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

Abstract

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 ( δ 18O) of terrestrial mammal faunas from the Late Miocene, Pliocene and Pleistocene of Spain, and compare these data with Late Miocene mammal δ 18O values from northern Libya. Since tooth enamel δ 18O from modern horses has been demonstrated to be a reasonable proxy for the δ 18O of local meteoric water, which is in turn strongly dependent on mean annual temperature (MAT), we use the δ 18O 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 δ 18O 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 δ 18O patterns to make interpretations about paleoecology and to qualitatively assess paleoaridity. Comparisons of δ 18O 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 δ 18O suggest slight diagenetic alteration of dentine, but we demonstrate that these δ 18O values can be used to reconstruct reasonable values of diagenetic water δ 18O. 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.