Highly intense wildfires exhibiting extreme combustion phenomena are becoming more common globally, yet little is known of their combustion temperatures compared to smaller fires. Fire behavior, postfire ecosystem recovery, and smoke constituents are sensitive to combustion temperature; while in-situ thermocouple measurements from experimental fires record temperatures <1500 degrees C, comparable measurements from extreme wildfires do not exist. Here, we investigate temperatures in the June 2023 megafires in Quebec via scanning transmission electron microscopy (STEM) and electron energy loss spectroscopy (EELS) analysis of the atomic ordering and nanoscale structure of carbon aerosols from the wildfire smoke, where higher combustion temperatures increase sp(2) CC bonding and ordered graphitic layering. From both direct lattice imaging and fine structure in EELS spectra, we observe features that are only present for highly graphitic carbons formed at heating regimes of 1900-2500 degrees C, temperatures that are >400-1000 degrees C higher than reported measurements of wildfire temperature. We interpret this disparity to result from a combination of extreme combustion phenomena such as pyrocumulonimbus clouds, which proliferated in Canada during the summer 2023 megafires, and limitations in the performance of thermocouples at such high temperatures. Although this study is limited in scope, our intention is to inspire researchers to question and revisit the convention on wildfire combustion temperatures and the processes that generate them. We propose that wider recognition of ultrahigh wildfire combustion temperatures may warrant a new paradigm in fire management, fire ecology, and air pollution for highly intense fires.

The impacts of sulfate aerosol from volcanic eruptions on the climate have been well recognized and simulated in climate models like the Community Earth System Model (CESM) 2.1.0. However, these models often neglect insoluble volcanic ash despite its substantial emission during eruptions and potential impact on the Earth system through mechanisms such as regional cooling, air quality degradation, and phytoplankton fertilization from deposition. Here, we incorporate volcanic ash into the CESM 2.1.0 for the first time and evaluate the model’s performance against both in situ and remote sensing observations of the 2010 Eyjafjallajökull eruption in Iceland. We further assess the impacts of volcanic ash from this eruption by conducting a suite of perturbation experiments to vary key parameters, including ash plume height and size distribution. The preliminary results suggest that the volcanic ash had an average global direct radiative forcing of 0.21 W/m 2 and a regional average of 23.6 W/m 2 during the approximately month-long eruptive phase. The volcano also added 0.08 Tg of soluble iron and increased local iron deposition approximately 28 to 38 times. These findings highlight the necessity of incorporating ash into the model to better understand how volcanic ash interacts with the Earth system.

Significant efforts are required to remove CO2 from the atmosphere to mitigate the worst effects of climate change. While several methods for CO2 capture and storage have been proposed, weathering of silicate-rich rocks—which releases divalent cations like magnesium and iron for subsequent carbonation—has the highest potential removal capacity. However, natural weathering and carbonation rates are far too slow to prevent significant atmospheric warming. Bio-accelerated weathering aims to use microorganisms to accelerate these processes, but while it has been explored in laboratories, its economic viability at large scale remains unknown. Here we calculate the costs and revenues of bio-accelerated weathering of ultramafic mine tailings by the mineral-dissolving microbe Gluconobacter oxydans. Without tax credits and with unfavorable feedstock market prices, the cost for capturing and storing one tonne of CO2 through bio-accelerated weathering could be as high as $3,465. However, under favorable feedstock pricing, tax credits, and revenue from co-leached metals, a profit of $3 per tonne of CO2 captured and stored could be obtained. This study identifies microbial feedstock costs as the major cost driver, suggesting that process optimization, alternative feedstock development, and genetic engineering are the efforts most likely to maximize economic viability. Our results suggest that bio-accelerated weathering warrants further exploration as a climate change mitigation strategy.

[This corrects the article DOI: 10.1371/journal.pone.0335161.].

