Institute of Earth Environment
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Interactions of organosulfates with water vapor under sub- and supersaturated conditions
No full textOrganosulfates (OSs) are important constituents of secondary organic aerosols, but their hygroscopic properties and cloud condensation nucleation (CCN) activities have not been well understood. In this work we employed three complementary techniques to characterize interactions of several OSs with water vapor under sub- and supersaturated conditions. A vapor sorption analyzer was used to measure mass changes in OS samples with relative humidity (RH, 0 %-90 %); among the 11 organosulfates examined, only sodium methyl sulfate (methyl-OS), sodium ethyl sulfate (ethyl-OS), sodium octyl sulfate (octyl-OS) and potassium hydroxyacetone sulfate were found to deliquesce as RH increased, and their mass growth factors at 90 % RH were determined to be 3.65 +/- 0.06, 3.58 +/- 0.02, 1.59 +/- 0.01 and 2.20 +/- 0.03. Hygroscopic growth of methyl-, ethyl- and octyl-OS aerosols was also studied using a humidity tandem differential mobility analyzer (H-TDMA); continuous hygroscopic growth was observed, and their growth factors at 90 % RH were determined to be 1.83 +/- 0.03, 1.79 +/- 0.02 and 1.21 +/- 0.02. We further investigated CCN activities of methyl-, ethyl- and octyl-OS aerosols, and their single hygroscopicity parameters (kappa(cnn)) were determined to be 0.459 +/- 0.021, 0.397 +/- 0.010 and 0.206 +/- 0.008. For methyl- and ethyl-OS aerosols, kappa(cnn) values agree reasonably well with those derived from H-TDMA measurements (kappa(gf)) with relative differences being < 25 %, whereas kappa(cnn) was found to be similar to 2.4 times larger than kappa(gf) for octyl-OS, likely due to both the solubility limit and surface tension reduction
The formation of iron oxides and magnetic enhancement mechanisms in northern Iranian loess-paleosol sequences: Evidence from diffuse reflectance spectrophotometry and temperature dependence of magnetic susceptibility
No full textThe magnetic properties of the loess-paleosol sequences from northern Iran provides a model for understanding pedogenic processes and their relationship to paleo-precipitation in this region. For the first time, we present diffuse reflectance spectrophotometry (DRS) analyses, color measurement analyses, and temperature-dependent susceptibility (chi-T) in argon from two late Pleistocene loess-paleosol sequences in northern Iran. Magnetic iron oxide minerals, principally magnetite, maghemite, hematite, and goethite were identified in the study sections. The results of DRS and color measurements show that a* values, the hematite to goethite ratio and the maghemite to hematite ratio, exhibit a significant positive correlation with the pedogenic process and paleosol formation and are superior to low-frequency susceptibility alone for estimating paleoprecipitation. Our data also indicates that pedogenic maghemite-magnetite formation and dissolution/reprecipitation are major contributors to the magnetic enhancement of loess-paleosol sequences and might indicate a seasonal aspect for pedogenic maghemite-magnetite formation. We propose the DRS-derived illite to chlorite ratio as a useful index for assessing the intensity of silicate mineral weathering in the northern Iranian loess-paleosol sequences. In addition, DRS can be used to discriminate between pedogenic and detrital hematite of loess-paleosol sequences. We also propose that the chi-T cooling and heating ratio model is a quantitative proxy for magnetic enhancement in soils and paleosols of loess-paleosol sequences
A 40,000 year record of vegetation, environment and climate change from Chongqing, Central China
No full textCongping is a wetland at about 2100 m asl in Chongqing Province. It is surrounded by a shrubby grassland which grades into a mixed conifer and deciduous woodland. A record based on pollen, microcharcoal and geochemistry has been used to reconstruct an environmental history covering the last approximately 40 kyr BP. The site was wooded throughout the entire record and there were two relatively warm periods; during Marine Isotope 3 (MIS 3) and for the Holocene from about 9 kyr BP. From 27 to 18 kyr BP a gradual cooling occurred and the coldest part of the record was between 22 and 18 kyr BP when a mixed conifer cool temperate deciduous forest occurred, The warmest part of the record lasted from about 9 to 1.5 kyr BP when mixed evergreen and deciduous forest occurred. The broad pattern of changes is in accord with pollen records from Dajiuhu in Hubei, and demonstrates that this was a regional signal. A moist central China at Last Glacial Maximum (LGM) shows that the East Asian Summer Monsoon was delivering enough moisture on the mainland to sustain forest cover, even at 2120 m asl. The large-scale changes are interpreted as relating to changes in Earth's orbital parameters and sea-level changes in the South China Sea which had an impact on moisture delivery into central China. It is surmised that the westerlies which created dry climates in northeastern China trapped the summer Monsoon influence enough to keep central China moist. The Younger Dryas (YD) is present in the weathering parameters as evident in several changes in elemental abundance delivered to the sediments. The Congping record shows no clear evidence of human impact on its vegetation, and there were no local fires to have caused any vegetation changes. In the last 1.5 kyr BP a slight cooling caused a rise in conifers, a decline in broad-leaved tree taxa and increased weathering rates
