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Abstract Stable isotope fractionation of sulfur offers a window into Io's tidal heating history, which is difficult to constrain because Io's dynamic atmosphere and high resurfacing rates leave it with a young surface. We constructed a numerical model to describe the fluxes in Io's sulfur cycle using literature constraints on rates and isotopic fractionations of relevant processes. Combining our numerical model with measurements of the34S/32S ratio in Io's atmosphere, we constrain the rates for the processes that move sulfur between reservoirs and model the evolution of sulfur isotopes over time. Gravitational stratification of SO2in the upper atmosphere, leading to a decrease in34S/32S with increasing altitude, is the main cause of sulfur isotopic fractionation associated with loss to space. Efficient recycling of the atmospheric escape residue into the interior is required to explain the34S/32S enrichment magnitude measured in the modern atmosphere. We hypothesize this recycling occurs by SO2surface frost burial and SO2reaction with crustal rocks, which founder into the mantle and/or mix with mantle‐derived magmas as they ascend. Therefore, we predict that magmatic SO2plumes vented from the mantle to the atmosphere will have lower34S/32S than the ambient atmosphere, yet are still significantly enriched compared to solar‐system average sulfur. Observations of atmospheric variations in34S/32S with time and/or location could reveal the average mantle melting rate and hence whether the current tidal heating rate is anomalous compared to Io's long‐term average. Our modeling suggests that tides have heated Io for >1.6 Gyr if Io today is representative of past Io.
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Sulfur isotopes reveal agricultural changes to the modern sulfur cycle
Abstract The environmental fates and consequences of intensive sulfur (S) applications to croplands are largely unknown. In this study, we used S stable isotopes to identify and trace agricultural S from field-to-watershed scales, an initial and timely step toward constraining the modern S cycle. We conducted our research within the Napa River Watershed, California, US, where vineyards receive frequent fungicidal S sprays. We measured soil and surface water sulfate concentrations ([SO42−]) and stable isotopes (δ34S–SO42−), which we refer to in combination as the ‘S fingerprint’. We compared samples collected from vineyards and surrounding forests/grasslands, which receive background atmospheric and geologic S sources. Vineyardδ34S–SO42−values were 9.9 ± 5.9‰ (median ± interquartile range), enriched by ∼10‰ relative to forests/grasslands (−0.28 ± 5.7‰). Vineyards also had roughly three-fold higher [SO42−] than forests/grasslands (13.6 and 5.0 mg SO42−–S l−1, respectively). Napa Riverδ34S–SO42−values, reflecting the watershed scale, were similar to those from vineyards (10.5 ± 7.0‰), despite vineyard agriculture constituting only ∼11% of the watershed area. Combined, our results provide important evidence that agricultural S is traceable at field-to-watershed scales, a critical step toward determining the consequences of agricultural alterations to the modern S cycle.
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- Award ID(s):
- 1945388
- PAR ID:
- 10366534
- Publisher / Repository:
- IOP Publishing
- Date Published:
- Journal Name:
- Environmental Research Letters
- Volume:
- 17
- Issue:
- 5
- ISSN:
- 1748-9326
- Page Range / eLocation ID:
- Article No. 054032
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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