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Coastal erosion rates are increasing along the Alaskan Beaufort Sea coast due to increases in wave action, the increasing length of the ice-free season, and warming permafrost. These eroding permafrost coastlines transport organic matter and inorganic nutrients to the Arctic Ocean, likely fueling biological production and CO2 emissions. To assess the impacts of Arctic coastal erosion on nearshore carbon and nitrogen cycling, we examined geochemical profiles from eroding coastal bluffs and estimated annual organic matter fluxes from 1955 to 2018 for a 9 km stretch of coastline near Drew Point, Alaska. Additionally, we conducted a laboratory incubation experiment to examine dissolved organic carbon (DOC) leaching and biolability from coastal soils/sediments added to seawater.Three permafrost cores (4.5 – 7.5 m long) revealed that two distinct horizons compose eroding bluffs near Drew Point: Holocene age, organic-rich (~12-45% total organic carbon; TOC) terrestrial soils and lacustrine sediments, and below, Late Pleistocene age marine sediments with lower organic matter content (~1% TOC), lower carbon to nitrogen ratios, and higher δ13C-TOC values. Organic matter stock estimates from the cores, paired with remote sensing time-series data, show that erosional TOC fluxes from this study coastline averaged 1,369 kg C m−1 yr−1 during the 21st century, nearly double the average flux of the previous half century. Annual TOC flux from this 9 km coastline is now similar to the annual TOC flux from the Kuparuk River, the third largest river draining the North Slope of Alaska.Experimental work demonstrates that there are distinct differences in DOC leaching yields and the fraction of biodegradable DOC across soil/sediment horizons. When core samples were submerged in seawater for 24 hours, the Holocene age organic-rich permafrost leached the most DOC in seawater (~6.3 mg DOC g-1 TOC), compared to active layer soils and Late-Pleistocene marine-derived permafrost (~2.5 mg DOC g-1 TOC). Filtered leachates were then incubated aerobically in the dark for 26 and 90 days at 20°C to examine biodegradable DOC (i.e. the proportion of DOC lost due to microbial uptake or remineralization). Of this leached DOC, Late Pleistocene permafrost was the most biolabile over 90 days (31 ± 7%), followed by DOC from active layer soils (24 ± 5%) and Holocene-age permafrost (14% ± 3%). If we scale these results to a typical 4 m tall eroding bluff at Drew Point, we expect that ~341 g DOC m-2 will rapidly leach, of which ~25% is biodegradable. These results demonstrate that eroding permafrost bluffs are an increasingly important source of biolabile DOC, likely contributing to greenhouse gas emissions and marine production in the coastal environment.

The success of geological carbon storage (GCS) depends on the sealing properties of caprocks, typically mudrocks, and their laminated variety – shales. In this study, we examined mineralogical changes in carbonate-rich Mancos Shale and corresponding changes in micro-mechanical properties following the reaction with carbon dioxide (CO2). Mineralogical changes of Mancos Shale depended on the pressure of CO2 during its exposure to the CO2-brine mixtures for up to 8 weeks. Dedolomitization was observed in the reactors pressurized with 100 psi of CO2, combined with the precipitation of gypsum. In the reactor pressurized with 2500 psi of CO2, the complete dissolution of calcite, partial dissolution of dolomite, and precipitation of magnesite and anhydrite were observed. Localized mechanical weakening was observed only for dolomite-muscovite-illite-rich laminae following whole shale puck alteration at 2500 psi of CO2, and a decrease of up to 50 ± 20% in scratch toughness was observed. The quartz-calcite-rich laminae did not exhibit a measurable difference in scratch toughness before and after reaction in CO2-rich brine. The predicted changes in mineralogy, porosity, density, and hardness of Mancos Shale are limited, according to the geochemical models describing alteration of shale by CO2-rich brine lasting for 5000 years. This study illustrates a coupled and localized chemical-mechanical response of caprock to the injection of CO2.

