Organic geochemistry of marine source rocks and pyrobitumen-containing reservoir rocks of the Sichuan Basin and neighbouring areas,SW China

Three bitumen fractions were obtained and systematically analysed for the terpane and sterane composition from 30 Paleozoic source rocks and 64 bitumen-containing reservoir rocks within the Upper Sinian, Lower Cambrian, Lower Silurian, Middle Carboniferous, Upper Permian and Lower Triassic strata in the Sichuan Basin and neighbouring areas, China. These bitumen fractions include extractable oils (bitumen I), oil-bearing fluid inclusions and/or closely associated components with the kerogen or pyrobitumen/mineral matrix, released during kerogen or pyrobitumen isolation and demineralization (bitumen II), and bound compounds within the kerogen or pyrobitumen released by confined pyrolysis (bitumen III). In addition, atomic H/C and O/C ratios and carbon isotopic compositions of kerogen and pyrobitumen from some of the samples were measured. Geochemical results and geological information suggest that: (1) in the Central Sichuan Basin, hydrocarbon gases in reservoirs within the fourth section of the Upper Sinian Dengying Formation were derived from both the Lower Cambrian and Upper Sinian source rocks; and (2) in the Eastern Sichuan Basin, hydrocarbon gases in Middle Carboniferous Huanglong Formation reservoirs were mainly derived from Lower Silurian source rocks, while those in Upper Permian and Lower Triassic reservoirs were mainly derived from both Upper Permian and Lower Silurian marine source rocks. For both the source and reservoir rocks, bitumen III fractions generally show relatively lower maturity near the peak oil generation stage, while the other two bitumen fractions show very high maturities based on terpane and sterane distributions. Tricyclic terpanes evolved from the distribution pattern C₂₀ < C₂₁ < C₂₃, through C₂₀ < C₂₁ > C₂₃, finally to C₂₀ > C₂₁ > C₂₃ during severe thermal stress. The concentration of C₃₀ diahopane in bitumen III (the bound components released from confined pyrolysis) is substantially lower than in the other two bitumen fractions for four terrigenous Upper Permian source rocks, demonstrating that this compound originated from free hopanoid precursors, rather than hopanoids bound to the kerogen.     

The potential of the greenness and radiation (GR) model to interpret 8-day gross primary production of vegetation

Remote sensing of vegetation gross primary production (GPP) is an important step to analyze terrestrial carbon (C) cycles in response to changing climate. The availability of global networks of C flux measurements provides a valuable opportunity to develop remote sensing based GPP algorithms and test their performances across diverse regions and plant functional types (PFTs). Using 70 global C flux measurements including 24 non-forest (NF), 17 deciduous forest (DF) and 29 evergreen forest (EF), we present the evaluation of an upscaled remote sensing based greenness and radiation (GR) model for GPP estimation. This model is developed using enhanced vegetation index (EVI) and land surface temperature (LST) from the Moderate Resolution Imaging Spectroradiometer (MODIS) and global course resolution radiation data from the National Center for Environmental Prediction (NCEP). Model calibration was achieved using statistical parameters of both EVI and LST fitted for different PFTs. Our results indicate that compared to the standard MODIS GPP product, the calibrated GR model improved the GPP accuracy by reducing the root mean square errors (RMSE) by 16%, 30% and 11% for the NF, DF and EF sites, respectively. The standard MODIS and GR model intercomparisons at individual sites for GPP estimation also showed that GR model performs better in terms of model accuracy and stability. This evaluation demonstrates the potential use of the GR model in capturing short-term GPP variations in areas lacking ground measurements for most of vegetated ecosystems globally.     

