Carbon dioxide sequestration: how much and when?

Carbon dioxide (CO₂) sequestration has been proposed as a key component in technological portfolios for managing anthropogenic climate change, since it may provide a faster and cheaper route to significant reductions in atmospheric CO₂ concentrations than abating CO₂ production. However, CO₂ sequestration is not a perfect substitute for CO₂ abatement because CO₂ may leak back into the atmosphere (thus imposing future climate change impacts) and because CO₂ sequestration requires energy (thus producing more CO₂ and depleting fossil fuel resources earlier). Here we use analytical and numerical models to assess the economic efficiency of CO₂ sequestration and analyze the optimal timing and extent of CO₂ sequestration. The economic efficiency factor of CO₂ sequestration can be expressed as the ratio of the marginal net benefits of sequestering CO₂ and avoiding CO₂ emissions. We derive an analytical solution for this efficiency factor for a simplified case in which we account for CO₂ leakage, discounting, the additional fossil fuel requirement of CO₂ sequestration, and the growth rate of carbon taxes. In this analytical model, the economic efficiency of CO₂ sequestration decreases as the CO₂ tax growth rate, leakage rates and energy requirements for CO₂ sequestration increase. Increasing discount rates increases the economic efficiency factor. In this simple model, short-term sequestration methods, such as afforestation, can even have negative economic efficiencies. We use a more realistic integrated-assessment model to additionally account for potentially important effects such as learning-by-doing and socio-economic inertia on optimal strategies. We measure the economic efficiency of CO₂ sequestration by the ratio of the marginal costs of CO₂ sequestration and CO₂ abatement along optimal trajectories. We show that the positive impacts of investments in CO₂ sequestration through the reduction of future marginal CO₂ sequestration costs and the alleviation of future inertia constraints can initially exceed the marginal sequestration costs. As a result, the economic efficiencies of CO₂ sequestration can exceed 100% and an optimal strategy will subsidize CO₂ sequestration that is initially more expensive than CO₂ abatement. The potential economic value of a feasible and acceptable CO₂ sequestration technology is equivalent – in the adopted utilitarian model – to a one-time investment of several percent of present gross world product. It is optimal in the chosen economic framework to sequester substantial CO₂ quantities into reservoirs with small or zero leakage, given published estimates of marginal costs and climate change impacts. The optimal CO₂ trajectories in the case of sequestration from air can approach the pre-industrial level, constituting geoengineering. Our analysis is silent on important questions (e.g., the effects of model and parametric uncertainty, the potential learning about these uncertainties, or ethical dimension of such geoengineering strategies), which need to be addressed before our findings can be translated into policy-relevant recommendations.     

The effect of hypothetical diproton stability on the universe

By calculation of the proton-proton capture cross-section, it is shown that the existence of a bound diproton state would not lead to significant production of diprotons during big bang nucleosynthesis, contrary to popular belief. In typical stellar interiors, the stability of diprotons would lead to a reaction pathway for converting protons to deuterons perhaps ∼10¹⁰ times faster than the usual weak capture reaction. This would prevent stars of the familiar hot, dense type from occurring in the universe. However, if diproton stability is achieved by an increase in the low-energy strong coupling, gs, then stars with temperatures and densities sufficiently reduced so as to offset the faster reaction pathway to deuterium will appear to meet elementary stability criteria. The claim that there is a fine-tuned, anthropic upper bound to the strong force which ensures diproton instability therefore appears to be unfounded.     

