The sulfur cycle in marine environments has been well-studied via the tool of sulfur isotope systematics expressed as δS. The modern global oceans have sulfur storage of , mainly occurring as sulfate with the δS value of +21‰.  The overall input flux is  with the sulfur isotope composition of ~3‰.  Riverine sulfate derived from the terrestrial weathering of sulfide minerals (δS = +6‰) is the primary input of sulfur to the oceans. Other sources are metamorphic and volcanic degassing and hydrothermal activity (δS = 0‰), which release reduced sulfur species (such as HS and S). There are two major outputs of sulfur from the oceans. The first sink is the burial of sulfate either as marine evaporites (such as gypsum) or carbonate-associated sulfate (CAS), which accounts for  (δS = +21‰). The second sulfur sink is pyrite burial in shelf sediments or deep seafloor sediments (; δS = −20‰).  The total marine sulfur output flux is  which matches the input fluxes, implying the modern marine sulfur budget is at steady state.  The residence time of sulfur in modern global oceans is 13,000,000 years.