Assessing the likelihood of widespread landholder adoption of afforestation and reforestation projects

Tree planting for carbon sequestration is a commonly proposed climate change mitigation strategy, with afforestation projects forming part of voluntary and mandatory carbon offset trading schemes. Afforestation is often promoted as a new economic opportunity for private landholders. While multiple studies have identified physical and economic opportunities for afforestation, few have examined the willingness of private landholders to adopt afforestation, and the factors that influence this willingness. We examine this using data from a survey of Australian landholders. The willingness of landholders to adopt afforestation for carbon sequestration varies substantially depending on how this afforestation is designed and implemented: landholders prefer small plantings on less productive land, which minimise the disturbance afforestation presents to land management, and to landholder values about appropriate uses of agricultural land. Landholders are less willing to consider afforestation if it involves planting the large areas required by many current carbon afforestation schemes. Willingness to adopt afforestation is influenced in particular by landholder's perceptions of its potential to provide a diversified income stream, and its impacts on flexibility of land management. More broadly, it is influenced by their views about the social acceptability of afforestation, particularly whether the landholder believes trees should be planted on agricultural land, and how they believe others in the community view afforestation. Our results suggest that widespread adoption requires designing afforestation so it (i) provides a range of socio-economic benefits that go beyond provision of income; (ii) minimises disruption to land management flexibility; and (iii) is compatible with landholder beliefs about appropriate use of agricultural land.     

Policy invention and entrepreneurship: Bankrolling the burying of carbon in the EU

This article presents the case of a policy invention where various kinds of entrepreneurship and a window of opportunity played important roles. In 2008 the EU adopted a new Carbon Capture and Storage (CCS) policy with an inventive funding instrument at its core: the NER 300 fund, based on revenues from the auctioning of emissions trading allowances. Thus far, the literature on policy entrepreneurs has focused more on success factors that enable particular persons to be especially influential than on the defining characteristics of entrepreneurship. We contribute to the literature on entrepreneurship and windows of opportunity by distinguishing two entrepreneurial techniques – framing and procedural engineering – and two categories of commitment – ‘tortoise’ and carpe diem. We conclude that ‘tortoises’ who contributed to creating the broad and general climate policy window paved the way for issue-specific carpe diemers who promoted the more specific NER 300 policy invention. Furthermore, we distinguish and discuss four different entrepreneurship mechanisms that may influence policy invention processes.     

Mapping and modelling trade-offs and synergies between grazing intensity and ecosystem services in rangelands using global-scale datasets and models

Vast areas of rangelands across the world are grazed with increasing intensity, but interactions between livestock production, biodiversity and other ecosystem services are poorly studied. This study explicitly determines trade-offs and synergies between ecosystem services and livestock grazing intensity on rangelands. Grazing intensity and its effects on forage utilization by livestock, carbon sequestration, erosion prevention and biodiversity are quantified and mapped, using global datasets and models. Results show that on average 4% of the biomass produced annually is consumed by livestock. On average, erosion prevention is 10% lower in areas with a high grazing intensity compared to areas with a low grazing intensity, whereas carbon emissions are more than four times higher under high grazing intensity compared to low grazing intensity. Rangelands with the highest grazing intensity are located in the Sahel, Pakistan, West India, Middle East, North Africa and parts of Brazil. These high grazing intensities result in carbon emissions, low biodiversity values, low capacity for erosion prevention and unsustainable forage utilization. Although the applied models simplify the processes of ecosystem service supply, our study provides a global overview of the consequences of grazing for biodiversity and ecosystem services. The expected increasing future demand for livestock products likely increase pressures on rangelands. Global-scale models can help to identify targets and target areas for international policies aiming at sustainable future use of these rangelands.     

Molecular and stable carbon isotopic compositions of saturated fatty acids within one sedimentary profile in the Shenhu,northern South China Sea: Source implications

