Dual clumped isotope thermometry of carbonates: resolving the effects of temperature from kinetics and diagenesis for accurate reconstruction of Earth’s surface temperature

• Applicant: Professor Dr. Jens Fiebig
• Subject Area: Palaeontology ; Mineralogy, Petrology and Geochemistry
• Term: since 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 451014668

How and why did our planet become habitable? Which boundary conditions triggered the evolution of life on Earth? How will climate evolve and how will it affect biodiversity? To find answers for these important questions it is essential to reconstruct the past interplay between atmospheric greenhouse gas abundances, Earth’s surface temperatures and biodiversity. Earth’s surface temperatures are reconstructed from chemical and isotopic proxy data from well-dated sedimentary archives. Yet, there is no proxy available that unambiguously records Earth’s surface temperature. Besides temperature, kinetic and diagenetic processes as well as the chemical and isotopic composition of the parent fluid exert control on the proxy composition of the sedimentary archive. Non-exclusive temperature control and secondary alteration of the original proxy composition introduce large uncertainties in reconstructed temperatures.My research group has most recently pioneered dual clumped isotope analysis of carbonates, i.e., the extremely challenging analysis of the abundance of rare molecules of 12C18O18O (Δ48) in CO2 evolved from phosphoric acid digestion of carbonates along with 13C18O16O (Δ47). Now, for the first time, dual clumped isotope thermometry, may allow us to resolve temperature from the kinetic and diagenetic information just from the analysis of a single carbonate phase, without requiring any further knowledge about the composition of the fluid from which the carbonate crystallized. It has the potential to become the method of choice for the reconstruction of accurate formation temperatures (unbiased by kinetics) with unprecedented precision (< ±2°C on the 95% confidence interval level).I request funding to systematically und comprehensively investigate the fundamental thermodynamic and kinetic systematics of carbonate (bio)mineralization in Δ47 vs. Δ48 space. This may allow us to reliably reconstruct the interplay between Earth’s surface temperature and greenhouse gas abundance for past high-pCO2 intervals. The provision of accurate paleo-latitudinal temperature gradients for epochs with pCO2 as high as predicted to be encountered in the near future is necessary to improve state-of-the-art models predicting future climate. Moreover, the exploration of fundamental thermodynamics and kinetics will provide information essential for further potential applications of the dual clumped isotope proxy. These include reconstructions of temperature-time paths of burial and uplift of rocks, the evolution of marine biological production, the response of carbonate biomineralization to anthropogenic CO2 forcing and the evolution of Earth’s surface temperature and habitability since the Archean.

• DFG Programme: Reinhart Koselleck Projects
• Cooperation Partners: Professor Dr. Michael E. Böttcher; Professor Dr. Martin Dietzel