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Two cavity ring‐down spectrometers were employed to accurately measure line intensities in a series of near‐infrared carbon dioxide bands including (30012) ← (00001), (30013) ← (00001), and (30014) ← (00001) near 1.6 μm. Relative combined standard uncertainties for these band intensities were less than 0.1% and showed significant, percent‐level deviations with respect to many existing spectroscopic databases (although close agreement was observed with the HITRAN 2016 database in the (30013) ← (00001) and (30014) ← (00001) bands). Further, the resulting line intensities were utilized in Total Carbon Column Observing Network retrievals and led to significantly reduced biases in the (30012) ← (00001) and (30013) ← (00001) bands. These results indicate that refinements of spectroscopic databases are required to meet the accuracy targets of both ground‐ and satellite‐based remote sensing missions. Key Points: Near‐infrared CO2 line intensities measured with combined standard uncertainties below 0.1%Deviations in excess of 1% were found between these measurements and existing databasesThese new intensities led to reduced biases in atmospheric retrievals of CO2 mixing ratios when using two near‐infrared bands [ABSTRACT FROM AUTHOR]

The Southern Annular Mode (SAM) is the dominant mode of climate variability in the Southern Ocean, but only a few observational studies have linked variability in SAM to changes in ocean circulation. Atmospheric potential oxygen (APO) combines atmospheric O2/N2 and CO2 data to mask the influence of terrestrial exchanges, yielding a tracer that is sensitive mainly to ocean circulation and biogeochemistry. We show that observed wintertime anomalies of APO are significantly correlated to SAM in 25‐ to 30‐year time series at three Southern Hemisphere sites, while CO2 anomalies are also weakly correlated. We find additional correlations between SAM and O2 air‐sea fluxes in austral winter inferred from both an atmospheric inversion of observed APO and a forced ocean biogeochemistry model simulation. The model results indicate that the correlation with SAM is mechanistically linked to stronger wind speeds and upwelling, which brings oxygen‐depleted deep waters to the surface. Plain Language Summary: The Southern Annular Mode (SAM) is characterized by variability in the strength of the westerly winds that encircle Antarctica. A more positive SAM index is associated with stronger westerly winds over the ocean at about 60°S latitude. Previous studies based mostly on model simulations have suggested that a positive SAM index is also associated with enhanced upwelling of carbon‐rich waters in the Southern Ocean, which influences the uptake and/or release of carbon dioxide to the atmosphere. The same deep waters that have high carbon also have low concentrations of dissolved oxygen, which can cause subtle variations in atmospheric oxygen levels measured at surface stations. We present an analysis of data sets from three Southern Hemisphere stations where air samples have been collected for 25–30 years. We find that during the Southern Hemisphere winter, anomalies in the atmospheric oxygen record are correlated to the SAM index; we find weaker correlations between anomalies in atmospheric carbon dioxide and the SAM index. These results are consistent with variability in air‐sea oxygen fluxes from a model simulation. The model results indicate that the observed relationship between SAM and air‐sea oxygen fluxes is due to both stronger wind speeds and increased upwelling of oxygen‐depleted deep waters. Key Points: Significant correlations are found between winter atmospheric potential oxygen and the Southern Annular Mode at three long‐term observing sitesA similar relationship between winter air‐sea O2 flux and SAM is found in APO inversion products and a hindcast ocean model simulationOcean model simulations indicate that negative winter APO anomalies are linked to stronger wind speeds and ventilation of O2‐depleted deep water [ABSTRACT FROM AUTHOR]

Understanding what physically sets the shape of temperature distributions will enable more robust predictions of local temperature with global warming. We derive the relationship between the temperature distribution shape and the advection of temperature conditionally averaged at each temperature percentile. This enables quantification of the shift of each percentile that is due to changes in the mean temperature, in horizontal temperature advection, and other processes (e.g., radiation and convection). We use this relationship to examine global model simulations in an idealized aquaplanet model with increasing carbon dioxide. Changes in the distribution with doubling and quadrupling of carbon dioxide are significant, and they are caused by different processes. We find that midlatitude temperature distributions can be explained mostly by the horizontal advection, except in the upper and lower 10% of the distribution. Key Points: Distributions of temperature for an aquaplanet model are explained in terms of horizontal advection of temperature and other processesThe shape of midlatitude distributions can be explained by horizontal advection, except in the upper and lower 10% of the distributionAt each percentile, we decompose changes to the distributions into changes in the mean, in horizontal advection, and in other processes [ABSTRACT FROM AUTHOR]

Friction and wear remain the primary modes for energy dissipation in moving mechanical components. Superlubricity is highly desirable for energy saving and environmental benefits. Macroscale superlubricity was previously performed under special environments or on curved nanoscale surfaces. Nevertheless, macroscale superlubricity has not yet been demonstrated under ambient conditions on macroscale surfaces, except in humid air produced by purging water vapor into a tribometer chamber. In this study, a tribological system is fabricated using a graphene‐coated plate (GCP), graphene‐coated microsphere (GCS), and graphene‐coated ball (GCB). The friction coefficient of 0.006 is achieved in air under 35 mN at a sliding speed of 0.2 mm s−1 for 1200 s in the developed GCB/GCS/GCP system. To the best of the knowledge, for the first time, macroscale superlubricity on macroscale surfaces under ambient conditions is reported. The mechanism of macroscale superlubricity is due to the combination of exfoliated graphene flakes and the swinging and sliding of the GCS, which is demonstrated by the experimental measurements, ab initio, and molecular dynamics simulations. These findings help to bridge macroscale superlubricity to real world applications, potentially dramatically contributing to energy savings and reducing the emission of carbon dioxide to the environment. [ABSTRACT FROM AUTHOR]

The plume composition at Enceladus contains clues about conditions and processes in the interior. We present new geochemical interpretations of Cassini mass spectrometry data from the plume gas and salt‐rich ice grains. It is found that self‐consistency between the data sets can be achieved with a derived range of 10−4.6 to 10−3.2 for the activity of CO2 in Enceladus' ocean. This range is compatible with long‐term buffering by reduced or oxidized seafloor rocks containing quartz, talc, and carbonate minerals in the MgO–FeO–SiO2–CO2–H2O system. Reaction path modeling shows that these types of rocks can be produced from accreted CO2‐rich fluids reacting with hydrous chondritic rocks over an intermediate regime of carbonation. These results, together with previous findings of silica and H2 at Enceladus, support the hypothesis of a heterogeneous structure for the rocky core (carbonated upper layer, serpentinized interior), which provides a geochemical gradient for habitability. Plain Language Summary: Enceladus, an ocean‐harboring moon of Saturn, erupts a plume that contains gases and frozen sea spray into space. By understanding the composition of the plume, we can learn about what the ocean is like, how it got to be this way, and whether it provides environments where life as we know it could survive. This study presents a new perspective for analyzing the plume composition to estimate the concentration of dissolved carbon dioxide in the ocean. We find that the derived range based on two different data sets is intriguingly similar to what would be expected from the dissolution and formation of certain mixtures of silicon‐ and carbon‐bearing minerals at the seafloor. The deduced combination of minerals may be indicative of a fundamental process that has sequestered a large amount of Enceladus' initial inventory of carbon dioxide into the rocky core. This inference echoes an emerging vision of a complex interior that hosts geochemically diverse environments. The dynamic interface of such complexity is where energy sources for possible life may arise. Key Points: New estimates of the thermodynamic activity of CO2 in Enceladus' ocean based on the carbonate chemistry of the plumeFormation of CO2‐buffering assemblages of quartz‐talc‐carbonate from partial carbonation of chondritic compositionsDistinct sources of observed CO2, silica, and H2 imply mineralogically and thermally diverse environments in the rocky core [ABSTRACT FROM AUTHOR]

Summary: Stomata are cellular breathing pores on leaves that open and close to absorb photosynthetic carbon dioxide and to restrict water loss through transpiration, respectively. Grasses (Poaceae) form morphologically innovative stomata, which consist of two dumbbell‐shaped guard cells flanked by two lateral subsidiary cells (SCs). This 'graminoid' morphology is associated with faster stomatal movements leading to more water‐efficient gas exchange in changing environments. Here, we offer a genetic and mechanistic perspective on the unique graminoid form of grass stomata and the developmental innovations during stomatal cell lineage initiation, recruitment of SCs and stomatal morphogenesis. Furthermore, the functional consequences of the four‐celled, graminoid stomatal morphology are summarized. We compile the identified players relevant for stomatal opening and closing in grasses, and discuss possible mechanisms leading to cell‐type‐specific regulation of osmotic potential and turgor. In conclusion, we propose that the investigation of functionally superior grass stomata might reveal routes to improve water‐stress resilience of agriculturally relevant plants in a changing climate. Significance Statement: A key challenge for plants is to efficiently use water, particularly when growing in a hot and dry climate. Stomata – cellular breathing pores on leaves that mediate gas exchange between plant and atmosphere – have a pivotal role in controlling water‐use efficiency. Stomata can adjust their pore size to balance carbon dioxide uptake with water vapour loss. Interestingly, grasses like the three most important food crops rice, maize and wheat have improved stomata that can regulate water use more efficiently by opening and closing faster than other plants. Rapid stomatal movements are linked to the grass stomata's unique morphology consisting of dumbbell‐shaped guard cells and lateral subsidiary or helper cells. Recently, work on domesticated and wild grass species has started to reveal some of the secrets regarding how grass stomata form and function more efficiently. [ABSTRACT FROM AUTHOR]

