Stable isotopic evidence for terrestrial latitudinal climate gradients in the Late Miocene of the Iberian Peninsula

The late Neogene of the Mediterranean region is marked by significant faunal and floral turnover in terrestrial ecosystems, paleogeographic and paleoceanographic changes associated with the Messinian Salinity Crisis (MSC), and regional climate transition associated with the onset of northern hemisphere glaciation. In this paper we report stable oxygen isotope compositions (δ¹⁸O) of terrestrial mammal faunas from the Late Miocene, Pliocene and Pleistocene of Spain, and compare these data with Late Miocene mammal δ¹⁸O values from northern Libya. Since tooth enamel δ¹⁸O from modern horses has been demonstrated to be a reasonable proxy for the δ¹⁸O of local meteoric water, which is in turn strongly dependent on mean annual temperature (MAT), we use the δ¹⁸O of fossil horse tooth enamel to estimate MAT. Our paleotemperature reconstructions are consistent with global cooling during the late Cenozoic, with MAT for the Late Miocene that is warmer than today by ∼ 1-2 °C in NE Spain and by ∼ 4-5 °C in SE Spain. The difference of ∼ 8-9 °C between NE and SE Spain for the Late Miocene is ∼ 60% greater than the MAT difference between these same areas today. The δ¹⁸O values from Libya are lower than those for southern Spain, and may suggest cooler and/or wetter climates in northeastern Africa during the latest Miocene and early Pliocene. We examined intrafaunal δ¹⁸O patterns to make interpretations about paleoecology and to qualitatively assess paleoaridity. Comparisons of δ¹⁸O values between clades are consistent with a semi-aquatic lifestyle for anthracotheres, hippopotamids, and castorids. We also compare intra-tooth samples of enamel and dentine to examine possible diagenetic alteration of these materials. Comparisons of enamel and dentine δ¹⁸O suggest slight diagenetic alteration of dentine, but we demonstrate that these δ¹⁸O values can be used to reconstruct reasonable values of diagenetic water δ¹⁸O. Overall, our data do not support large climatic changes in the Iberian Peninsula during the MSC, but are consistent with long-term global cooling and sharper latitudinal climate gradients in Spain during the Neogene.