Institute of Earth Environment
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Late Holocene land use evolution and vegetation response to climate change in the watershed of Xingyun Lake, SW China
No full textKnowledge of the past interactions between climate and human land use is essential for understanding the possible future relationships between global change and human societies. In this study, we used pollen and other multi-proxy analyses of the sediments from Xingyun Lake in central Yunnan Plateau to reconstruct the history of land use and ecosystem dynamics during the last 3,200 years. The pollen results indicate that the vegetation became more open gradually and many secondary forests began to grow during the last 100 years. During the Medieval Climatic Anomaly (MCA), the vegetation is dominated by broad-leaved trees, while during the Little Ice Age (LIA) the broad-leaved trees declined but Picea/Abies expanded. Human land use has impacted on the regional vegetation and landscape since 50 CE; large-scale human land use occurred after 750 CE. The sediment accumulation rate (SAR), pollen record, and C-14 age offsets reveal that soil erosion is well correlated with human activity and changes in vegetation cover. Before 750 CE, soil erosion was probably limited, but after 750 CE it increased drastically as a result of human activity, and then decreased during the last 100 years. According to the results of the redundancy analysis (RDA), we conclude that climate had an important impact on the regional vegetation, and the late Holocene vegetation changes of Xingyun Lake catchment were mainly influenced by temperature
Weak Mesoscale Variability in the Optimum Interpolation Sea Surface Temperature (OISST)-AVHRR-Only Version 2 Data before 2007
No full textMesoscale sea surface temperature (SST) variability triggers mesoscale air-sea interactions and is linked to ocean subsurface mesoscale dynamics. The National Oceanic and Atmospheric Administration (NOAA) daily Optimum Interpolation SST (OISST) products, based on various satellite and in situ SST data, are widely utilized in the investigation of multi-scale SST variabilities and reconstruction of subsurface and deep-ocean fields. The quality of OISST datasets is subjected to temporal inhomogeneity due to alterations in the merged data. Yet, whether this issue can significantly affect mesoscale SST variability is unknown. The analysis of this study detects an abrupt enhancement of mesoscale SST variability after 2007 in the OISST-AVHRR-only version 2 and version 2.1 datasets (hereafter OI.v2-AVHRR-only and OI.v2.1-AVHRR-only). The contrast is most stark in the subtropical western boundary current (WBC) regions, where the average mesoscale SST variance during 2007-2018 is twofold larger than that during 1993-2006. Further comparisons with other satellite SST datasets (TMI, AMSR-E, and WindSAT) suggest that the OISST-AVHRR-only datasets have severely underestimated mesoscale SST variability before 2007. An evaluation of related documents of the OISST data indicates that this bias is mainly caused by the change of satellite AVHRR instrument in 2007. There are no corresponding changes detected in the associated fields, such as the number and activity of mesoscale eddies or the background SST gradient in these regions, confirming that the underestimation of mesoscale SST variability before 2007 is an artifact. Another OISST product, OI.v2-AVHRR-AMSR, shows a similar abrupt enhancement of mesoscale SST variability in June 2002, when the AMSR-E instrument was incorporated. This issue leaves potential influences on scientific research that utilize the OISST datasets. The composite SST anomalies of mesoscale eddies based on the OI.v2-AVHRR-only data are underestimated by up to 37% before 2007 in the subtropical WBC regions. The underestimation of mesoscale variability also affects the total (full-scale) SST variability, particularly in winter. Other SST data products based on the OISST datasets were also influenced; we identify suspicious changes in J-OFURO3 and CFSR datasets; the reconstructed three-dimensional ocean products using OISST data as input may also be inevitably affected. This study reminds caution in the usage of the OISST and relevant data products in the investigation of mesoscale processes
Weak Mesoscale Variability in the Optimum Interpolation Sea Surface Temperature (OISST)-AVHRR-Only Version 2 Data before 2007
No full textMesoscale sea surface temperature (SST) variability triggers mesoscale air-sea interactions and is linked to ocean subsurface mesoscale dynamics. The National Oceanic and Atmospheric Administration (NOAA) daily Optimum Interpolation SST (OISST) products, based on various satellite and in situ SST data, are widely utilized in the investigation of multi-scale SST variabilities and reconstruction of subsurface and deep-ocean fields. The quality of OISST datasets is subjected to temporal inhomogeneity due to alterations in the merged data. Yet, whether this issue can significantly affect mesoscale SST variability is unknown. The analysis of this study detects an abrupt enhancement of mesoscale SST variability after 2007 in the OISST-AVHRR-only version 2 and version 2.1 