Basalts from the Samoan volcanoes sample contributions from all of the classical mantle endmembers, including extreme EM II and high3He/4He components, as well as dilute contributions from the HIMU, EM I, and DM components. Here, we present multiple sulfur isotope data on sulfide extracted from subaerial and submarine whole rocks (
Mangaia, an ocean island in the Cook‐Austral volcanic chain, is the type locality for the HIMU mantle reservoir and has also been shown to exhibit evidence for recycled sulfur with anomalous δ34S and Δ33S that has been attributed an Archean origin. Here we report bulk S‐isotope data from sulfide inclusions in olivine and pyroxene phenocrysts from one of the previously analyzed and four additional Mangaia basalts to further test for the prevalence of anomalous S in the HIMU mantle source feeding Mangaia. We document compositions that range from −5.13‰ to +0.21‰ (±0.3 2σ), +0.006‰ to +0.049‰ (±0.016 2σ), −0.81‰ to +0.69‰ (±0.3 2σ) for δ34S, Δ33S, and Δ36S, respectively. These data extend the range of measured compositions and suggest S‐isotope heterogeneity in the HIMU mantle source at Mangaia. We show that S‐isotope compositions of bulk sulfide in olivine is not in isotopic equilibrium with bulk sulfide in pyroxene from the same samples and that samples from a confined area (M4, M10, M12, and M13) in the northern central part of the island show a distinct covariation for δ34S and Δ33S. This isotopic variation (forming an array) suggests mixing of sulfur from two sources that were captured at different stages of crystallization by phenocrysts in the Mangaia HIMU sulfur endmember.
more » « less- NSF-PAR ID:
- 10452281
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Geochemistry, Geophysics, Geosystems
- Volume:
- 21
- Issue:
- 10
- ISSN:
- 1525-2027
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Rationale Sulfur isotope analysis of organic sulfur‐containing molecules has previously been hindered by challenging preparatory chemistry and analytical requirements for large sample sizes. The natural‐abundance sulfur isotopic compositions of the sulfur‐containing amino acids, cysteine and methionine, have therefore not yet been investigated despite potential utility in biomedicine, ecology, oceanography, biogeochemistry, and other fields.
Methods Cysteine and methionine were subjected to hot acid hydrolysis followed by quantitative oxidation in performic acid to yield cysteic acid and methionine sulfone. These stable, oxidized products were then separated by reversed‐phase high‐performance liquid chromatography (HPLC) and verified via offline liquid chromatography/mass spectrometry (LC/MS). The sulfur isotope ratios (δ34S values) of purified analytes were then measured via combustion elemental analyzer coupled to isotope ratio mass spectrometry (EA/IRMS). The EA was equipped with a temperature‐ramped chromatographic column and programmable helium carrier flow rates.
Results On‐column focusing of SO2in the EA/IRMS system, combined with reduced He carrier flow during elution, greatly improved sensitivity, allowing precise (0.1–0.3‰ 1 s.d.) δ34S measurements of 1 to 10 μg sulfur. We validated that our method for purification of cysteine and methionine was negligibly fractionating using amino acid and protein standards. Proof‐of‐concept measurements of fish muscle tissue and bacteria demonstrated differences up to 4‰ between the δ34S values of cysteine and methionine that can be connected to biosynthetic pathways.
Conclusions We have developed a sensitive, precise method for measuring the natural‐abundance sulfur isotopic compositions of cysteine and methionine isolated from biological samples. This capability opens up diverse applications of sulfur isotopes in amino acids and proteins, from use as a tracer in organisms and the environment, to fundamental aspects of metabolism and biosynthesis.
