Institute of Earth Environment
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The impacts of volcanic eruptions and climate changes on the development of Hani peatland in northeastern China during the Holocene
No full textPeatland development is closely correlated with regional environment and climate changes. In this study, two sediment cores covering the past 13.8 cal kyr BP were collected from Hani peatland in northeastern China. The organic content, carbonate content, Rb/Sr and Zr/Rb ratios were obtained to discuss the peat development process and associated environment and climate changes. The results showed that there were two deposition events in Hani peatland during 11.2-9.3 cal kyr BP and 2-1.4 cal kyr BP, when the organic content and Rb/Sr ratio decreased sharply, the carbonate content and Zr/Rb ratio increased dramatically. The synchronous occurrence of these two events and nearby volcanic eruptions, combining with tephra observed in sediments, indicated that volcanic activities have some impacts on the peat development. Except for the two events, the organic content of peat sediments increased gradually from the early to mid Holocene, and was highest at 8-6 cal kyr BP, then decreased gradually from the mid to late Holocene. The comparison with regional vegetation and paleoclimate records, together with the chemical weathering intensity obtained from the Rb/Sr, suggested that the orbital scale peat development in Hani during the Holocene was closely coupled with regional climate changes, including both temperature and precipitation. In addition, the 0.5-2 ka band filtering results of organic content showed similar oscillations with the drift ice indices of the North Atlantic Ocean and the atmospheric Delta C-14 record, implying that the North Atlantic climate and solar activities could also leave footprints on peat development of Hani on millennial timescale
Soil temperature and brGDGTs along an elevation gradient on the northeastern Tibetan Plateau: A test of soil brGDGTs as a proxy for paleoelevation
No full textThe uplift history of the Tibetan Plateau is poorly constrained. A key problem is the discrepancy between reconstructions based on different paleoaltimeters. Branched glycerol dialkyl glycerol tetraethers (brGDGTs) produced by soil-dwelling bacteria offer a potential tool for paleoaltimetry reconstruction. However, because insitu soil temperature-the direct link between brGDGTs and altitude-is generally not well-constrained, the reliability and uncertainty of this approach remain uncertain. Here, we investigated brGDGT distributions and in-situ soil temperature along an altitudinal gradient at 2300-4000 m on Mt. Laji, northeastern Tibetan Plateau, to test the relationships among altitude, temperature, and brGDGTs. The results show that: 1. the measured mean annual soil temperature (MAST) is strongly correlated with altitude (R-2 = 0.73), but compared with those for mean annual air temperature (MAAT) derived from weather stations, the absolute values are substantially higher particularly at higher altitudes, while the lapse rate (-0.39 degrees C/100 m) is much lower; 2. brGDGT-reconstructed MAST using published soil temperature calibrations is generally consistent with in-situ soil temperature measurements, displaying similar lapse rates (-0.48 degrees C/100 m for MAST(ST) and - 0.41 degrees C/100 m for MAST(STS) at the sunny slope) to that for measured MAST; 3. the slope aspect may affect both measured and brGDGT-reconstructed MAST by up to >3 degrees C. Overall, our results demonstrate that soil brGDGTs can quantitatively capture elevation-dependent soil temperature variation on the Tibetan Plateau. However, the use of ex-situ air temperature instead of in-situ soil temperature, and the effect of slope aspect on temperature, may introduce uncertainties in evaluating the brGDGT paleoaltimeter in this region. In paleo-applications, suitable calibrations are required and soil temperature lapse rates should be constrained before applying brGDGTs to quantitatively reconstruct past uplift histories
Climate Change along the Silk Road and Its Influence on Scythian Cultural Expansion and Rise of the Mongol Empire
No full textClimate change and cultural exchange both influenced cultural development along the continental Silk Road during the late Holocene, but climate change and its influence on nomadic civilizations during that time has yet to be systematically assessed. In this study, we analyzed records of climate change along the Silk Road covering key periods in the late Holocene, based on multiproxies from various archives including lake sediments, shorelines/beach ridges, peatlands, ice cores, tree rings, aeolian sediments, moraines, and historical documents. Combined with archaeological data, we assessed the influence of climate on development and expansion of representative pastoral nomadism. Our results show that the most notable climate changes in Central Asia were characterized by decreasing temperature, expanding glaciers, increasing precipitation, and increasing humidity during transitions from the Sub-Boreal to Sub-Atlantic Period (ca. 9-8th century BC) and from the Medieval Warm Period to the Little Ice Age (ca. 13-14th century AD). The two periods coincided with Scythian Cultural expansion across the steppe landscape of Central Asia and rise of the Mongol Empire, respectively. These temporal coincidences are interpreted as causally related, where temperature fall and glacial advance may have forced the pastoral nomadism to southward migration. Coeval wetness and southward migration of steppe landscape in Central Asia were beneficial for these cultural expansions, which spanned the Eurasian arid and semi-arid zone westward. Therefore, during the historical period when productivity was underdeveloped, although expansions of pastoral nomadism were closely related to internal social structures, climate change was possibly the most critical controlling factor for sustainability development and collapse
Impacts of primary emissions and secondary aerosol formation on air pollution in an urban area of China during the COVID-19 lockdown
No full textRestrictions on human activities were implemented in China to cope with the outbreak of the Coronavirus Disease 2019 (COVID-19), providing an opportunity to investigate the impacts of anthropogenic emissions on air quality. Intensive real-time measurements were made to compare primary emissions and secondary aerosol formation in Xi?an, China before and during the COVID-19 lockdown. Decreases in mass concentrations of particulate matter (PM) and its components were observed during the lockdown with reductions of 32-51%. The dominant contributor of PM was organic aerosol (OA), and results of a hybrid environmental receptor model indicated OA was composed of four primary OA (POA) factors (hydrocarbon-like OA (HOA), cooking OA (COA), biomass burning OA (BBOA), and coal combustion OA (CCOA)) and two oxygenated OA (OOA) factors (less oxidized OOA (LO-OOA) and more-oxidized OOA (MO-OOA)). The mass concentrations of OA factors decreased from before to during the lockdown over a range of 17% to 58%, and they were affected by control measures and secondary processes. Correlations of secondary aerosols/Delta CO with Ox (NO2 + O-3) and aerosol liquid water content indicated that photochemical oxidation had a greater effect on the formation of nitrate and two OOAs than sulfate; however, aqueous-phase reaction presented a more complex effect on secondary aerosols formation at different relative humidity condition. The formation efficiencies of secondary aerosols were enhanced during the lockdown as the increase of atmospheric oxidation capacity. Analyses of pollution episodes highlighted the importance of OA, especially the LO-OOA, for air pollution during the lockdown
Potential health risk assessment of HFRs, PCBs, and OCPs in the Yellow River basin
No full textThe concentrations of PBDEs, NBFRs, DP, PCBs, and OCPs were analyzed in water samples of the Yellow River Basin (YRB) and in soil and maize samples collected from basin irrigation areas to understand the status of POPs and associated health risks. The results showed: (1) the congeners of eight PBDEs and seven NBFRs were detected in 10 tributaries, with average concentrations of 1575 and 4288 pg. L-1. Thirty-three congeners of PCBs were detected, and the average concentration of PCB was 232 pg. L-1. Five HCHs were the primary congeners among twenty-three congeners of OCPs in the ten tributaries, accounting for 79% of the total. The average concentration of OCPs was 8287 pg. L-1. (2) Similar congeners of HFRs, PCBs, and OCPs were found in the trunk water. The ranking based on the HFR concentration was upstream > downstream > midstream, and that of the PCB and OCP concentration was downstream > upstream > midstream. (3) PCBs and OCPs in the trunk water of the YRB and in the soil and maize irrigated with river water pose potential carcinogenic and non-carcinogenic risks. The results indicate considerable organic pollution in the YRB, suggesting that national emission standards for POPs should be implemented soon. (C) 2021 Elsevier Ltd. All rights reserved
Grain size variation in two lakes from margin of Asian Summer Monsoon and its paleoclimate implications
No full textA wealth of research has demonstrated that polymodal grain/particle size distributions (GSD or PSD) in lake sediments can be mathematically decomposed to serve as a more precise tool for paleoenvironmental reconstructions. However, linking grain size subcomponents to specific environmental parameters is sometimes ambiguous, as grain size in lake sediments depends on local characteristics of individual lakes. In view of this, illustrative case studies with widespread practical significance are needed. Here, GSD datasets of two lake sediments from the Asian Summer Monsoon (ASM) marginal zone were decomposed and compared with nearby surficial lacustrine/eolian sediments with clear geological origins, to study the dominant sedimentary processes-grain size regimes of these two representative lakes. The decomposition and comparison clarify the geologic properties of certain grain size parameters and minimizes extraneous signals. Based on this information, we interpret certain size fractions as regional climate indicators associated with ASM intensity changes. We also consider centennial-timescale climate variability during the last half of the Holocene, and discuss the driving forces controlling centennial moisture variability in the studied area
Grain size variation in two lakes from margin of Asian Summer Monsoon and its paleoclimate implications
