Astronomic forcing on the planktonic foraminifera assemblage in the Piacenzian Punta Piccola section (Southern Italy).

A high-resolution quantitative analysis of the calcareous planktonic assemblages (planktonic foraminifers and calcareous nannofossils) at the Punta Piccola section (at the base of which, the global standard stratotype-section and point of the Piacenzian stage is defined) provided a more accurate biostratigraphy for the Mediterranean middle Pliocene (2.6–3.6 Ma). In particular, an astronomically calibrated age of 2.87 Ma was estimated for the Pliocene first occurrence of Neogloboquadrina atlantica instead of the younger previously proposed age of 2.72 Ma. Spectral analysis performed on the Globigerinoides species (spp.) planktonic foraminifera assemblage along with cross-spectral analysis between the same record and the astronomic target curve La(041,1) calculated for the summer season (June–July) at 65°N provided solid evidence that the Globigerinoides spp. group of planktonic species is a reliable recorder of orbital forcing and can be appropriately used for astronomical tuning of marine sedimentary records. The same procedures of spectral analysis were applied to the individual species that constitute the Globigerinoides spp. group (G. ruber, G. obliquus, and G. quadrilobatus), thus resolving their different frequency structures and species-specific response to the different astronomic periodicities. Whereas G. obliquus and G. quadrilobatus appear primarily controlled by precession, G. ruber is largely forced by obliquity. Small ecological differences, mainly related to dissimilar food quality requirements, were assumed to distinctively control the time distribution of the two groups of species. Precessionally forced oligotrophic conditions in the surface Mediterranean waters, induced by summer continental runoff, led to a dominance of copepods-based dietary, typical of G. quadrilobatus. Conversely, obliquity cycles drove the abundance distribution of G. ruber in the sea surface waters of the Mediterranean, influencing the sea surface temperature, light intensity, and/or phytoplankton distribution. Sub-Milankovitch periodicities (cycles <1500, 2500, 3000, and 4500 years long) are reliably detected in the faunal records, suggesting that millennial-scale variability punctuated the Mediterranean climate regime during the interval of the middle Pliocene Northern Hemisphere glaciation.