The surface characterization of rocky exoplanets via emission spectroscopy represents a frontier of current (JWST) and future (HWO) observational efforts. Here, we implement new features in the open-source retrieval code to fully account for an emitting and reflecting planetary surface and an overlying absorbing and scattering atmosphere. We show that realistic rocky surfaces (with wavelength-dependent albedos derived from laboratory measurements) affect emission spectra by imparting mid-infrared diagnostic absorption features, imprinting pseudo-features due to atmospheric transparency windows, and flipping absorption features to emission via surface-atmosphere interface pseudo-temperature inversions. We demonstrate that current JWST spectral data can distinguish between tenuous (low surface pressure, ≤ 1 bar) and thick (high surface pressures, ≥ 0.1 bar) atmospheres by performing atmosphere + surface retrievals on published JWST emission data of the rocky worlds TOI-1685b and 55 Cancri e. We then explore JWST MIRI LRS's capability to constrain surface geology of rocky worlds, finding that with sufficient SNR retrievals can distinguish between granite-like and basaltic surfaces for synthetic datasets. Finally, we provide an open-source database of lab-derived surface albedos (in the form of directional-hemispherical reflectances), organized by geologic classification and include supplemental tables developed to foster future collaboration between geology and exoplanet science. Our atmosphere + surface retrieval technique provides a pathway to probe geologic processes on rocky exoplanets, showing that upcoming JWST data for terrestrial worlds will enable a deeper exploration of rocky surfaces beyond our Solar System.

Atmospheric deposition of micro-nutrients like Fe has been shown to be important for ocean biogeochemistry. The largest source of atmospheric Fe and other elements (e.g., Ca, Al, Si, and Ti) is desert dust, although there are significant non-dust sources in some regions (e.g., combustion, sea salts, volcanoes). However, past estimates of these elements have been substantially uncertain due to limited information about the composition of the desert source regions. Here we use elemental distributions estimated from new Earth Surface Mineral Dust Source Investigation (EMIT) observations, which provide mineralogical composition at the surface of the Earth based on imaging spectroscopy measurements from the International Space Station. We focus on total elemental amounts, not on the soluble fraction. We add in other sources of these elements (anthropogenic and natural) and compare to a compilation of available surface concentration data from stations over land and from shipborne observations. The combined observational and model synthesis provides new information about the distribution and deposition of these elements. Our results suggest that the modeled distribution is similar to available observations, but discrepancies still exist in both natural desert dust regions as well as regions dominated by anthropogenic sources. Comparisons between the model estimated Ca/Al ratios and observations in some dust dominated regions suggest an underestimate of Ca/Al ratios. Global budgets for Ca, Al, Fe, Si, and Ti suggest that desert dust remains the dominant source, although volcanic and anthropogenic contributions are important in some regions. Changes in elemental distributions since preindustrial times were also estimated.

Abstract Carbon mineralization using ultramafic rocks is a promising approach for long-term carbon dioxide removal. Here, we investigate whether a genetically engineered strain of Gluconobacter oxydans (B58 ∆pstS, P112:mgdh) can simultaneously achieve carbon mineralization and bioleach critical elements. Olivine and enstatite were bioleached at low-temperature conditions (30 °C) and with 5% pulp density. Direct G. oxydans -mineral contact promotes Fe 2+ oxidation and leads to higher leaching efficiency compared to leaching with a cell-free biolixiviant. Importantly, G. oxydans facilitates the precipitation of magnesium oxalate, a compound with twice the carbon storage capacity of magnesite. Oxalic acid was detected in the G. oxydans -produced biolixiviant, and solid-phase Mg-oxalate formed most efficiently at low pH. SEM and XRD analyses reveal extensive olivine dissolution and secondary coating by Mg-oxalate and amorphous silica, which may inhibit further leaching. Mass balance calculations show that G. oxydans leached up to 75% of the Mg hosted in the starting materials, while only 11% of leached Mg reacted to sequester carbon as Mg-oxalate after 15 days. The enhanced sequestration potential of Mg-oxalate combined with bioaccelerated critical element leaching to offset costs represents a promising opportunity for global carbon storage that is worthy of further investigation. (193/200)