Summary: The intricate and interconnecting reactions of C3 photosynthesis are often limited by one of two fundamental processes: the conversion of solar energy into chemical energy, or the diffusion of CO2 from the atmosphere through the stomata, and ultimately into the chloroplast. In this review, we explore how the contributions of stomatal morphology and distribution can affect photosynthesis, through changes in gaseous exchange. The factors driving this relationship are considered, and recent results from studies investigating the effects of stomatal shape, size, density and patterning on photosynthesis are discussed. We suggest that the interplay between stomatal gaseous exchange and photosynthesis is complex, and that a disconnect often exists between the rates of CO2 diffusion and photosynthetic carbon fixation. The mechanisms that allow for substantial reductions in maximum stomatal conductance without affecting photosynthesis are highly dependent on environmental factors, such as light intensity, and could be exploited to improve crop performance. Significance Statement: Plant photosynthesis relies on diffusion of CO2 from the atmosphere to the chloroplasts through the stomatal pores. The distribution and morphological characteristics of stomata influence this and are of particular importance when attempting to understand or improve on rates of carbon fixation. Nonetheless, alterations expected to affect stomatal conductance do not always cause corresponding alterations in photosynthetic carbon assimilation. This review explores the factors that are likely to cause this observed disconnect between maximum stomatal conductance and photosynthesis. [ABSTRACT FROM AUTHOR]

New Finding: What is the central question of this study?Transition to supine posture induces an inspiratory load associated with cortical activation in awake healthy subjects. Some obstructive sleep apnoea patients exhibit this cortical activity in the sitting position contributing to the arousal‐dependent compensation of their upper airway abnormalities. Does a transition to the supine posture in awake obstructive sleep apnoea patients increase this cortical activity?What is the main finding and its importance?The transition to supine posture induces a reduction in the cortical activity despite evidence of an increase in genioglossus activity, suggesting that genioglossus activation is not driven by cortical activity. The anatomy and mechanical properties of the upper airway (UA) depend on posture. Lying in a supine position causes cephalad fluid shift to the neck, thus narrowing the UA and predisposing the individual to obstructive sleep apnoea (OSA). Increased UA dilator muscle activity during wakefulness prevents the UA collapse but the underlying mechanism has not yet been elucidated. In the sitting position during wakefulness, some OSA patients exhibit preinspiratory cortical activity (preinspiratory potential, PIP) probably related to UA abnormalities. The aim of this study was to investigate changes in the preinspiratory cortical activity and UA dilator muscle in OSA patients during postural challenge. An electroencephalogram was used to detect PIP, and the genioglossus electromyographic activity and ventilation were analysed in 17 awake, male OSA patients while they were sitting, just after lying down, and then in response to leg positive pressure to enhance cephalad fluid shift. The prevalence of PIP decreased from 53% (sitting) to 12% (supine) (P = 0.002) in association with increased genioglossus activity (tonic from median (25th, 75th centiles) 2.3 (1.8, 2.8)% to 3.6 (1.7, 5.0)% of voluntary deglutition, P = 0.019; phasic from 2.3 (1.9, 2.8)% to 3.7 (2.0, 6.1)%, P = 0.024), and with increased transcutaneous carbon dioxide pressure (from 43.0 (42.4, 44.2) to 44.6 (43.5, 45.2) mmHg). No change was observed during leg‐positive‐pressure application. Moving from the sitting position to the supine position reduces respiratory‐related premotor cortical activity in awake OSA patients. The concomitant increase in genioglossus activity, therefore, is not driven by cortical respiratory activity. [ABSTRACT FROM AUTHOR]

Summary: Plants grow and transpire during the night. The aim of the present work was to assess the relative flows of carbon, water and solutes, and the energy involved, in sustaining night‐time transpiration and leaf expansive growth under control and salt‐stress conditions.Published and unpublished data were used, for barley plants grown in presence of 0.5–1 mM NaCl (control) and 100 mM NaCl.Night‐time leaf growth presents a more efficient use of taken‐up water compared with day‐time growth. This efficiency increases several‐fold with salt stress. Night‐time transpiration cannot be supported entirely through osmotically driven uptake of water through roots under salt stress. Using a simple three‐ (root medium/cytosol/vacuole) compartment approach, the energy required to support cell expansion during the night is in the lower percentage region (0.03–5.5%) of the energy available through respiration, under both, control and salt‐stress conditions. Use of organic (e.g. hexose equivalents) rather than inorganic (e.g. Na+, Cl−, K+) solutes for generation of osmotic pressure in growing cells, increases the energy demand by orders of magnitude, yet requires only a small portion of carbon assimilated during the day.Night‐time transpiration and leaf expansive growth should be considered as a potential acclimation mechanism to salinity. See also the Commentary on this article by Sanders, 225: 1047–1048. [ABSTRACT FROM AUTHOR]

This study presents a comprehensive approach for the distribution system expansion planning (DSEP) that considers investment, operation, carbon dioxide emission and reliability costs, as well as uncertainties over load demand and wind-based distributed generation. A restoration strategy is taken into account for obtaining the energy not supplied under the 'N - 1' criterion and the corresponding reliability cost over a planning horizon. The problem is modelled as mixed-integer non-linear programming by using the artificial immune system algorithm. Also, two methods to represent uncertainties are applied and compared: an interval technique through an interval power flow and a scenario-based approach. Network constraints are considered, as the limits of current, voltage and power from substations, as well as the obtaining of radial and connected topology. The novelty of the proposed interval DSEP consists of handling the uncertainties over operation in an efficient manner through a single step, instead of the several deterministic evaluations of the scenario-based approach. Numerical results are presented for well known test systems, which show the potentials of the proposed approach. [ABSTRACT FROM AUTHOR]

Carbon allocated to roots accounts for a large portion of net primary productivity, but the fate of that carbon is poorly understood. Absorptive fine roots are the primary way in which plants acquire nutrients. Previous studies have evaluated relationships among root morphological traits, including specific root length, root tissue density, and mycorrhizal colonization, across broad functional and taxonomic groups to test for the existence of a root economics spectrum (RES). Fine roots also release carbon dioxide through respiration, and other studies have found relationships between root morphological traits and root respiration within individual tree species. The objective of this study was to measure a suite of root traits in six co-occurring temperate tree species that represent a diverse set of aboveground traits to determine whether and how root characteristics influenced root respiration both within and among species. At the Harvard Forest in Petersham, Massachusetts, USA, we measured fine root respiration, root morphology, percent colonization for ectomycorrhizal species, and carbon and nitrogen concentrations on 292 roots from six tree species in June and July 2018. We found that most fine root morphological characteristics varied nearly as much within each tree species as they did among the six species. Root traits were dynamic over time during the two months of our study, where the magnitude of weekly mean trait values varied 32-95% across the study period. Strong correlations among traits suggested trade-offs on a spectrum from resource acquisition (long, thin, high-nitrogen roots) to resource conservation (thick, dense, low-nitrogen roots), and traits were not clustered by tree species within this spectrum. Along with temperature and weekly temporal variation, the resource acquisition strategy (long and thin roots that were high in nitrogen) was associated with higher root respiration, and this relationship was consistent among the six species. This study supported a strong link between the RES and respiration independent of species identity, which provides insight into functional axes for scaling root respiration from individual trees to the forest stand to better quantify belowground carbon flux. [ABSTRACT FROM AUTHOR]

An introduction is presented in which the editor discusses articles in the issue on topics including role of physiological gases like carbon dioxide in health and disease, impact of intermittent hypoxia on adipose tissue, and impact of hypercapnia on the lung.

The author comments on two studies published in the current issue of "The Journal of Physiology" which examined changes in cerebral blood flow velocity over a range of carbon dioxide concentrations. According to the author, there is a need to consider middle cerebral artery flow velocity in detecting disease risks and physiological changes. The author also points out the possibility that regional differences in cerebrovascular reactivity are underestimated when expressed as velocity.

The author comments on the contributions of skeletal muscles to the respiratory function of human. He says that the increase in carbon dioxide concentration in the respiratory neurones allows the central synaptic effects to activate the cardiovascular and respiratory effectors. According to the author, abnormal cardiorespiratory responses may be associated with inappropriate reflex information generated by the muscle.

