Middle Miocene stepwise climate evolution in the Mediterranean region through high-resolution stable isotopes and calcareous plankton records

The middle Miocene is marked by a changeover from a warm climatic period (Miocene Climatic Optimum, ~17-14.7 Ma), to a transitional phase (Middle Miocene Climatic Transition), culminating in a cold stage (Icehouse Mode, ~13.8 Ma). This period is associated with a positive excursion of δ13C (“Monterey Excursion”), showing a series of δ13C maxima (CM events) highlighted by cooling peaks in the δ18O values (Mi events). DSDP Site 372 obtained a high-resolution record of the middle Miocene of the western Mediterranean (Balearic Islands), and represents one of the best marine sedimentary records for the considered time interval. In this study, high-resolution stable isotope and quantitative calcareous plankton records for the Langhian to the early Serravallian time interval are presented. The stable oxygen and carbon isotope records allowed us to recognize and chronologically frame the Mi and CM events falling between 15.82 and 13.04 Ma. Furthermore, by integrating the stable isotope data with those obtained by the quantitative analyses of the calcareous plankton content, the three-folded climatic and environmental evolution was outlined for the considered time interval in the Mediterranean region. During the first stage (Miocene Climatic Optimum = MCO; from 17 up to 14.55 Ma), an initial warm-surface-water, oligotrophic, high salinity and restricted environment is followed by an open marine setting (starting from 15.18 Ma) within still warm-surface-water and oligotrophic conditions. The re-opening of the connections between the Mediterranean Sea and the Indian Ocean would have likely triggered this latter environmental change. From 14.55 to 13.75 Ma (second stage; Middle Miocene Climatic Transition; MMCT) an initial (up to 14.05 Ma) temperate-warm-surface-water and eutrophic environment occurred, followed by the onset of warm-surface-water, oligotrophic and slightly restricted marine conditions. The third stage (Icehouse Mode = IHM; from 13.75 Ma onwards) points to the development of a cold-water, eutrophic, high salinity environment in an open-marine setting.