Sediment is the ultimate sink of phosphorus (P), the common limiting nutrient in marine ecosystems. The balance between P sedimentation and burial determines the return of bioavailable P, namely dissolved phosphate (PO₄³⁺) and regulates the primary productivity in P-limiting coastal oceans. In iron (Fe)-rich coastal sediments, sediment P cycle is strongly coupled to Fe speciation: PO₄³⁺ will be bound by ferric Fe oxides, or precipitate with ferrous ion (Fe²⁺) to form vivianite. On the other hand, active sulfur (S) cycles in marine sediments can decouple the Fe and P cycle by immobilizing Fe (e.g., to form pyrite), increasing sediment PO₄^3- release. Understanding the mechanisms of Fe-S-regulated P recycles is crucial in not only constraining regional geochemical budgets but also predicting how diverse systems respond to future climate scenarios. In this talk, we will share some preliminary data from sediments under diverse geochemical regimes, including sediments of intertidal zones, lagoons, near-shore seas, continental slope, and methane seeps. We will show how redox conditions, particularly the depths of oxygen penetration, together with the Fe and S geochemistry, shape the sediment P cycle and regulate P long-term burial and flux.