Dual Carbonate Clumped Isotope Analysis Resolves Interspecific Differences Underlying Biomineralization in Marine Calcifiers

The geochemistry of marine biominerals is measured as proxies for environmental conditions. However, these correlations depend on the assumption that biominerals are forming in equilibrium with the surrounding seawater. For many organisms, biomineralization is a controlled process, leading this key assumption to be violated and impeding the use of their biominerals as paleoenvironmental proxies. Carbonate "clumped" isotope geochemistry has been used to constrain mineral formation temperatures and previous work suggests that dual clumped isotope analysis (Δ47—Δ48) of carbonates can be used to identify and correct for kinetic isotope effects.

Here, we explore bulk (δ13C and δ18O) and carbonate clumped isotope signatures (Δ47 and Δ48) recorded in biominerals from a diverse array of 12 marine calcifiers that were cultured in aquaria using a single seawater source, a single temperature (25°C), and a range of pCO2 (409, 606, 903, 2856 ppm). Their calcification responses, polymorph mineralogies, δ11B-estimates of calcifying fluid pH, and elemental compositions have been previously characterized and reported. Thereby, this study presents a unique opportunity to explore broad-scale patterns of bulk and clumped carbonate isotope incorporation in a suite of ecologically and economically important marine calcifying organisms through a comparative framework. Our current results unveil evidence for kinetic effects in most specimens and posit the potential for multi-isotope analyses to constrain interspecific differences underlying isotope disequilibrium in biominerals.