Seasonality of the altitude effect on leaf wax n-alkane distributions, hydrogen and carbon isotopes along an arid transect in the Qinling Mountains
No full textReconstructing paleoelevation allows the temporal evolution of biogeochemical processes and hydroclimate regimes to be understood and quantified. A dual-isotope biomarker of clumped hydrogen and carbon isotopes of leaf wax n-alkanes was recently proposed in humid tropical forests, and it was proven to be superior to a single-isotope proxy that was previously reported. However, it remains unknown whether the dual-isotope biomarker is suitable in arid conditions. The present study investigated leaf wax n-alkane distribution, hydrogen (delta H-2(wax)) and carbon (delta C-13(wax)) isotopes in terrestrial plants along an arid mountainous transect. We found that the effects of seasonality on n-alkane distribution, delta H-2(wax) and delta C-13(wax) were minimal for all species (p > 0.05), and that species-specific delta H-2(wax) values remained almost unchanged for most species, in contrast to delta C-13(wax) values. Significant correlations between altitude and delta H-2(wax) values (R-2 = 0.54, 0.58, and 0.75 for spring, summer, and autumn, respectively), instead of delta C-13(wax) values (R-2 = 0.08, 0.43, and 0.12 with p = 0.24, 0.01, and 0.19 for spring, summer, and autumn, respectively), were observed, suggesting that delta H-2(wax) values, but not delta C-13(wax) values, can be reliably used as a proxy for reconstructing paleoelevation in arid conditions. Therefore, it will be necessary to identify other proxies to supplement delta H-2(wax) values under a dual-isotope approach in future research. (C) 2021 Elsevier B.V. All rights reserved
Spatial variation and distribution of soil organic carbon in an urban ecosystem from high-density sampling
No full textWith acceleration of urban expansion, urban soils are increasingly becoming critical in the global carbon cycle. However, spatial variations and distributions of soil organic carbon (SOC) across urban centers are rarely investigated. Here, 1018 soil samples were collected from the upper 20 cm soil layer in Xi'an - a typical historical city under rapid urbanization in China. The aims were to: i) determine current levels and variations in SOC; ii) identify main driving factors of SOC density (SOCD); and iii) compare different interpolation methods in predicting spatial distributions of SOCD in Xi'an City study area. Results showed that the range of SOC concentration (SOCC) was 1.57-38.58 g kg(-1) (mean of 13.59 g kg(-1)) and the range of SOCD was 0.47-9.48 kg m(-2) (mean of 3.59 kg m 2). Analysis of coefficient of variation showed that there were moderate variations in SOCC (54.0%) and SOCD (49.4%) in the study area. Combined correlation analysis, principal component analysis and minimum dataset compilation showed that sand content, distance to civic center, land use type and vegetation type were closely correlated with spatial variations in SOCD. Geostatistical analysis showed that isotropic exponential model with a range of 1776 m was the best fit for SOCD semi-variogram. Spatial distribution of SOCD was further predicted using four approaches - ordinary kriging (OK), inverse distance weighting (IDW), multiple linear regression (MLG) and regression kriging (RK). The spatial prediction accuracy was ranked in order of RK > MLR > OK > IDW. However, there was relatively low interpolation accuracy for the four approaches. This was attributed to the high spatial variations in urban milieu, impacted by intense anthropogenic activities. The findings in this study added to current knowledge on global carbon cycle as influenced by urban soils, which is a critical guide to land management in urban areas
Prolonged cooling interrupted the Bronze Age cultures in northeastern China 3500 years ago
No full textThe role of climatic change in the social transition in NE China during the Bronze Age is poorly understood due to the lack of reliable climate proxy records. Here we report a 3600-yr-long climate record based on branched glycerol dialkyl glycerol tetraether distributions in the Jinchuan peat core, Northeastern (NE) China. Our record shows a persistent cooling between ca.3.5-3.0 ka, which coincides with the societal transition from a settled to a mobile lifestyle. Comparing existing records suggests that this event represents a hemispherical-scale cooling probably driven by the prolonged El Nino conditions. The low temperatures caused unfavorable conditions for the agriculture-based society during the Lower Xiajiadian period and thus drove people to flee southward into the North China and Central China Plains, leading to a culturally desolated area that was gradually occupied by pastoralists in about 250 years. Our results highlight the need to consider the interplay of climatic dynamics with social upheaval in understanding the evolution of prehistorical civilization in NE Asia
Coupled action of rock weathering and aquatic photosynthesis: Influence of the biological carbon pump effect on the sources and deposition of organic matter in Ngoring Lake, Qinghai-Tibet Plateau, China
