Institute of Earth Environment
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Carbonate weathering dominates magnesium isotopes in large rivers: Clues from the Yangtze River
No full textCarbonate weathering regulates the short-term carbon (C) cycle and global climate due to its fast response to hydrological processes. The carbonate weathering flux needs to be well constrained to better understand the climate change at short time scale. Riverine magnesium (Mg) isotopes are sensitive to primary mineral dissolution and so have great potential to trace carbonate weathering. Global large rivers draining continental crust dominate weathering flux to the oceans, but how riverine Mg isotopes respond to carbonate weathering remains unclear. The Yangtze River drainage basin (YRDB) was selected to test the robustness of riverine Mg isotopes (delta Mg-26) in tracing continental carbonate weathering because it spans a wide range in lithology, geomorphology and climate. The riverine delta Mg-26 values within the YRDB show a decreasing trend from the headwater to the mainstream ranging from -1.36 parts per thousand to -0.59 parts per thousand The dissolved delta Mg-26 have strong negative correlations with carbonate weathering rate and intensity within the YRDB, indicating a sensitive response of riverine delta Mg-26 to the carbonate weathering flux. In a compilation of Mg fluxes and delta Mg-26 in the world's largest rivers, there is similar dominance of carbonate weathering on riverine Mg fluxes and isotopes. Therefore, we propose that riverine delta Mg-26 in large rivers are a robust tracer of carbonate weathering intensity. Intensifying carbonate weathering under global warming tends to increase riverine Mg and C fluxes to the oceans and thus the atmospheric CO2 sink at the millennial time scale
Ice sheet and terrestrial input impacts on the 100-kyr ocean carbon cycle during the Middle Miocene
No full textThe Middle Miocene (similar to 16-11.6 Ma) had atmospheric CO2 levels comparable to the present day, and thus the mechanisms controlling the interactions of the climate system and the carbon cycle during the Middle Miocene may have significant implications for future climate change. In this study, we examined the phase relationship between benthic foraminiferal delta O-18 and delta C-13 records, within the 100-kyr band, during the Late Quaternary and the Middle Miocene. Our results suggest that benthic foraminiferal delta O-18 and delta C-13 were highly coherent and inphase within the 100-kyr band during the Middle Miocene, in contrast to the anti-phased relationship during the Late Quaternary. However, the causes of this contrast remain elusive. We used a biogeochemical box model to explore the mechanisms of the in-phase relationship in the 100-kyr band during the Middle Miocene. The model results show that the in-phase relationship can be attributed to two mechanisms: (1) a shelf-basin carbonate shift regulated by sea-level fluctuations which originated from the growth and decay of the Antarctic ice sheet, within the 100-kyr band; and (2) changes in terrestrial carbon inputs and the biological pump driven by the discharge of riverine nutrients, which was regulated by precipitation variability in low latitudes, within the eccentricity-modulated precessional band. Thus, we propose that both high- and low-latitude processes played critical roles in the Middle Miocene carbon cycle, within the 100-kyr band. We further show that chemical weathering played a potential role in regulating the atmospheric pCO(2) on the orbital time scale during the Middle Miocene
Ice sheet and terrestrial input impacts on the 100-kyr ocean carbon cycle during the Middle Miocene
No full textThe Middle Miocene (similar to 16-11.6 Ma) had atmospheric CO2 levels comparable to the present day, and thus the mechanisms controlling the interactions of the climate system and the carbon cycle during the Middle Miocene may have significant implications for future climate change. In this study, we examined the phase relationship between benthic foraminiferal delta O-18 and delta C-13 records, within the 100-kyr band, during the Late Quaternary and the Middle Miocene. Our results suggest that benthic foraminiferal delta O-18 and delta C-13 were highly coherent and inphase within the 100-kyr band during the Middle Miocene, in contrast to the anti-phased relationship during the Late Quaternary. However, the causes of this contrast remain elusive. We used a biogeochemical box model to explore the mechanisms of the in-phase relationship in the 100-kyr band during the Middle Miocene. The model results show that the in-phase relationship can be attributed to two mechanisms: (1) a shelf-basin carbonate shift regulated by sea-level fluctuations which originated from the growth and decay of the Antarctic ice sheet, within the 100-kyr band; and (2) changes in terrestrial carbon inputs and the biological pump driven by the discharge of riverine nutrients, which was regulated by precipitation variability in low latitudes, within the eccentricity-modulated precessional band. Thus, we propose that both high- and low-latitude processes played critical roles in the Middle Miocene carbon cycle, within the 100-kyr band. We further show that chemical weathering played a potential role in regulating the atmospheric pCO(2) on the orbital time scale during the Middle Miocene
Sediment Soot Radiocarbon Indicates that Recent Pollution Controls Slowed Fossil Fuel Emissions in Southeastern China
No full textFossil fuel (FF) combustion emissions account for a large, but uncertain, amount of the soot in the atmosphere, play an important role in climate change, and adversely affect human health. However, historical estimates of FF contributions to air pollution are limited by uncertainties in fuel usage and emission factors. Here, we constrained FF soot emissions from southeastern China over the past 110 years, based on a novel radiocarbon method applied to sedimentary soot. The reconstructed soot accumulations reflect the integrated effects of increased FF use caused by economic development and reductions in emissions due to pollution controls. A sharp increase in FF soot started in 1950 as southeastern China industrialized and developed economically, but decreased FF soot fluxes in recent years suggest that pollution controls reduced soot emissions. We compare FF soot history to changes in CO2 emissions, industrial and economic activities, and pollution controls and show that FF soot fluxes are more readily controlled than atmospheric CO2. Our independent FF soot record provides insights into the effects of economic development and controls on air pollution and the environmental impacts from the changes in soot emissions
Water Flow Characteristics Controlled by Slope Morphology under Different Rainfall Capacities and Its Implications for Slope Failure Patterns
No full textThe high sensitivity of loess slopes to water has been emphasized in many studies. However, it is still limited in terms of the understanding of slope morphological differentiation on the overall and local failure patterns in slopes, as well as on the acquisition method of hydrological dynamics. In this study, rainfall characteristics and slope surface morphological differences were introduced. Geoelectric and environmental factors were monitored. On this basis, apparent resistivity corrected by seasonal temperature and its relationship with soil water content was calibrated. The water migration characteristics and potential failure patterns of three slope morphologies were evaluated. The results are: (i) the improved resistivity method can better reflect the water flow movement within the slope, and it performs well after being corrected by temperature; (ii) the characteristics of surface runoff and water infiltration are directly affected by the cumulative rainfall value, and especially when the cumulative rainfall is >70 mm threshold, the surface runoff quickly infiltrates into the deep of the slope along the preferential paths; (iii) the interception ability of loess slope morphology to the surface runoff is concave slope > convex slope > linear slope; (iv) with the continuous rainfall, the convex surface of a slope is prone to be damaged by saturated mud flow. When the cumulative rainfall threshold is 70 mm, the preferential flow is easily excited on the concave surface of the slope, resulting in local collapse at the slope toe and mid-deep landslides
The Heavy Particulate Matter Pollution During the COVID-19 Lockdown Period in the Guanzhong Basin, China