Since the 1960s, continental serpentinization-influenced environments have served as natural laboratories for investigating low-temperature aqueous geochemistry involving dissolved H-2 and CH4, with broad implications for deep Earth elemental cycles, energy resources, and astrobiology. Here, we compiled, homogenised, and analysed geochemical data (aqueous and dissolved gas) from 34 studies focused exclusively on hyperalkaline spring seepage manifestations. The resulting database includes 2309 individual measurements spanning 16 physical and chemical variables. Tropical environments exhibited higher median values in Fe, Ni, CO32-, dissolved inorganic carbon, and dissolved CH4. Dissolved H-2 presented the highest median values in arid and cold continental settings. The arid environment also showed the highest median values in electrical conductivity (EC) and major ions (Na+, K+, Ca2+, Cl-). PCA dimension 1 (49.7%) was dominated by major ions, EC, Fe, Ni, CH4, and H-2, reflecting strong controls on solute and redox-related chemistry, while Dimension 2 (8.7%) was primarily associated with water temperature. Tropical sites clustered toward Ni, Fe, oxidation-reduction potential, and Mg2+, reflecting oxidising conditions and elevated metal concentrations, which are potentially derived from intense rock and soil monsoonal weathering. Arid sites trend toward OH-, Cl-, Ca2+, Na+, EC, and H-2, consistent with higher surface evaporative concentration and salinity in more evolved groundwater flows. Cold and temperate sites show greater variability, with hyperalkaline fluids tending toward higher pH and H-2. Our global comparison provides a systematic synthesis and framework for identifying both common patterns and site-specific differences in low-temperature continental serpentinization, underscoring the potential influence of regional hydrology, particularly groundwater flow and residence times, and water availability, in regulating conditions for H-2 and CH4 production.

ABSTRACT Since the 1960s, continental serpentinization‐influenced environments have served as natural laboratories for investigating low‐temperature aqueous geochemistry involving dissolved H 2 and CH 4 , with broad implications for deep Earth elemental cycles, energy resources, and astrobiology. Here, we compiled, homogenised, and analysed geochemical data (aqueous and dissolved gas) from 34 studies focused exclusively on hyperalkaline spring seepage manifestations. The resulting database includes 2309 individual measurements spanning 16 physical and chemical variables. Tropical environments exhibited higher median values in Fe, Ni, CO 3 2− , dissolved inorganic carbon, and dissolved CH 4 . Dissolved H 2 presented the highest median values in arid and cold continental settings. The arid environment also showed the highest median values in electrical conductivity (EC) and major ions (Na + , K + , Ca 2+ , Cl − ). PCA dimension 1 (49.7%) was dominated by major ions, EC, Fe, Ni, CH 4 , and H 2 , reflecting strong controls on solute and redox‐related chemistry, while Dimension 2 (8.7%) was primarily associated with water temperature. Tropical sites clustered toward Ni, Fe, oxidation–reduction potential, and Mg 2+ , reflecting oxidising conditions and elevated metal concentrations, which are potentially derived from intense rock and soil monsoonal weathering. Arid sites trend toward OH − , Cl − , Ca 2+ , Na + , EC, and H 2 , consistent with higher surface evaporative concentration and salinity in more evolved groundwater flows. Cold and temperate sites show greater variability, with hyperalkaline fluids tending toward higher pH and H 2 . Our global comparison provides a systematic synthesis and framework for identifying both common patterns and site‐specific differences in low‐temperature continental serpentinization, underscoring the potential influence of regional hydrology, particularly groundwater flow and residence times, and water availability, in regulating conditions for H 2 and CH 4 production.

Ultramafic rocks are an abundant source of cations for CO2 mineralization (e.g., Mg) and elements for sustainability technologies (e.g., Ni, Cr, Mn, Co, Al). However, there is no industrially useful process for dissolving ultramafic materials to release cations for CO2 sequestration or mining them for energy-critical elements. Weathering of ultramafic rocks by rainwater, release of metal cations, and subsequent CO2 mineralization already naturally sequesters CO2 from the atmosphere, but this natural process will take thousands to hundreds of thousands of years to remove excess anthropogenic CO2, far too late to deal with global warming that will happen over the next century. Mechanical acceleration of weathering by grinding can accelerate cation release but is prohibitively expensive. In this article we show that gluconic acid-based lixiviants produced by the mineral-dissolving microbe Gluconobacter oxydans accelerate leaching of Mg2+ by 20× over deionized water, and that leaching of Mg, Mn, Fe, Co, and Ni further improves by 73% from 24 to 96 h. At low pulp density (1%) the G. oxydans biolixiviant is only 6% more effective than gluconic acid. But, at 60% pulp density the G. oxydans biolixiviant is 3.2× more effective than just gluconic acid. We demonstrate that biolixiviants made with cellulosic hydrolysate are not significantly worse than biolixiviants made with glucose, dramatically improving the feedstock available for bioleaching. Finally, we demonstrate that we can reduce the number of carbon atoms in the biolixiviant feedstock (e.g., glucose or cellulosic hydrolysate) needed to release one Mg2+ ion and mineralize one atom of carbon from CO2 from 525 to 1.

