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Title: Modular terpene synthesis enabled by mild electrochemical couplings
Modifying electrodes with silver nanoparticles is broadly enabling for electrochemical formation of carbon–carbon bonds.
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  1. Blue carbon habitats, such as mangroves and salt marshes, have been recognized as carbon burial hotspots; however, methods on measuring blue carbon stocks have varied and thus leave uncertainty in global blue carbon stock estimates. This study analyzes blue carbon stocks in northern Florida wetlands along the Atlantic and Gulf coasts. Carbon measurements within 1–3m length vibracores yield total core stocks of 9.9–21.5 kgC·m −2 and 7.7–10.9 kgC·m −2 for the Atlantic and Gulf coast cores, respectively. Following recent IPCC guidelines, blue carbon stock estimates in the top meter are 7.0 kgC·m −2 –8.0 kgC·m −2 and 6.1 kgC·m −2more »–8.6 kgC·m −2 for the Atlantic and Gulf cores, respectively. Changes in stable isotopic (δ 13 C, C/N) and lignin biomarker (C/V) indices suggest both coastlines experienced salt marsh and mangrove transgressions into non-blue carbon habitats during the mid- to late-Holocene following relative sea-level rise. These transgressions impact carbon storage within the cores as the presence of carbon-poor soils, characteristic of non-blue carbon habitats, result in lower 1m carbon stocks in north Florida Gulf wetlands, and a deeper extent of carbon-rich soils, characteristic of blue carbon habitats, drive higher 1m and total carbon stocks in north Florida Atlantic wetlands. Future blue carbon research should assess carbon stocks down to bedrock when possible, as land-cover and/or climate change can impact different depths across localities. Ignoring carbon-rich soil below the top meter of soil may underestimate potential carbon emissions based on these changes.« less
  2. While a reinvigoration of ocean circulation and CO 2 marine geologic carbon release over the last 20,000 years. Much of this evidence points to outgassing is the leading explanation for atmospheric CO rise since the Last Glacial Maximum (LGM), there is also evidence of regions of the mid-depth Pacific Ocean, where multiple radiocarbon (1 4 C) records show anomalously low 14 C/C values, potentially caused by the addition of carbon [1,2]. To better constrain this geologic carbon release hypothesis, we aim to place 14 C-free geologic an upper bound limit on the amount of carbon that may have been added,more »in addition to the geochemical pathway of that carbon. To do so, we numerical invert a carbon cycle model based on observational atmospheric CO 2 and 14 C records. Given these observational constraints, we use data assimilation techniques and an optimization algorithm to calculate the rate of carbon addition and its alkalinity-to-carbon ratio (R ) over the last 20,000 A/C years. Using the modeled planetary radiocarbon budget calculated in Hain et al. [3], we find observations allow for only ~300 Pg of carbon to be added, as a majority of the deglacial atmospheric 14 C decline is already explained by magnetic field strength changes and ocean circulation changes [3]. However, when we adjust the initial state of the model by increasing C by 75‰ to match the observational C records, we find that observations 14 14 allow for ~3500 Pg of carbon addition with an average R of ~1.4. A/C These results allow for the possibility of a large release of 14C-free geologic carbon, which could provide local and regional 14C anomalies, as the records have in the Pacific [1,2]. As this geological carbon was added with a RA/C of ~1.4, these results also imply that 14C evidence for significant geologic carbon release since the LGM may not be taken as contributing to deglacial CO2 rise, unless there is evidence for significant local acidification and corrosion of seafloor sediments. If the geologic carbon cycle is indeed more dynamic than previously thought, we may also need to rethink the approach to estimate the land/ocean carbon repartitioning from the deglacial stable carbon isotope budget. [1] Rafter et al. (2019), GRL 46(23), 13950–13960. [2] Ronge et al. (2016), Nature Communications 7(1), 11487. [3] Hain et al. (2014), EPSL 394, 198–208.« less
  3. Abstract Background

    Woody biomass has been considered as a promising feedstock for biofuel production via thermochemical conversion technologies such as fast pyrolysis. Extensive Life Cycle Assessment studies have been completed to evaluate the carbon intensity of woody biomass-derived biofuels via fast pyrolysis. However, most studies assumed that woody biomass such as forest residues is a carbon–neutral feedstock like annual crops, despite a distinctive timeframe it takes to grow woody biomass. Besides, few studies have investigated the impacts of forest dynamics and the temporal effects of carbon on the overall carbon intensity of woody-derived biofuels. This study addressed such gaps by developingmore »a life-cycle carbon analysis framework integrating dynamic modeling for forest and biorefinery systems with a time-based discounted Global Warming Potential (GWP) method developed in this work. The framework analyzed dynamic carbon and energy flows of a supply chain for biofuel production from pine residues via fast pyrolysis.


