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The end-Triassic mass extinction overlapped with the eruption of the Central Atlantic Magmatic Province (CAMP), and release of CO 2 and other volcanic volatiles has been implicated in the extinction. However, the timing of marine biotic recovery versus CAMP eruptions remains uncertain. Here we use Hg concentrations and isotopes as indicators of CAMP volcanism in continental shelf sediments, the primary archive of faunal data. In Triassic–Jurassic strata, Muller Canyon, Nevada, Hg levels rise in the extinction interval, peak before the appearance of the first Jurassic ammonite, remain above background in association with a depauperate fauna, and fall to pre-extinction levels during significant pelagic and benthic faunal recovery. Hg isotopes display no significant mass independent fractionation within the extinction and depauperate intervals, consistent with a volcanic origin for the Hg. The Hg and palaeontological evidence from the same archive indicate that significant biotic recovery did not begin until CAMP eruptions ceased. The association between Central Atlantic Magmatic Province (CAMP) eruption volatiles and the end-Triassic mass extinction remains ambiguous. Here, the authors present mercury and palaeontological evidence from the same archive and show that significant biotic recovery did not begin until CAMP eruptions ceased.

Wildfire alters the hydrologic cycle, with important implications for water supply and hazards including flooding and debris flows. In this study we use a combination of electrical resistivity and stable water isotope analyses to investigate the hydrologic response during storms in three catchments: one unburned and two burned during the 2020 Bobcat Fire in the San Gabriel Mountains, California, USA. Electrical resistivity imaging shows that in the burned catchments, rainfall infiltrated into the weathered bedrock and persisted. Stormflow isotope data indicate that the amount of mixing of surface and subsurface water during storms was similar in all catchments, despite higher streamflow post-fire. Therefore, both surface runoff and infiltration likely increased in tandem. These results suggest that the hydrologic response to storms in post-fire environments is dynamic and involves more surface-subsurface exchange than previously conceptualized, which has important implications for vegetation regrowth and post-fire landslide hazards for years following wildfire. This study tracks changes in post-fire hydrology in the San Gabriel Mountains, California, USA, and finds that rapid infiltration and storage of subsurface water in burned catchments contributes to increased streamflow during storms.

Rapid warming in the Arctic threatens to destabilize mercury (Hg) deposits contained within soils in permafrost regions. Yet current estimates of the amount of Hg in permafrost vary by ∼4 times. Moreover, how Hg will be released to the environment as permafrost thaws remains poorly known, despite threats to water quality, human health, and the environment. Here we present new measurements of total mercury (THg) contents in discontinuous permafrost in the Yukon River Basin in Alaska. We collected riverbank and floodplain sediments from exposed banks and bars near the villages of Huslia and Beaver. Median THg contents were 49 +13 / −21 ng THg g sediment −1 and 39 +16 / −18 ng THg g sediment −1 for Huslia and Beaver, respectively (uncertainties as 15th and 85th percentiles). Corresponding THg:organic carbon ratios were 5.4 +2.0 / −2.4 Gg THg Pg C −1 and 4.2 +2.4 / −2.9 Gg THg Pg C −1 . To constrain floodplain THg stocks, we combined measured THg contents with floodplain stratigraphy. Trends of THg increasing with smaller sediment size and calculated stocks in the upper 1 m and 3 m are similar to those suggested for this region by prior pan-Arctic studies. We combined THg stocks and river migration rates derived from remote sensing to estimate particulate THg erosional and depositional fluxes as river channels migrate across the floodplain. Results show similar fluxes within uncertainty into the river from erosion at both sites (95 +12 / −47 kg THg yr −1 and 26 +154 / −13 kg THg yr −1 at Huslia and Beaver, respectively), but different fluxes out of the river via deposition in aggrading bars (60 +40 / −29 kg THg yr −1 and 10 +5.3 / −1.7 kg THg yr −1 ). Thus, a significant amount of THg is liberated from permafrost during bank erosion, while a variable but generally lesser portion is subsequently redeposited by migrating rivers.

Mass extinctions have repeatedly perturbed the history of life, but their causes are often elusive. Ocean acidification has been implicated during Triassic–Jurassic environmental perturbations, but this interval lacks direct reconstructions of ocean pH. Here, we present boron isotope data from well-preserved fossil oysters, which provide evidence for acidification of ≥ 0.29 pH units coincident with a 2 ‰ negative carbon isotope excursion (the “main” CIE) following the end–Triassic extinction. These results suggest a prolonged interval of CO 2 -driven environmental perturbation that may have delayed ecosystem recovery. Earth system modelling with cGENIE paired with our pH constraints demonstrates this was driven by predominantly mantle-derived carbon. Ocean acidification therefore appears to be associated with three of the five largest extinction events in Earth history, highlighting the catastrophic ecological impact of major perturbations to the carbon cycle in Earth’s past, and possibly Earth’s anthropogenically perturbed future. A pulse of ocean acidification is reconstructed from the boron isotope composition of fossilized oysters at the Triassic-Jurassic boundary, implicating ocean acidification from volcanic outgassing as a kill mechanism during the extinction event.

The mass of carbon stored as organic matter in terrestrial systems is sufficiently large to play an important role in the global biogeochemical cycling of CO2 and O2. Field measurements of radiocarbon-depleted particulate organic carbon (POC) in rivers suggest that terrestrial organic matter persists in surface environments over millennial (or greater) timescales, but the exact mechanisms behind these long storage times remain poorly understood. To address this knowledge gap, we developed a numerical model for the radiocarbon content of riverine POC that accounts for both the duration of sediment storage in river deposits and the effects of POC cycling. We specifically target rivers because sediment transport influences the maximum amount of time organic matter can persist in the terrestrial realm and river catchment areas are large relative to the spatial scale of variability in biogeochemical processes.Our results show that rivers preferentially erode young deposits, which, at steady state, requires that the oldest river deposits are stored for longer than expected for a well-mixed sedimentary reservoir. This geometric relationship can be described by an exponentially tempered power-law distribution of sediment storage durations, which allows for significant aging of biospheric POC. While OC cycling partially limits the effects of sediment storage, the consistency between our model predictions and a compilation of field data highlights the important role of storage in setting the radiocarbon content of riverine POC. The results of this study imply that the controls on the terrestrial OC cycle are not limited to the factors that affect rates of primary productivity and respiration but also include the dynamics of terrestrial sedimentary systems.

Sulphide oxidation coupled to carbonate dissolution can provide a transient source of carbon dioxide to Earth’s atmosphere and so balance the Cenozoic increase in carbon dioxide consumption by silicate weathering, reconciling this increase with the need for mass balance in the long-term carbon cycle. Balancing the Cenozoic carbon budget It is thought that mountain uplift stimulated carbon dioxide consumption by silicate mineral weathering during the Cenozoic era, roughly spanning the past 66 million years, but there are no signs of a corresponding increase in volcanic carbon dioxide emissions that could balance the carbon budget. This paper suggests that some of the missing carbon dioxide could have been produced by coupled sulphide oxidation and carbonate dissolution, a process that may also have been accelerated in response to uplift. This hypothesis is consistent with isotopic records and may help explain the interactions between the long-term carbon cycle, tectonics, and Earth's climate. The observed stability of Earth’s climate over millions of years is thought to depend on the rate of carbon dioxide (CO 2 ) release from the solid Earth being balanced by the rate of CO 2 consumption by silicate weathering 1 . During the Cenozoic era, spanning approximately the past 66 million years, the concurrent increases in the marine isotopic ratios of strontium, osmium and lithium 2 , 3 , 4 suggest that extensive uplift of mountain ranges may have stimulated CO 2 consumption by silicate weathering 5 , but reconstructions of sea-floor spreading 6 do not indicate a corresponding increase in CO 2 inputs from volcanic degassing. The resulting imbalance would have depleted the atmosphere of all CO 2 within a few million years 7 . As a result, reconciling Cenozoic isotopic records with the need for mass balance in the long-term carbon cycle has been a major and unresolved challenge in geochemistry and Earth history. Here we show that enhanced sulphide oxidation coupled to carbonate dissolution can provide a transient source of CO 2 to Earth’s atmosphere that is relevant over geological timescales. Like drawdown by means of silicate weathering, this source is probably enhanced by tectonic uplift, and so may have contributed to the relative stability of the partial pressure of atmospheric CO 2 during the Cenozoic. A variety of other hypotheses 8 , 9 , 10 have been put forward to explain the ‘Cenozoic isotope-weathering paradox’, and the evolution of the carbon cycle probably depended on multiple processes. However, an important role for sulphide oxidation coupled to carbonate dissolution is consistent with records of radiogenic isotopes 2 , 3 , atmospheric CO 2 partial pressure 11 , 12 and the evolution of the Cenozoic sulphur cycle, and could be accounted for by geologically reasonable changes in the global dioxygen cycle, suggesting that this CO 2 source should be considered a potentially important but as yet generally unrecognized component of the long-term carbon cycle.

The isotopic composition of iron, zinc, copper, and cadmium (δ56Fe, δ66Zn, δ65Cu, and δ114Cd) are novel and promising tools to study the metabolism and homeostasis of trace metals in the human body. Serum δ65Cu has been proposed as a potential tool for diagnosis of cancer in liquid biopsy, and other metals may have similar utility. However, accurate analysis of trace metal isotopes is challenging because of the difficulties in purifying the metals from biological samples. Here we developed a simple and rapid method for sequential purification of Cu, Fe, Zn, and Cd from a single blood plasma sample. By using a combination of 11 M acetic acid and 4 M HCl in the first steps of column chemistry on AG-MP1 resin, we dramatically improve the separation of Cu from matrix elements compared to previous methods which use concentrated HCl alone. Our new method achieves full recovery of Cu, Fe, Zn, and Cd to prevent column-induced isotope fractionation effects, and effectively separates analytes from the matrix in order to reduce polyatomic interferences during isotope analysis. Our methods were verified by the analysis of isotope standards, a whole blood reference material, and a preliminary sample set including five plasma samples from healthy individuals and five plasma samples from cancer patients. This new method simplifies preparation of blood samples for metal isotope analysis, accelerating multi-isotope approaches to medical studies and contributing to our understanding of the cycling of Fe, Zn, Cu, and Cd in the human body.

Connections between glaciation, chemical weathering, and the global carbon cycle could steer the evolution of global climate over geologic time, but even the directionality of feedbacks in this system remain to be resolved. Here, we assemble a compilation of hydrochemical data from glacierized catchments, use this data to evaluate the dominant chemical reactions associated with glacial weathering, and explore the implications for long-term geochemical cycles. Weathering yields from catchments in our compilation are higher than the global average, which results, in part, from higher runoff in glaciated catchments. Our analysis supports the theory that glacial weathering is characterized predominantly by weathering of trace sulfide and carbonate minerals. To evaluate the effects of glacial weathering on atmospheric pCO₂, we use a solute mixing model to predict the ratio of alkalinity to dissolved inorganic carbon (DIC) generated by weathering reactions. Compared with nonglacial weathering, glacial weathering is more likely to yield alkalinity/DIC ratios less than 1, suggesting that enhanced sulfide oxidation as a result of glaciation may act as a source of CO₂ to the atmosphere. Back-of-the-envelope calculations indicate that oxidative fluxes could change ocean–atmosphere CO₂ equilibrium by 25 ppm or more over 10 ky. Over longer timescales, CO₂ release could act as a negative feedback, limiting progress of glaciation, dependent on lithology and the concentration of atmospheric O₂. Future work on glaciation–weathering–carbon cycle feedbacks should consider weathering of trace sulfide minerals in addition to silicate minerals.

The evolution of the global carbon and silicon cycles is thought to have contributed to the long-term stability of Earth’s climate 1 – 3 . Many questions remain, however, regarding the feedback mechanisms at play, and there are limited quantitative constraints on the sources and sinks of these elements in Earth’s surface environments 4 – 12 . Here we argue that the lithium-isotope record can be used to track the processes controlling the long-term carbon and silicon cycles. By analysing more than 600 shallow-water marine carbonate samples from more than 100 stratigraphic units, we construct a new carbonate-based lithium-isotope record spanning the past 3 billion years. The data suggest an increase in the carbonate lithium-isotope values over time, which we propose was driven by long-term changes in the lithium-isotopic conditions of sea water, rather than by changes in the sedimentary alterations of older samples. Using a mass-balance modelling approach, we propose that the observed trend in lithium-isotope values reflects a transition from Precambrian carbon and silicon cycles to those characteristic of the modern. We speculate that this transition was linked to a gradual shift to a biologically controlled marine silicon cycle and the evolutionary radiation of land plants 13 , 14 . Analysis of shallow-water marine carbonate samples from 101 stratigraphic units allows construction of a record of lithium isotopes from the past 3 billion years, tracking the evolution of the global carbon and silicon cycles.

Evidence for relationships between seismotectonic activity and dissolved weathering fluxes remains limited. Motivated by the occurrence of new springs emerging after the 2016 Kumamoto earthquake and supported by historical groundwater data, this study focuses on the long-term effect of near-surface structural deformation on the contribution of deep, highly saline fluids to the solute fluxes from the Aso caldera, Kyushu, Japan. Available hydrologic and structural data suggest that concentrated, over-pressured groundwaters migrate to the surface when new hydraulic pathways open during seismic deformation. These new springs have a hydrochemical fingerprint (including δD H2O , δ 18 O H2O , δ 7 Li, δ 11 B, δ 18 O SO4 , and δ 34 S SO4 ) indistinguishable from long-established confined groundwater that likely reflects a mixture of infiltrated meteoric water with high-sulfate hydrothermal fluids. A comparison of historical hydrochemistry data and patterns of past seismicity suggests that discharge of deep fluids is associated with similar deformation structures to those observed during the Kumamoto earthquake, and that seismic activity plays an important role over historic timescales in delivering the majority of the solutes to the caldera outlet, sustaining fluxes that are amongst the world’s highest. This upwelling mechanism might be relevant for other systems too, and could contribute to the over-proportional share of active volcanic areas in global weathering fluxes.