In this installment of SAS Board Reading Recommendations, SAS President Elect Paul Szpak selected “Major excursions in sulfur isotopes linked to permafrost change in Eurasia during the last 50,000 years” by Rhiannon Stevens et al., published in Nature Geosciences in August 2025. Stevens et al. determined the sulfur isotope composition (δ34S) of the bone collagen of over 700 14C-dated mammalian megafauna from Eurasia. They found unusually low sulfur isotope values in some regions between 30,000 and 15,000 years BP, which they dub the Late Pleniglacial Sulfur Excursion. They suggest that this pattern of very low sulfur isotope values was driven by changing permafrost dynamics, specifically in areas that had extensive permafrost that later melted. This melting altered the water availability in the soil, creating conditions that favoured waterlogged conditions, encouraging the production of sulfides via bacterial dissimilatory sulfate reduction. Of the chemical elements common in organic compounds (CHONS), sulfur is notoriously difficult to analyze via stable isotope analysis: it is not very abundant and the SO2 that is produced during analysis is very ‘sticky’. Because it has been less commonly analyzed, we are just starting to gain a deeper understanding of how and why sulfur isotopes vary in the biosphere. The paper by Stevens et al., is one of several recent studies that have found that wetlands and similar environments produce characteristically low sulfur isotope values, meaning that they could serve as a marker of exploitation of these environments by past human and animal populations.
Stevens, R.E., Reade, H., Sayle, K.L., Tripp, J.A., Frémondeau, D., Lister, A., Barnes, I., Germonpré, M., Street, M., Murton, J.B., Bottrell, S.H., James, D.H., Higham, T.F.G., 2025. Major excursions in sulfur isotopes linked to permafrost change in Eurasia during the last 50,000 years. Nat. Geosci. 18, 961–965. https://doi.org/10.1038/s41561-025-01760-x
See also:
Guiry, E.J., Orchard, T.J., Needs-Howarth, S., Szpak, P., 2022. Freshwater wetland–driven variation in sulfur isotope compositions: Implications for human paleodiet and ecological research. Front. Ecol. Evol. 10. https://doi.org/10.3389/fevo.2022.953042
Lamb, A.L., Chenery, C.A., Madgwick, R., Evans, J.A., 2023. Wet feet: developing sulfur isotope provenance methods to identify wetland inhabitants. R. Soc. Open Sci. 10, 230391. https://doi.org/10.1098/rsos.230391
Metcalfe, J.Z., Eady-Sitar, L.E., Hyodo, A., Belot, T., 2024. Sulfur isotope analysis of collagen: Quality controls and proboscidean wetland habitats. Quaternary Environments and Humans 2, 100040. https://doi.org/10.1016/j.qeh.2024.100040