The contents of N and P in marine sediments increase with decreasing grain size of the sediments, but the reverse is true of the Si content. The contents of these elements vary with different oceanic regions, terrestrial inputs, seasonal variations, interstitial water advection and biological production process. The factors controlling the deposition, release and cycling of N, P and S at the marine sediment-seawater interface include the concentrations of organic matter and dissolved oxygen, ratios of C,N,P and Si in organic matter, redox environment near the sediment-seawater interface, bioturbation, temperature, depth of overlying water, pH, hydro-logic dynamic conditions, concentrations of S occurring in different forms, and concentrations of metallic elements such as. Fe2+, A13+ and Mn2+. Generally, the fluxes of NH4+ , PO43- and Si(OH)4 move from sediment to overlying water, but the fluxes of nitrate and nitrite move in an opposite direction, i. e. from overlying water to sediment. The magnitude of the fluxes across the sediment-water interface differs significantly in different o-ceanic regions.