Carbon isotope geochemistry of organic matter in volcanic paleosols constrains paleo-environmental variations

The Fiorano quarry paleosol developed within the Colli Albani volcanic district (Italy) in the time interval bracketed by the deposition of the Pozzolanelle pyroclastic-flow unit (365 ± 4 ka) and the emplacement of the Capo di Bove lava flow (277 ± 2 ka). The paleosol is characterized by an accretionary feature produced by the progressive accumulation of clastic material eroded from the surrounding volcanic landscape. The δ13C composition of soil organic matter (δ13COM) shows limited but systematic variations with stratigraphic age (from −20.77‰ to −27.29‰), reflecting changes in plants' contribution and organic matter input during pedogenesis. The δ13COM record also matches global and local proxies over the 365–277 ka interval, spanning Marine Isotopic Stage 10 (MIS) to MIS 8.5. These data suggest that δ13COM values were primarily controlled by variation in vegetation density and cover at the paleosol surface. The Fiorano paleosol thus preserves a well-resolved continental stable isotope record for MIS 9 in the central Mediterranean area, showing the potential of δ13COM variations in paleosols to constrain paleo-environmental and paleo-climatological conditions in the central Mediterranean area during the middle Pleistocene.