta O-18(SHELL) profiles and compared with internal and external growth lines. Estimations of age based on external lines were unreliable, resulting in overestimation of age and underestimation of growth rates, likely due to the disturbance lines being wrongly identified as annual. Analysis of internal lines may lead to over-or underestimation of age and was more reliable in recent portions of the shell