Temperature dependence of clumped isotopes (∆47) in aragonite

Abstract

Wang et al., 2004), carbonate clumped isotope analysis has developed into a valuable tool for paleothermometry in the geosciences. Clumped isotope analysis is based on the thermodynamic principle that molecules with multiple heavy isotopes (so-called "multiply-substituted isotopologues") have lower vibrational energies than molecules containing lighter isotopes (Urey, 1947). Consequently, the increase in system entropy at higher temperatures causes a decrease in the occurrence of multiply-substituted isotopologues, and "clumping" of heavy isotopes within the same molecule is favored in low-energy systems (Eiler, 2007). In carbonates, this principle causes heavy carbonate ions (e.g., 13 C 18 O 16 O 2 ; mass 63 or 12 C 18 O 2 16 O; mass 64) to become more abundant with decreasing calcification temperatures (Ghosh et al., 2006). The distribution of these isotopologues is proportional in the CO 2 gas after reaction of carbonates with acid (e.g., 13 C 18 O 16 O; mass 47 and 12 C 18 O 2 , mass 48 respectively) and is measured with reference to the distribution of isotopologues in a fully scrambled heated CO 2 gas with the same isotopic composition: