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The mid-Proterozoic was a time of apparent prolonged biological and geochemical stability, preceeding the environmental turmoil and rapid biological innovations that characterized the Neoproterozoic. Despite an upswing in work on the mid-Proterozoic over the past decade, basic aspects of the carbon cycle and Earth9s surface redox state during this time period remain poorly understood. To provide a new window into the mid-Proterozoic environmental evolution, we have investigated carbonates in the well-exposed Muskwa Assemblage located in NE British Columbia, Canada, for a combined stratigraphic and geochemical study. Rare Earth Elements and Yttrium (REE+Y) geochemistry was applied to carbonate rocks deposited over a marine paleoenvironmental depth gradient in order to characterize prevailing water column redox conditions. These data provide evidence for an extremely shallow chemocline with oxic surface waters being restricted to within storm-wave base, which is consistent with globally low oxygen in the ocean-atmosphere system. Furthermore, there is evidence for facies-dependent carbonate δ13C variability within the Muskwa Assemblage comparable in scale to typical stratigraphic variability recorded in carbonate strata of this age, highlighting the problems of using small carbon isotope excursions for chemostratigraphy.

Summary Concerns have been voiced that implementing climate change mitigation measures could come at the cost of employment, especially in the context of the US coal sector. However, repurposing US coal plants presents an opportunity to address emission mitigation and job creation, if the right technology change is adopted. In this study, the transformation of the US coal sector until 2050 is modeled to achieve ambitious climate targets. Results show that the cost-optimal strategy for meeting 2050 emission reductions consistent with 2°C stabilization pathways is through the early deployment of BECCS and by replacing 50% of aging coal plants with natural gas plants. This strategy addresses the concerns surrounding employment for coal workers by retaining 40,000 jobs, and creating 22,000 additional jobs by mid-century. Climate change mitigation does not have to come at the cost of employment, and policymakers could seek to take advantage of the social co-benefits of mitigation.

In a modeling study, optimizing the transformation of the US coal sector to achieve emissions reductions consistent with the 2°C target, we include all current coal-fired power plants of the US fleet, a large part of which will need to be replaced due to their high age. Coal-fired power plants can either be (1) replaced by higher efficiency coal plants or (2) natural gas plants while units are not yet at the end of their lifetime and can be (3) retrofitted with carbon capture and storage (CCS) or (4) retrofitted to cofire coal and biomass coupled with CCS (BECCS) thereby achieving negative emissions. Our results show that if the 2°C emissions mitigation target should be achieved, the cost-optimal way of doing so is through an early implementation of BECCS. This strategy also helps to address the US Administrations’ concern for coal workers: there is a more gradual phaseout of coal, which allows to retain 40,000 jobs that would be loss due to the fleet retirement for aging. In addition, 22,000 new workers would be permanently employed in the coal sector by the end of midcentury, especially in areas where the deployments of BECCS would start already by 2030. Our modeling results indicate the Great Lakes area and the southeast United States as the greatest winners of this negative emissions strategy. If planned in an integrated and forward-looking way, climate change mitigation can boost employment and competitiveness.

Fractures present environmental risks for subsurface engineering activities, such as geologic storage of greenhouse gases, because of the possibility of unwanted upward fluid migration. The risks of fluid leakage may be exacerbated if fractures are subjected to physical and chemical perturbations that alter their geometry. This study investigated this by constructing a 2D fracture model to numerically simulate fluid flow, acid-driven reactions, and mechanical deformation. Three rock mineralogies were simulated: a limestone with 100% calcite, a limestone with 68% calcite, and a banded shale with 34% calcite. One might expect transmissivity to increase fastest for rocks with more calcite due to its high solubility and fast reaction rate. Yet, results show that initially transmissivity increases fastest for rocks with less calcite because of their ability to deliver unbuffered-acid downstream faster. Moreover, less reactive minerals become persistent asperities that sustain mechanical support within the fracture. However, later in the simulations, the spatial pattern of less reactive mineral, not abundance, controls transmissivity evolution. Results show that a banded mineral pattern creates persistent bottlenecks, prevents channelization, and stabilizes transmissivity. For sites for geologic storage of CO