Paleoclimatic changes in the Serravallian record of the Mediterranean Area

Planktonic foraminiferal and oxygen isotope records of the astronomically tuned S. Nicola composite section (Tremiti Islands, Mediterranean basin) provide new insight into the paleoclimatic evolution during the Middle to early Late Miocene (between 12.60 and 11.10 Ma). The application of PCA (Principal Component Analysis) to high-resolution data enabled us to examine the interactions among the foraminiferal proxies and to identify a series of paleoclimatic events of long and short duration that took place in the Mediterranean basin during the late Serravallian. The long term trend in PCA-1 score plot shows that the faunal composition of the studied sedimentary record changed significantly at 11.80 Ma. This change coincides with the significant shift from negative to positive loading in PCA-1 and it has been correlated with the onset of the Mi5 event, which in the Mediterranean area is testified by the first influx of neogloboquadrinids. Such a major change is preceded by other minor events at 12.38, 12.21, and 12.00 Ma, which indicate the progressive deterioration from warm to colder climatic conditions. The most evident step coincides with a sharp decrease in abundance of surface species at 12.00 Ma and the relative increase of intermediate species, suggesting a contraction of the habitat of warm faunas and increasingly eutrophic conditions. This cooling (of sea surface water) is also supported by a gradual shift in the bulk δ18O from –2.38‰ (12.374 Ma) to -0.28‰ (11.963 Ma). The comparison between oxygen isotope oscillations and the eccentricity records revealed a good correspondence of the light δ18O values to eccentricity maxima. In addition, the vanishing from the Mediterranean of the neogloboquadrinids between 11.54 Ma and 11.21 Ma has been related to the intensification of monsoon activity with an increase in runoff. This hypothesis is supported by more negative values in δ18O. The Mediterranean results are compared with those from the Equatorial and North Atlantic Ocean. keywords. paleoclimatology, planktonic foraminifera, stable isotope, late Middle Miocene, Mediterranean.