This study examined the distributions and stable carbon isotopic compositions of saturated fatty acids (SaFAs) in one 300 cm long sedimentary profile, which was named as Site4B in Shenhu, northern South China Sea. The concentrations of total SaFAs in sediments ranged from 1.80 to 10.16 μg/g (μg FA/g dry sediment) and showed an even-over-odd predominance in the carbon chain of C₁₂ to C₃₂, mostly with n-C₁₆ and n-C₁₈ being the two major components. The short-chain fatty acids (ScFAs; n-C₁₂ to n-C₁₈) mainly from marine microorganisms had average δ¹³C values of −26.7‰ to −28.2‰, whereas some terrigenous-sourced long-chain fatty acids (LcFAs; n-C₂₁ to n-C₃₂) had average δ¹³C values of −29.6‰ to −34.1‰. The other LcFAs (n-C₂₄ & n-C₂₆ ∼ n-C₂₈; average δ¹³C values are −26.1‰ to −28.0‰) as well as n-C₁₉ and n-C₂₀ SaFAs (average δ¹³C values are −29.1‰ and −29.3‰, respectively) showed a mixed signal of carbon isotope compositions.The relative bioproductivity calculation (marine vs. terrigenous) demonstrated that most of organic carbon accumulation throughout the sedimentary profile was contributed by marine organism. The high marine productivity in Shenhu, South China Sea may be related to the hydrocarbon seepage which evidenced by diapiric structures. Interestingly, there is a sever fluctuation of terrigenous inputs around the depth of 97 cm below the seafloor (bsf), probably resulting from the influence of the Dansgaard–Oeschger events and the Younger Dryas event as revealed by ¹⁴C age measurements.     

Organic geochemistry of the Vindhyan sediments: Implications for hydrocarbons

The organic geochemical methods of hydrocarbon prospecting involve the characterization of sedimentary organic matter in terms of its abundance, source and thermal maturity, which are essential prerequisites for a hydrocarbon source rock. In the present study, evaluation of organic matter in the outcrop shale samples from the Semri and Kaimur Groups of Vindhyan basin was carried out using Rock Eval pyrolysis. Also, the adsorbed low molecular weight hydrocarbons, methane, ethane, propane and butane, were investigated in the near surface soils to infer the generation of hydrocarbons in the Vindhyan basin. The Total Organic Carbon (TOC) content in shales ranges between 0.04% and 1.43%. The S₁ (thermally liberated free hydrocarbons) values range between 0.01–0.09 mgHC/gRock (milligram hydrocarbon per gram of rock sample), whereas the S₂ (hydrocarbons from cracking of kerogen) show the values between 0.01 and 0.14 mgHC/gRock. Based on the T_max (temperature at highest yield of S₂) and the hydrogen index (HI) correlations, the organic matter is characterized by Type III kerogen. The adsorbed soil gas, CH₄ (C₁), C₂H₆ (C₂), C₃H₈ (C₃) and nC₄H₁₀, (nC4), concentrations measured in the soil samples from the eastern part of Vindhyan basin (Son Valley) vary from 0 to 186 ppb, 0 to 4 ppb, 0 to 5 ppb, and 0 to 1 ppb, respectively. The stable carbon isotope values for the desorbed methane (δ¹³C₁) and ethane (δ¹³C₂) range between −45.7‰ to −25.2‰ and −35.3‰ to −20.19‰ (VPDB), respectively suggesting a thermogenic source for these hydrocarbons. High concentrations of thermogenic hydrocarbons are characteristic of areas around Sagar, Narsinghpur, Katni and Satna in the Son Valley. The light hydrocarbon concentrations (C₁–C₄) in near surface soils of the western Vindhyan basin around Chambal Valley have been reported to vary between 1–2547 ppb, 1–558 ppb, 1–181 ppb, 1–37 ppb and 1–32 ppb, respectively with high concentrations around Baran-Jhalawar-Bhanpur-Garot regions (Kumar et al., 2006). The light gaseous hydrocarbon anomalies are coincident with the wrench faults (Kota – Dholpur, Ratlam – Shivpuri, Kannod – Damoh, Son Banspur – Rewa wrench) in the Vindhyan basin, which may provide conducive pathways for the migration of the hydrocarbons towards the near surface soils.     