Heterogeneous redox reactions on clay mineral surfaces control mobility and bioavailability of redox-sensitive nutrients and contaminants. Iron (Fe) residing in clay mineral structures can either catalyze or directly participate in redox reactions; however, chemical controls over its reactivity are not fully understood. In our previous work we demonstrated that converting a minor portion of Fe(III) to Fe(II) (partial reduction) in the octahedral sheet of natural Fe-rich clay mineral nontronite (NAu-1) activates its surface, making it redox-active. In this study we produced and characterized synthetic ferric nontronite (SIP), highlighting structural and chemical similarities and differences between this synthetic nontronite and its natural counterpart NAu-1, and probed whether mineral surface is redox-active by reacting it with arsenic As(III) under oxic and anoxic conditions. We demonstrate that synthetic nontronite SIP undergoes the same activation as natural nontronite NAu-1 following the partial reduction treatment. Similar to NAu-1, SIP oxidized As(III) to As(V) under both oxic (catalytic pathway) and anoxic (direct oxidation) conditions. The similar reactivity trends observed for synthetic nontronite and its natural counterpart make SIP an appropriate analog for laboratory studies. The development of chemically pure analogs for ubiquitous soil minerals will allow for systematic research of the fundamental properties of these minerals.

Storing carbon dioxide in the subsurface as carbonate minerals has the benefit of long-term stability and immobility. Ultramafic rock formations have been suggested as a potential reservoir for this type of storage due to the availability of cations to react with dissolved carbon dioxide and the fast reaction rates associated with minerals common in ultramafic formations; however, the rapid reactions have the potential to couple with the mechanical and hydraulic behavior of the rocks and little is known about the extent and mechanisms of this coupling. In this study, we argue that the dissolution of primary minerals and the precipitation of secondary minerals along pre-existing fractures in samples lead to reductions in both the apparent Young's modulus and shear strength of aggregates, accompanied by reduction in permeability. Hydrostatic and triaxial deformation experiments were run on dunite samples saturated with de-ionized water and carbon dioxide-rich solutions while stress, strain, permeability and pore fluid chemistry were monitored. Sample microstructures were examined after reaction and deformation using scanning electron microscopy (SEM). The results show that channelized dissolution and carbonate mineral precipitation in the samples saturated with carbon dioxide-rich solutions modify the structure of grain boundaries, leading to the observed reductions in stiffness, strength and permeability. A geochemical model was run to help interpret fluid chemical data, and we find that the apparent reaction rates in our experiments are faster than rates calculated from powder reactors, suggesting mechanically enhanced reaction rates. In conclusion, we find that chemo-mechanical coupling during carbon mineralization in dunites leads to substantial modification of mechanical and hydraulic behavior that needs to be accounted for in future modeling efforts of in situ carbon mineralization projects.

The reactivity of co-occurring arsenic (As) and uranium (U) in mine wastes was investigated using batch reactors, microscopy, spectroscopy, and aqueous chemistry. Analyses of field samples collected in proximity to mine wastes in northeastern Arizona confirm the presence of As and U in soils and surrounding waters, as reported in a previous study from our research group. In this study, we measured As (< 0.500 to 7.77 μg/L) and U (0.950 to 165 μg/L) in waters, as well as mine wastes (< 20.0 to 40.0 mg/kg As and < 60.0 to 110 mg/kg U) and background solids (< 20.0 mg/kg As and < 60.0 mg/kg U). Analysis with X-ray fluorescence (XRF) and electron microprobe show the co-occurrence of As and U with iron (Fe) and vanadium (V). These field conditions served as a foundation for additional laboratory experiments to assess the reactivity of metals in these mine wastes. Results from laboratory experiments indicate that labile and exchangeable As(V) was released to solution when solids were sequentially reacted with water and magnesium chloride (MgCl(2)), while limited U was released to solution with the same reactants. The predominance of As(V) in mine waste solids was confirmed by X-ray absorption near edge (XANES) analysis. Both As and U were released to solution after reaction of solids in batch experiments with HCO(3)(−). Both X-ray photoelectron spectroscopy (XPS) and XANES analysis determined the predominance of Fe(III) in the solids. Mössbauer spectroscopy detected the presence of nano-crystalline goethite, Fe(II) and Fe(III) in (phyllo)silicates, and an unidentified mineral with parameters consistent with arsenopyrite or jarosite in the mine waste solids. Our results suggest that As and U can be released under environmentally relevant conditions in mine waste, which is applicable to risk and exposure assessment.

