Younger Dryas – early Holocene transition in the south-eastern Iberian Peninsula: insights from land snail shell middens



The land snail Sphincterochila candidissima from archeological records in Villena (SE Spain) was studied isotopically to estimate the Younger Dryas (YD)–early Holocene transition in the western Mediterranean. Live-collected individuals exhibited body (−21.8 ± 1.6‰) and shell (−5.8 ± 1.4‰) δ13C values typical of a C3 plant diet, probably combined with carbonate ingestion. Calculations of a carbon flux balance-mixing model suggest that living specimens experienced similar metabolic rates, with comparable ratio of input and output fluxes of bicarbonate from the snail hemolymph. All fossil shells showed comparable δ13C values among each other, but values were ∼2‰ higher than living specimens. This may be explained by higher water stress at the YD–Holocene transition or by the Suess effect. Shell δ18O values averaged +1.3 ± 0.8‰ for living individuals, −0.5 ± 0.8‰ for Holocene (8.4–10.2 cal ka BP) specimens and +0.4 ± 0.6‰ for YD (12.0–12.4 cal ka BP) snails. An oxygen flux balance-mixing model suggests that YD shells precipitated during relative humidity (RH) values of ∼79–82%, after which RH increased gradually reaching maximum values of ∼87–88% at ∼8.4–8.6 cal ka BP and, from there, RH eventually declined to present values of ∼82%. Comparisons with other snail data suggest that the xerophilous Sphincterochila records different environmental signatures fro other contemporaneous taxa.