Age and impacts of the caldera-forming Aniakchak II eruption in western Alaska

The mid-Holocene eruption of Aniakchak volcano (Aniakchak II) in southwest Alaska was among the largest eruptions globally in the last 10,000 years (VEI-6). Despite evidence for possible impacts on global climate, the precise age of the eruption is not well-constrained and little is known about regional environmental impacts. A closely spaced sequence of radiocarbon dates at a peatland site over 1000 km from the volcano show that peat accumulation was greatly reduced with a hiatus of approximately 90–120 yr following tephra deposition. During this inferred hiatus no paleoenvironmental data are available but once vegetation returned the flora changed from a Cyperaceae-dominated assemblage to a Poaceae-dominated vegetation cover, suggesting a drier and/or more nutrient-rich ecosystem. Oribatid mites are extremely abundant in the peat at the depth of the ash, and show a longer-term, increasingly wet peat surface across the tephra layer. The radiocarbon sample immediately below the tephra gave a date of 1636–1446 cal yr BC suggesting that the eruption might be younger than previously thought. Our findings suggest that the eruption may have led to a widespread reduction in peatland carbon sequestration and that the impacts on ecosystem functioning were profound and long-lasting.     

Note on the isotopic geochemistry of fossil-lacustrine tufas in carbonate plateau—A study from Dungul region (SW Egypt)

Lithological, chemical, and stable isotope data are used to characterize lacustrine tufas dating back to pre-late Miocene and later unknown times, capping different surfaces of a Tertiary carbonate (Sinn el-Kedab) plateau in Dungul region in the currently hyperarid south-western Egypt. These deposits are composed mostly of calcium carbonate, some magnesium carbonate and clastic particles plus minor amounts of organic matter. They have a wide range of (Mg/Ca)_molar ratios, from 0.03 to 0.3. The bulk-tufa carbonate has characteristic isotope compositions: (δ¹³C_mean = −2.49 ± 0.99‰; δ¹⁸O_mean = −9.43 ± 1.40‰). The δ¹³C values are consistent with a small input from C4 vegetation or thinner soils in the recharge area of the tufa-depositing systems. The δ¹⁸O values are typical of fresh water carbonates. Covariation between δ¹³C and δ¹⁸O values probably is a reflection of climatic conditions such as aridity. The tufas studied are isotopically similar to the underlying diagenetic marine chalks, marls and limestones (δ¹³C_mean = −2.06 ± 0.84‰; δ¹⁸O_mean = −10.06 ± 1.39‰). The similarity has been attributed to common meteoric water signatures. This raises large uncertainties in using tufas (Mg/Ca)_molar, δ¹³C and δ¹⁸O records as proxies of paleoclimatic change and suggests that intrinsic compositional differences in material sources within the plateau may mask climatic changes in the records.     

Research Progress in Responses of Modern Terrestrial Plant Carbon Isotope Composition to Climate Change

Global climate change has been one of the most concerned environmental problems in the world since the 1980s. Since stable carbon composition (¹³C) in plant tissues can record abundant information on climate changes, it has been widely used as an important climate proxy in global change studies and becomes a powerful tool for obtaining paleoclimate information, understanding paleoenvironment reconstruction and modern climate change, and predicting future climate trends. However, a lot of potential uncertainties have always involved in the reconstruction of paleoclimate and paleoenvironment by carbon isotope of the past period sediment or fossils. Among them, the most dominant uncertainty is due to our poor understanding of the relations between carbon isotope ratios of plants and climatic factors and the climatic and environmental significance indicated by modern plant ¹³C. This may limit the application of plant ¹³C in the study of climatic and environmental changes. Based on the Summary of plant ¹³C fractionation and carbon isotope distribution of different photosynthetic plants, the effects of environmental factors, e.g., temperature, precipitation, atmospheric CO₂ concentration, and altitude on terrestrial plant ¹³C and their relationships were reviewed in this paper, and the response mechanism of plant ¹³C to climate changes were also analyzed. Furthermore, the current existing problems and the future prospects in carbon isotope study were discussed. It is pointed out that strengthening some studies such as the response of C₄ plants ¹³C to climate environmental parameters, the transformation relation of different scale plant ¹³C, intersection and permeation of related disciplines, and various proxies and scientific method, will undoubtedly make us have a more accurate understanding of the climate history and eventually broaden the development of the field during the process of global change study by plant carbon isotope techniques.