A response by Sin et al. to a letter to the editor about their paper, which claims that ventilatory equivalents for carbon dioxide and oxygen are measures of ventilatory efficiency and not of pulmonary gas exchange efficiency, is presented.

Low temperature plasma treatment using radio frequency (RF) discharge of nitrogen and carbon dioxide gases was employed to enhance hydrophilicity of the polyacrylonitrile copolymer membrane surface. Influence of various plasma operating conditions, namely, power and exposure time on improvement of surface energy, permeability, and hydrophilicity of the membrane was investigated. Surface energy of RF nitrogen plasma‐treated membrane (70 W, 8 min) was enhanced by 70%. Surface etching due to plasma treatment was confirmed by weight loss of the treated membranes. About 78% increase in average pore size was obtained using RF carbon dioxide plasma treatment due to surface etching. Hydrophilicity of nitrogen plasma modified membrane was enhanced by 32% and it was maintained up to 100 days. The pore enlargement due to plasma etching is more effective compared to surface energy in enhancing permeability (70%) of RF carbon dioxide modified (70 W, 6 min) membrane throughout the aging period. The permeability of nitrogen RF plasma‐treated membrane is affected by surface energy and pore enlargement for initial 20 days of aging. After that, the permeability of treated PAN only depends on pore enlargement due to plasma etching. The nitrogen plasma modified surfaces appear to retain their functionality better than carbon dioxide plasma‐treated samples. Oxygen and nitrogen functional groups were identified to be responsible for surface hydrophilicity. POLYM. ENG. SCI., 59:2148–2158, 2019. © 2019 Society of Plastics Engineers [ABSTRACT FROM AUTHOR]

The fracture system is a vital component of fractured low‐permeability reservoirs. The presence of fractures can improve reservoir flow capacity and injected carbon dioxide (CO2) utilization, thus leading to higher oil recovery. In this study, the effects of the presence of fracture, fracture morphology, soaking time, and CO2 injection volume on CO2 huff and puff were investigated through 11 low‐permeability cores with different properties. The experimental results indicated that the presence of fractures enhanced cyclic oil recovery and increased the effective cycle numbers during CO2 huff and puff in low‐permeability cores. Moreover, compared with low‐permeability cores without fractures, ultimate oil recovery of CO2 huff and puff was risen up by ~11% in fractured cores. Longer soaking time was conducive to enhancing ultimate oil recovery of CO2 huff and puff in fractured low‐permeability cores, but the excessive soaking time had little effect on ultimate oil recovery. Meanwhile, excessive CO2 injection volume did not significantly improve the performance of CO2 huff and puff, but it did reduce the CO2 utilization. Moreover, gravity caused the produced oil to deposit on the bottom surface of the blowout end of the fracture, which made oil recovery of the core with a horizontal fracture slightly higher (~7%) than that of the core with a vertical fracture. In addition, variation in the intersection angle of fractures had little effect on ultimate oil recovery of CO2 huff and puff in fractured low‐permeability cores. It, however, did change the conductivity of the entire core, thus affecting oil recovery during the first two cycles remarkably. [ABSTRACT FROM AUTHOR]

Small water systems are important hotspots of greenhouse gas (GHG) emission, but estimates are poorly constrained as data are scarce. Small ponds are often constructed in urban areas, where they receive large amounts of nutrients and therefore tend to be highly productive. Here, we investigated GHG emissions, seasonal and diel variation, and net ecosystem production (NEP) from an urban pond. In monthly 24‐h field campaigns during 11 months, diffusive water–atmosphere methane (CH4) and carbon dioxide (CO2) fluxes and CH4 ebullition and oxidation were quantified. With oxygen (O2) measurements, NEP was assessed. The pond was a net GHG source the entire year, with an emission of 3.4 kg CO2 eq m−2 yr−1. The dominant GHG emission pathway was CH4 ebullition (bubble flux, 50%), followed by diffusive emissions of CO2 (38%) and CH4 (12%). Sediment CH4 release was primarily driven by temperature and especially ebullition increased exponentially above a temperature threshold of 15°C. The pond's atmospheric CO2 exchange was not related to NEP or temperature but likely to a high allochthonous carbon (C) input via runoff and anaerobic mineralization of C. We expect urban ponds to show a large increase in GHG emission with increasing temperature, which should be considered carefully when constructing ponds in urban areas. Emissions may partly be counteracted by pond management focusing on a reduction of nutrient and organic matter input. [ABSTRACT FROM AUTHOR]

The equilibrium climate sensitivity, that is, the global‐mean surface‐air temperature change in response to a doubling of the carbon dioxide concentration is a widely used metric in climate change studies. Its exact value is rarely known because its estimation requires a long integration time of several thousand years. We propose a method to estimate an accurate value of the equilibrium response from fully coupled climate models at a reasonable computational cost. Using this method, our state‐of‐the‐art climate model CNRM‐CM6‐1 reaches a stationary state after only few hundred of years of integration. This "Fast‐Forward" method consists of an optimal two‐step forcing pathway designed using the framework of a two‐layer energy balance model. It can be applied easily to any coupled climate model. Key Points: A simple method for estimating the equilibrium climate sensitivity is proposedThe method allows to simulate the stationary climate corresponding to any given radiative perturbation with a limited computational costThe method can be applied to any atmosphere‐ocean coupled climate model [ABSTRACT FROM AUTHOR]

Mangroves are considered one of the most productive ecosystems in the world with significant contributions as carbon sinks in the biosphere. Yet few attempts have been made to assess global patterns in mangrove net primary productivity, except for a few assumptions relating litterfall rates to variation in latitude. We combined geophysical and climatic variables to predict mangrove litterfall rates at continental scale. On a per-area basis, carbon flux in litterfall in the neotropics is estimated at 5 MgC.ha-1.yr-1, between 20% and 50% higher than previous estimates. Annual carbon fixed in mangrove litterfall in the neotropics is estimated at 11.5 TgC, which suggests that current global litterfall estimates extrapolated from mean reference values may have been underestimated by at least 5%. About 5.8 TgC of this total carbon fixed in the neotropics is exported to estuaries and coastal oceans, which is nearly 30% of global carbon export by tides. We provide the first attempt to quantify and map the spatial variability of carbon fixed in litterfall in mangrove forests at continental scale in response to geophysical and climatic environmental drivers. Our results strengthen the global carbon budget for coastal wetlands, providing blue carbon scientists and coastal policy makers with a more accurate representation of the potential of mangroves to offset carbon dioxide emissions. [ABSTRACT FROM AUTHOR]

Mankind is constantly pursuing economic growth and social development, and while these bring convenience to people, they involve large amounts of greenhouse gas emissions under the heavy use of energy, which produces quite serious air pollution, which not only affects people's health but also leads to ecological environmental damage. Nowadays, the impact of the environment and the negative impacts of the world's economies while promoting economic growth are the most important issues for economies to achieve balanced development. This study uses the dynamic slack‐based data envelopment analysis (DEA) model to assess the environmental energy efficiency of high‐income economies (including China) and explore the negative impacts on the environment, to obtain a basis for energy‐saving emission reduction methods or configurations by using 48 high‐income economies (including China) from 2010 to 2014. The interperiod (carryover) variable is gross domestic product (GDP). The empirical results show that economies with high energy efficiency have a large consumption of energy and are unable to reduce carbon dioxide emissions. We also find that there exists a difference in the results depending on whether GDP is considered as the carryover variable. European economies are more efficient in energy consumption than others, and Asian economies are the most inefficient. In order to pursue GDP growth, economies need to consider reducing their energy consumption and CO2 emissions and improve their energy usage efficiency, further implementing sustainability. [ABSTRACT FROM AUTHOR]

Restoring overstocked forests by thinning and pyrolyzing residual biomass produces biochar and other value‐added products. Forest soils amended with biochar have potential to sequester carbon (C), improve soil quality, and alter greenhouse gas (GHG) emissions without depleting nutrient stocks. Yet, few studies have examined the effects of biochar on GHG emissions and tree growth in temperate forest soils. We measured GHG emissions, soil C content, and tree growth at managed forest sites in Idaho, Montana, and Oregon. We applied biochar amendments of 0, 2.5, or 25 Mg/ha to the forest soil surface. Flux of carbon dioxide and methane varied by season; however, neither were affected by biochar amendment. Flux of nitrous oxide was not detected at these nitrogen‐limited and unfertilized forest sites. Biochar amendment increased soil C content by 41% but did not affect tree growth. Overall, biochar had no detrimental effects on forest trees or soils. We conclude that biochar can be used harmlessly for climate change mitigation in forests by sequestering C in the soil. Forest soils amended with biochar made from forest residues have potential to modify tree growth, alter greenhouse gas emissions, and enhance long‐term soil carbon storage. In our study, various biochar amendments did not affect forest tree growth or greenhouse gas emissions but did increase soil carbon content up to 41%. We conclude that biochar can be safely applied to forest soils for the purpose of sequestering carbon. [ABSTRACT FROM AUTHOR]

Formulation of efficient absorbing solutions for carbon dioxide capture is essential to reduce the operation costs of industrial gas treatment plants. Recently, mixed amine systems, typically composed of a tertiary and a primary or secondary amine, have been a growing interest in academic and industrial research. In particular, the so‐called activated methyldiethanolamine (aMDEA), which contains small amounts of piperazine (PZ), has become one of the most promising new candidates. This work intends to perform a comparison between the performance of single amines on the one hand and their blends on the other hand with the aim of elucidating how PZ and MDEA can interact in the latter situation. In the first part, aqueous solutions made up of a pure reagent (either MDEA or PZ) were studied. Rates of CO2 transfer from a gas phase to unloaded and loaded solutions, up to nearly saturation points, were experimentally investigated for a wide range of operating conditions using a membrane contactor. Observed CO2 transfer rates were reproduced with a simple yet effective model that captured the main physical and chemical aspects. [ABSTRACT FROM AUTHOR]

Summary: Photosynthesis in bryophytes and lycophytes has received less attention than terrestrial plant groups. In particular, few studies have addressed the nonstomatal diffusion conductance to CO2gnsd of these plant groups.Their lower photosynthetic rate per leaf mass area at any given nitrogen concentration compared with vascular plants suggested a stronger limitation by CO2 diffusion. We hypothesized that bryophyte and lycophyte photosynthesis is largely limited by low gnsd. Here, we studied CO2 diffusion inside the photosynthetic tissues and its relationships with photosynthesis and anatomical parameters in bryophyte and lycophyte species in Antarctica, Australia, Estonia, Hawaii and Spain.On average, lycophytes and, specially, bryophytes had the lowest photosynthetic rates and nonstomatal diffusion conductance reported for terrestrial plants. These low values are related to their very thick cell walls and their low exposure of chloroplasts to cell perimeter.We conclude that the reason why bryophytes lie at the lower end of the leaf economics spectrum is their strong nonstomatal diffusion conductance limitation to photosynthesis, which is driven by their specific anatomical characteristics. [ABSTRACT FROM AUTHOR]

During the early to mid‐Miocene, benthic δ18O records indicate large ice volume fluctuations of the Antarctic ice sheet (AIS) on multiple timescales. Hitherto, research has mainly focused on how CO2 and insolation changes control an equilibrated AIS. However, transient AIS dynamics remain largely unexplored. Here, we study Miocene AIS variability, using an ice sheet‐shelf model forced by climate model output with various CO2 levels and orbital conditions. Besides equilibrium simulations, we conduct transient experiments, gradually changing the forcing climate state over time. We show that transient AIS variability is substantially smaller than equilibrium differences. This reduces the contribution of the AIS to δ18O fluctuations by more than two thirds on a 40‐kyr timescale, hence requiring a larger contribution by deep‐sea‐temperature variability. The growth rates are much slower than the decay rates, which ensures variability around a preferred small state. Finally, if the bedrock topography enlarges the West Antarctic land surface, AIS self‐sustenance increases. Key Points: The contribution of transient Antarctic ice sheet variations to Miocene δ18O signals is smaller than indicated by equilibrium differencesTransient ice volume variability is centered around a preferred small state and is dependent on the timescale of the forcingEnlarging the West Antarctic land surface increases the self‐sustenance of the Miocene Antarctic ice sheet, decreasing the variability [ABSTRACT FROM AUTHOR]

Inference of CO2 surface fluxes using atmospheric CO2 observations in atmospheric inversions depends critically on accurate representation of atmospheric transport. Here we characterize regional‐scale CO2 transport uncertainties due to uncertainties in meteorological fields using a mesoscale atmospheric model and an ensemble of simulations with flow‐dependent transport errors. During a 1‐month summer period over North America, transport uncertainties yield an ensemble spread in instantaneous CO2 at 100 m above ground level comparable to the CO2 uncertainties resulting from 48% relative uncertainty in 3‐hourly natural CO2 fluxes. Temporal averaging reduces transport uncertainties but increases the influence of CO2 uncertainties from the lateral boundaries. The influence of CO2 background uncertainties is especially large for column‐averaged CO2. These results suggest that transport errors and CO2 background errors limit regional atmospheric inversions at two distinct timescales and that the error characteristics of transport and background errors should guide the design of regional inversion systems. Plain Language Summary: Accurate estimates of regional‐scale CO2 surface fluxes are essential to improve our understanding of the carbon cycle and to verify human CO2 emission inventories. CO2 surface fluxes can be inferred from atmospheric CO2 measurements through inversion methods, which use atmospheric transport models to relate CO2 concentration to fluxes. However, previous studies have shown that inversion results can be sensitive to errors in the simulated atmospheric transport. To better understand how to account for such transport errors, we characterize the uncertainties in simulated CO2 concentration due to uncertainties in atmospheric transport by running an ensemble of perturbed transport simulations in a regional atmospheric model. Our results show that CO2 uncertainties due to transport uncertainties are about half the magnitude as uncertainties due to erroneous CO2 surface fluxes while displaying similar spatial and temporal patterns. Transport uncertainties are reduced when CO2 is time averaged, but at the same time the influence of uncertainties in the CO2 background concentration is increased at longer timescales. Thus, the flux signals in regional inversions are degraded by transport errors and CO2 background errors at different timescales, and it is imperative to properly account for these errors to obtain reliable regional‐scale CO2 flux estimates. Key Points: We quantify CO2 transport uncertainties due to uncertainties in meteorological fields at the regional scale and submonthly timescalesAtmospheric CO2 estimates that are strongly influenced by CO2 surface fluxes tend to also have large transport uncertaintiesThe signal‐to‐noise ratio in in situ CO2 is limited by transport errors at subweekly timescales and CO2 background errors at longer scales [ABSTRACT FROM AUTHOR]

CO2 reservoirs and high CO2 content gas reservoirs in marine sediments generally have complex pressure system, which usually encounters supercritical CO2(SC‐CO2) invasion into the wellbore during drilling process. The wellbore transient flow and phase transition along the wellbore during the drilling process has not been thoroughly investigated, because the CO2 physical properties and the reservoirs petrophysical properties could affect the transient flow of mixed fluid and phase transition of CO2 along the well. A numerical model is presented in this research to analyze the transient flow in wellbores and to predict phase transition of CO2 during formation SC‐CO2 invasion in the drilling process. The main considerations were the following: multiphase transient flow in wellbores was coupled with the non‐Darcy flow through the formation; wellbore temperature, pressure and the mixture of drilling fluid and SC‐CO2 were calculated in the method of coupling; the invaded SC‐CO2 could affect the mixed fluid physical properties in the annulus; the change of physical properties of CO2 (eg, solubility, phase transition) was considered and integrated. The research results indicate that as the mixture of drilling fluid and SC‐CO2 flows from the bottom to the surface, the invaded CO2 is difficult to be detected at the early invasion stage because of high CO2 density and solubility; the CO2 would change from supercritical to gas phase and the dissolved quantity and density of CO2 rapidly decrease near the wellhead, and further cause well‐control issues. Furthermore, the bottom‐hole pressure (BHP) would decrease and could not provide sufficient balance to the formation pressure, which could significantly increase the risk of well blowout. Sensitivity analysis was utilized to evaluate the effects of the choke pressure, drilling fluid pumping rate, initial pressure difference, reservoir permeability, and drilled reservoir thickness on the BHP and the depth of phase transition of CO2. A numerical model coupling the flow‐temperature distribution in wellbores with the non‐Darcy seepage through formation media was formulated to study the transient multiple‐phase flow during SC‐CO2 invasion. With proposed numerical method and field data, the characteristics of gas‐liquid two‐phase transient flow and phase transition of CO2 were further investigated. The mechanisms for well blowout triggered by solubility variation and phase transition of CO2 were studied. [ABSTRACT FROM AUTHOR]