Subduction Influence on Oxygen Fugacity and Trace and Volatile Elements in Basalts Across the Cascade Volcanic Arc

Fluids or melts derived from a subducting plate are often citedas a mechanism for the oxidation of arc magmas. What remainsunclear is the link between the fluid, oxygen fugacity, andother major and trace components, as well as the spatial distributionof the impact of those fluids. To test the potential effectsof addition of a subduction-derived fluid or melt to the sub-arcmantle, olivine-hosted melt inclusions from primitive basalticlavas sampled from across the central Oregon Cascades (43°–45°N)have been analyzed for major, trace and volatile elements andfO₂. Oxygen fugacity was determined in melt inclusions fromsulfur speciation determined by electron microprobe and fromolivine–chromite oxygen geobarometry. The overall rangein fO₂ based on sulfur speciation measurements is from <–0·25log units to + 1·9 log units (FMQ, where FMQ is fayalite–magnetite–quartzbuffer). Oxygen fugacity is positively correlated with fluid-mobiletrace element and light rare earth element contents in basaltsgenerated by relatively low-degree partial melting. Establishinga further correlation between fO₂ and fluid-mobile trace elementabundances with position along the arc requires the basaltsto be subdivided into shoshonitic, calc-alkaline, low-K tholeiiteand enriched intraplate basalt groups. Melt inclusions fromenriched intraplate and shoshonitic lavas show increasing fO₂and trace element abundances closer to the trench, whereas calc-alkalinemelt inclusions exhibit no significant across-arc variations.Low-K tholeiitic melt inclusions record an increase in incompatibletrace elements closer to the trench; however, there is no correlatedincrease in fO₂. The correlation observed in enriched intraplateand shoshonitic melt inclusions is interpreted to reflect aprogressively greater proportion of a fluid-rich, oxidized subductioncomponent in magmas generated nearer the subduction zone. Significantly,calc-alkaline melt inclusions with high ratios of large ionlithophile elements to high field strength elements, characteristicof ‘typical’ arc magmas, have oxidation states indistinguishablefrom low-K tholeiite and enriched intraplate basalt melt inclusions.The lack of across-arc geochemical variation in calc-alkalinemelt inclusions may suggest that these basalts are not necessarilythe most appropriate magmas for examining recent addition ofa subduction component to the sub-arc mantle. Flux and batchmelt model results produce a wide range of predicted amountsof melting and subduction component added to the mantle source;however, general trends characterized by increased melting andproportion of the subduction component from enriched intraplate,to low-K tholeiite, to calc-alkaline are robust. The model resultsdo not require enriched intraplate, low-K tholeiite and calc-alkalinemagmas to be produced from the same more fertile mantle source.However, enriched intraplate magmas, in contrast to calc-alkalineand low-K tholeiite magmas, cannot be generated from a depletedmantle source. Flux or batch melting of either the more fertileor depleted mantle sources used to generate the low-K tholeiite,calc-alkaline, and enriched intraplate magmas cannot reproduceshoshonitic compositions, which require a significantly depletedmantle source strongly metasomatized by a subduction component.The potential mantle source for shoshonitic basalts has a predictedfO₂ (after oxidation) from + 0·3 to + 2·4 logunits (FMQ) whereas the mantle source for low-K tholeiite, calc-alkaline,and enriched intraplate magmas may range from –1·1to + 0·7 log units (FMQ). KEY WORDS: basalt; Cascades; melt inclusions; oxidation state; volatiles     

Identification of a sulfide derivative with a bicyclic hydrocarbon skeleton related to squalene. Part II: synthesis of a S-spiro-like dithiolane triterpenoid

A sulfide with a bicyclic squalene hydrocarbon skeleton present in sediments from various depositional settings and of different geological age has been identified by synthesis of a reference compound. In contrast to previous expectations [cf. Schouten, S., Sinninghe Damsté, J.S., de Leeuw, J.W., 1995. A novel triterpenoid carbon skeleton in immature sulphur-rich sediments. Geochimica et Cosmochimica Acta 59, 953–958; Gug, S., Schaeffer, P., Adam, P., Klein, S., Motsch, E., Albrecht, P., 2009. Identification of a sulfide derivative with a bicyclic hydrocarbon skeleton related to squalene. Part I: Synthesis of a dithiane triterpenoid. Organic Geochemistry 40, 876–884.], this sulfide bears two “S-spiro type“ thiolane moities, but not the two thiochromane moieties originally envisaged. The synthesis resulted in the formation of a complex isomeric mixture of compounds, all co-eluting in gas chromatography (GC) in the form of one broad peak, as is the case with the geochemical compound. The spiro-type sulfide was formed by intramolecular sulfurization of a polyunsaturated bicyclic squalene derivative of unknown biological origin. The presence of this sulfide in a number of Triassic to Miocene marine sediments from various and contrasting depositional settings (upwelling environments, shallow continental platforms, lagoonal sub-basins, hypersaline environments), all characterized by strongly anoxic conditions, but with or without photic zone anoxia, indicates that the microorganisms biosynthesizing the precursor bicyclic squalene occupy diverse ecological niches.     

