Mineralogical Controls on Redox-Driven Phosphorus Cycling in the Precambrian Ferruginous Ocean

ongoing

Earth’s early oxygenation history played a pivotal role in the evolution of complex life. Phosphorus (P) is widely recognised as the ultimate limiting nutrient on geological time scales, and hence P exerted a fundamental role in regulating global marine primary productivity, organic carbon burial, and ultimately the oxygen flux to the ocean-atmosphere system throughout the Precambrian Era (~4.6–0.541 billion years ago). Several geochemical proxies have been developed to reconstruct the Precambrian marine P reservoir and links to Earth’s oxygenation history, but all have inherent limitations linked to uncertainty over key processes involved in P cycling. In particular, mineralogical controls on P cycling under anoxic ferruginous (Fe(II)-containing) conditions, which reflect the dominant redox state of the ocean throughout most of the Precambrian, are very poorly understood. One such process concerns the extent of P uptake to (meta)stable, mixed-valence green rust, which has emerged as a key mineral precipitating in Precambrian ferruginous oceans, and the subsequent behaviour of P upon ageing to magnetite and Fe-rich clay minerals. Therefore, the PaleoNutrient project will investigate these key processes by a series of carefully controlled experiments performed under Precambrian ferruginous ocean conditions. These experimental results will then be validated by geochemical and mineralogical investigation of select Precambrian marine rocks deposited under varying types of ferruginous oceanic conditions. The new insight gained from experiments and the evaluation of the rock record will then be used to update existing biogeochemical models, with an ultimate aim to revolutionise our understanding of bioavailable P, primary productivity, and hence Earth’s oxygenation history across critical intervals of the Precambrian Era that dictated the trajectory of Earth’s habitability.