Evaluating the S-isotope fractionation associated with Phanerozoic pyrite burial

Wu, Nanping; Farquhar, James; Strauß, Harald; Kim, Sang‐Tae; Canfield, Donald E.

doi:10.1016/j.gca.2009.12.012

Cited by 89 publications

(67 citation statements)

References 79 publications

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“…Records of 34 e GEO and 33 λ GEO from Phanerozoic sedimentary basins provide a time-series approximation of the mean isotopic difference between coeval sulfates and sulfides ( Fig. 3 and Table S1) (13,54). In parallel, we use recent estimates for the areal extent of continental shelf and abyssal ocean across Phanerozoic time (Table S1) (55,56).…”

Section: Decoupling the Isotopic Effects Of Sulfate Reduction Rates Fmentioning

confidence: 99%

Influence of sulfate reduction rates on the Phanerozoic sulfur isotope record

Leavitt

Halevy

Bradley

et al. 2013

Proc. Natl. Acad. Sci. U.S.A.

305

276

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Phanerozoic levels of atmospheric oxygen relate to the burial histories of organic carbon and pyrite sulfur. The sulfur cycle remains poorly constrained, however, leading to concomitant uncertainties in O 2 budgets. Here we present experiments linking the magnitude of fractionations of the multiple sulfur isotopes to the rate of microbial sulfate reduction. The data demonstrate that such fractionations are controlled by the availability of electron donor (organic matter), rather than by the concentration of electron acceptor (sulfate), an environmental constraint that varies among sedimentary burial environments. By coupling these results with a sediment biogeochemical model of pyrite burial, we find a strong relationship between observed sulfur isotope fractionations over the last 200 Ma and the areal extent of shallow seafloor environments. We interpret this as a global dependency of the rate of microbial sulfate reduction on the availability of organic-rich sea-floor settings. However, fractionation during the early/mid-Paleozoic fails to correlate with shelf area. We suggest that this decoupling reflects a shallower paleoredox boundary, primarily confined to the water column in the early Phanerozoic. The transition between these two states begins during the Carboniferous and concludes approximately around the Triassic-Jurassic boundary, indicating a prolonged response to a Carboniferous rise in O 2 . Together, these results lay the foundation for decoupling changes in sulfate reduction rates from the global average record of pyrite burial, highlighting how the local nature of sedimentary processes affects global records. This distinction greatly refines our understanding of the S cycle and its relationship to the history of atmospheric oxygen.Phanerozoic oxygen | sulfate-reducing bacteria T he marine sedimentary sulfur isotope record encodes information on the chemical and biological composition of Earth's ancient oceans and atmosphere (1, 2). However, our interpretation of the isotopic composition of S-bearing minerals is only as robust as our understanding of the mechanisms that impart a fractionation. Fortunately, decades of research identify microbial sulfate reduction (MSR) as the key catalyst of the marine S cycle, both setting the S cycle in motion and dominating the massdependent fractionation preserved within the geological record (1, 3, 4). Despite the large range of S-isotope variability observed in biological studies (4-6), attempts to calibrate the fractionations associated with MSR are less mechanistically definitive (7, 8) than analogous processes influencing the carbon cycle (9, 10). What is required is a means to predict S isotope signatures as a function of the physiological response to environmental conditions (e.g., reduction-oxidation potential).Microbial sulfate reduction couples the oxidation of organic matter or molecular hydrogen to the production of sulfide, setting in motion a cascade of reactions that come to define the biogeochemical S cycle. In modern marine sediments, sulfide i...

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Section: Decoupling the Isotopic Effects Of Sulfate Reduction Rates Fmentioning

confidence: 99%

Influence of sulfate reduction rates on the Phanerozoic sulfur isotope record

Leavitt

Halevy

Bradley

et al. 2013

Proc. Natl. Acad. Sci. U.S.A.

305

276

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“…M is the concentration of seawater sulfate and δ is its sulfur isotopic composition, known from the fluid inclusion data and the δ 34 S compilations, respectively (7)(8)(9)(10). J e and J p are the burial fluxes of sulfate evaporite and pyrite, respectively.…”

Section: Modelsmentioning

confidence: 99%

“…The value of Δ is taken from (8), who used records of δ 34 S from CAS, evaporite and barite and coeval sedimentary pyrite together with constraints on the mass-law of bacterial sulfate reduction. Below is a brief description of each of the models.…”

Section: Modelsmentioning

confidence: 99%

Sulfate Burial Constraints on the Phanerozoic Sulfur Cycle

Halevy

Peters

Fischer

2012

Science

150

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More than a Dash of Sea Salt The cycling of major elements, such as sulfur, in the oceans depends on a number of processes, from bacterial respiration of organic matter to venting of gases from hydrothermal vents on the seafloor. Over geologic time, sediment deposited on the seafloor preserves chemical records of major changes in sulfur cycling and seawater chemistry (see the Perspective by Hurtgen ). Halevy et al. (p. 331 ) observed swings in sulfur isotopes in a stratigraphic database covering North America and the Caribbean that, when modeled, corresponded to variable evaporite preservation and high turnover of sedimentary pyrite. Wortmann and Paytan (p. 334 ) modeled the two most recent major swings in sedimentary sulfur isotopes over the last 130 million years and suggest that short periods of rapid fluxes in sulfur cycling were at least in part caused by the growth and dissolution of evaporite deposits.

