PALEOCLIMATE AND PALEOENVIRONMENT OF ISERNIA LA PINETA (MOLISE, ITALY)

To investigate the paleoclimate and paleoenvironment of the archeological and paleontological site of Isernia La Pineta (Molise, Italy), we analyzed the carbon and oxygen stable isotope composition of the carbonate component of enamel from 17 rhino (Stephanorhinus hundsheimensis) teeth. These teeth were collected from four different stratigraphic layers (from lowermost to uppermost: 3coll, 3s10, 3s6-9, and 3s1-5). Layer 3coll has been recently dated at ~600 ka.

Stable carbon isotope ratios in fossil tooth enamel can be used to investigate the proportion of C3 vs. C4 plants in the paleoenvironment or, in a pure C3 ecosystem, can be used as a proxy for mean annual precipitation (MAP) and vegetation structure. Enamel oxygen isotope ratios in water dependent mammals can instead be used to reconstruct the composition of meteoric precipitation. Because the stable isotope composition of mid-latitude meteoric precipitation correlates with temperature, oxygen isotope ratios in enamel can be used as a temperature proxy.

Enamel carbon isotope ratios indicate feeding in a pure C3 ecosystem. Average (±1 se) δ¹³C values (vs. V-PDB) in layers 3coll (-13.56±0.06‰) and 3s1-5 (-13.46±0.05‰) are indistinguishable. In contrast, layers 3s10 (-14.01±0.08) and 3s6-9 (-13.84±0.06‰) show lower average δ¹³C, suggesting slightly higher MAP during the deposition of those layers. Intra-tooth variability in enamel δ¹³C is very small, perhaps indicating uniform precipitation throughout the year.

With respect to oxygen isotopes, average (±1 se) enamel δ¹⁸O (vs. V-SMOW) in layers 3coll (23.98±0.07‰) and 3s1-5 (24.00±0.05‰) are also indistinguishable whereas layers 3s10 (25.18±0.17‰) and 3s6-9 (24.64±0.09‰) show higher average values, suggesting slightly warmer conditions during the deposition of the two middle layers. Calculated values of mean annual temperature for the four layers (~11°C) are slightly lower than the modern one (13.1°C). Finally, intra-tooth variability in enamel δ¹⁸O is very small in all four layers, perhaps reflecting lower temperature seasonality 600 ka ago than today. This temperate and seasonally equable climate might have been an important factor in favoring the human colonization of this part of the European continent during the Middle Pleistocene.