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RESEARCH PRODUCT

An intractable climate archive — Sclerochronological and shell oxygen isotope analyses of the Pacific geoduck, Panopea abrupta (bivalve mollusk) from Protection Island (Washington State, USA)

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Abstract Annual growth increment patterns of cardinal teeth (CT) of Panopea abrupta (Conrad) can reportedly provide information about past climate variations. However, little is known about the intra-annual timing and rate of shell growth necessary to interpret such records. In addition, it remains unclear whether actual temperatures can be reliably inferred from δ18O values of geoduck {goo'e-duk} shells. This study compared high-resolution environmental records (hourly to monthly resolved temperature, bi-weekly to monthly δ18Owater and salinity data) with temperatures reconstructed from oxygen isotope values of the outer shell layer (Tδ18OOSL) and cardinal tooth portions (Tδ18OCT) of different contemporaneous specimens alive at the same locality. Results indicate that shell growth mainly occurred between March/April and November/December with a maximum during May–August. This finding must be considered when comparing the “annual” growth increment width chronologies to environmental parameters. In addition, intra-annual δ18Oshell values require the calculation of weighted averages instead of arithmetic means. During ontogeny, the duration of the growing season remained nearly unchanged; an important finding for paleoclimate studies based on inter-annual growth patterns. Seasonal shell growth was strongly correlated with temperature (R = 0.93, R2 = 0.86, p