COMBINING Δ47 AND WHOLE-ROCK GEOCHEMICAL PROXIES IN PALEOSOLS TO CONSTRAIN TEMPERATURE SEASONALITY

While marine records often reflect shifts in global climate, terrestrial records tend to be more regionally variable. Paleosols offer a long-term, time-averaged climate archive with established proxies that quantify annual climate variables, including mean annual temperature and precipitation. However, important aspects of terrestrial climate, such as seasonality, are often difficult to constrain. A combination of mean annual and warm season temperatures proxies would allow for a more complete characterization of terrestrial paleoclimate.

Here we investigate the utility of paired paleosol whole-rock geochemistry and pedogenic carbonate Δ₄₇ data. Whole-rock geochemical proxies developed for paleosols can be used to estimate mean annual temperature, whereas the Δ₄₇ of pedogenic carbonate is thought to represent warm month temperatures. We first applied this approach to modern soils with instrumental climate records from Arizona, New Mexico, and South Dakota as a proof of concept. Insights from that work were then applied to paleosols from the Ebro Basin of Spain that span the Eocene-Oligocene transition, a global event characterized by declining temperatures and falling atmospheric pCO₂. Previous results from this section suggest that chemical weathering decreased across the transition in response to decreasing atmospheric pCO. However, estimates of mean annual temperature and precipitation remained unchanged, as in many Eocene-Oligocene transition records from endorheic basins. This paradox may potentially be explained by decreasing summer temperatures as recorded by Δ₄₇ values of pedogenic carbonates.