Thermal convection in ice-I shells of Titan and Enceladus

Cassini-Huygens observations have shown that Titan and Enceladus are geologically active icy satellites. Mitri and Showman [Mitri, G., Showman, A.P., 2005. Icarus 177, 447-460] and McKinnon [McKinnon, W.B., 2006. Icarus 183, 435-450] investigated the dynamics of an ice shell overlying a pure liquid-water ocean and showed that transitions from a conductive state to a convective state have major implications for the surface tectonics. We extend this analysis to the case of ice shells overlying ammonia-water oceans. We explore the thermal state of Titan and Enceladus ice-I shells, and also we investigate the consequences of the ice-I shell conductive-convective switch for the geology. We show that thermal convection can occur, under a range of conditions, in the ice-I shells of Titan and Enceladus. Because the Rayleigh number Ra scales with δ³/ηb, where δ is the thickness of the ice shell and ηb is the viscosity at the base of the ice-I shell, and because ammonia in the liquid layer (if any) strongly depresses the melting temperature of the water ice, Ra equals its critical value for two ice-I shell thicknesses: for relatively thin ice shell with warm, low-viscosity base (Onset I) and for thick ice shell with cold, high-viscosity base (Onset II). At Onset I, for a range of heat fluxes, two equilibrium states—corresponding to a thin, conductive shell and a thick, convective shell—exist for a given heat flux. Switches between these states can cause large, rapid changes in the ice-shell thickness. For Enceladus, we demonstrate that an Onset I transition can produce tectonic stress of ∼500 bars and fractures of several tens of km depth. At Onset II, in contrast, we demonstrate that zero equilibrium states exist for a range of heat fluxes. For a mean heat flux within this range, the satellite experiences oscillations in surface heat flux and satellite volume with periods of ∼50-800 Myr even when the interior heat production is constant or monotonically declining in time; these oscillations in the thermal state of the ice-I shell would cause repeated episodes of extensional and compressional tectonism.     

A decline in molluscan carbonate production driven by the loss of vegetated habitats encoded in the Holocene sedimentary record of the Gulf of Trieste

Carbonate sediments in non‐vegetated habitats on the north‐east Adriatic shelf are dominated by shells of molluscs. However, the rate of carbonate molluscan production prior to the 20th century eutrophication and overfishing on this and other shelves remains unknown because: (i) monitoring of ecosystems prior to the 20th century was scarce; and (ii) ecosystem history inferred from cores is masked by condensation and mixing. Here, based on geochronological dating of four bivalve species, carbonate production during the Holocene is assessed in the Gulf of Trieste, where algal and seagrass habitats underwent a major decline during the 20th century. Assemblages of sand‐dwelling Gouldia minima and opportunistic Corbula gibba are time‐averaged to >1000 years and Corbula gibba shells are older by >2000 years than shells of co‐occurring Gouldia minima. This age difference is driven by temporally disjunct production of two species coupled with decimetre‐scale mixing. Stratigraphic unmixing shows that Corbula gibba declined in abundance during the highstand phase and increased again during the 20th century. In contrast, one of the major contributors to carbonate sands – Gouldia minima – increased in abundance during the highstand phase, but declined to almost zero abundance over the past two centuries. Gouldia minima and herbivorous gastropods associated with macroalgae or seagrasses are abundant in the top‐core increments but are rarely alive. Although Gouldia minima is not limited to vegetated habitats, it is abundant in such habitats elsewhere in the Mediterranean Sea. This live–dead mismatch reflects the difference between highstand baseline communities (with soft‐bottom vegetated zones and hard‐bottom Arca beds) and present‐day oligophotic communities with organic‐loving species. Therefore, the decline in light penetration and the loss of vegetated habitats with high molluscan production traces back to the 19th century. More than 50% of the shells on the sea floor in the Gulf of Trieste reflect inactive production that was sourced by heterozoan carbonate factory in algal or seagrass habitats.     

