| Before reconstructing potential climate information preserved in Holocene archaeological shells of the European limpet, Patella vulgata, we studied the controls on delta18O and delta 13C in modern specimens. We evaluated whether P. vulgata shells precipitate in isotopic equilibrium with the ambient water by comparing delta 18OSHELL with expected values. Comparison revealed that delta 18OSHELL 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 delta18O SHELL in tropical species displays vital effects and the disequilibrium would be constant and predictable. Our results indicated P. stellaeformis delta18OSHELL exhibits a negative offset from expected equilibrium. Differences in mineralogy or growth rates at different latitudes may influence mechanisms that cause vital effects. |
