Strong local, not global, controls on marine pyrite sulfur isotopes.
basic_science · Level V
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- Record sourced from PubMed, PMID 33637519.
- Also identified by DOI 10.1126/sciadv.abb7403 and PMC identifier 7909874.
- Licence recorded as CC BY-NC.
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Abstract
Understanding variation in the sulfur isotopic composition of sedimentary pyrite (δ<sup>34</sup>S<sub>pyr</sub>) is motivated by the key role of sulfur biogeochemistry in regulating Earth's surface oxidation state. Until recently, the impact of local depositional conditions on δ<sup>34</sup>S<sub>pyr</sub> has remained underappreciated, and stratigraphic variations in δ<sup>34</sup>S<sub>pyr</sub> were interpreted mostly to reflect global changes in biogeochemical cycling. We present two coeval δ<sup>34</sup>S<sub>pyr</sub> records from shelf and basin settings in a single sedimentary system. Despite their proximity and contemporaneous deposition, these two records preserve radically different geochemical signals. Swings of ~65‰ in shelf δ<sup>34</sup>S<sub>pyr</sub> track short-term variations in local sedimentation and are completely absent from the abyssal record. In contrast, a long-term ~30‰ decrease in abyssal δ<sup>34</sup>S<sub>pyr</sub> reflects regional changes in ocean circulation and/or sustained pyrite formation. These results highlight strong local controls on δ<sup>34</sup>S<sub>pyr</sub>, calling for reevaluation of the current practice of using δ<sup>34</sup>S<sub>pyr</sub> stratigraphic variations to infer global changes in Earth's surface environment.