datasets (hereafter OI.v2-AVHRR-only and OI.v2.1-AVHRR-only). The contrast is most stark in the subtropical western boundary current (WBC) regions, where the average mesoscale SST variance during 2007-2018 is twofold larger than that during 1993-2006. Further comparisons with other satellite SST datasets (TMI, AMSR-E, and WindSAT) suggest that the OISST-AVHRR-only datasets have severely underestimated mesoscale SST variability before 2007. An evaluation of related documents of the OISST data indicates that this bias is mainly caused by the change of satellite AVHRR instrument in 2007. There are no corresponding changes detected in the associated fields, such as the number and activity of mesoscale eddies or the background SST gradient in these regions, confirming that the underestimation of mesoscale SST variability before 2007 is an artifact. Another OISST product, OI.v2-AVHRR-AMSR, shows a similar abrupt enhancement of mesoscale SST variability in June 2002, when the AMSR-E instrument was incorporated. This issue leaves potential influences on scientific research that utilize the OISST datasets. The composite SST anomalies of mesoscale eddies based on the OI.v2-AVHRR-only data are underestimated by up to 37% before 2007 in the subtropical WBC regions. The underestimation of mesoscale variability also affects the total (full-scale) SST variability, particularly in winter. Other SST data products based on the OISST datasets were also influenced; we identify suspicious changes in J-OFURO3 and CFSR datasets; the reconstructed three-dimensional ocean products using OISST data as input may also be inevitably affected. This study reminds caution in the usage of the OISST and relevant data products in the investigation of mesoscale processes
Large contribution from worship activities to the atmospheric soot particles in northwest China
No full textWorship activities like burning joss paper during the Chinese Hanyi festival is a common, traditional custom in northwest China. However, the pollutants of e.g., soot particles, released from joss paper burning and the cor-responding impacts on urban air quality were poorly investigated, which can be a particular concern since these activities are conducted in an uncontrolled manner. In this study, a long time-of-flight (LToF) soot particle aerosol mass spectrometry (SP-AMS) was deployed to characterize the refractory black carbon (rBC) emitted from the joss paper burning, as well as crop residue, coal combustion, and traffic during the Hanyi Festival in mid-November 2020 in the northwestern city of Xi'an in China. Large difference (from 5% to 100%) in the fragmentation patterns (C-n(+)) for the measured rBC from different source emissions were found when compared to the reference Regal Black. Using the receptor model of positive matrix factorization (PMF) with the multilinear engine (ME-2) algorithm, the obtained rBC mass spectra were used as the anchoring profiles to evaluate the emission strengths of different source types to the atmospheric rBC. Our results show that the burning of joss paper accounted for up to 42% of the atmospheric rBC mass, higher than traffic (14-17%), crop residue (10-17%), coal (18-20%) during the Hanyi festival in northwest China. Moreover, we show that the overall air quality can be worsened due to the practice of uncontrolled burning of joss paper during the festival, which is not just confined to the people who do the burning. Although worship activities occur mainly during festival periods, the pollution events contributed by joss paper burning may pose an acute exposure risk for public health. This is particularly important since burning joss paper during worship activities is common in China and most Asian countries with similar traditions
Plutonium isotopes in the northwestern South China Sea: Level, distribution, source and deposition
No full textThe spatial distribution of plutonium isotopes (Pu-239, Pu-240) in the surface sediments collected from the northwestern South China Sea (SCS) in 2018 was investigated. The Pu-239,Pu-240 concentrations in surface sediments vary from 0.048 to 0.960 mBq/g (with mean of 0.282 +/- 0.242 mBq/g) depending on the geographical feature of the sampling location such as the river estuary, continental shelf, slope and deep basin. Higher Pu-240/Pu-239 atomic ratios (0.24-0.31) in the surface sediment of the SCS compared to the global fallout value of 0.18 were observed, this is attributed to the input of close-in fallout of the Pacific Proving Ground (PPG) transported by the North Equatorial Current and Kuroshio Current to the northern SCS. The contribution of the PPG derived plutonium in the SCS sediment was estimated to be 39%-78% using a simple two-end member mixing model based on the measured Pu-240/Pu-239 atomic ratios in the sediment. Besides the soluble Pu-239,Pu-240 level in seawater, load of suspended particulate matter from the river runoff and biological debris, hydrographic and hydrodynamic conditions are key parameters influencing the deposition process of plutonium to the sediment
The Reading Palaeofire Database: an expanded global resource to document changes in fire regimes from sedimentary charcoal records
