Before reconstructing potential climate information preserved in Holocene archaeological shells of the European limpet, Patella vulgata, we studied the controls on δ¹⁸O and δ ¹³C in modern specimens. We evaluated whether P. vulgata shells precipitate in isotopic equilibrium with the ambient water by comparing δ ¹⁸O_SHELL with expected values. Comparison revealed that δ ¹⁸O_SHELL values were 1.51±0.21‰ higher than expected (corresponding estimated SST was 6.5±2.5°C lower than observed SST). However, an adjustment can account for this predictable vital effect to reliably reconstruct SST.

Tropical species, P. stellaeformis, was evaluated to determine whether it displays a similar positive offset from equilibrium as P. vulgata. We tested the hypotheses that δ¹⁸O _SHELL in tropical species displays vital effects and the disequilibrium would be constant and predictable. Our results indicated P. stellaeformis δ¹⁸O_SHELL exhibits a negative offset from expected equilibrium. Differences in mineralogy or growth rates at different latitudes may influence mechanisms that cause vital effects.