Significance of the Terrestrial Sink in the Biogeochemical Sulfur Cycle

Abstract

Earth's oxidation state and climate are both a cause and consequence of biogeochemical element cycles. As the sixth most abundant element present in both the geosphere and biosphere (Brychkova et al., 2007;Mandeville, 2010;Torres et al., 2014) in variable oxidation states, sulfur plays a major role in shaping Earth's surface environments (Berner & Raiswell, 1983;Fike et al., 2015). Terrestrial environments form a critical part of the global sulfur cycle as continental weathering provides the primary source of sulfate to the ocean, overwhelming magmatic inputs (Holser et al., 1989). Recently, increasing attention has turned toward possible feedback loops among atmospheric CO 2 , glaciation, and oxidative weathering of pyrite exposed on land (Bufe et al., 2021;Calmels et al., 2007;Torres et al., 2014Torres et al., , 2017. Quantitative models calculating pyrite-derived sulfate fluxes in rivers often assume conservative mixing of isotopically distinct sources (Chillrud et al., 1994;Szynkiewicz et al., 2015); however, catchment-scale studies report deviations from simple isotope mass balance (Finley et al., 1995;Turchyn et al., 2013). More importantly, the rate of global pyrite oxidation on land, estimated assuming conservative mixing between terrestrial end-members, does not balance with that of marine pyrite burial (Burke et al., 2018). These discrepancies, notwithstanding inherent uncertainties in calculations using a single isotope-mass balance model, suggest that weathering alone fails to capture the complex nature of the terrestrial sulfur cycle, jeopardizing our understanding of the global redox budget.To address this gap, we revisit the role of terrestrial environments in the biogeochemical sulfur cycle at both local and global scales. In the fluvial system downstream of the Jostedal Glacier, Norway (Figure 1), we examine the limitations of a conservative mixing model, using the sulfur isotope compositions of a range of geologic and

Arctic Permafrost Thawing Enhances Sulfide Oxidation

“…Furthermore, the oxidation of low valent sulfur species back to $${{\text{SO}}_{4}}^{2-}$$ can incorporate environmental oxygen and alter $${\delta }^{18}{\mathrm{O}}_{{\text{SO}}_{4}}$$ values without necessarily changing $${\delta }^{34}{\mathrm{S}}_{{\text{SO}}_{4}}$$ values (Mills et al., 2016). Microbial processes have previously been suggested to increase fluvial $${\delta }^{34}{\mathrm{S}}_{{\text{SO}}_{4}}$$ and $${\delta }^{18}{\mathrm{O}}_{{\text{SO}}_{4}}$$ values in permafrost settings and other landscapes (Joo et al., 2022; Jones et al., 2020), but there is also evidence that $${\delta }^{34}{\mathrm{S}}_{{\text{SO}}_{4}}$$ (Kemeny et al., 2021b) and $${\delta }^{18}{\mathrm{O}}_{{\text{SO}}_{4}}$$ (Burt et al., 2021) can behave conservatively in river systems.…”

Sulfur Isotope Geochemistry of Ice‐Wedges in Yakutia, East Siberia

“…For example, in certain aqueous and subsurface environments where the supply of atmospheric oxygen is limited, sulfate can be microbially reduced to sulfide with strong discrimination against heavier sulfur isotopes [19]. Given that plants assimilate sulfate from soil water, the sulfur isotopic offset, if any, between atmospheric sulfate and organic sulfur archived in the ice-wedge can help deduce the hydrogeochemical regimes of the study sites [20][21][22][23][24]. One of the major obstacles to sulfur isotope analysis of natural ice samples has been their low sulfur content compared with the sample requirements for conventional sulfur isotope analysis, but over the past decade, the use of multicollector inductively coupled plasma mass spectrometry (MC-ICP-MS) has reduced the sample size required for sulfur isotope analysis to a few nanomoles of sulfur [25,26].…”

What Controls the Sulfur Isotope Fractionation during Dissimilatory Sulfate Reduction?

“…5 Therefore, changes in the biogeochemical sulfur cycle, largely representing the flow of sulfur between the oxidized, soluble sulfate and the reduced, less soluble sulfide, have interacted extensively with the redox cycle of other elements, including the evolution of atmospheric oxygen. 5,6 Sulfur has four stable isotopes, 32 S (95.04%), 33 S (0.75%), 34 S (4.20%), and 36 S (0.015%), 7 patterns of sulfur isotope distribution in the Earth's surface environments. Instead of absolute abundance, the sulfur isotope compositions are conventionally reported with the delta notation in per mil variations relative to the Vienna Canyon Diablo Troilite (VCDT): δ X S = 1000 × ( X R sample / X R VCDT − 1), where X R is the X S/ 32 S ratio (X = 33, 34, or 36).…”

“…Such burial of sulfur reduced at the expense of oxygenically produced organic carbon leaves dioxygen behind in the ocean and atmosphere . Therefore, changes in the biogeochemical sulfur cycle, largely representing the flow of sulfur between the oxidized, soluble sulfate and the reduced, less soluble sulfide, have interacted extensively with the redox cycle of other elements, including the evolution of atmospheric oxygen. , …”

“… 5 Therefore, changes in the biogeochemical sulfur cycle, largely representing the flow of sulfur between the oxidized, soluble sulfate and the reduced, less soluble sulfide, have interacted extensively with the redox cycle of other elements, including the evolution of atmospheric oxygen. 5 , 6 …”