Shell of the Great Scallop Pecten maximus as a high-frequency archive of paleoenvironmental changes Laurent Chauvaud IUEM-UBO, UMR CNRS 6539, Technopo ˆle Brest-Iroise, Place Copernic, F-29280 Plouzane ´, France Anne Lorrain IRD-CRHMT, UR THETIS, Avenue Jean Monnet BP 171, 34203 Se `te, France (anne.lorrain@ird.fr) Robert B. Dunbar Department of Geological and Environmental Sciences, Stanford University, Stanford, California 94305-2115, USA Yves-Marie Paulet, Ge ´rard Thouzeau, and Fre ´de ´ric Jean IUEM-UBO, UMR CNRS 6539, Technopo ˆle Brest-Iroise, Place Copernic, F-29280 Plouzane ´, France Jean-Marc Guarini UMR 10, IFREMER/CNRS, CREMA-L’Houmeau, BP 5, 17137 L’Houmeau Cedex, France David Mucciarone Department of Geological and Environmental Sciences, Stanford University, Stanford, California 94305-2115, USA [1] We investigate the environmental and biological controls on oxygen isotope ratios in the shells of modern Pecten maximus bivalves collected alive in the Bay of Brest (France). Seasonal d 18 O profiles, obtained by drilling the daily calcite ridges deposited at the surface of the left valve, were compared with in situ measurements of temperature and salinity. We show that P. maximus d 18 O values accurately track seasonal variations in bottom water temperature. Shell growth rate has no significant effect on shell d 18 O values. Our study demonstrates that daily variations in water temperature can be reconstructed within about 0.5°C. Temperatures estimated with the paleotemperature equation established in this study were compared with temperatures derived from previously published equations. The comparison indicates that the most commonly used paleotemperature equation for biogenic calcite (Epstein et al., 1953) provides inaccurate temperature estimates, but the Kim and O’Neil (1997) equation, established from abiogenic calcite precipitation, provides results very similar to ours and should therefore be used for scallop individuals coming from populations where proper empirical calibration cannot be done. Pecten maximus bivalves precipitate calcite in isotopic equilibrium with seawater, produce large daily growth striae, are stenohaline, and are well preserved in archeological and geological deposits, making them an excellent high-frequency archive of paleoenvironmental change. Components: 7991 words, 8 figures, 1 table. Keywords: bivalve; biogenic calcite; isotopes; oxygen; shell growth rate; temperature. Index Terms: 4227 Oceanography: General: Diurnal, seasonal, and annual cycles (0438); 4825 Oceanography: Biological and Chemical: Geochemistry; 4870 Oceanography: Biological and Chemical: Stable isotopes (0454, 1041). Received 30 November 2004; Revised 13 May 2005; Accepted 25 May 2005; Published 2 August 2005. Chauvaud, L., A. Lorrain, R. B. Dunbar, Y.-M. Paulet, G. Thouzeau, F. Jean, J.-M. Guarini, and D. Mucciarone (2005), Shell of the Great Scallop Pecten maximus as a high-frequency archive of paleoenvironmental changes, Geochem. Geophys. Geosyst., 6, Q08001, doi:10.1029/2004GC000890. G 3 G 3 Geochemistry Geophysics Geosystems Published by AGU and the Geochemical Society AN ELECTRONIC JOURNAL OF THE EARTH SCIENCES Geochemistry Geophysics Geosystems Article Volume 6, Number 8 2 August 2005 Q08001, doi:10.1029/2004GC000890 ISSN: 1525-2027 Copyright 2005 by the American Geophysical Union 1 of 15