Restoring degraded freshwater wetlands may help to maximize soil carbon sequestration. In this study, we use 18 210Pb‐dated sediment cores to determine the organic carbon (OC) accumulation rates from two hydrologically restored freshwater coastal acid sulfate soil (CASS) wetlands. Recent OC accumulation rates (from ~1980 to present) were estimated to be 251 ± 26 g·m−2·year−1 in the seasonally inundated CASS and 227 ± 50 g·m−2·year−1 in the permanently inundated CASS. The average OC accumulation during the previous century (190 ± 20 g·m−2·year−1) was within the range of blue carbon ecosystems (saltmarshes, mangroves, and seagrasses). Considering their large area and carbon accumulation rate, we estimate that Australian CASS wetlands sequester approximately 7.8 ± 0.8 Tg of carbon annually, which is equivalent to ~8% of the CO2 emission from fossil fuels in Australia. Hence, preserving or restoring CASS may be a good climate change mitigation strategy. Key Points: Because of their large areal extent and OC accumulation rates, CASS wetlands may be an important component of Australia's carbon accountingEighteen 210Pb‐dated sediment cores were used to determine carbon accumulation in coastal acid sulfate soil (CASS) wetlandsOrganic carbon (OC) accumulation from two hydrologically restored freshwater CASS wetlands were estimated to be near 190 ± 20 g·m−2·year−1 Plain Language Summary: Coastal freshwater wetlands are highly productive and can sequester large amounts of carbon. The carbon accumulation rates here suggest that coastal acid sulfate soils (CASS) are also a substantial sink of CO2. By extrapolating our observations, we show that approximately 7.79 Tg of carbon is sequestered in Australian CASS wetlands annually which is equivalent to ~8% of the CO2 emission from fossil fuels in Australia. Hence, managing CASS wetlands to protect their soil carbon store function may help offset anthropogenic sources of greenhouse gasses and their hydrological remediation could be an important component to the global carbon cycle. [ABSTRACT FROM AUTHOR]

In 2016, Hurricane Matthew accounted for 25% of the annual riverine C loading to the Neuse River Estuary‐Pamlico Sound, in eastern North Carolina. Unlike inland watersheds, dissolved organic carbon (DOC) was the dominant component of C flux from this coastal watershed and stable carbon isotope and chromophoric dissolved organic matter evidence indicated the estuary and sound were dominated by wetland‐derived terrigenous organic matter sources for several months following the storm. Persistence of wetland‐derived DOC enabled its degradation to carbon dioxide (CO2), which was supported by sea‐to‐air CO2 fluxes measured in the sound weeks after the storm. Under future increasingly extreme weather events such as Hurricane Matthew, and most recently Hurricane Florence (September 2018), degradation of terrestrial DOC in floodwaters could increase flux of CO2 from estuaries and coastal waters to the atmosphere. Plain Language Summary: Recent hurricanes along the Southeastern and Gulf coasts of the United States have received much attention, because these extreme events have led to immense societal and economic impacts. Wetlands in coastal watersheds store large amounts of organic matter and upon flooding during extreme weather events are poised to release this material into adjacent rivers and estuaries where its decomposition can generate carbon dioxide. Alteration of carbon balances in these events can shift impacted coastal ecosystems from states of carbon sinks to carbon sources for periods of weeks to months. Understanding the balance between these states is important to our understanding of how, and how long, regional carbon cycling is impacted after such extreme weather events. A biweekly record of dissolved and particulate organic matter quantity and quality from a coastal watershed in North Carolina in the 3 months following Hurricane Matthew in 2016 illustrated a major input of wetland carbon to coastal waters caused by this storm and its substantial lingering effect on coastal carbon cycling. Key Points: Hurricane Matthew delivered 25% of the annual carbon loading to North Carolina coastal waters in 2016Wetland‐derived terrestrial organic matter persisted in coastal waters for several months following Hurricane MatthewDegradation of terrestrial organic matter in coastal waters supported vertical CO2 fluxes months after the storm [ABSTRACT FROM AUTHOR]

Summary: Phosphenolpyruvate carboxylase (PEPC)‐catalysed fixation of bicarbonate to C4 acids is commonly believed to represent a rather small flux in illuminated leaves. In addition, its potential variation with O2 and CO2 is not documented and thus is usually neglected in gas‐exchange studies.Here, we used quantitative NMR analysis of sunflower leaves labelled with 13CO2 (99% 13C) under controlled conditions and measured the amount of 13C found in the four C‐atom positions in malate, the major product of PEPC activity.We found that amongst malate 13C‐isotopomers present after labelling, most molecules were labelled at both C‐1 and C‐4, showing the incorporation of 13C at C‐4 by PEPC fixation and subsequent redistribution to C‐1 by fumarase (malate–fumarate equilibrium). In addition, absolute quantification of 13C content showed that PEPC fixation increased at low CO2 or high O2, and represented up to 1.8 μmol m−2 s−1, that is, 40% of net assimilation measured by gas exchange under high O2/CO2 conditions.Our results show that PEPC fixation represents a quantitatively important CO2‐fixing activity that varies with O2 and/or CO2 mole fraction and this challenges the common interpretation of net assimilation in C3 plants, where PEPC activity is often disregarded or considered to be constant at a very low rate. [ABSTRACT FROM AUTHOR]

Objective: Cardiac dysfunction has been described in 60% of fetuses undergoing open myelomeningocele (MMC) repair. Routine Doppler evaluation of the umbilical artery (UA) and ductus venosus (DV) is challenging during fetal surgery. The aim of this study was to describe Doppler changes in the UA and DV in a cohort of fetuses during fetoscopic MMC repair.Methods: This was a retrospective study of fetuses that underwent fetoscopic repair of MMC at a single institution between 2014 and 2017. Ultrasound images taken intraoperatively were analyzed to describe the changes in Doppler parameters of the UA and DV during fetoscopic MMC repair. The timing of Doppler changes was matched with the phase of surgery to determine whether a pattern to their appearance could be ascertained.Results: Of the thirty-five cases of fetoscopic MMC repair performed during the study period, Doppler data were available for 15. Of these, UA Doppler data were obtained in 12 cases, and DV Doppler data were obtained in 13 cases. Of the 12 cases for which there were UA data, nine (75%) showed transient absence of end-diastolic flow (EDF), with five (41.7%) of them progressing to reversal of EDF. Of the 13 cases for which there were DV data, nine had elevated pulsatility index; however, none of them had absent or reversed blood flow during atrial contraction. Of the nine cases with absent EDF in the UA, this abnormality first appeared during fetoscopic repair in five (55.6%), after uterus exteriorization but before CO2 insufflation in two (22.2%), after uterus replacement but before skin closure in one (11.1%) and after CO2 insufflation but before the start of the MMC repair in one (11.1%). Doppler abnormalities in four fetuses with reversed EDF and in three with absent EDF resolved during surgery. Follow-up examination 1 day after surgery demonstrated resolution of UA and DV Doppler abnormalities in all fetuses.Conclusion: Transient Doppler abnormalities of the UA, without significant changes in the DV, can be seen during fetoscopic MMC repair. The clinical significance of these Doppler findings remains unclear due to their transient and intermittent nature. Copyright © 2018 ISUOG. Published by John Wiley & Sons Ltd. [ABSTRACT FROM AUTHOR]

Ecological research has increasingly highlighted the importance of intraspecific variation in shaping the structure and function of communities and ecosystems. Indeed, the effects of intraspecific variation can match or exceed those of interspecific variation. Previous reviews of intraspecific variation in plant traits across heterogeneous environments have focused primarily on mean phenotypic effects. We propose that a richer and fuller understanding of the ecological causes and consequences of intraspecific variation would be provided by partitioning trait variance into its subcomponents (genetic, environment, genotype by environment interaction).We used a meta‐analysis of 352 sets of genetic, environment and genotype by environment (G×E) variation estimates from 72 studies of Salicaceae to compare these sources of variation across plant traits (growth, foliar nitrogen, defence compounds), insect herbivore performance metrics (e.g., survival, growth, fecundity) and environmental conditions (e.g., soil nutrients, water, defoliation).Our findings revealed that variation in levels of defence compounds (both condensed tannins and salicinoids) and insect herbivore performance were primarily genetically determined, while variation in plant growth and foliar nitrogen was more environmentally determined.Plasticity in plant growth, foliar nitrogen levels and insect herbivore performance varied substantially across different sites (year × location), and nutrient, water and carbon dioxide environments. Plasticity was lowest for chemical defence traits and all traits in contrasting ozone and defoliation environments.Our quantitative review also revealed several gaps in the literature, including a need for surveying more mature plants, a wider variety of insect herbivore species (e.g., leaf‐galling insects, specialist insects) and underrepresented environmental treatments (e.g., competition, defoliation, disease, light and water availability).Findings from this analysis highlight the importance of, and patterns within, intraspecific variation with respect to shaping the evolvability and plasticity of traits and governing the interactions of plants and insects. A plain language summary is available for this article. Plain Language Summary [ABSTRACT FROM AUTHOR]

