Phosphorus-limited conditions in the early Neoproterozoic ocean maintained low levels of atmospheric oxygen

This is the author accepted manuscript. The final version is available from Nature Research via the DOI in this record.All data generated and analysed for the current study are attached, and are available from data repository https://doi.org/10.5285/72c9a48f-4813-4507-9137-a97d7e6bd2d9.The redox chemistry of anoxic continental margin settings evolved from widespread sulfide-containing (euxinic) conditions to a global ferruginous (iron-containing) state in the early Neoproterozoic era (from ~1 to 0.8 billion years ago). Ocean redox chemistry exerts a strong control on the biogeochemical cycling of phosphorus, a limiting nutrient, and hence on primary production, but the response of the phosphorus cycle to this major ocean redox transition has not been investigated. Here, we use a geochemical speciation technique to investigate the phase partitioning of phosphorus in an open marine, early Neoproterozoic succession from the Huainan Basin, North China. We find that effective removal of bioavailable phosphorus in association with iron minerals in a globally ferruginous ocean resulted in oligotrophic (nutrient limited) conditions, and hence a probable global decrease in primary production, organic carbon burial and, subsequently, oxygen production. Nevertheless, phosphorus availability and organic carbon burial were sufficient to maintain an oxidizing atmosphere. These data imply substantial nutrient-driven variability in atmospheric oxygen levels through the Proterozoic, rather than the stable levels commonly invoked.Royal Society (Charity)Natural Environment Research Council (NERC)Chinese Academy of SciencesNational Natural Science Foundation of Chin