Calibration of the carbonate 'clumped isotope' paleothermometer for otoliths

Paleothermometry is an essential tool for understanding past changes in climate. The 'carbonate clumped isotope thermometer' is a temperature proxy related to ordering of C-13 and 180 in the carbonate lattice (based on measurements of (COO)-C-13-O-18-O-16 in CO2 produced by acid digestion of carbonate). This thermometer has been previously calibrated for inorganic calcite and aragonitic corals [Ghosh P., Adkins J., Affek H., Balta B., Guo W. F., Schauble E. A., Schrag D., and Eiler J. M. (2006) C-13-O-18 bonds in carbonate minerals: a new kind of paleothermometer. Geochim. Cosmochim. Acta 70 (6), 14391456]. Here we determine the relationship between growth temperatures of aragonitic fish otoliths and abundances of (COO)-C-13-O-18-O-16 produced by acid digestion of those otoliths. Our calibration is based on analyses of otoliths from six species from four genera of modern fish sampled from a latitudinal transect of the Atlantic Ocean between 54 degrees S and 65 degrees N, plus one species from the tropical western Pacific. The temperatures at which fish otoliths precipitated were estimated by the mean temperature in the waters in which they lived, averaged over their estimated lifetimes. Estimated growth temperatures of our samples vary between 2 and 25 C. Our results show that the abundance of (OOO)-O-13-O-18-O-16 in CO2 produced by acid digestion of fish otolith aragonite is a function of growth temperature, following the relationship: Delta(47) = 0.0568 x 10(6)/T-2 = -0.0045, where Delta(47) is the enrichment, in per mil, of (COO)-C-13-O-18-O-16 in CO2 relative to the amount expected for a stochastic (random) distribution of isotopes among all CO2 isotopologues, and T is the temperature in Kelvin. This relationship closely approaches that previously documented for inorganic calcite and aragonitic coral (Ghosh et al., 2006). (c) 2007 Elsevier Ltd. All rights reserved.