Coastal wetlands are a significant carbon (C) sink since they store carbon in anoxic soils. This ecosystem service is impacted by hydrologic alteration and management of these coastal habitats. Efforts to restore tidal flow to former salt marshes have increased in recent decades and are generally associated with alteration of water inundation levels and salinity. This study examined the effect of water level and salinity changes on soil organic matter decomposition during a 60‐day incubation period. Intact soil cores from impounded fresh water marsh and salt marsh were incubated after addition of either sea water or fresh water under flooded and drained water levels. Elevating fresh water marsh salinity to 6 to 9 ppt enhanced CO2 emission by 50%−80% and most typically decreased CH4 emissions, whereas, decreasing the salinity from 26 ppt to 19 ppt in salt marsh soils had no effect on CO2 or CH4 fluxes. The effect from altering water levels was more pronounced with drained soil cores emitting ~10‐fold more CO2 than the flooded treatment in both marsh sediments. Draining soil cores also increased dissolved organic carbon (DOC) concentrations. Stable carbon isotope analysis of CO2 generated during the incubations of fresh water marsh cores in drained soils demonstrates that relict peat OC that accumulated when the marsh was saline was preferentially oxidized when sea water was introduced. This study suggests that restoration of tidal flow that raises the water level from drained conditions would decrease aerobic decomposition and enhance C sequestration. It is also possible that the restoration would increase soil C decomposition of deeper deposits by anaerobic oxidation, however this impact would be minimal compared to lower emissions expected due to the return of flooding conditions. Salt marsh restoration, with increasing salinity and water level, could reduce methane emissions, but its effect on soil C decomposition would be highly depended on inundation levels: higher water level would greatly decrease aerobic decomposition and benefit C sequestration, and vice versa. [ABSTRACT FROM AUTHOR]

Gas flaring is a commonly used practice in the oil and gas sector that leads to key air pollutant and greenhouse gas emissions. Here we use multipollutant (NO2, SO2) satellite observations from 2005 to 2017 to quantify gas flaring activity in Mexico's offshore production cluster, which produces ~50–70% of the country's oil and is among the world's largest oil fields. We estimate annual flared gas volume ranging from 5.5 to 20 × 109 m3 over the Mexican offshore corresponding to >40% associated gas production, which is significantly larger than for instance offshore United States where reportedly <3% of associated gas is flared. The 13‐year record of satellite‐derived gas flaring indicates a drastic increase until 2008 and a decline afterward. While the increased flaring is associated with efforts to enhance oil production, the post‐2008 decline is linked to an expanding capacity of associated gas utilization, providing a continuing opportunity to reduce flaring for environmental and economic benefits. Plain Language Summary: Gas flaring, a commonly used practice in the oil and gas sector to burn off associated natural gas, leads to significant economic loss and emissions of key air pollutants (e.g., SO2 and NO2) and greenhouse gases (e.g., methane and carbon dioxide). Global efforts have been underway to reduce gas flaring, which is considered a viable mitigation option to reduce criteria air pollutants and greenhouse gas emissions, because of technology availability and potential economic gains. In this context, it becomes increasingly important to independently quantify and track gas flaring activity over time, as well as independently evaluate progress in oil/gas regulations and policy implementation, toward mitigation measures. Here we applied a combined analysis of satellite NO2 and SO2 observations over offshore Mexico, one of the world's largest offshore oil production complexes, during 2005–2017. The 13‐year record showed an increase in gas flaring until 2008 associated with efforts to enhance oil production and a decline after 2008 linked to an expanding capacity of associated gas utilization. Key Points: A combined analysis of satellite NO2 and SO2 observations is useful for quantifying and tracking gas flaring activities over timeSatellite‐derived flared gas volume well captures the interannual variability of the reported flaring activity in offshore MexicoGas flaring activity in offshore Mexico peaked in 2008 and declined steadily after 2008, reflecting progress in policy implementation [ABSTRACT FROM AUTHOR]

Winter data of surface ocean temperature (SST), salinity (SSS) and CO2 fugacity (fCO2) collected on the VOS M/V Nuka Arctica in the subpolar North Atlantic between 2004 and 2017 are used to establish trends, drivers, and interannual variability. Over the period, waters cooled and freshened, and the fCO2 increased at a rate similar to the atmospheric CO2 growth rate. When accounting for the freshening, the inferred increase in dissolved inorganic carbon (DIC) was found to be approximately twice that expected from atmospheric CO2 alone. This is attributed to the cooling. In the Irminger Sea, fCO2 exhibited additional interannual variations driven by atmospheric forcing through winter mixing. As winter fCO2 in the region is close to the atmospheric, the subpolar North Atlantic has varied between being slightly supersaturated and slightly undersaturated over the investigated period. Plain Language Summary: The global oceans take up roughly a quarter of carbon dioxide (CO2) from fossil fuels and industry per year. As the emissions of CO2 increase, the amount of CO2 taken up by the oceans should increase in proportion; however, the ability of the ocean to remove CO2 from the atmosphere varies on interannual to decadal time scales. Here we assess processes that drive short‐term variability and long‐term trends of the subpolar North Atlantic carbon sink based on observational data obtained during winters between 2004 and 2017. We find that the subpolar North Atlantic has indeed kept pace with rising emissions over the entire period of time, which was mainly attributed to solubility‐driven uptake of CO2. Year‐to‐year changes of the surface ocean partial pressure of CO2 can be linked to the depth of the winter mixed layer as well as atmospheric forcing. In general, the North Atlantic has shifted between a small source and a small sink of atmospheric CO2 during wintertime. Our results underline the need to maintain long‐term physical, chemical, and biological observations in order monitor the ocean CO2 sink and understand the processes driving variability. Key Points: Subpolar North Atlantic winter surface ocean fCO2 growth rates track the atmospheric CO2 growth rate between 2004 and 2017DIC‐driven fCO2 changes are twice as large as expected from atmospheric trends in fCO2, a result of substantial surface coolingInterannual fCO2 variability in the Irminger Sea is linked to mixed layer depth and the North Atlantic Oscillation [ABSTRACT FROM AUTHOR]

C4 photosynthesis is a complex trait that boosts productivity in warm environments. Paradoxically, it evolved independently in numerous plant lineages, despite requiring specialised leaf anatomy. The anatomical modifications underlying C4 evolution have previously been evaluated through interspecific comparisons, which capture numerous changes besides those needed for C4 functionality. Here, we quantify the anatomical changes accompanying the transition between non‐C4 and C4 phenotypes by sampling widely across the continuum of leaf anatomical traits in the grass Alloteropsis semialata. Within this species, the only trait that is shared among and specific to C4 individuals is an increase in vein density, driven specifically by minor vein development that yields multiple secondary effects facilitating C4 function. For species with the necessary anatomical preconditions, developmental proliferation of veins can therefore be sufficient to produce a functional C4 leaf anatomy, creating an evolutionary entry point to complex C4 syndromes that can become more specialised. [ABSTRACT FROM AUTHOR]

Understanding the capillary and wetting behavior of supercritical CO2 (scCO2) and brine in reservoir rocks is crucial for reliable predictions of geologic carbon storage, as it strongly impacts CO2 migration and residual trapping in the reservoir. The wetting state of such systems can be assessed through laboratory measurements of the capillary pressure characteristic curve. However, while some studies reported consistent scaling with strongly water wet systems, some others observed deviations from hydrophilic conditions. We present core‐flooding drainage capillary pressure measurements using scCO2/water and N2/water on a Berea sandstone, untreated, then fired, and then exposed to scCO2 for 28 days. The purpose is to investigate the impact of firing and longer exposure to scCO2, two potential sources for variability in experimental observations, on capillarity and wettability. The results show excellent agreement among all the core‐flooding capillary pressure data, suggesting no change in wetting state due to firing or longer exposure. Plain Language Summary: Carbon capture and storage is a promising technology to limit anthropogenic greenhouse gas emissions responsible for global warming. It consists in capturing CO2 from large point source emitters and transporting it to a site where it will be injected in deep geological formations for storage. One important property of a rock in the presence of two nonmiscible fluids (here CO2 and formation brine) is the preference of one fluid over another to be in contact with the rock's surface, a property called wettability. Wettability directly impacts the way injected CO2 will flow in the subsurface and will stay trapped in the rock. However, although considerable effort has been made in the past decade to determine the wettability of storage rocks with respect to CO2 and brine, there is considerable variability in the reported data. This study focuses on two particular factors that could lead to the differences in experimental observations: the preparation of the rock sample used for measurements and the duration of exposure to CO2. We observed no change of wettability and general conditions favorable for CO2 trapping in the studied rock, a sandstone. Key Points: Drainage capillary pressure measurements were repeated on a Berea core untreated, fired and then exposed to supercritical CO2Firing the rock core does not impact the strongly water wetting state of the systemNo wettability alteration is observed after the Berea core is exposed to supercritical CO2 for a month [ABSTRACT FROM AUTHOR]