The long-term carbon dioxide storage capacity of reservoirs can be impacted by chemical reactions, mass transport, and mechanical deformation of the reservoir and caprock following the injection of CO 2 . Mineral mass removal can lead to microcracking and compaction, thus affecting the mechanical integrity of the reservoir–caprock system. The short-term (days, months) and long-term (hundreds to thousands of years) chemical effects, such as the dissolution of intergranular cement and mineral precipitation, can lead to a coupled chemical-mechanical response. This chemical-mechanical coupling occurs at multiple temporal and spatial scales. For instance, chemical processes at the crack-tip (micrometer) scale affect fracture networks with complex fracture architecture all the way to the reservoir scale. This chapter addresses chemical effects on the mechanical response of reservoir and caprock lithologies considered for geological carbon storage. Particular emphasis is on sandstone reservoir and mudrock (shale) caprock, as they are the most typical formations targeted for the injection of CO 2 . This chapter examines the existing laboratory, field, and modeling studies that address the coupled chemical-mechanical response of sandstone and mudrock lithologies to the injection of CO 2 . These coupled chemical-mechanical responses during geological carbon storage can result in the development of preferential flow paths and CO 2 leakage.

Lead (Pb) and antimony (Sb) associated with bullets pose a long term contamination risk in shooting ranges because bullet fragments weather over years to decades. In this study we analyzed bullet and soil samples from a historic military shooting range in interior Alaska. Bulk speciation analysis coupled with micro-scale analytical methods demonstrate the presence of Sb(V) in octahedral coordination with 5.3(1) O and a second shell of 3(1) Fe atoms is the primary species present in the weathered bullet crust. However, trivalent Sb bound to 3.1(2) O atoms is likely the initial oxidation species as detected at the soil/alloy interface of a weathered bullet from this study. Similar analysis shows that cerussite (PbCO3), hydrocerussite (Pb3(CO3)2(OH)2), and litharge (PbO) comprise the majority of the Pb species in the weathering crust but Pb(II) adsorbed to Fe(III) oxides are also present in the soil distal to the source material. These results show differences in speciation between the weathering crust and soil fraction in shooting range samples and highlight the natural association of Pb and Sb with Fe. Understanding metal speciation is a critical first step in developing and implementing remediation strategies in small arms shooting ranges.

© 2017 Elsevier B.V. Fine-grained sedimentary rocks – namely mudrocks, including their laminated fissile variety — shales – make up about two thirds of all sedimentary rocks in the Earth's crust and a quarter of the continental land mass. Organic-rich shales and mudstones are the source rocks and reservoirs for conventional and unconventional hydrocarbon resources. Mudrocks are relied upon as natural barriers for geological carbon storage and nuclear waste disposal. Consideration of mudrock multi-scale physics and multi-scale spatial and temporal behavior is vital to address emergent phenomena in shale formations perturbed by engineering activities. Unique physical characteristics of shales arise as a result of their layered and highly heterogeneous and anisotropic nature, low permeability fabric, compositional complexity, and nano-scale confined chemical environments. Barriers of lexicon among geoscientists and engineers impede the development and use of conceptual models for the coupled thermal-hydraulic-mechanical-chemical-biological (THMCB) processes in mudrock formations. This manuscript reviews the THMCB process couplings, resulting emergent behavior, and key modeling approaches. We identify future research priorities, in particular fundamental knowledge gaps in understanding the phase behavior under nano-scale confinement, coupled chemo-mechanical effects on fractures, the interplay between physical and chemical processes and their rates, and issues of non-linearity and heterogeneity. We develop recommendations for future research and integrating multi-disciplinary conceptual models for the coupled multi-scale multi-physics behavior of mudrocks. Consistent conceptual models across disciplines are essential for predicting emergent processes in the subsurface, such as self-focusing of flow, time-dependent deformation (creep), fracture network development, and wellbore stability.

