MODEL OF DUAL ISOTOPES OF PALEOSOL CARBONATES SHOWS SPATIAL PATTERNS OF CLIMATE CHANGE OVER THE PALEOCENE-EOCENE THERMAL MAXIMUM (PETM)

The PETM was a rapid warming event ~56 Ma characterized by a carbon isotope excursion (CIE) that reflects a large injection of carbon into the ocean/atmosphere system. Marine and terrestrial records indicate that climate seasonality changed over the PETM, but details of the spatial patterns of these changes are poorly understood. Here we show that pedogenic carbonates in paleosols record carbon and oxygen isotope excursions of varying magnitudes in four northern mid-latitude sites, with strong coupling between the magnitudes for carbon and oxygen. This oxygen-carbon isotope excursion coupling could indicate that similar, spatially heterogeneous, climatic drivers influenced these values for both isotopic systems over the PETM. Pedogenic carbonates usually precipitate in association with soil drying; therefore, their carbon and oxygen isotope values can reflect the influence of both annual and seasonal environmental conditions. Assessing the major controls on carbon and oxygen isotopic values of pedogenic carbonate in reveals that they share a common set of seasonal and annual climatic drivers. We developed a mechanistic model of the dual isotope system in pedogenic carbonates. This model was applied to the coupled paleosol carbonate oxygen and carbon isotopic records over the PETM using a Bayesian inverse technique. Model results suggest that site-specific changes in seasonality of temperature could drive the variability and coupling of carbon and oxygen isotopic excursions in these continental sites over the PETM.