The Paleocene‐Eocene Thermal Maximum was a transient, carbon‐induced global warming event, considered the closest analog to ongoing climate change. Impacts of a decrease in deepwater formation during the onset of the Paleocene‐Eocene Thermal Maximum suggested by proxy data on the carbon cycle are not yet fully understood. Using an Earth System Model, we find that changes in overturning circulation are key to reproduce the deoxygenation and carbonate dissolution record. Weakening of the Southern Ocean deepwater formation and enhancement of ocean stratification driven by warming cause an asymmetry in carbonate dissolution between the Atlantic and Pacific basins suggested by proxy data. Reduced ventilation results in accumulation of remineralization products (CO2 and nutrients) in intermediate waters, thereby lowering O2 and increasing CO2. As a result, carbonate dissolution is triggered throughout the water column, while the ocean surface remains supersaturated. Our findings contribute to understanding of the long‐term response of the carbon cycle to climate change. Plain Language Summary: The Paleocene‐Eocene Thermal Maximum, characterized by a relatively rapid carbon release to the atmosphere and global warming, has received ample scientific attention owing to its analogy to ongoing climate change. We perform Earth system model projections of concomitant changes in climate, ocean circulation, and marine biogeochemical cycles during the onset of the Paleocene‐Eocene Thermal Maximum. In our simulations global warming (induced by atmospheric emissions of CO2) leads to a weakening of the meridional overturning circulation and reduced ventilation of the ocean interior which is more pronounced in the Atlantic than in the Pacific Ocean. As a result of this ocean stagnation, respiratory CO2 released via bacterial remineralization of organic matter (oxygen is thereby consumed) builds up in intermediate waters. This triggers carbonate dissolution and deoxygenation. This mechanism alone is sufficient to explain the asymmetry in the carbonate dissolution proxy record between the Pacific and Atlantic Oceans. Key Points: CO2‐induced warming at the onset of PETM leads to reduced ventilation of the ocean interior, more pronounced in the Atlantic than in the Pacific OceanReduced ventilation results in accumulation of respiratory CO2 and nutrients in intermediate waters, thereby lowering O2Carbonate dissolution is triggered in ocean interior, while the surface remains supersaturated; asymmetry in the carbonate dissolution proxy record between the Pacific and Atlantic Oceans is thereby reproduced [ABSTRACT FROM AUTHOR]

We determined decadal‐scale increases of anthropogenic CO2 in the water column using data sets collected 17 years apart (1994–1996 and 2012–2013) along a transect at nominal 62°S in the Indian and western Pacific sectors of the Southern Ocean. Large increases of anthropogenic CO2 (up to 9.1 ± 1.5 μmol/kg), closely following atmospheric CO2 increases, were found in Antarctic Bottom Water (AABW), previously considered a small sink of anthropogenic CO2. Vertical distributions of anthropogenic CO2 increases showed significant positive correlations with those of changes in CFC‐12 and SF6, implying that the distributions were mainly controlled by physical processes such as ventilation and circulation. Calculated uptake rates of anthropogenic CO2 by AABW were between 0.29 and 0.39 mol·m−2·yr−1 in five longitudinal segments of the transect. In accounting for the large increase of anthropogenic CO2 in AABW, sea surface conditions in the formation region of AABW are important. Plain Language Summary: The ocean absorbs about 30% of CO2 emitted into the atmosphere as a result of human activities, which we term "anthropogenic CO2." The Southern Ocean undertakes about 40% of anthropogenic CO2 entering the ocean. Therefore, to investigate Southern Ocean CO2 uptake is an important task for the prediction of global warming caused by anthropogenic CO2 increases in the atmosphere. Here we focus anthropogenic CO2 in the bottom layers below approximately 2,500 m deep, where storage of anthropogenic CO2 has been considered to be little. Using high‐quality data for oceanic CO2, we find significant increases of anthropogenic CO2 in the bottom layers. Our findings highlight the importance of anthropogenic CO2 stored in the bottom layers in estimates of the global carbon budget, because the anthropogenic CO2 in the bottom layers is transported into the entire world ocean through the ocean circulation. Key Points: Anthropogenic CO2 increased up to 9.1 ± 1.5 μmol/kg over 17 years in Antarctic Bottom Water (AABW), previously considered a small CO2 sinkCO2 increases correlate with increased CFC‐12 and SF6, implying that ventilation and circulation control anthropogenic CO2 uptake by AABWFor a high uptake of anthropogenic CO2 by AABW, sea surface conditions in the formation region of AABW are important [ABSTRACT FROM AUTHOR]

ContentsSummary652I.Introduction652II.Discrepancy in predicting the effects of rising [CO2] on the terrestrial C sink655III.Carbon and nutrient storage in plants and its modelling656IV.Modelling the source and the sink: a plant perspective657V.Plant‐scale water and Carbon flux models660VI.Challenges for the future662Acknowledgements663Authors contributions663References663 Summary: The increase in atmospheric CO2 in the future is one of the most certain projections in environmental sciences. Understanding whether vegetation carbon assimilation, growth, and changes in vegetation carbon stocks are affected by higher atmospheric CO2 and translating this understanding in mechanistic vegetation models is of utmost importance. This is highlighted by inconsistencies between global‐scale studies that attribute terrestrial carbon sinks to CO2 stimulation of gross and net primary production on the one hand, and forest inventories, tree‐scale studies, and plant physiological evidence showing a much less pronounced CO2 fertilization effect on the other hand. Here, we review how plant carbon sources and sinks are currently described in terrestrial biosphere models. We highlight an uneven representation of complexity between the modelling of photosynthesis and other processes, such as plant respiration, direct carbon sinks, and carbon allocation, largely driven by available observations. Despite a general lack of data on carbon sink dynamics to drive model improvements, ways forward toward a mechanistic representation of plant carbon sinks are discussed, leveraging on results obtained from plant‐scale models and on observations geared toward model developments. [ABSTRACT FROM AUTHOR]

Tropical forest responses are an important feedback on global change, but changes in forest composition with projected increases in CO2 and drought are highly uncertain. Here we determine shifts in the most competitive plant hydraulic strategy (the evolutionary stable strategy or ESS) from changes in CO2 and drought frequency and intensity. Hydraulic strategies were defined along a spectrum from drought avoidance to tolerance by physiology traits. Drought impacted competition more than CO2, with elevated CO2 reducing but not reversing drought‐induced shifts in the ESS towards more tolerant strategies. Trait plasticity and/or adaptation intensified these shifts by increasing the competitive ability of the drought tolerant relative to the avoidant strategies. These findings predict losses of drought avoidant evergreens from tropical forests under global change, and point to the importance of changes in precipitation during the dry season and constraints on plasticity and adaptation in xylem traits to forest responses. [ABSTRACT FROM AUTHOR]

Effects of wave‐driven Langmuir turbulence on the air‐sea flux of carbon dioxide (CO2) are examined using large eddy simulations featuring actively reacting carbonate chemistry in the ocean mixed layer at small scales. Four strengths of Langmuir turbulence are examined with three types of carbonate chemistry: time‐dependent chemistry, instantaneous equilibrium chemistry, and no reactions. The time‐dependent model is obtained by reducing a detailed eight‐species chemical mechanism using computational singular perturbation analysis, resulting in a quasi steady state approximation for hydrogen ion (H+); that is, fixed pH. The reduced mechanism is then integrated in two half‐time steps before and after the advection solve using a Runge‐Kutta‐Chebyshev scheme that is robust for stiff systems of differential equations. The simulations show that as the strength of Langmuir turbulence increases, CO2 fluxes are enhanced by rapid overturning of the near‐surface layer, which rivals the removal rate of CO2 by time‐dependent reactions. Equilibrium chemistry and nonreactive models are found to bring more and less carbon, respectively, into the ocean as compared to the more realistic time‐dependent model. These results have implications for Earth system models that either neglect Langmuir turbulence or use equilibrium, instead of time‐dependent, chemical mechanisms. Key Points: Detailed carbonate chemistry is solved in large eddy simulations of upper ocean turbulenceLangmuir turbulence increases the air‐sea flux of CO2, resulting in increased dissolved inorganic carbonEquilibrium chemistry leads to overpredicted fluxes of CO2 into the upper ocean [ABSTRACT FROM AUTHOR]

