Is orogenesis a net sink or source of atmospheric CO2?

In global carbon cycle models, orogenesis is often viewed as a sink for atmospheric CO₂, acting on tectonic timescales. However, recent attempts to quantify fluxes for CO₂ produced by metamorphic reactions and released to the atmosphere suggest that these are an order‐of‐magnitude greater than CO₂ uptake by chemical weathering of silicate minerals, and that metamorphic CO₂ is released on millennial timescales. These hypotheses have gained support from both measurements of CO₂ emissions from present‐day orogenic hot springs and chromatographic modelling of carbonation reactions in metamorphic rocks from ancient orogens. In this article I review research that attempts to quantify metamorphic CO₂ release fluxes, focussing specifically on studies conducted in the SW Scottish Highlands.     

Geochemistry of large river suspended sediments: silicate weathering or recycling tracer?

This study focuses on the major and trace element composition of suspended sediments transported by the world’s largest rivers. Its main purpose is to answer the following question: is the degree of weathering of modern river-borne particles consistent with the estimated river dissolved loads derived from silicate weathering?In agreement with the well known mobility of elements during weathering of continental rocks, we confirm that river sediments are systematically depleted in Na, K, Ba with respect to the Upper Continental Crust. For each of these mobile elements, a systematics of weathering indexes of river-borne solids is attempted. A global consistency is found between all these indexes. Important variations in weathering intensities exist. A clear dependence of weathering intensities with climate is observed for the rivers draining mostly lowlands. However, no global correlation exists between weathering intensities and climatic or relief parameters because the trend observed for lowlands is obscured by rivers draining orogenic zones. An inverse correlation between weathering intensities and suspended sediment concentrations is observed showing that the regions having the highest rates of physical denudation produce the least weathered sediments. Finally, chemical and physical weathering are compared through the use of a simple steady state model. We show that the weathering intensities of large river suspended sediments can only be reconciled with the (silicate-derived) dissolved load of rivers, by admitting that most of the continental rocks submitted to weathering in large river basins have already suffered previous weathering cycles. A simple graphical method is proposed for calculating the proportion of sedimentary recycling in large river basins. Finally, even if orogenic zones produce weakly weathered sediments, we emphasize the fact that silicate chemical weathering rates (and hence CO₂ consumption rates by silicate weathering) are greatly enhanced in mountains simply because the sediment yields in orogenic drainage basins are higher. Hence, the parameters that control chemical weathering rates would be those that control physical denudation rates.     

Sulfuric acid as a weathering agent of carbonate weathering constrained by δ~(13)C: Examples from Southwest China

Rock weathering by carbonic acid is one of the important atmosphere CO2 sequestration. Actually, it depends on whether carbonic acid or other acids as weathering agents, which is important to understand the model of global carbon cycle. For example, sulfu…     

Impact of household expenditures on CO2 emissions in China: Income-determined or lifestyle-driven?

The aim of this paper is to analyze the relationship between household expenditure and CO₂ emissions among different income groups of urban and rural households in China. Having employed the 2007 Social Accounting Matrix of China, this study examines the direct and indirect CO₂ emissions caused by household demand. The results show that within both urban and rural households, the higher the income level is, the higher the per capita emissions are; the CO₂ emissions per unit expenditure due to savings and taxes are generally much larger than those from consumption of goods and services; and these emissions per unit consumption expenditures mainly come from indirect emissions. To deeply explore the relationships between consumption patterns and CO₂ emissions, two scenarios are established to eliminate the differences in income level and consumption propensity among different groups step by step. Main results indicate that (1) the income gap is the primary cause of the significant differences in emission levels among each group; (2) the difference in consumption propensity is also a notable reason; and (3) the rural higher income groups spend a larger share of their income on those carbon-intensive goods (e.g., electricity, transportation, energy products), thus making their consumption patterns more carbon-intensive, while for the urban, the consumption patterns of lower income groups are more carbon-intensive. Finally, policy recommendations on the reduction of household emissions are also made.

     

Heavy-metal enrichment in surficial sediments in the Oder River discharge area: source or sink for heavy metals?

