The clumped (13C18O) isotope composition of echinoid calcite: Further evidence for “vital effects” in the clumped isotope proxy

Carbonate clumped isotope thermometry is based on the thermodynamically dependent relative abundance of 13Csingle bond18O bonds (quantified as Δ47) within the carbonate crystal lattice. The clumping of 13Csingle bond18O in carbonates is based on a self-reaction of isotope exchange that occurs rapidly at near neutral pH. Similar Δ47-temperature relationships between biogenic and inorganically precipitated carbonate in initial studies led to the promise of a proxy free of biologically driven disequilibrium effects, commonly referred to as “vital effects”. This has been largely the case for most organisms investigated. Biologically mediated disequilibrium precipitation has however been reported in corals and cephalopods and brachiopod molluscs. Echinoderms, despite their complex inter-cellular bio-mineralization strategy, large inter-skeletal fractionation of δ18O, δ13C and rapid calcite precipitation have …