No full textNationwide restrictions on human activities (lockdown) in China since 23 January 2020, to control the 2019 novel coronavirus disease pandemic (COVID-19), has provided an opportunity to evaluate the effect of emission mitigation on particulate matter (PM) pollution. The WRF-Chem simulations of persistent heavy PM pollution episodes from 20 January to 14 February 2020, in the Guanzhong Basin (GZB), northwest China, reveal that large-scale emission reduction of primary pollutants has not substantially improved the air quality during the COVID-19 lockdown period. Simultaneous reduction of primary precursors during the lockdown period only decreases the near-surface PM2.5 mass concentration by 11.6% (12.6 mu g m(-3)), but increases ozone (O-3) concentration by 9.2% (5.5 mu g m(-3)) in the GZB. The primary organic aerosol and nitrate are the major contributor to the decreased PM2.5 in the GZB, with the reduction of 28.0% and 21.8%, respectively, followed by EC (10.1%) and ammonium (7.2%). The increased atmospheric oxidizing capacity by the O-3 enhancement facilitates the secondary aerosol (SA) formation in the GZB, increasing secondary organic aerosol and sulphate by 6.5% and 3.3%, respectively. Furthermore, sensitivity experiments suggest that combined emission reduction of NOX and VOCs following the ratio of 1:1 is conducive to lowering the wintertime SA and O-3 concentration and further alleviating the PM pollution in the GZB
Potential paleoceanographic application of cold-water bamboo coral in the South China Sea
No full textDiurnal Variations of Isoprene, Monoterpenes, and Toluene Oxidation Products in Aerosols at a Rural Site of Guanzhong Plain, Northwest China
No full textIn this study, the characteristics and formation mechanism of summertime isoprene, monoterpene, and toluene-derived secondary organic aerosols (SOAs) were investigated in a rural area of Guanzhong Plain, Northwest China. The variations in key indicators of primary sources indicated a significant influence of biomass burning on PM2.5 during the observation period. The concentrations of total measured SOA tracers from isoprene, monoterpene, and toluene were 40.85 +/- 17.31, 24.27 +/- 7.50, and 10.61 +/- 0.33 ng/m(3), respectively. The average ratio of cis-pinonic and pinic acids to 3-Methyl-1,2,3-butanetricarboxylic acid (MBTCA)(P/M) were 0.45 and 0.85 by day and by night, respectively. The low ratio in the daytime was mainly due to the stronger photo-degradation and particle-to-gas distribution of semi-volatile cis-pinonic and pinic acids. The monoterpene SOA tracers were significantly correlated with levoglucosan at night (R-2 = 0.51, p 0.67, p < 0.01), indicating the significant contribution of biomass combustion to these SOAs. The mass concentration of isoprene-, monoterpenes-, and toluene-derived SOC was estimated by using the tracer yield method. The total calculated SOCs by day and by night were 0.25-0.71 (average: 0.46) and 0.26-0.78 (average: 0.42) mu gC/m(3), accounting for 3.35-10.58% and 3.87-13.51% of OC by day and by night, respectively
Highly Selective Photocatalytic CO2 Methanation with Water Vapor on Single-Atom Platinum-Decorated Defective Carbon Nitride
No full textSolar-driven CO2 methanation with water is an important route to simultaneously address carbon neutrality and produce fuels. It is challenging to achieve high selectivity in CO2 methanation due to competing reactions. Nonetheless, aspects of the catalyst design can be controlled with meaningful effects on the catalytic outcomes. We report highly selective CO2 methanation with water vapor using a photocatalyst that integrates polymeric carbon nitride (CN) with single Pt atoms. As revealed by experimental characterization and theoretical simulations, the widely explored Pt-CN catalyst is adapted for selective CO2 methanation with our rationally designed synthetic method. The synthesis creates defects in CN along with formation of hydroxyl groups proximal to the coordinated Pt atoms. The photocatalyst exhibits high activity and carbon selectivity (99 %) for CH4 production in photocatalytic CO2 reduction with pure water. This work provides atomic scale insight into the design of photocatalysts for selective CO2 methanation
Oxygen vacancy engineering of photocatalytic nanomaterials for enrichment, activation, and efficient removal of nitrogen oxides with high selectivity: a review
No full textAir pollution by trace levels of nitric oxide (NO) pollution is threatening human health by causing acid rain and haze pollution through photochemical reactions. Here, we review photocatalytic technologies that use oxygen vacancy engineering-mediated nanomaterials for the control of air pollutants such as NO and nitrogen dioxide. We present oxygen vacancy parameters and reactor regulation mechanisms. We explain the functions of oxygen vacancies in the adsorption and enrichment processes of NO on the photocatalyst surface. We highlight the relationship between oxygen vacancies and O-2 activation in photocatalytic reactions. The mechanisms ruling selectivity in NO photodegradation, and the suppression of photocatalyst deactivation are discussed.
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