The transition to a sustainable energy economy will require an enormous increase in the supply of rare earth elements (REEs). Bioleaching offers a promising alternative to conventional hydrometallurgical methods for REE extraction from low-grade ores. However, exploiting this potential remains challenging due to large gaps in our understanding of the genetics involved, and inadequate biological tools to address them. We generated a highly non-redundant whole-genome knockout collection for the bioleaching microbe Gluconobacter oxydans B58, reducing redundancy by 85% compared to the previous best collection. This new collection was directly screened for bioleaching neodymium from a synthetic monazite powder, identifying 89 genes important for bioleaching, 68 of which have not previously been associated with this mechanism. We conducted bench-scale experiments to validate the extraction efficiency of promising strains: 8 demonstrated significant increases in extraction by up to 111% (δGO_1598, disruption of the gene encoding the orotate phosphoribosyltransferase enzyme PyrE), and one strain significantly reduced it by 97% (δGO_1096, disruption of the gene encoding the GTP-binding protein TypA). Notable changes in pH were only observed for 3 strains, suggesting an important role for non-acid mechanisms in bioleaching. These findings provide valuable insights into further enhancing REE-bioleaching by G. oxydans through genetic engineering.

Carbon mineralization sequesters atmospheric CO2 by reacting it with cations from rock weathering to form carbonates. However, natural rates are too slow, and acceleration with chemical or mechanical methods is expensive. Microbial processes (acidolysis, redoxolysis, complexolysis) could speed weathering with less energy. However, no microorganisms have been employed at industrial scale to dissolve ultramafic rocks. Although some microbes dissolve ultramafic rocks), their performance remains poorly understood. Here, we compare the dissolution of dunite (> 90% olivine) by three mineral-dissolving microbes: Gluconobacter oxydansSphingomonas desiccabilis and Penicillium simplicissimum. G. oxydans outperformed the others, producing the most acidic biolixiviant (pH 2.15 at 1% pulp density) and extracting the most magnesium (3,130 mg/L at 3% pulp density). It also co-dissolved nine metals, including eight critical for energy technologies (Cr, Mn, Co, Ni, Cu, Zn) reaching up to 33 mg/L Ni. Increasing pulp density boosted metal dissolution by G. oxydans and S. desiccabilis but inhibited P. simplicissimum above 2% pulp density. These results show G. oxydans is best suited for engineering to enhance bio-accelerated weathering, reducing costs and environmental impacts. Finally, both G. oxydans and P. simplicissimum can use cellulosic hydrolysate instead of glucose, lowering substrate costs for biolixiviant production.

Water (hydrogen) is crucial to the geochemical and dynamic evolution of Earth by modulating a variety of Earth's interior properties and processes, which govern differentiation, plate tectonics, and volcanism. Water addition is also expected to promote thinning and removal of lithosphere roots, as water can markedly decrease the viscosity of the lithospheric mantle. While the source of deep water is controversial, recent evidence suggests that a possible reservoir for volatiles is the mantle transition zone (MTZ) that can be sampled at the mid-ocean rift system. Geophysical and geochemical evidence collectively suggests that volcanism in the South China Sea (SCS) resulted from the interaction of the subducting slabs with the MTZ, making it an ideal location to help solve this puzzle. We present data of glasses and melt inclusions from SCS samples with high H2O/Ce (similar to 248-649, considerably higher than global mid-ocean ridge basalt values). These data, combined with increased depletion in highly incompatible elements and low oxygen fugacity in the SCS, are consistent with the presence of subducted serpentinized mantle in the MTZ, which was later recycled during mantle upwelling and triggered lithospheric thinning and rifting. Water originating from the MTZ was likely responsible for the initial hydration of the upper mantle during early Earth's history, potentially facilitating the development and maintenance of plate tectonics.

