A phosphate-rich marine reservoir in the redox stratified Ediacaran ocean

Phosphorus (P) is the key nutrient thought to limit primary productivity on geological timescales, and hence P bioavailability exerted a major influence on Earth’s surface oxygenation dynamics through the Precambrian, with ensuing implications for biological evolution. Here, we document highly elevated P contents in non-glacial Ediacaran (635–541 Ma) iron formations from Northwestern China, with P dominantly occurring as carbonate fluorapatite formed during early diagenesis. These analyses, in combination with marine sediment P contents and phosphorite abundance data, point to a state change in oceanic P concentrations during the Ediacaran, which we attribute to enhanced recycling from marine sediments under redox-stratified conditions. Subsequent elevated rates of primary productivity and organic carbon production may have sustained the contemporaneous first appearance of complex deep marine habitats, and would have increased the extent and stability of surface water oxygen concentrations, leading to conditions conducive to the subsequent evolution of more complex animals.