Reconstruction of seasonal temperature variability in the tropical Pacific Ocean from the shell of the scallop, Comptopallium radula

Julien Thébault (1, 2) , Laurent Chauvaud (1) , Jacques Clavier (1) , Jennifer Guarini (3) , Robert B. Dunbar (4) , Renaud Fichez (2, 5) , David A. Mucciarone (4) , Eric Morize (1)

1 LEMAR - Laboratoire des Sciences de l'Environnement Marin (LEMAR)
2 CAMELIA - Caractérisation et modélisation des échanges dans des lagons soumis aux influences terrigènes et anthropiques
3 OOB - Observatoire océanologique de Banyuls
4 GS - Department of Geological Sciences [Stanford]
5 COM - Centre d'océanologie de Marseille

We investigated the oxygen isotope composition (d¹⁸O) 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 (d¹⁸O_{shell calcite}) measured at almost weekly resolution on calcite accreted between August 2002 and July 2003 accurately tracks bottom-water temperatures. A new empirical paleotemperature equation for this scallop species relates temperature and d¹⁸O_{shell calcite}: t(°C)=20.00(+/-0.61)-3.66(+/-0.39)x(d¹⁸O_{shell calcite VPDB} -d¹⁸O_{water VSMOW}) The mean absolute accuracy of temperature estimated using this equation is 1.0 °C at temperatures between 20 and 30 °C. Uncertainties regarding the precise timing of CaCO₃ deposition and the actual variations in d¹⁸O_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 ¹⁸O by ~0.7‰ relative to equilibrium. Given the direction of this offset and the lack of correlation between shell growth rate and d¹⁸O_{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 d¹⁸O_{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.

Domains: Environmental Sciences; Geochemistry; Global Changes

Julien Thébault, Laurent Chauvaud, Jacques Clavier, Jennifer Guarini, Robert B. Dunbar, et al.. Reconstruction of seasonal temperature variability in the tropical Pacific Ocean from the shell of the scallop, Comptopallium radula. Geochimica et Cosmochimica Acta, 2007, 71 (4), pp.918-928. ⟨10.1016/j.gca.2006.10.017⟩. ⟨hal-00449317⟩