Wednesday 2 June, 4 PM CET
Dr. Jens Fiebig
ABSTRACT: In the last century, Earth’s surface temperatures have been extensively reconstructed from the analysis of elemental and oxygen isotope abundance ratios in marine carbonates. However, in addition to temperature, the chemical and isotopic compositions of these carbonates is controlled by the chemical and isotopic composition of the seawater and by reaction kinetics occurring during carbonate formation. Moreover, after their formation and deposition, the carbonates can be exposed to secondary, diagenetic processes which may alter their primary chemical and isotopic compositions. These poorly constrained parameters and processes can introduce large scatter and biases in reconstructed Earth’s surface temperatures of up to tens of degrees C. In the last two decades, the establishment of the Δ47 clumped isotope proxy has helped to overcome the uncertainty associated with the unknown composition of the paleo-seawater. Moreover, the Δ47 paleo-thermometer allowed reconstruction of terrestrial surface temperatures and body temperatures of extinct vertebrates. Unfortunately, its applicability is still limited by kinetics occurring during primary formation and diagenetic alteration of the carbonates. In 2019, it has become possible to analyze Δ48 along with Δ47. Combined analysis of Δ48 and Δ47, termed dual clumped isotope thermometry, for the first time, allows to deconvolve temperature from the kinetic information recorded in the single carbonate phase. It bears great potential for the identification of the nature and extent of kinetics involved in carbonate (bio)mineralization and for accurate temperature reconstructions, even if the carbonates were affected by diagenesis.