Significance of the Terrestrial Sink in the Biogeochemical Sulfur Cycle

An imbalance in pyrite weathering and burial is a primary mechanism responsible for oxygenation of the atmosphere and oceans, but key processes governing the terrestrial sulfur cycle remain nebulous. Here, we investigate components of the terrestrial sulfur cycle in a highly productive, glacier-fed catchment, and use a global mass balance model to constrain riverine sulfur fluxes. Chemistry of stream water and plant debris in the Jostedal watershed, Norway suggests sulfur isotope discrimination is occurring in the porewater. Global models also corroborate additional, previously overlooked pyrite burial with a modest isotope fractionation (<20 parts per thousand), similar to values reported from freshwater ecosystems. Collectively, our results indicate that a significant amount of sulfate produced by weathering remains trapped in terrestrial environments. This terrestrial sulfur sink might have waxed and waned over geologic time in response to major biogeochemical events such as terrestrial afforestation.