    The mean carbon intensity of biofuel given by Monte Carlo simulation across three pine growth cases ranges from 40.8–41.2 g CO2e MJ−1(static method) to 51.0–65.2 g CO2e MJ−1(using the time-based discounted GWP method) when combusting biochar for energy recovery. If biochar is utilized as soil amendment, the carbon intensity reduces to 19.0–19.7 g CO2e MJ−1(static method) and 29.6–43.4 g CO2e MJ−1in the time-based method. Forest growth and yields (controlled by forest management strategies) show more significant impacts on biofuel carbon intensity when the temporal effect of carbon is taken into consideration. Variation in forest operations and management (e.g., energy consumption of thinning and harvesting), on the other hand, has little impact on the biofuel carbon intensity.


    The carbon temporal effect, particularly the time lag of carbon sequestration during pine growth, has direct impacts on the carbon intensity of biofuels produced from pine residues from a stand-level pine growth and management point of view. The carbon implications are also significantly impacted by the assumptions of biochar end-of-life cases and forest management strategies.

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  4. Forests store a large amount of terrestrial carbon, but this storage capacity is vulnerable to wildfire. Combustion, and subsequent tree mortality and soil erosion, can lead to increased carbon release and decreased carbon uptake. Previous work has shown that non-constant fire return intervals over the past 4000 years strongly shaped subalpine forest carbon trajectories. The extent to which fire-regime variability has impacted carbon trajectories in other subalpine forest types is unknown. Here, we explored the interactions between fire and carbon dynamics of 14 subalpine watersheds in Colorado, USA. We tested the impact of varying fire frequency over a ~2000 yearmore »period on ecosystem productivity and carbon storage using an improved biogeochemical model. High fire frequency simulations had overall lower carbon stocks across all sites compared to scenarios with lower fire frequencies, highlighting the importance of fire-frequency in determining ecosystem carbon storage. Additionally, variability in fire-free periods strongly influenced carbon trajectories across all the sites. Biogeochemical trajectories (e.g., increasing or decreasing total ecosystem carbon and carbon-to-nitrogen (C:N) ratios) did not vary among forest types but there were trends that they may vary by elevation. Lower-elevations sites had lower overall soil C:N ratios, potentially because of higher fire frequencies reducing carbon inputs more than nitrogen losses over time. Additional measurements of ecosystem response to fire-regime variability will be essential for improving estimates of carbon dynamics from Earth system models.« less
  5. Ponderosa pine forests in the southwestern United States of America are overly dense, increasing the risk of high-intensity stand-replacing wildfires that result in the loss of terrestrial carbon and release of carbon dioxide, contributing to global climate change. Restoration is needed to restore forest structure and function so that a more natural regime of higher frequency, lower intensity wildfires returns. However, restoration has been hampered by the significant cost of restoration and other institutional barriers. To create additional revenue streams to pay for restoration, the National Forest Foundation supported the development of a methodology for the estimation and verification ofmore »carbon offsets generated by the restoration of ponderosa pine forests in northern Arizona. The methodology was submitted to the American Carbon Registry, a prominent carbon registry, but it was ultimately rejected. This paper presents a post-mortem examination of that methodology and the reasons it was rejected in order to improve the development of similar methodologies in the future. Using a mixed-methods approach, this paper analyzes the potential atmospheric carbon benefits of the proposed carbon offset methodology and the public and peer-reviewed comments from the associated review of the methodology. Results suggest a misalignment between the priorities of carbon registries and the context-specific ecosystem service benefits of this type of restoration; although findings confirm the potential for reductions in released carbon due to restoration, these results illuminate barriers that complicate registering these reductions as voluntary carbon offsets under current guidelines and best practices, especially on public land. These barriers include substantial uncertainty about the magnitude and timing of carbon benefits. Overcoming these barriers will require active reflexivity by the institutions that register voluntary carbon offsets and the institutions that manage public lands in the United States. Such reflexivity, or reconsideration of the concepts and purposes of carbon offsets and/or forest restoration, will allow future approaches to better align objectives for successfully registering restoration-based voluntary carbon offsets. Therefore, the results of this analysis can inform the development of future methodologies, policies, and projects with similar goals in the same or different landscapes.« less