Sulfate Burial Constraints on the Phanerozoic Sulfur Cycle

Sulfate is the second most abundant anion (behind chloride) in modern seawater, and its cycling is intimately coupled to the cycling of organic matter and oxygen at the Earth's surface. For example, the reduction of sulfide by microbes oxidizes vast amounts of organic carbon and the subsequent reaction of sulfide with iron produces pyrite whose burial in sediments is an important oxygen source to the atmosphere. The concentrations of seawater sulfate and the operation of sulfur cycle have experienced dynamic changes through Earth's history, and our understanding of this history is based mainly on interpretations of the isotope record of seawater sulfates and sedimentary pyrites. The isotope record, however, does not give a complete picture of the ancient sulfur cycle. This is because, in standard isotope mass balance models, there are more variables than constraints. Typically, in interpretations of the isotope record and in the absence of better information, one assumes that the isotopic composition of the input sulfate to the oceans has remained constant through time. It is argued here that this assumption has a constraint over the last 390 Ma from the isotopic composition of sulfur in coal. Indeed, these compositions do not deviate substantially from the modern surface-water input to the oceans. When applied to mass balance models, these results support previous interpretations of sulfur cycle operation and counter recent suggestions that sulfate has been a minor player in sulfur cycling through the Phanerozoic Eon.

Section: Modeling From Metastratigraphic Datacontrasting

confidence: 47%

Section: Modeling From Metastratigraphic Datamentioning

confidence: 99%

mentioning

confidence: 99%

See 1 more Smart Citation

Sulfur isotopes in coal constrain the evolution of the Phanerozoic sulfur cycle

Canfield

2013

“…Continental oxidative weathering and mantlederived sulfur are fluxes that have a depleted sulfur and oxygen isotopic composition compared with seawater sulfate (4,24,27). Evaporite formation and successive burial (with a negligible fractionation) is a sink of sulfate, but its importance depends largely on the extent of suitable environments for deposition [with net evaporation rates (28)]. In contrast to the isotope value of sulfate sulfur, δ 18 O SO4 is considerably affected by MSR and microbial sulfur disproportionation (29).…”

Section: Resultsmentioning

confidence: 99%

Flourishing ocean drives the end-Permian marine mass extinction

Schobben

Stebbins

Ghaderi

et al. 2015

The end-Permian mass extinction, the most severe biotic crisis in the Phanerozoic, was accompanied by climate change and expansion of oceanic anoxic zones. The partitioning of sulfur among different exogenic reservoirs by biological and physical processes was of importance for this biodiversity crisis, but the exact role of bioessential sulfur in the mass extinction is still unclear. Here we show that globally increased production of organic matter affected the seawater sulfate sulfur and oxygen isotope signature that has been recorded in carbonate rock spanning the Permian−Triassic boundary. A bifurcating temporal trend is observed for the strata spanning the marine mass extinction with carbonate-associated sulfate sulfur and oxygen isotope excursions toward decreased and increased values, respectively. By coupling these results to a box model, we show that increased marine productivity and successive enhanced microbial sulfate reduction is the most likely scenario to explain these temporal trends. The new data demonstrate that worldwide expansion of euxinic and anoxic zones are symptoms of increased biological carbon recycling in the marine realm initiated by global warming. The spatial distribution of sulfidic water column conditions in shallow seafloor environments is dictated by the severity and geographic patterns of nutrient fluxes and serves as an adequate model to explain the scale of the marine biodiversity crisis. Our results provide evidence that the major biodiversity crises in Earth's history do not necessarily implicate an ocean stripped of (most) life but rather the demise of certain eukaryotic organisms, leading to a decline in species richness.sulfur cycle | end-Permian mass extinction | primary productivity

“…Volumes of organic-rich sediments required for volume flux calculations were based on sediment coverage area, unit thickness, and proportional abundance of organic-rich sediment within each unit (i.e., proportional lithological abundance was used to determine the thickness of the organic-rich component of a single Macrostrat unit). Our overall approach to volume flux calculation is comparable to that of Halevy et al (135). Raw data are available at the following Macrostrat application program interface (API): https://macrostrat.org/ api/v2/units?lith_type=organic&project_id=1&format=csv.…”

Section: Methodsmentioning

confidence: 68%

Delayed fungal evolution did not cause the Paleozoic peak in coal production

Nelsen

DiMichele

Peters

et al. 2016

Self Cite

114

Organic carbon burial plays a critical role in Earth systems, influencing atmospheric O 2 and CO 2 concentrations and, thereby, climate. The Carboniferous Period of the Paleozoic is so named for massive, widespread coal deposits. A widely accepted explanation for this peak in coal production is a temporal lag between the evolution of abundant lignin production in woody plants and the subsequent evolution of lignin-degrading Agaricomycetes fungi, resulting in a period when vast amounts of lignin-rich plant material accumulated. Here, we reject this evolutionary lag hypothesis, based on assessment of phylogenomic, geochemical, paleontological, and stratigraphic evidence. Lignin-degrading Agaricomycetes may have been present before the Carboniferous, and lignin degradation was likely never restricted to them and their class II peroxidases, because lignin modification is known to occur via other enzymatic mechanisms in other fungal and bacterial lineages. Furthermore, a large proportion of Carboniferous coal horizons are dominated by unlignified lycopsid periderm with equivalent coal accumulation rates continuing through several transitions between floral dominance by lignin-poor lycopsids and lignin-rich tree ferns and seed plants. Thus, biochemical composition had little relevance to coal accumulation. Throughout the fossil record, evidence of decay is pervasive in all organic matter exposed subaerially during deposition, and high coal accumulation rates have continued to the present wherever environmental conditions permit. Rather than a consequence of a temporal decoupling of evolutionary innovations between fungi and plants, Paleozoic coal abundance was likely the result of a unique combination of everwet tropical conditions and extensive depositional systems during the assembly of Pangea.lignin | carbon cycle | wood rot | fungi | lignin degradation