No full textA wealth of research has demonstrated that polymodal grain/particle size distributions (GSD or PSD) in lake sediments can be mathematically decomposed to serve as a more precise tool for paleoenvironmental reconstructions. However, linking grain size subcomponents to specific environmental parameters is sometimes ambiguous, as grain size in lake sediments depends on local characteristics of individual lakes. In view of this, illustrative case studies with widespread practical significance are needed. Here, GSD datasets of two lake sediments from the Asian Summer Monsoon (ASM) marginal zone were decomposed and compared with nearby surficial lacustrine/eolian sediments with clear geological origins, to study the dominant sedimentary processes-grain size regimes of these two representative lakes. The decomposition and comparison clarify the geologic properties of certain grain size parameters and minimizes extraneous signals. Based on this information, we interpret certain size fractions as regional climate indicators associated with ASM intensity changes. We also consider centennial-timescale climate variability during the last half of the Holocene, and discuss the driving forces controlling centennial moisture variability in the studied area
Vertical profile of particle hygroscopicity and CCN effectiveness during winter in Beijing: insight into the hygroscopicity transition threshold of black carbon
No full textThe hygroscopicity and ability of aerosol particles to act as cloud condensation nuclei (CCN) is important in determining their lifetime and role in aerosol-cloud interactions, thereby influencing cloud formation and climate. Previous studies have used the aerosol hygroscopic properties measured at the ground to evaluate the influence on cloud formation in the atmosphere, which may introduce uncertainty associated with aerosol hygroscopicity variability with altitude. In this study, the CCN behaviour and hygroscopic properties of daily filter collections of PM2.5 from three different heights (8, 120, 260 m) on a tower in Beijing were determined in the laboratory using water, water/methanol and methanol as the atomization solvents. Whilst there was substantial temporal variability in particle concentration and composition, there was little obvious difference in aerosol CCN and hygroscopic behaviour at different heights, although the planetary boundary layer height (PBLH) reduced to below the tower height during the nighttime, suggesting that use of surface hygroscopicity measurements is sufficient for the estimation of aerosol particle activation in clouds. Additionally, the critical coating thickness (in terms of mass ratio of coating/refractory BC, MRc) defining the BC transition between being hydrophobic to hydrophilic, was determined by combining hygroscopic tandem differential mobility analyser (H-TDMA), centrifugal particle mass analyzer (CPMA) and single particle soot photometer (SP2) measurements. The MRc of 250 nm BC-containing particles increased from a background value of between 0.8 and 1.6 to around 4.6 at the onset of the growth event of nanoparticles, decreasing monotonically back to the background level as the event progressed. This indicates that large particles do not act as an effective pre-existing condensation sink of the hygroscopic vapours during the nanoparticle growth events, leading to the 250 nm BC particles requiring more coating materials to transition between being hydrophobic and hydrophilic. These findings show that large particles may be less important in suppressing the new particle formation and subsequent growth in the atmosphere
A study of the gas-water characteristics and their implications for the coalbed methane accumulation modes in the Southern Junggar Basin, China
No full textGas and water samples were collected from coalbed methane (CBM) wells, rivers, and springs in the southern Junggar Basin (SJB). These samples were analyzed for gas composition, stable isotopes, 16s ribosomal ribonucleic acid sequence, chemical compositions, and radioisotopes. The objective of this study was to understand CBM genesis in the Junggar Basin, the reason for abnormal CO2 accumulation, the development of microbial communities, the source of coalbed water, and the timing of methanogenesis. The CBM genesis is complex in the SJB, but it is closely related to microbial activities. The stagnant zone, which experiences limited groundwater recharge, may represent a relatively closed system where CO2 is easily trapped and the residual CO2 becomes progressively enriched in C-13. Only two families of methanogens (i. e., Methanobacteriaceae and Methanospirillaceae) are present in the coalbed waters, indicating that CO2 reduction is the main pathway for generating microbial gas. The coalbed water samples from the Houxia and Manasi-Hutubi regions plot around the local meteoric water line (LMWL), indicating recharge by modern meteoric water and rivers. However, the samples from the Miquan and Fukang regions plot below the LMWL, reflecting older snowmelt water recharge. Isotopic dating indicates that the age of coalbed water in the Miquan and Fukang regions is 43.5-2000 ka. Early coalification and later hydrological events collectively determined the regional variations in CBM genesis and gas composition in the SJB
Pre-nuclear values for I-129/I-127 in Chinese sediments and their geochronological implications
No full textLarge variations in pre-nuclear I-129/I-127 ratios in terrestrial environments have been observed, but few investigations have been carried out on how the isotopic composition varies and how it is affected by the terrestrial environment. In this work, lake and river sediments were studied for the first time with the aim of exploring the possible connections between the natural iodine isotopic composition and its sources. The observed higher natural I-129/I-127 ratios compared to those in the marine system suggested that the isotopes did not reach a steady state. Decreasing I-129/I-127 ratios with increasing I-127 contents indicated perturbation of old iodine, and a narrower range of initial equilibrium ratios was suggested based on pre-nuclear ratios derived in the studied sediments