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“…The ultimate origin of the observed asymmetry in the ∆ 33 S record (i.e., the presence of a weatherable sulphur reservoir with a positive ∆ 33 S value) can be linked to the relative transport and removal processes of the two main sulphur redox species upon introduction to the hydrosphere -sulphate aerosols, which transfer negative ∆ 33 S anomalies, and zero-valent sulphur, which carries positive ∆ 33 S anomalies. Atmospheric sulphate aerosols would have been incorporated into the relatively well-mixed seawater sulphate reservoir and a significant portion of this reservoir would thus have been sequestered in deep-sea sediments through hydrothermal [42][43][44] (thermochemical) or microbial sulphate reduction and subsequently subducted into an isotopically well-buffered mantle.…”

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confidence: 99%

“…Elemental sulphur aerosols would typically have much more limited transport from point sources associated with subaerial volcanism 45,46 , a result of limited aqueous solubility of elemental sulphur in systems that are not sulphide-buffered 47 . The end result of these processes would have been preferential burial of sulphur with positive ∆ 33 S values in marginal and epicontinental settings, which will have a higher potential (than deep-sea sediments) of becoming incorporated into the weatherable shell. In other words, the empirical record is asymmetric, and this is exactly what one would predict considering the current paradigm for the formation and transport of ∆ 33 S anomalies.…”

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confidence: 99%

Long-term sedimentary recycling of rare sulphur isotope anomalies

Reinhard

Planavsky

Lyons

2013

Nature

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Sulphur Isotope Database:An extensive sulphur isotope database was used in the construction of Main Text Figure 1. These data were compiled from primary references 1-37 , although in some cases age constraints for certain units were obtained from other sources [38][39][40][41] or estimated. For Main Text Figure 1b, we calculated the cumulative average ∆ 33 S value for all samples up to each year of publication. The average values reported here thus include some contribution from sulphate minerals. However, the overwhelming majority of the data are sulphide mineral phases, and given that most sulphate data are characterized by negative ∆ 33 S values their inclusion will largely attenuate the pattern emphasized here, rendering our argument conservative. Furthermore, the overall effect of their inclusion is quite small (Fig. S1a,b). We also examined the effect of filtering data from analyses made via secondary ion mass spectrometry (SIMS) and analyses of macroscopic pyrite textures, which are not likely to be representative of bulk weathering crust, but again note that the basic pattern remains unchanged (Fig. S1a,b).The mean ∆ 33 S values shown in Fig. 1 are presented as unweighted averages. We consider this approach qualitatively justified, in that the database is composed largely of fine-grained siliciclastic sedimentary rocks that are relatively organic carbon and sulphur rich. Such rocks will not only be, on average, the most sulphur-enriched phases of the crust, but they will also likely hold the majority of the weathering sulphur reservoir at Earth's surface. Nonetheless, it is important to consider the possibility that there is a bias related to systematic relationships between the sulphur content of sedimentary rocks and their ∆ 33 S value. For this purpose, we compiled the available sulphur concentration data for the units within the isotope database and performed concentration-weighted statistical analyses.There does not appear to be any systematic relationship between rare sulphur isotope composition and sulphur content within the database (Fig. S2a). In addition, the cumulative unweighted average is nearly indistinguishable from the concentration-weighted average within this subset of the database (Fig. S2a,b). When the evolution of the overall ∆ 33 S value of the database is concentration-weighted, it shows a generally similar pattern through time to that of the overall mean values (Fig. S2b). Indeed, the mean ∆ 33 S value when weighted by concentration is more positive than the unweighted mean for a given population from the database. We stress the caveat that many of the published rare sulphur isotope datasets do not contain sulphur concentration data, so unfortunately this analysis cannot be performed on the entire database. However, the coupled isotope and concentration data represent well over 500 samples that range in sulphur content over three orders of magnitude. These considerations lead us to conclude that the pattern expressed in the overall mean ∆ 33 S values through time is robust and is ...

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Evaluating the S-isotope fractionation associated with Phanerozoic pyrite burial

Cited by 89 publications

References 79 publications

Influence of sulfate reduction rates on the Phanerozoic sulfur isotope record

Influence of sulfate reduction rates on the Phanerozoic sulfur isotope record

Sulfate Burial Constraints on the Phanerozoic Sulfur Cycle

Long-term sedimentary recycling of rare sulphur isotope anomalies

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