Earth's ancient rocks are quietly breathing carbon dioxide into the atmosphere, and a new project will measure exactly how much. The problem is that scientists cannot currently quantify two key organic carbon fluxes: how much carbon gets buried in ocean sediments (which pulls CO₂ out of the air), and how much gets released when ancient organic matter in exposed rocks weathers and oxidises. These uncertainties limit understanding of what drove past climate shifts and what conditions allowed complex life to emerge or collapse. DISTILL will use two novel chemical tracers—cadmium isotopes to track past marine carbon burial, and osmium isotopes combined with Earth system models to reconstruct oxidative weathering fluxes—to fill this gap. This is fundamental science with no immediate practical application. But the carbon cycle governs the planet's long-term climate stability, and the same organic matter feedbacks that operated over the last billion years are still active today. A clearer picture of how these fluxes behaved during past environmental crises could sharpen the models used to project future climate change and inform how natural carbon sinks might respond to human CO₂ emissions.
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DISTILL aims to improve the quantification of steady-state and transient organic carbon burial and weathering fluxes over the last billion years of Earth's history. The production, burial, mobilisation and oxidation of organic carbon are critical parts of Earth's carbon cycle. The burial of organic carbon lowers atmospheric carbon dioxide, while the oxidative weathering of organic carbon from exposed continental rocks emits carbon dioxide. Quantifying the size of organic carbon fluxes across the billion-year scale evolution of Earth's surface environments, and across shorter-term episodes of profound carbon cycle disturbance, is a major challenge. Uncertainty in the size of these fluxes currently limits our understanding of the causes of environmental change and of the conditions that primed the planet for the emergence and demise of complex life. DISTILL will exploit the emergence of the cadmium isotope proxy to reconstruct past marine organic carbon burial fluxes; and will combine osmium isotope measurements with the recent parameterisation of geochemical tracers in Earth System models to reconstruct oxidative carbon weathering fluxes. DISTILL will also address important areas of uncertainty in the behaviour of the Cd isotope proxy and will test the utility of stable rhenium and osmium isotopes as new proxies for oxidative carbon weathering. The PI will lead a team of three post-doctoral researchers and two PhD students, who will each take charge of specific areas of the methodology: cadmium isotope geochemistry, osmium isotope geochemistry, Earth system modelling and the application of these techniques to specific intervals of Earth's history. The project will advance our understanding of the exogenic carbon cycle, and the ways in which organic matter cycling could have played a fundamental role in changing Earth's climate and biosphere.
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