No full textSedimentary charcoal records are widely used to reconstruct regional changes in fire regimes through time in the geological past. Existing global compilations are not geographically comprehensive and do not provide consistent metadata for all sites. Furthermore, the age models provided for these records are not harmonised and many are based on older calibrations of the radiocarbon ages. These issues limit the use of existing compilations for research into past fire regimes. Here, we present an expanded database of charcoal records, accompanied by new age models based on recalibration of radiocarbon ages using IntCal20 and Bayesian age-modelling software. We document the structure and contents of the database, the construction of the age models, and the quality control measures applied. We also record the expansion of geographical coverage relative to previous charcoal compilations and the expansion of metadata that can be used to inform analyses. This first version of the Reading Palaeofire Database contains 1676 records (entities) from 1480 sites worldwide. The database (RPDv1b - Harrison et al., 2021) is available at https://doi.org/10.17864/1947.000345
An automated method for thermal-optical separation of aerosol organic/elemental carbon for C-13 analysis at the sub-mu gC level: A comprehensive assessment
No full textWe describe and thoroughly evaluate a method for C-13 analysis in different fractions of carbonaceous aerosols, especially elemental carbon (EC). This method combines a Sunset thermal-optical analyzer and an isotope ratio mass spectrometer (IRMS) via a custom-built automated separation, purification, and injection system. Organic carbon (OC), EC, and other specific fractions from aerosol filter samples can be separated and analyzed automatically for C-13 based on thermal-optical protocols (EUSAAR_2 in this study) at sub-pgC levels. The main challenges in isolating EC for C-13 analysis are the possible artifacts during OC/EC separation, including the premature loss of EC and the formation of pyrolyzed OC (pOC) that is difficult to separate from EC. Since those artifacts can be accompanied with isotope fractionation, their influence on the stable isotopic composition of EC was comprehensively investigated with various test compounds. The results show that the thermal-optical method is relatively successful in OC/EC separation for C-13 analysis. The method was further tested on real aerosols samples. For biomass-burning source samples, (partial) inclusion of pOC into CC has negligible influence on the C-13 signature of CC. However, for ambient samples, the influence of pOC on the C-13 signature of CC can be significant, if it is not well separated from CC, which is true for many current methods for measuring C-13 on EC. A case study in Xi'an, China, where pOC is enriched in C-13 compared to EC, shows that this can lead to an overestimate of coal and an underestimate of traffic emissions in isotope-based source apportionment. (C) 2021 Elsevier B.V. All rights reserved
Paleoclimatic changes during the penultimate interglacial period archived by multiple proxies of Xiashu Loess in the Chaohu Lake Basin, East China
No full textThe interglacial periods of the Pleistocene (MIS 5) and Holocene have been widely studied as analogs, whereas the records of the penultimate interglacial complex (MIS 7) are relatively sparse. In this study, based on a multitude of proxies, such as magnetic susceptibility, geochemical elements and their ratios, and grain size spanning MIS 7 of Xiashu Loess, the paleoclimatic changes that are synchronous with the five episodes during MIS 7 are reconstructed in the Chaohu Lake Basin, East China. It is proposed that the paleoclimate change in the Chaohu Lake Basin during MIS 7, on orbital time scale, might be controlled by low-latitude insolation; on millennium scales, might be directly driven by the global ice volume variations
Constructing Pd/ferroelectric Bi4Ti(3)O(12) nanoflake interfaces for O-2 activation and boosting NO photo-oxidation
No full textPhoto-oxidative NOx removal often encountered with sluggish charge carrier separation kinetics and poor selectivity. Herein, Pd/ferroelectric Bi4Ti3O12 nanoflakes (Pd/BTO NF) were constructed to investigate the photo-excited charge separation, O2 activation and the generated reactive oxygen species (ROS) in dictating NO removal. Results showed that the depolarization field of ferroelectric BTO NF significantly promoted bulk charge separation, leading to boosted NO removal reaction kinetics (10 times higher) for Pd/BTO NF comparing with Pd/TiO2. Revealed by electronic paramagnetic resonance and radical scavenging tests, it is observed that the primary O2 activation species differed among Pd, Ag and Pt supported BTO NF photocatalysts, which resulted in different selectivity. The underlying mechanism of NO photo-oxidative conversion pathway was studied by in situ diffuse reflectance infrared Fourier transform spectroscopy. This work illustrate that metal/ferroelectric interfaces can be tuned to obtain differing O2 activation species, and notable selectivity changes in photocatalysis mediated environmental remediation reactions
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