Increasing air temperatures in the Arctic have the potential to degrade permafrost and promote the downward migration of the seasonally thawed active layer into previously frozen material. This may expose frozen soils to mineral weathering that could affect the geochemical composition of surface waters. Determining watershed system responses to drivers such as a changing climate relies heavily on understanding seasonal controls on freshwater processes. The majority of studies on elemental concentrations in Arctic river systems have focused on sampling only from spring snowmelt to the summer season. Consequently, there remains a limited understanding of surface water geochemistry, particularly with respect to trace metals, during late fall and early winter. To examine the variability of metal concentrations as a function of seasonality, we measured trace metal concentrations from spring melt to fall freeze-up in 2010 in two high Arctic watersheds: Imnavait Creek, North Slope, Alaska and Roche Mountanee Creek, Brooks Range, Alaska. We focused on aluminum (Al), barium (Ba), iron (Fe), manganese (Mn), nickel (Ni) and zinc (Zn). Concentrations of ‘dissolved’ (

article The KantishnaHills miningdistrictofinteriorAlaska,USA,locatedwithin DenaliNational ParkandPreserve,con- tains a number of antimony lode deposits, including Alaska's historically largest antimony producer, the Stam- pede mine. Oxidative weathering of sulfidic tailings and waste rock associated with historic mining operations has impacted water quality in the region. In the Stampede and Slate Creek watersheds, antimony and arsenic concentrations instream waters were as high as 720 μg/L and 239 μg/L, respectively. Antimony inall watersam- plesispredominantlypresentasSb(V),whereasarsenicwasdetectedinvaryingratiosofAs(III)andAs(V).Based onX-rayabsorptionspectroscopy(XAS)measurementsreducedAs(III)andSb(III)wereidentifiedinminewaste materials, whereas predominantly oxidized forms, As(V) and Sb(V), were found in downstream sediments. Elevated antimony concentrations extend for more than 8 km downstream from the antimony lodes, whereas arsenic quickly attenuates within 1.5 km. The difference between antimony and arsenic aqueous phase specia- tion suggests that antimony oxidation is more rapid than arsenic within this system. A high correlation is ob- served between antimony, arsenic, and iron concentrations in fine-fraction streambed sediments downstream of the source lodes. This suggests that sorption and co-precipitation with iron (hydr)oxides are important path- ways for the attenuation of antimony and arsenic in these interior Alaska watersheds. Further XAS characteriza- tion of the downstream sediments corroborates these observations and indicates that antimony is adsorbed to Fe-oxide phases as inner-sphere bi-dentate edge and corner sharing complexes. The trace element redox states, as well as downstream partitioning, are mainly controlled by iron speciation based on the strong correlation be- tween redox potentials calculated from iron (Fe(II)/Fe(III)) and arsenic (As(III)/As(V)).

The use of geothermal fluids for the production of electricity poses a risk of contaminating surface waters when spent fluids are discharged into (near) surface environments. Arsenic (As) in particular is a common component in geothermal fluids and leads to a degradation of water quality when present in mobile and bioavailable forms. We have examined changes in arsenic speciation caused by quick transition from high temperature reducing conditions to surface conditions, retention mechanisms, and the extent of transport associated with the release of spent geothermal fluids at the Dachny geothermal fields (Mutnovsky geothermal region), Kamchatka, Russia — a high temperature field used for electricity production. In the spent fluids, the arsenic concentration reaches 9 ppm, while in natural hot springs expressed in the vicinity of the field, the As concentration is typically below 10 ppb. The aqueous phase arsenic speciation was determined using Liquid Chromatography (LC) coupled to an Inductively Coupled Plasma Mass Spectrometer (ICP-MS). The arsenic speciation in the bottom sediments ( − from the deep well fluids as a tracer. Analysis of the Extended X-ray Absorption Fine Structure (EXAFS) spectra shows that sediment phase arsenic is associated with both Al- and Fe-rich phases with a bi-dentate corner sharing local geometry. The geothermal waste fluids released in the surface water create a localized area of arsenic contamination. The extent of transport of dissolved As is limited to ~ 7 km downstream from the source, while As associated with bottom sediment travels ~ 3 km farther.