Thébault Julien, Chauvaud L., Clavier J., Guarini J., Dunbar R. B., Fichez Renaud, Mucciarone D. A., Morize Eric. (2007). Reconstruction of seasonal temperature variability in the tropical Pacific Ocean from the shell of the scallop, Comptopallium radula. Geochimica et Cosmochimica Acta, 71 (4), p. 918-928. ISSN 0016-7037.
Titre du document
Reconstruction of seasonal temperature variability in the tropical Pacific Ocean from the shell of the scallop, Comptopallium radula
Thébault Julien, Chauvaud L., Clavier J., Guarini J., Dunbar R. B., Fichez Renaud, Mucciarone D. A., Morize Eric
Geochimica et Cosmochimica Acta, 2007,
71 (4), p. 918-928 ISSN 0016-7037
We investigated the oxygen isotope composition (delta O-18) of shell striae from juvenile Comptopallium radula (Mollusca; Pectinidae) specimens collected live in New Caledonia. Bottom-water temperature and salinity were monitored in-situ throughout the study period. External shell striae form with a 2-day periodicity in this scallop, making it possible to estimate the date of precipitation for each calcite sample collected along a growth transect. The oxygen isotope composition of shell calcite (delta O-18(shell calcite)) measured at almost weekly resolution on calcite accreted between August 2002 and July 2003 accurately tracks bottom-water temperatures. A new empirical paleo-temperature equation for this scallop species relates temperature and delta O-18(shell calcite). t(degrees C) = 20.00(+/- 0.61) - 3.66(+/- 0.39) x (delta O-18(shell calcite VPDB) - delta O-18(water VSMOW)) The mean absolute accuracy of temperature estimated using this equation is 1.0 degrees C at temperatures between 20 and 30 degrees C. Uncertainties regarding the precise timing of CaCO3 deposition and the actual variations in delta O-18(water) at our study sites probably contribute to this error. Comparison with a previously published empirical paleotemperature equation indicates that C. radula calcite is enriched in O-18 by similar to 0.7 parts per thousand relative to equilibrium. Given the direction of this offset and the lack of correlation between shell growth rate and delta O-18(shell) calcite, this disequilibrium is unlikely to be related to kinetic isotope effects. We suggest that this enrichment reflects (1) a relatively low pH in the scallop's marginal extrapallial fluid (EPF), (2) an isotopic signature of the EPF different from that of seawater, or (3) Rayleigh fractionation during the biocalcification process. Relative changes in delta O-18 shell calcite reflect seawater temperature variability at this location and we suggest that the shell of C radula may be useful as an archive of past seawater temperatures.