Soil pore water evaporation and temperature influences on clay mineral paleothermometry

Clay mineral isotope paleothermometry is fundamental to understanding Earth’s climate system and landscape evolution. Status quo methods, however, assume constant factors, such as formation temperature and water isotopic compositions, and ignore seasonality, soil water evaporation and depth-dependent temperature changes. We propose first-order modifications to address these factors and test them in a modeling framework using published data from various settings. Our forward model reveals that neglecting evaporation and seasonal soil temperature variability may lead to significant underestimations of clay formation temperatures, especially in Mediterranean settings. Our inverse model indicates that high-latitude Eocene clay formation temperatures were ~8 °C warmer than modern, while Eocene river sediments in the Sierra Nevada show evaporation-influenced trends, suggesting that previous paleoelevation estimates were underestimated. Our framework demonstrates that explicit consideration of soil pore water evaporation and temperature variability is necessary when interpreting clay mineral isotope data in the context of temperature, hydroclimate and elevation reconstructions.