No full textA critical problem in the study of global climate change is how to identify "missing" carbon sinks. The carbon sink resulting from the weathering of carbonate and silicate minerals may make a major contribution, and it is often coupled with aquatic photosynthesis (the biological carbon pump effect - 'BCP'). However, the lack of relevant field studies hinders our understanding of rock weathering and the carbon cycle. To address this issue, we analyzed the pH, [HCO3-], carbon isotopic composition of dissolved inorganic carbon (delta C-13(DIC)), total organic carbon (TOC), total nitrogen (TN), TOC/TN, and the stable carbon isotopic composition of TOC (delta C-13(org)) and CaCO3 (delta C-13(carb)) in the modern surface sediments of Ngoring Lake, in the northeastern Qinghai-Tibet Plateau (QTP), China. The results show that the efficiency of aquatic photosynthesis may be an important factor affecting the delta C-13(DIC) in Ngoring Lake. delta C-13(org) in the surface sediments is positively correlated with the delta C-13(carb) of inorganic carbon produced within the lake, especially in shallow water (<10 m). In addition, the increase in the TOC content of the surface sediment samples is accompanied by an increase in the CaCO3 content. These observations suggest that the BCP effect is the major mechanism driving the observed synchronous increases in TOC and CaCO3 in the sediments, and the range of observed carbon isotope values. Furthermore, organic carbon in the surface sediments is characterized by a relatively low C/N ratio and delta C-13(org), suggesting it is mainly autochthonous, and is transformed within the aquatic ecosystem from rock weathering-derived DIC via the BCP effect. Therefore, the BCP effect plays an important role in the stabilization of the rock weathering carbon sink. Our results emphasize the importance of the carbon sink of coupled rock weathering and aquatic photosynthesis in the evolution of the carbon cycle in lakes in the QTP
MINERAL-MICROBE INTERACTIONS: BACTERIALLY INDUCED HYDRATION OF BIOTITE
No full textThe interaction between microbes and minerals occurring in the soil is an important geochemical process in the Earth's surface system. Investigating the weathering of potassium-bearing silicate minerals by microorganisms is of great importance in understanding the process of soil development and the provision of nutrient for plants. One of the major gaps in studies of weathering is the lack of sufficient evidence from X-ray diffraction to indicate of the formation of secondary minerals in the weathering of primary minerals. The present study aims to investigate whether or not secondary minerals formed during laboratory experiments can be detected by XRD (X-ray diffraction, XRD). For this reason, a series of culture experiments using biotite and Paenibacillus mucilaginous strain YM-1 were performed over a period of 450 days. The results demonstrate that preliminary treatment by sedimentation-centrifugation according to Stokes's law to enrich the fine particles with grain size less than 1 mu m and subsequent detection by XRD are practicable methods for investigating the presence of secondary minerals. The XRD results of the fraction with grain size less than 1 mu m indicated that a part of the biotite flakes altered into hydrobiotite on day 60 in experiments with strain YM-1, while hydrobiotite occurred on day 390 for experiments without bacteria. In summary, it is demonstrated that strain YM-1 of Paenibacillus mucilaginous evidently accelerated biotite weathering
Why Does Extreme Rainfall Occur in Central China during the Summer of 2020 after a Weak El Nino?
No full textIn summer 2020, extreme rainfall occurred throughout the Yangtze River basin, Huaihe River basin, and southern Yellow River basin, which are defined here as the central China (CC) region. However, only a weak central Pacific (CP) El Nino happened during winter 2019/20, so the correlations between the El Nino-Southern Oscillation (ENSO) indices and ENSO-induced circulation anomalies were insufficient to explain this extreme precipitation event. In this study, reanalysis data and numerical experiments are employed to identify and verify the primary ENSO-related factors that cause this extreme rainfall event. During summer 2020, unusually strong anomalous southwesterlies on the northwest side of an extremely strong Northwest Pacific anticyclone anomaly (NWPAC) contributed excess moisture and convective instability to the CC region, and thus, triggered extreme precipitation in this area. The tropical Indian Ocean (TIO) has warmed in recent decades, and consequently, intensified TIO basinwide warming appears after a weak El Nino, which excites an extremely strong NWPAC via the pathway of the Indo-western Pacific Ocean capacitor (IPOC) effect. Additionally, the ENSO event of 2019/20 should be treated as a fast-decaying CP El Nino rather than a general CP El Nino, so that the circulation and precipitation anomalies in summer 2020 can be better understood. Last, the increasing trend of tropospheric temperature and moisture content in the CC region after 2000 is also conducive to producing heavy precipitation
Air Pollution Zone Migrates South Driven by East Asian Winter Monsoon and Climate Change
No full textA variety of climatological indices have been established to illustrate the impact of climate change on air pollution in China, but major facts for causing variations of air pollution attributed to climate change are still unclear. Here, using in-situ PM2.5 (particles with the aerodynamic diameter less than 2.5 mu m) measurement, atmospheric reanalysis data and a chemical transport model, we show that meridional distribution of PM2.5 loadings is strongly modulated by the intensity of East Asian winter monsoon (EAWM). The EAWM drives the heavily polluted zone in eastern China to migrate southward, i.e., under stronger EAWM, more southward migration of air pollution occurs. We expect that the migration will likely re-distribute carbon sources- and sinks-related ecosystem, posing a new challenge for the Chinese government, who needs to implement region-different emission reduction plans in the future, to mitigate air pollution and to go carbon neutral