Enhanced phosphorus recycling during past oceanic anoxia amplified by low rates of apatite authigenesis

Enhanced recycling of phosphorus as ocean deoxygenation expanded under past greenhouse climates contributed to widespread organic carbon burial and drawdown of atmospheric CO2. Redox-dependent phosphorus recycling was more efficient in such ancient anoxic marine environments, compared to modern anoxic settings, for reasons that remain unclear. Here, we show that low rates of apatite authigenesis in organic-rich sediments can explain the amplified phosphorus recycling in ancient settings as reflected in highly elevated ratios of organic carbon to total phosphorus. We argue that the low rates may be partly the result of the reduced saturation state of sediment porewaters with respect to apatite linked to ocean warming and acidification and/or a decreased availability of calcium carbonate, which acts as a template for apatite formation. Future changes in temperature and ocean biogeochemistry, induced by elevated atmospheric CO2, may similarly increase phosphorus availability and accelerate ocean deoxygenation and organic carbon burial.

Automated summary

Enhanced phosphorus recycling due to ocean deoxygenation under past greenhouse climates led to widespread organic carbon burial and reduced atmospheric CO2 levels. Low rates of apatite authigenesis in organic-rich sediments in ancient settings explain the amplified phosphorus recycling, and future changes in temperature and ocean biogeochemistry may increase phosphorus availability further.