Ultramafic lamprophyre (UML) intrusions in western Kentucky and southern Illinois are spatially associated with the Coefield Magnetic Anomaly and Hicks Dome in the Illinois-Kentucky Fluorspar District. While Hicks Dome has been a focus of rare earth element (REE) studies, the Coefield Magnetic Anomaly remains less explored. This study investigates the origin and alteration history of these UML intrusions, with a focus on REE distribution. Samples from legacy drill cores were analyzed using thin section petrography as well as whole-rock and in-situ geochemistry. The UML intrusions exhibit intense alteration, with primary mafic minerals largely replaced by serpentine and carbonates. Despite low bulkrock REE concentrations (64-620 ppm), anatase and apatite host significant REE enrichment, with anatase containing up to 95,620 ppm REEs. Elemental mapping suggests REE enrichment in anatase results from micron-to sub-micron-sized Ce-phosphate (monazite) inclusions. The restriction of REE minerals to the vicinity of anatase suggests perovskite alteration by magmatic-hydrothermal fluids led to REE redistribution.

Details of the study’s sample information, analytical methods, analytical data, and data plots.

Fluid release associated with serpentinite dehydration (de-serpentinization) during subduction plays a key role in fundamental geological processes such as element transport and recycling, seismicity, and arc magmatism. Although the importance of these fluids is well-known, evidence of de-serpentinization remains scarce in the rock record. Here, we investigated the effects of de-serpentinization and fluid circulation in exhumed metaperidotites from the Raspas Complex (Ecuador). This Early Cretaceous complex records warm subduction (similar to 13.5 degrees C/km) and has been hypothesized to represent a coherent slab sliver that preserves the mantle-crust contact (moho) between eclogite-facies metaperidotites and the corresponding crustal section. Petrological observations reveal that titanian-clinohumite-bearing metadunites and banded metaperidotites underwent de-serpentinization after reaching peak pressure-temperatures (P-T) of similar to 1.3-1.6 GPa and 620-650 degrees C. The peak paragenesis is partially obscured by a strong retrograde overprint, driven by crust-derived metamorphic fluids (delta 11B similar to -6 to +8 parts per thousand) that infiltrated at varying fluid/rock ratios, triggering the re-serpentinization of metaperidotites during exhumation (P < 1.3 GPa and 320-400 degrees C). Thermodynamic forward modeling reveals that fluid release in the Raspas paleo-subduction zone is controlled by brucite breakdown and de-serpentinization, which occur at depths of 25-30 km and similar to 50 km, respectively, accounting for a total of up to 10 wt. % H2O of water stored in the rock. Comparatively, dehydration of the crustal section, albeit a minor component, promotes enhanced fluid circulation between 25 and 45 km. During exhumation, circulating crust-derived metamorphic fluids heavily metasomatized the ascending slab sliver and effectively modified its geochemical signature. The depth range of the dehydration reactions overlap the depth of non-volcanic tremors and slow-slip events in warm, active subduction zones worldwide (25-65 km). Thus, the Raspas Complex offers an in-situ window into the fluids responsible for triggering these seismic events.

Determining the pressures and temperatures at which melts are stored in the crust and upper mantle, and the major element composition, redox state and volatile contents of these melts, is vital to constrain the structure and dynamics of magmatic plumbing systems. In turn, constraining these parameters helps understand the geochemical and structural evolution of the Earth’s lithosphere, and periods of unrest at active volcanoes. We review common thermobarometers, hygrometers and chemometers based on mineral and/or liquid compositions, before discussing recent advances in melt and fluid inclusion barometry, Raman-based elastic thermobarometry, and thermodynamic modelling methods. Where possible, we investigate the accuracy and precision of each technique, and the implications for the application of each method to different research questions.

The global demand for critical rare earth elements (REE) is rising 1 with the increase in demand for sustainable energy technologies like wind turbines 2,3 , electric vehicles 2,3 , and high efficiency lighting 4 . Current processes for producing REE require high energy inputs and can produce disproportionate amounts of hazardous waste. Biological methods for REE production are a promising solution to this problem. In earlier work we identified the most important genetic mechanisms contributing to the REE-bioleaching capability of Gluconobacter oxydans B58 5 . Here we have targeted two of these mechanisms to generate a high-efficiency bio-mining strain of G. oxydans . Disruption of the phosphate-specific transport system through a clean deletion of pstS constitutively turns on the phosphate starvation response, yielding a much more acidic biolixiviant, and increasing bioleaching by up to 30%. Coupling knockout of pstS with the over-expression of the mgdh membrane-bound glucose dehydrogenase gene, results in up to 73% improvement of REE-bioleaching.