Balancing the marine sulfur cycle

Abstract

Sulfate (SO₄²⁻) reduction is a major SO₄²⁻ output flux from Earth's oceans, but an imbalance between recent estimates of this flux and corresponding input fluxes suggests inaccuracy in our understanding. Here, we combine global geographic trends in aqueous and dissolved-phase sedimentary data to resolve this inaccuracy. [SO₄²⁻] profiles from 700+ sites partition into geographically-distinct k-means clusters based on net sulfate reduction rate (nSRR). Pairing nSRRs with literature-derived pyrite accumulation rates confirms that shelf and slope pyrite burial dominate burial globally. Our results also suggest that sampling and measurement biases have led to erroneously high prior global output estimates and can account for the flux imbalance. Disparate mean δ³⁴S values for shelf versus deeper ocean pyrite indicate that sea level change may be an overlooked mechanism for forcing past changes in seawater δ³⁴S.