The Oder river drains a highly polluted industrial area and enters the Baltic Sea through a system of shallow lagoons. Surficial sediments in the discharge area of the Oder are highly enriched in heavy metals compared to their preindustrial background levels. Pore-water studies in short sediment cores reveal anoxic environments over the entire sediment column, except for a suboxic layer in the uppermost 5 to 20 mm of the sediment where Mn- and Fe-oxyhydroxides are reduced by organic matter. Heavy metals (such as Cu, Zn and Pb) are mobilized within the suboxic zones in the inner lagoon (represented by the Oder Lagoon) and in the open Baltic (represented by the Arkona Basin). The Achterwasser, located between the Oder Lagoon and the Arkona Basin, is directly affected by sea-level fluctuations in the Baltic. Pore-water studies indicate that, in contrast to the situation in the Oder Lagoon and Arkona Basin, surficial sediments of the Achterwasser represent a sink for heavy metals. This is associated with the high rate of Fe-sulphide formation occurring there, at least seasonally during salt-water inflow.     

Settling and resuspended particles: A source or a sink of phosphate in two contrasting oligotrophic high mountain lakes?

This study focuses on two Mediterranean oligotrophic high mountain lakes located in the Sierra Nevada National Park (southern Spain): Río Seco (RS) and La Caldera (LC). A combination of field measurements and laboratory experiments is used: (i) to quantify in situ settling fluxes; (ii) to study the soluble reactive phosphorus (SRP) release or uptake by settling and resuspended particles; and (iii) to discriminate between the biotic and abiotic contribution for such patterns. In general, all suspensions (lake water untreated and lake water enriched with settling and with resuspended matter) in both study lakes release significantly more SRP to the solution when biological activity was suppressed. Biological uptake from settling and resuspended matter is likely to be limited by the bacterial consumption of P. Despite of these similarities, this study has revealed notable differences in the effect of sediment resuspension on SRP dynamics in both study lakes, when simulating natural conditions (biotic and abiotic processes). While in LC, the enrichment of lake water with settling and with resuspended matter did not cause an increase in SRP concentrations in lake water, SRP concentrations in RS at the end of the experiment were significantly higher (probability P < 0.05) in lake water enriched with resuspended matter (3.2 μg/l) than in natural lake water (lower than the detection limit). Accordingly, it is reasonable to expect that sediment resuspension, which occurs more frequently in RS compared with LC, affects drastically the SRP availability in the water column in RS.     

Changes in Atlantic Thermohaline Circulation under Different Atmospheric CO2 Scenarios in a Climate Model

INTRODUCTIONThermohaline circulation(THC)is normally de-fined as the density-driven global-scale oceanic circu-lation,which flows northwardin the upper layer andsouthward in the deeper layer in the Atlantic.Itplays ani mportant role in the global meridional heatand the freshwater transports(Marotzke,2000).Thus,changes in the THC alter the global oceanheat transport and affect the global cli mate(Broeck-er,1991).The increase in the concentration of greenhousegases will reduce the effici…     

The role of sulfur cycling in carbonate weathering: Isotope geochemistry of sulfur in the Wujiang River catchment, Southwest China

Water samples from the Wujiang River, a typical karst river system, were analyzed for major ion concentrations and δ34S values of dissolved sulfate in order to identify the sources of sulfate, quantify the sulfate export flux and understand the role of s…     

大气CO2汇:硅酸盐风化还是碳酸盐风化的贡献?

至今人们仍普遍认为:是硅酸盐的化学风化碳汇作用在控制着长时间尺度的气候变化,而碳酸盐的化学风化作用不具有这一功能,因为碳酸盐溶解过程中消耗的所有CO<,2>又通过海洋中相对快速的碳酸盐沉积而返回大气.本研究发现,碳酸盐溶解的快速动力学特性(比硅酸盐快100倍以上)以及硅酸盐流域中少量碳酸盐矿物在控制流域溶解无机碳(DI...     

Mantle hydrocarbons: abiotic or biotic?

Analyses of 227 rocks from fifty localities throughout the world showed that mantle derived rocks such as tectonized peridotites in ophiolite sequences (tectonites) arid peridotite xenoliths in alkali basalts contain heavier hydrocarbons (n-alkanes), whereas igneous rocks produced by magmas such as gabbro arid granite lack them. The occurrence of hydrocarbons indicates that they were not derived either from laboratory contamination or from held contamination; these compounds found in the mantle-derived rocks are called here "mantle hydrocarbons." The existence of hydrocarbons correlates with petrogenesis. For example, peridotite cumulates produced by magmatic differentiation lack hydrocarbons whereas peridotite xenoliths derived from the mantle contain them. Gas chromatographic-mass spectrometric records of the mantle hydrocarbons resemble those of aliphatics in meteorites and in petroleum. Features of the hydrocarbons are that (a) the mantle hydrocarbons reside mainly along grain boundaries and in fluid inclusions of minerals; (b) heavier isoprenoids such as pristane and phytane are present; and (c) delta 13C of the mantle hydrocarbons is uniform (about -27%). Possible origins for the mantle hydrocarbons are as follows. (1) They were in organically synthesized by Fischer-Tropsch type reaction in the mantle. (2) They were delivered by meteorites and comets to the early Earth. (3) They were recycled by subduction. The mantle hydrocarbons in the cases of (1) and (2) are abiogenic and those in (3) are mainly biogenic. It appears that hydrocarbons may survive high pressures and temperatures in the mantle, but they are decomposed into lighter hydrocarbon gases such as CH4 at lower pressures when magmas intrude into the crust; consequently, peridotite cumulates do not contain heavier hydrocarbons but possess hydrocarbon gases up to C4H10.     

Atmospheric input vs in situ weathering in the genesis of calcretes: an Sr isotope study at Gálvez (Central Spain)

Strontium isotopes have been analyzed in a typical calcrete profile developed on granite in the Toledo mountains, Central Spain. The pedogenic carbonates show clear petrographic evidence of pseudomorphic replacement of the weathered parent granite.Calcretes display ⁸⁷Sr/⁸⁶Sr ratios between 0.70961 and 0.71059 in sharp contrast to the granite whole rock (0.72856) and minerals (0.71359 to 0.91351). This difference shows that the contribution of Sr from the granite to the calcretes is at most 33% and may be as low as 3%. Direct measurements in rains and aerosols show that the allochtonous source of Ca and Sr is clearly related to the atmospheric input, mainly as dry deposit.A slight decrease of Sr concentration is observed from the upper horizon composed of continuous calcrete to the deeper calcrete veins in the saprolite. This may be due to a kinetic control of the Sr/Ca fractionation, and different crystallization rates of the carbonates in the different units of the profile.Finally, local groundwaters have Sr isotopic compositions similar to the calcretes and the atmospheric input, very different from waters running on the granite.     

黑钨矿有效沉淀机制:CO2逃逸

黑钨矿是石英脉钨矿床的主要矿石矿物,其沉淀机制一直存在争议。CO₂逃逸能否造成黑钨矿有效沉淀尚缺乏定量模型的评价。文章建立了W-Fe-Cl-Na-O-C-H体系的反应平衡模型,涉及22种组分和16个化学反应;相关热力学参数来自SUPCRT数据库。模型计算结果表明,pH与流体压力呈负相关关系,而钨溶解度与流体压力呈正相关关系;当成矿流体压力从静岩压力降至静水压力水平,钨溶解度降幅可达到27%~47%,降幅与温度和深度成正比。因而,降压造成的CO₂逃逸是黑钨矿沉淀的有效机制之一。      

Preliminary assessment of CO2 transport and storage costs of promising source–sink matching scenarios in Guangdong province,China

Guangdong is the most economically developed province in China, which is a large CO₂ emitter and hence is faced with severe carbon reduction pressures. In this paper, a cost assessment methodology based on scenario analysis is presented. A CO₂ source and sink database was built at Guangdong after detailed investigations on the point sources and sedimentary basins. Fifteen transport and five storage scenarios were defined and studied, respectively. Cost estimates based on these scenarios show that during its lifetime, the costs of both transport and storage depend on the amount of CO₂ processed. More CO₂ being processed will bring down the unit costs of both transport and storage. However, it was observed that there is a cost inflection point between the storage amount of 35.2 and 52.8 Mt/year, which means that as the storage amount increases, the storage cost will first decrease and then increase. Source region S1 in Guangdong has been recommended for an early chance of CO₂ storage. Preliminary cost comparisons have shown that the results presented in this study are reasonable, but to improve the cost assessment accuracy of offshore CO₂ storage, a methodology based on a CO₂ storage design that can integrate local prices needs to be further developed.     

