Deciphering the atmospheric signal in marine sulfate oxygen isotope composition

Waldeck, Anna R.; Cowie, B.; Bertran, Emma; Wing, Boswell A.; Halevy, Itay; Johnston, David T.

doi:10.1016/j.epsl.2019.06.013

Cited by 19 publications

(33 citation statements)

References 57 publications

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“…distributed over the anoxic oceanic water mass and underlying sediment. This value is several times lower than estimates of modern sulfate reduction rates (56), implying that the Ediacaran sulfur cycle may have been smaller than it is today. Therefore, it is likely that the deep ocean remained ferruginous across this transition, consistent with redox proxy records (33,49,50).…”

Section: Resultsmentioning

confidence: 60%

Ediacaran reorganization of the marine phosphorus cycle

Laakso

Sperling

Johnston

et al. 2020

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

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The Ediacaran Period (635 to 541 Ma) marks the global transition to a more productive biosphere, evidenced by increased availability of food and oxidants, the appearance of macroscopic animals, significant populations of eukaryotic phytoplankton, and the onset of massive phosphorite deposition. We propose this entire suite of changes results from an increase in the size of the deep-water marine phosphorus reservoir, associated with rising sulfate concentrations and increased remineralization of organic P by sulfate-reducing bacteria. Simple mass balance calculations, constrained by modern anoxic basins, suggest that deep-water phosphate concentrations may have increased by an order of magnitude without any increase in the rate of P input from the continents. Strikingly, despite a major shift in phosphorite deposition, a new compilation of the phosphorus content of Neoproterozoic and early Paleozoic shows little secular change in median values, supporting the view that changes in remineralization and not erosional P fluxes were the principal drivers of observed shifts in phosphorite accumulation. The trigger for these changes may have been transient Neoproterozoic weathering events whose biogeochemical consequences were sustained by a set of positive feedbacks, mediated by the oxygen and sulfur cycles, that led to permanent state change in biogeochemical cycling, primary production, and biological diversity by the end of the Ediacaran Period.

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Section: Resultsmentioning

confidence: 60%

Ediacaran reorganization of the marine phosphorus cycle

Laakso

Sperling

Johnston

et al. 2020

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

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“…Sulfate ∆ 17 O trends corroborate the importance of MSR and secondary sulfur recycling in downstream catchments. Although the mass-dependent relationship describing MSR (θ MSR ) is poorly constrained, it likely lies between 0.5270 and 0.5305 (58). If we assume pyrite oxidation throughout the catchment generates primary sulfate with an isotope composition similar to that observed in high-elevation headwater streams, then fractionation by MSR would lead to the observed increase in δ 18 O as well as a slight decrease in ∆ 17 O of residual sulfate (Fig.…”

Section: Resultsmentioning

confidence: 98%

Triple oxygen isotope insight into terrestrial pyrite oxidation

Hemingway

Olson

Turchyn

et al. 2020

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

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The mass-independent minor oxygen isotope compositions (Δ′17O) of atmospheric O2andCO2are primarily regulated by their relative partial pressures,pO2/pCO2. Pyrite oxidation during chemical weathering on land consumesO2and generates sulfate that is carried to the ocean by rivers. The Δ′17O values of marine sulfate deposits have thus been proposed to quantitatively track ancient atmospheric conditions. This proxy assumes directO2incorporation into terrestrial pyrite oxidation-derived sulfate, but a mechanistic understanding of pyrite oxidation—including oxygen sources—in weathering environments remains elusive. To address this issue, we present sulfate source estimates and Δ′17O measurements from modern rivers transecting the Annapurna Himalaya, Nepal. Sulfate in high-elevation headwaters is quantitatively sourced by pyrite oxidation, but resulting Δ′17O values imply no direct troposphericO2incorporation. Rather, our results necessitate incorporation of oxygen atoms from alternative,17O-enriched sources such as reactive oxygen species. Sulfate Δ′17O decreases significantly when moving into warm, low-elevation tributaries draining the same bedrock lithology. We interpret this to reflect overprinting of the pyrite oxidation-derived Δ′17O anomaly by microbial sulfate reduction and reoxidation, consistent with previously described major sulfur and oxygen isotope relationships. The geologic application of sulfate Δ′17O as a proxy for pastpO2/pCO2should consider both 1) alternative oxygen sources during pyrite oxidation and 2) secondary overprinting by microbial recycling.

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“…For the measurement of Δ 17 O SO4 values, two methods are in use: (1) laser fluorination 24 and (2) pyrolysis 25 . Laser fluorination generates O 2 from >10 μmol of natural sulfate converted into BaSO 4 with a precision in Δ 17 O of 0.02–0.05‰ 17,24,26 . For smaller sample sizes, e.g., aerosol sulfate from ice cores, the pyrolysis method is used 5–8 .…”

Section: Introductionmentioning

confidence: 99%

“…are recorded as variable Δ 17 O SO4 values in sulfates from ice cores [5][6][7][8] or desert soils. [9][10][11] These records trace the global-scale intra-decadal ENSO climate cycles, 12 and the distribution and biologic cycling of SAS deposition.…”

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confidence: 99%

Optimizing sulfate pyrolysis triple oxygen isotope analysis for samples from desert environments

Klipsch

Herwartz

Staubwasser

2021

Rapid Comm Mass Spectrometry

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Rationale The triple oxygen isotope composition of sulfate may reveal the formation pathway and depositional sources and may indicate slow biologic cycling in the environment. Pyrolysis mass spectrometry is better suited for large sample workloads during environmental profiling but sufficient precision and a thorough verification of accuracy are required for comparison with higher precision laser fluorination data. Methods Quantitative sulfate extraction from soil samples at neutral pH, purification, conversation into Ag‐sulfate, and pyrolysis mass spectrometry were modified for high sample throughput. Samples were analyzed after pyrolysis in quartz cups and gold capsules in a modified EuroVector model 3000 elemental analyzer. Sample O2 was measured in continuous He‐flow after purification by cryo‐trapping and chromatography on a Thermo Finnigan MAT253 isotope ratio mass spectrometer. A protocol for routine quality control and data normalization ensures long‐term accuracy of the pyrolysis method. Results The 1σ SD external reproducibility is 0.12‰ for Δ17OSO4 values on 30 μmol samples. Careful normalization for a daily analytical session accounts for changing pyrolysis conditions over the course of multiple sessions. The precision and accuracy obtained with quartz cups are comparable with those obtained with gold capsules. Pyrolysis and fluorination data for in‐house standards from four laboratories and from an Atacama Desert gypsum‐soil profile are identical and demonstrate the accuracy of our simplified method. Conclusions Pyrolysis of sulfate in quartz cups and a modified simple elemental analyzer setup allows for accurate, precise, fast, cost‐efficient, and non‐hazardous mass spectrometric analysis. Exchangeability of data from pyrolysis and laser fluorination methods was demonstrated by repeat analysis of standards and natural samples despite high contents of interfering, easily soluble nitrates and chlorides.

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Deciphering the atmospheric signal in marine sulfate oxygen isotope composition

Cited by 19 publications

References 57 publications

Ediacaran reorganization of the marine phosphorus cycle

Ediacaran reorganization of the marine phosphorus cycle

Triple oxygen isotope insight into terrestrial pyrite oxidation

Optimizing sulfate pyrolysis triple oxygen isotope analysis for samples from desert environments

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