A dual clumped isotope approach to characterize disequilibrium in terrestrial carbonates

Carbonate minerals (e.g. calcite, calcium carbonate) record information about the environment in their chemical and isotopic compositions, and are a primary archive of how Earth’s climate system, ocean and atmospheric chemistry, and biology have evolved through time. Continental environments experience greater negative consequences of climate change, such as fire, drought, and floods, than marine ecosystems, and thus it is critical that we understand how to correctly map chemical signals in terrestrial sediments to climatic and environmental parameters (e.g. temperature, water scarcity). Carbonates that form in terrestrial environments often precipitate rapidly before equilibrium is achieved between the mineral and water, skewing the chemistry recorded by the mineral. This research will investigate the role of disequilibrium imparted during rapid mineral formation on important climate archives through an investigation of modern and fossil carbonates formed in lakes and wetlands in the western US and Canada. Understanding how Earth’s surface environments and water resources have responded to varied climate states, and in particular, globally warm periods, is crucial in developing viable strategies to mitigate the effects on human populations. This study will provide new context to stable isotope-based records of land surface water availability and temperatures. The research team will also develop in-person and virtual climate science curriculum and STEM career programming in rural Pennsylvania high schools, and publish virtual education modules to an open-access repository for K-12 educators.To understand the response of terrestrial ecosystems to global or regional hydroclimate perturbations and hyperthermal events, we must understand how terrestrial sediments archive paleoenvironmental information. Carbonate minerals often precipitate rapidly—potentially before isotopic equilibrium is achieved—within lakes, wetlands, and soils due to natural fluctuations in temperature, water balance, and mineral saturation state. Interpreting the isotopic compositions of these minerals as a record of thermodynamic equilibrium can lead to significant error in temperature and hydroclimate reconstructions. This study will characterize disequilibrium dual clumped isotope signals (∆47-∆48) in a suite of calcium carbonate facies that form by different mechanisms in modern (Cariboo Plateau, Canada), Pleistocene (Mono Lake, California), and Paleogene (Green River Fm, Colorado/Wyoming/Utah) lakes and wetlands to generate a more robust isotopic framework for interpreting terrestrial carbonates in the geologic record at different stages of diagenesis. Sedimentology will be partnered with isotope analyses to discern the ∆47-∆48 “disequilibrium signal”—the magnitude and trend from thermodynamic equilibrium—for specific modes of terrestrial carbonate production. The researchers predict that terrestrial carbonate facies that form rapidly will record ∆47 and ∆48 disequilibrium whereas facies that form more slowly will record equilibrium, with the facies-specific dependence due to the carbon cycling mechanisms within each mineral formation micro-environment.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.