Structural analysis and paleoenvironmental potential of dog cockle shells (Glycymeris glycymeris) in Brittany, northwest France

Abstract : To compensate for the lack of high resolution data on variation in environmental parameters before the establishment of monitoring networks, we evaluated dog cockle shells (Glycymeris glycymeris; Mollusca: Bivalvia) as archives for temperature and climate perturbations such as the North Atlantic Oscillation (NAO) over the last 50 years. Oxygen isotope compositions were measured from annual increments of shells collected from the Bay of Brest and the Chausey Islands in northwestern France. Simultaneously, sclerochronological analyses were performed on the same shells. Oxygen isotopic ratios measured in shells collected from the Bay of Brest were compared to in situ temperature and salinity data from monitoring stations and buoys in order to build a specific paleotemperature equation (r2 = 0.87; p < 0.001) for the dog cockle. The specific equation was used to estimate sea surface temperatures around the Chausey Islands between 1966 and 1994. Standardized growth indices (SGI) calculated through sclerochronological methods were strongly correlated to oxygen isotope-derived temperatures. The SGI however did not capture the area's predominant climate pattern, the NAO. This study demonstrates that dog cockle shells can be used for long-term high-resolution reconstructions of past sea surface temperatures.