Elemental sulfur dynamics in the contemporary redox-driven cycles of coastal lowland acid sulfate soils

Elemental sulfur has an important role in the digenic transformation of precursor iron monosulfide minerals to pyrite. It and related polysulfide intermediates are known to enable the rapid formation of pyrite, including complex framboidal morphologies, and it is a key component for pyrite formation in sub-oxic environments such as sub-tidal sediments. Lesser known for elemental sulfur is its role in the contemporary sulfur-cycle of coastal lowland acid sulfate soil landscapes involving iron monosulfide formation and acidifying oxidation processes. We present new data on the occurrence and dynamics of elemental sulfur from coastal acid sulfate soil landscapes and laboratory oxidative resuspensions and reductive incubations. Our results show the formation of elemental sulfur is a primary and short-lived product of iron monosulfide oxidation. The kinetics of its formation and further oxidation to sulfate (accompanied by the liberation of acidity) or reduction to sulfide are presented. These observations illustrate that elemental sulfur has a fundamental role in contemporary sulfur cycling in acid sulfate soil landscapes. Elemental sulfur reactions provide anew depth to our understanding of the controls and limits of contemporary sulfur cycling in acid sulfate landscapes. In particular, the kinetics of iron sulfide oxidation and acidification and the rate limiting steps and formation pathways of iron monosulfide (FeS(s)) and pyrite.