Is soil natural organic matter a sink or source for mobile radioiodine (I) at the Savannah River Site?

¹²⁹I is one of the three major radiation risk contributors to the public as a consequence of past nuclear processing activities at Department of Energy (DOE) facilities. Elevated levels of ¹²⁹I are present in the surface soils of F-Area of Savannah River Site, which used to be an isotope separation facility for the production of nuclear weapons components. The ¹²⁹I in soils is thought to be bound predominantly to soil organic matter (SOM). Measurements of stable ¹²⁷I and radioactive ¹²⁹I in humic acids (HAs) and fulvic acids (FAs) obtained by five successive alkaline, two glycerol and one citric acid-alkaline extraction, demonstrated that these extractable humic substances (HS) together account for 54-56% and 46% of the total ¹²⁷I and ¹²⁹I in the soil, respectively. The remainder was likely bound to residual SOM. The iodine content (μg-I/g-C) generally decreased with each subsequent extract, while ¹²⁹I/¹²⁷I increased concurrently. The coincident variations in chemical compositions, aromaticity (estimated by UV spectroscopy), functional groups (e.g., aliphatic), degree of humification, relative migration in the hydrophobic interaction column, and molecular weight indicated that: (1) iodine in different HAs was bound to a small-size aromatic subunit (∼10 kDa); (2) the large-size subunit (∼90 kDa), which likely linked the small-size unit through some weak chemical forces (hydrogen bonds, hydrophobic or electrostatic interactions), determined the relative mobility of iodine bound to organic matter; (3) from the strong correlation between iodine content and aromaticity in the HAs, we suggested that iodine incorporation into the SOM via covalent aromatic C-I bond is the key mechanism controlling iodine behavior in this system. However, this relationship is not universal for all fractions of organic matter as evidenced from the different slopes of this relationship at the two sampling sites, as well as from the different relationships for HAs and FAs, respectively. These differences in iodination are due to different SOM molecular sizes, compositions, and availability of preferred iodination sites. ¹²⁹I in the soil downstream from the contaminated site and near a wetland abruptly dropped below our detection limit (0.5 pCi-¹²⁹I/g-soil), which suggests that the high SOM in the plume soil around the ¹²⁹I-contaminated F-Area might be a natural barrier to scavenge radioiodine released from the nuclear waste repository by forming organo-iodine compounds. Soil resuspension experiments showed that mobile ¹²⁹I was mostly associated with a low average molecular weight amphiphilic organic carrier (13.5-15 kDa). SOM clearly behaves as a sink for iodine at the Savannah River Site F-Area. However, this work demonstrates that a small fraction of the SOM can also behave as a source, namely that a small fraction that may be readily dispersible under some environmental conditions and presumably release iodine in the organic-colloidal form. This radioiodinated organo-colloid likely can get into the groundwater through infiltration or surface runoff where it might migrate further into the wetlands. Results from this study provide the geochemical basis for future ¹²⁹I migration controls, remediation, and/or land-groundwater management strategies.     

Experimental identification of CO2–oil–brine–rock interactions: Implications for CO2 sequestration after termination of a CO2-EOR project

Carbon dioxide enhanced oil recovery (CO₂-EOR) has been widely applied to the process of carbon capture, utilization, and storage (CCUS). Here, we investigate CO₂–oil–water–rock interactions under reservoir conditions (100 °C and 24 MPa) in order to understand the fluid–rock interactions following termination of a CO₂-EOR project. Our experimental results show that CO₂-rich fluid remained the active fluid controlling the dissolution–precipitation processes in an oil-undersaturated sandstone reservoir; e.g., the dissolution of feldspar and calcite, and the precipitation of kaolinite as well as solid phases comprising O, Si, Al, Na, C, and Ti. Mineral dissolution rates were reduced in the case that mineral surfaces were coated by oil. Mineral wettability and composition, and oil saturation were the main controls on the exposed surface area of grains, and mineral wettability in particular led to selective dissolution. In addition, the permeability of the reservoir decreased substantially due to the precipitation of kaolinite and solid-phase particles, and due to the clogging of less soluble mineral particles released by the dissolution of K-feldspar and carbonate cement, whereas porosity increased. The results provide insight into potential formation damage resulting from CO₂-EOR projects.