A Double‐Edged Sword: The Role of Sulfate in Anoxic Marine Phosphorus Cycling Through Earth History
Michael A. Kipp
Abstract
Abstract Modern anoxic marine sediments release phosphorus (P) to seawater, driving feedbacks at multiple timescales. On sub‐Myr timescales, anoxic P regeneration amplifies ocean deoxygenation; on multi‐Myr timescales, it stabilizes atmospheric O 2 . Some authors have extended this thinking to the Precambrian: by analogy, widespread ocean anoxia would imply extensive P regeneration from sediments. However, this neglects the role of sulfate in P regeneration. While abundant in seawater today, sulfate was scarce in the Precambrian. Here a simple model is used to isolate the role of sulfate in anoxic P cycling. The model reproduces known feedbacks driven by anoxic P regeneration in a high‐sulfate world, but shows muted P regeneration in low‐sulfate, anoxic sediments. The transition between “limited” and “enhanced” P regeneration is thus controlled by sulfate. As a result, sulfate is a double‐edged sword wielded by the anoxic P cycle: it can amplify oxygenation or deoxygenation depending on environmental context.