Soil Carbon Isotope Values and Paleoprecipitation Reconstruction

Anthropogenic climate change has significant impacts at the ecosystem scale including widespread drought, flooding, and other natural disasters related to precipitation extremes. To contextualize modern climate change, scientists often look to ancient climate changes, such as shifts in ancient precipitation ranges. Previous studies have used fossil leaf organic geochemistry and paleosol inorganic chemistry as paleoprecipitation proxies, but have largely ignored the organic soil layer, which acts as a bridge between aboveground biomass and belowground inorganic carbon accumulation, as a potential recorder of precipitation. We investigate the relationship between stable carbon isotope values in soil organic matter (delta C-13(SOM)) and a variety of seasonal and annual climate parameters in modern ecosystems and find a statistically significant relationship between delta C-13(SOM) values and mean annual precipitation (MAP). After testing the relationship between actual and reconstructed precipitation values in modern systems, we test this potential paleoprecipitation proxy in the geologic record by comparing precipitation values reconstructed using delta C-13(SOM) to other reconstructed paleoprecipitation estimates from the same paleosols. This study provides a promising new proxy that can be applied to ecosystems post-Devonian (similar to 420 Ma) to the Miocene (similar to 23 Ma), and in mixed C-3/C-4 ecosystems in the geologic record with additional paleobotanical and palynological information. It also extends paleoprecipitation reconstruction to more weakly developed paleosol types, such as those lacking B- horizons, than previous inorganic proxies and is calibrated for wetter environments.

Automated summary

This study explores the relationship between stable carbon isotope values in soil organic matter and climate parameters in modern ecosystems, proposing a potential new paleoprecipitation proxy that can be applied from the Devonian period to the Miocene period. It provides a promising method for extending paleoprecipitation reconstruction in geological records and is calibrated for wetter environments.