CONTROLS ON SHELL d18O OF THE EUROPEAN LIMPET, PATELLA VULGATA : A NEW ARCHIVE FOR LATE HOLOCENE CLIMATE CHANGE

Climate archives contained in shells of the European or common limpet, Patella vulgata, from Viking archaeological deposits can potentially provide much needed information about Late Holocene environmental change in coastal areas. Moreover, sites from northern Europe and the United Kingdom are particularly critical locations because they are under the influence of the North Atlantic Oscillation, a prominent component of the climate system in that region. Before reconstructing climate information preserved in these zooarchaeological records, we developed a temperature proxy using oxygen isotope ratios (d¹⁸O) contained in modern shells of P. vulgata. This was achieved by comparing measured shell values to expected values calculated using temperature measurements recorded over the life of live-collected individuals.

Three specimens were collected alive from St. Mary's lighthouse, Whitley Bay, northeastern England in 2001. We completed a sclerochronologic analysis to identify annual growth lines, which defined the microsampling protocol. We sampled the shells at 0.05 to 0.1 mm intervals for d¹⁸O analysis to achieve submonthly to subweekly resolution. d¹⁸O_SHELL values ranged from +0.64 to +3.44‰ (VPDB).

We constructed expected d¹⁸O_SHELL using observed sea surface temperature (SST) records, assuming d¹⁸O_WATER is +0.10‰ (VSMOW), and assuming equilibrium fractionation. Expected d¹⁸O ranged from -0.77‰ to +2.02‰ (VPDB). Comparison of d¹⁸O_SHELL with expected values revealed that d¹⁸O_SHELL values were higher than expected by +1.51±0.21‰. Consequently, SST estimates calculated from d¹⁸O_SHELL were 6.50±2.45°C lower than observed SSTs. However, because of the relatively uniform offset between observed and expected d¹⁸O, an adjustment can be made to account for this predictable vital effect. Thus, past climate can be reliably reconstructed using sclerochronology and variation in d¹⁸O_SHELL of P. vulgata once the predictable offset is taken into account.