Carbon dioxide enters metabolism via six known CO2 fixation pathways, of which only one is linear, exergonic in the direction of CO2‐assimilation, and present in both bacterial and archaeal anaerobes – the Wood‐Ljungdahl (WL) or reductive acetyl‐CoA pathway. Carbon monoxide (CO) plays a central role in the WL pathway as an energy rich intermediate. Here, we scan the major biochemical reaction databases for reactions involving CO and CO2. We identified 415 reactions corresponding to enzyme commission (EC) numbers involving CO2, which are non‐randomly distributed across different biochemical pathways. Their taxonomic distribution, reversibility under physiological conditions, cofactors and prosthetic groups are summarized. In contrast to CO2, only 15 reaction classes involving CO were detected. Closer inspection reveals that CO interfaces with metabolism and the carbon cycle at only two enzymes: anaerobic carbon monoxide dehydrogenase (CODH), a Ni‐ and Fe‐containing enzyme that generates CO for CO2 fixation in the WL pathway, and aerobic CODH, a Mo‐ and Cu‐containing enzyme that oxidizes environmental CO as an electron source. The CO‐dependent reaction of the WL pathway involves carbonyl insertion into a methyl carbon‐nickel at the Ni‐Fe‐S A‐cluster of acetyl‐CoA synthase (ACS). It appears that no alternative mechanisms to the CO‐dependent reaction of ACS have evolved in nearly 4 billion years, indicating an ancient and mechanistically essential role for CO at the onset of metabolism. Carbon monoxide (CO) is essential for CO2 fixation in many microbes that inhabit strictly anaerobic environments. Here, we scan major biochemical databases for the involvement of CO and CO2 in metabolism. While CO2 participates in hundreds of reactions, CO enters metabolism at only two. CO2 assimilation via CO is one of biochemistry's most ancient and conserved reactions. CO is apparently special. [ABSTRACT FROM AUTHOR]

This work describes the development of an optimized spin dope for the production of open‐porous, mechanically stable fiber sorbents. The fiber sorbents in this work consist of Torlon® polymer matrix with dispersed zeolite particles to act as the sorbent sites. Initial spinning attempts with dopes consisting of Torlon®, 13X, n‐methylpyrrolidone (NMP) and water yielded fibers that were prone to breaks during production and had a large number of macrovoids. To remedy this, polyvinylpyrrolidone (PVP) was introduced in the dope as a pore former and macrovoid suppressant. A separate phase diagram was developed to accommodate PVP and a new preferred spin dope composition was identified. Fibers were spun based on this concentration with adequate spinning behavior. Microscopy analysis showed that PVP was successful in reducing the prevalence of macrovoids in the fiber cross section. High sorbent wall permeance was also retained with the PVP. Further analysis of permeance measurements revealed that Knudsen flow was dominant over Poiseuille flow. The estimated pore sizes implying that the transport process lies in the transition region between molecular and Knudsen diffusion. POLYM. ENG. SCI., 58:2106–2114, 2018. © 2018 Society of Plastics Engineers [ABSTRACT FROM AUTHOR]

Abstract The aim of this paper is to evaluate (i) the relevance of currently proposed measures of competitive intensity to elevated CO2 studies by means of an example analysis, hypothesizing that competitive intensity is increased under elevated CO2 ; and (ii) an alternative method for predicting species performance in mixtures from monocultures. Relative competition intensity (RCI), relative physiological performance and normalized ecological performance were used to characterize the competitive ability of two grasses (Danthonia richardsonii Cashmore, Phalaris aquatica L.) and two legumes (Lotus pedunculatus Cav., Trifolium repens L.) grown in monocultures and mixtures of the four species along a N gradient under conditions of ambient and elevated CO2 . Relative competition intensity could not be used to predict competitive outcomes in mixtures under conditions of elevated CO2 because it failed to account for changes in the size of interspecific differences along the N gradient and between CO2 concentrations. Relative physiological performance and relative ecological performance were more useful for investigating biomass production in mixtures and to predict species performance in mixtures from their performance in monocultures. Both indices of relative performance showed an increase in competitive intensity under elevated CO2 conditions. They also showed a decrease in competitive intensity with increasing N supply over most of the range of N supply, but a reversal of that trend at high levels of N supply. The merits and utility of these relative performance indices for elevated CO2 are discussed. [ABSTRACT FROM AUTHOR]

Direct and interactive effects of CO2 and light on tree phytochemistry and insect fitness parameters were examined through experimental manipulations of plant growth conditions and performance ofinsect bioassays. Three species of deciduous trees (quaking aspen, Populus tremuloides; paper birch, Betula papyrifera; sugar maple, Acersaccharum) were grown under ambient (387 8 mu L/L) and elevated (696 2 mu L/L) levels of atmospheric CO2, with low and high light availability (375 and 855 mu mol ? m-2 ? s-1 at solar noon). Effects on the population and individual performance of a generalist phytophagous insect, the white-marked tussock moth (Orgyia leucostigma) were evaluated. Caterpillars were reared on experimental trees for the duration of the larval stage, and complementary short-term (fourth-instar) feeding trials were conducted with insects fed detached leaves. Phytochemical analyses demonstrated strong effects of both CO2 and light on all foliar nutritional variables (water, starch and nitrogen). For all species, enriched CO2 decreased water content and increased starch content, especially under high light conditions. High CO2 availability reduced levels of foliar nitrogen, but effects were species specific and most pronounced for high light aspen and birch. Analyses of secondary plant compounds revealed that levels of phenolic glycosides (salicortin and tremulacin) in aspen and condensed tannins in birch and maple were positively influenced by levels of both CO2 and light. In contrast, levels of condensed tannins in aspen were primarily affected by light, whereas levels of ellagitannins and gallotanninsin maple responded to light and CO2, respectively. [ABSTRACT FROM AUTHOR]

A thermal dissociation process (ideally, 100% atom utilization) to regenerate the amine extractant and to produce gaseous HCl which is the key to realizing the CO2 mineralization with metal chloride waste liquids was investigated. Solvent effects on the thermal dissociation of tri‐n‐octylamine hydrochloride (TOAHCl) were predicted to be prominent via analyzing structure parameters, charge distribution, solvation free energy, apparent basicity, and N‐H frequency with the help of molecular simulation and experiments. Inert solvents with low polarity such as decalin, dodecane were favorable in thermal dissociation experiments. In particular, decalin enhanced the dissociation most effectively which is in agreement with the prediction. In dilute solutions, the thermal dissociation kinetics was shown to be first order. The apparent reaction rate (3.0 × 10−4−1.5 × 10−2 min−1) and activation energy (58.219‐121.827 kJ/mol) differ a lot at 180‐190°C in various solvents, confirming a strong solvent effect. A two‐stage reaction scheme in dilute solutions has been proposed from the experimental study. The overall process is entropically driven, with the removal of HCl into gas phase from the solvated state. The work could offer a fundamental direction for the further actual process. The solvent effect of thermal dissociation of tri‐octylamine hydrochloride was investigated systematically with both experimental and molecular simulation approaches. Decalin was selected as the best solvent. [ABSTRACT FROM AUTHOR]

Abstract: This study reports biomass gasification in a fluidized CREC Riser Simulator. Steam‐CO2 and steam‐inert gas were used as gasifier agents. Three biomass feedstocks were evaluated in terms of gasification performance, based on carbon conversion, product molar fraction, and H2/CO ratios. Results showed that gasification bed temperature influences syngas yields, as well as tar formation. This is the case regardless of the gasifier agent used. It was also shown that steam‐CO2 gasification significantly reduces tar formation while improving carbon conversion and increasing H2 and CO yields. Experimentally‐observed product molar fractions were compared with thermodynamic equilibrium model results. This thermodynamic equilibrium model accounts for biomass elemental composition, bed temperature, and gasifying agents. It was proven that for steam‐CO2 gasification, the thermodynamic equilibrium model predictions are close to the experimental results obtained in the fluidized CREC Riser Simulator. It was also demonstrated that steam‐carbon dioxide gasification leads to a zero CO2 gain, and therefore, a negligible carbon footprint. [ABSTRACT FROM AUTHOR]

Abstract: Although the Southern Ocean is thought to account for a significant portion of the contemporary oceanic uptake of carbon dioxide (CO2), flux estimates in this region are based on sparse observations that are strongly biased toward summer. Here we present new estimates of Southern Ocean air‐sea CO2 fluxes calculated with measurements from biogeochemical profiling floats deployed by the Southern Ocean Carbon and Climate Observations and Modeling project during 2014–2017. Compared to ship‐based CO2 flux estimates, the float‐based fluxes find significantly stronger outgassing in the zone around Antarctica where carbon‐rich deep waters upwell to the surface ocean. Although interannual variability contributes, this difference principally stems from the lack of autumn and winter ship‐based observations in this high‐latitude region. These results suggest that our current understanding of the distribution of oceanic CO2 sources and sinks may need revision and underscore the need for sustained year‐round biogeochemical observations in the Southern Ocean. [ABSTRACT FROM AUTHOR]

A BSTRACT: We propose a regime‐switching Poisson process incorporating climate and carbon dioxide (CO2) indices (RPCM) to model hurricane frequency. Model accuracy shows that two‐state RPCM (2‐RPCM) is superior to the existing climate methods, as forecast errors under 2‐RPCM are smaller than previous models by about 60–75 percent. We derive the pricing formula of reinsurance premiums by assuming the aggregate loss following the regime‐switching compound process. Pricing errors under 2‐RPCM for reinsurance premiums are 35–54 percent lower than those from previous models. The climate and regime‐switching effects dominate the CO2 effect in reducing pricing errors and producing more effective tail value at risk. [ABSTRACT FROM AUTHOR]