Long-term hydrology and aquatic biogeochemistry data from H. J. Andrews Experimental Forest,Cascade Mountains,Oregon

The H. J. Andrews Experimental Forest (HJA) encompasses the 6400 ha Lookout Creek watershed in western Oregon, USA. Hydrologic, chemistry and precipitation data have been collected, curated, and archived for up to 70 years. The HJA was established in 1948 to study the effects of harvest of old-growth conifer forest and logging-road construction on water quality, quantity and vegetation succession. Over time, research questions have expanded to include terrestrial and aquatic species, communities and ecosystem dynamics. There are nine small experimental watersheds and 10 gaging stations in the HJA, including both reference and experimentally treated watersheds. Gaged watershed areas range from 8.5 to 6242 ha. All gaging stations record stage height, water conductivity, water temperature and above-stream air temperature. At nine of the gage sites, flow-proportional water samples are collected and composited over 3-week intervals for chemical analysis. Analysis of stream and precipitation chemistry began in 1968. Analytes include dissolved and particulate species of nitrogen and phosphorus, dissolved organic carbon, pH, specific conductance, suspended sediment, alkalinity, and major cations and anions. Supporting climate measurements began in the 1950s in association with the first small watershed experiments. Over time, and following the initiation of the Long Term Ecological Research (LTER) grant in 1980, infrastructure expanded to include a set of benchmark and secondary meteorological stations located in clearings spanning the elevation range within the Lookout Creek watershed, as well as a large number of forest understory temperature stations. Extensive metadata on sensor configurations, changes in methods over time, sensor accuracy and precision, and data quality control flags are associated with the HJA data.     

Meltwater discharge during the Holocene from the Wilkes subglacial basin revealed by beryllium isotope analysis of marine sediments

Understanding Antarctic Ice Sheet dynamics related to global climate change is of scientific and societal interest as the future behaviour of the ice sheet under the currently changing climate is unknown. We present beryllium‐10 (¹⁰Be) analysis of a high‐resolution marine sediment core from the Adélie Basin near the eastern Wilkes Land margin, which is susceptible to marine ice sheet instability due to the low‐lying nature and down‐sloping trough of the Wilkes Subglacial Basin. Combined with a newly constructed age model using compound specific radiocarbon dates, the data reveal three events associated with high meteoric ¹⁰Be at ca. ~10 ka, ca. ~6.5 ka and from ca. ~4 ka. We interpret these high meteoric ¹⁰Be events to be derived from the deposition of ¹⁰Be released from the ice sheet during meltwater discharge. In particular, the shift to higher meteoric ¹⁰Be concentration at~4 ka may correspond to changes in climate patterns at this time. Copyright © 2019 John Wiley & Sons, Ltd.     

Cognitive and Affective Predictors of Illinois Residents’ Perceived Risks from Gray Wolves

Abstract

Increasing wolf populations are a concern for wildlife managers in the Midwestern U.S. Understanding the psychological mechanisms that contribute to public perceptions of risk will enable development of strategies that seek to mitigate these risks, and suggest where outreach efforts may facilitate acceptance of wolves. We examined the psychological factors that influence Illinois residents’ perceived risks from wolves. We hypothesized that individuals’ perceived risks from wolves were a function of their attitudes toward wolves, negative affect toward wolves, and basic beliefs about wildlife. Data were obtained from a survey of the Illinois public (n?=?784). Negative affect and attitudes toward wolves were direct predictors of perceived risks. Basic beliefs predicted attitudes and negative affect toward wolves. Negative affect predicted attitudes. Basic beliefs had direct and indirect effects on perceived risks.