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Faecal biomarkers as tools to reconstruct land-use history in maar sediments in the Westeifel Volcanic Field, Germany
No full textThe analysis of faecal biomarkers in lake sediments has been used to reconstruct human population densities and animal husbandry practices in an increasing number of studies in recent years. However, terrigenous biomarkers can decompose in soils, can be stored and redeposited in colluvium and on flood-plains prior to their ultimate deposition in lakes. These and other effects can blur and distort biomarker signals. Therefore, we analysed sediments from two maars in Westeifel to evaluate whether signals of the faecal biomarkers (5 beta-stanols, bile acids) demonstrate statistically significant differences between contrasting periods in land-use intensity. In Holzmaar, palaeoenvironmental data showed evidence for agriculture including cereal cultivation and grassland during the pre-Roman Iron Age and Middle Ages compared with those from periods that were less influenced by land use and showed a higher abundance of broadleaf forest. However, the specific domesticated taxa of livestock in the locale from these periods remain speculative. We found statistically significantly different faecal biomarker signals, which we interpret to be related to an enhanced deposition of faeces of horses, pigs and ruminants in the core sections that represented periods of amplified land use. The analyses of grass- and broadleaf-tree characteristic n-alkanes supported the applicability of biomarkers for land-use reconstruction. Stanol data from a core section dating to the Mesolithic showed no clear results. Analyses of two core sections from Ulmener Maar, which covered periods before and after the decline of elm in the Neolithic, indicated input of pig faeces in the younger section. This study provides important evidence that faecal biomarkers can be used for land-use reconstruction in central European lakes with small catchment areas for time periods from the Neolithic onwards. The results underscore the importance of bile acid analyses in addition to stanol analyses for an identification of faeces inputs from different animals
Petrogenesis and tectonic setting of Late Devonian high-Mg andesites in the Beishan orogen, NW China
No full textHigh-Mg andesites (HMAs) are crucial for the reconstruction of plate tectonics, continental margin formation and lithospheric evolution. In this study, we present new fossil age, whole-rock geochemical and Sr-Nd isotope data on the newly discovered Dundunshan Group HMAs in the Dundunshan area of the Beishan orogen (central-southern Central Asian Orogenic Belt). The Dundunshan HMA samples are characterized by high MgO (6.47-7.02 wt%) contents and high Mg-# values (67.27-68.77), with SiO2 (58.57-62.13 wt%), Al2O3 (14.49-16.07 wt%) and CaO (5.05-6.24 wt%) resembling typical HMAs. The Dundunshan HMA samples are calc-alkaline and strongly enriched in light rare earth elements (LREEs) and large-ion lithophile elements (LILEs), with slightly negative Eu anomaly and high-field-strength element (HFSE) depletions. Their (Sr-87/Sr-86)(i) ratios (0.7041-0.7057) and epsilon(Nd(t)) (3.73-5.59) indicate that the Dundunshan HMAs were mainly formed by the interactions between subducted oceanic sediment-derived melts and mantle peridotites. Fossil evidence and published radiometric age data constrain the formation of the Dundunshan HMAs to early Late Devonian time. Sedimentological features of the Middle Devonian Sangejing Formation and regional tectonic correlation suggest that the Hongliuhe-Niujuanzi-Xichangjing Ocean in the Dundunshan area was likely closed during late Middle Devonian time, and that the Dundunshan HMAs were formed in a post-collision extensional setting
Seasonal and Inter-Annual Variations of Stable Isotopic Characteristics of Rainfall and Cave Water in Shennong Cave, Southeast China, and Its Paleoclimatic Implication
No full textSpeleothem calcite stable oxygen isotope (delta O-18(C)) is one of the most widely used proxies in paleoclimate research, and understanding its seasonal-annual variability is very significant for palaeoclimate reconstruction. Five-year precipitation and karst cave water from 2016 to 2021 were monitored in Shennong cave, Jiangxi Province, Southeast China. The local meteoric water line (LMWL) is delta D = 8.20 x delta O-18 + 13.34, which is similar to the global meteoric water line. The stable hydrogen and oxygen isotope (delta D and delta O-18) characteristics of precipitation and cave water were studied. delta O-18 and delta D of precipitation and cave water show obvious seasonal variations. Lower precipitation delta O-18 and delta D generally occur during summer and autumn compared with higher delta O-18 and delta D values during winter and spring. Meanwhile, low precipitation delta O-18 values do not only appear in June-July when precipitation is the highest of the year but also appear in August-September when precipitation is limited. The back-trajectory analysis of monsoon precipitation moisture sources shows that the moisture uptake regions vary little on inter-annual scales; the water vapor of rainfall in June-July comes from the South China Sea and the Bay of Bengal, while the moisture source in August-September is mainly from the West Pacific and local area. The El Nino-Southern Oscillation is an important factor affecting the value of delta O-18 by modulating the percentage of summer monsoon precipitation in the annual precipitation and moisture source. The relationship between amount-weighted monthly mean precipitation delta O-18 and Nino-3.4 index shows that the East Asian summer monsoon (EASM) intensifies during La Nina phases, resulting in more precipitation in monsoon season (May to September, MJJAS) and lower delta O-18 values, and vice versa during El Nino phases
Nitrate debuts as a dominant contributor to particulate pollution in Beijing: Roles of enhanced atmospheric oxidizing capacity and decreased sulfur dioxide emission
No full textImplementation of strict emission mitigation measures since 2013 has significantly changed air pollutants in the Beijing-Tianjin-Hebei region (BTH), China. Observations show that ozone (O-3) concentrations have increased by 62.40% (27.84%) and SO2 concentrations have decreased by 56.42% (35.07%) during particulate pollution episodes in Beijing (BTH) in the autumn from 2013 to 2015. The measured nitrate concentration in Beijing has increased markedly, which to a large degree offsets the sulfate decrease caused by SO2 emission mitigation. Using the WRF-Chem model, we demonstrate that the enhanced nitrate formation is primarily attributed to increasing atmospheric oxidizing capacity (AOC) and decreasing sulfate competition for base ions. A 9.41-46.24% (7.58-40.97%) decrease in OH radical (O-3) concentrations in October 2015 reduces nitrate and fine particulate matters (PM2.5) concentrations by 2.51-18.18% and 3.15-18.90% in Beijing, respectively. Based on the scenario in October 2015, if the SO2 emission increases by 20.00-100.00%, the PM2.5 concentration increases by 3.02-11.21%, but the nitrate level decreases by 2.48-21.87% simultaneously. Our results suggest that the nitrate aerosol has become a dominant contributor to particulate pollution in Beijing and that decreasing AOC is critical to mitigate nitrate and PM2.5 concentrations
Elevational differences in Holocene thermal maximum revealed by quantitative temperature reconstructions at similar to 30 degrees N on eastern Tibetan Plateau
No full textMeteorological data indicate that the increase in temperature at high-elevation sites with the background of global warming is much higher than the global average. However, there are few studies trying to evaluate temperature changes in high elevational areas over longer time scales. Here, we use brGDGTs in a sediment core collected from Hongyuan Peatland (3503 m a.s.l.), to reconstruct an independently-dated, high-resolution (similar to 100 years), quantitative record of mean annual temperature (MAT) over the past 13,300 yr BP on the eastern Tibetan Plateau. Our data, consisting with other quantitative local reconstructions, show a peak warmth in the middle Holocene (6100-5600 yr BP). Together with other published MAT records from similar to 30 degrees N in China, we find that the timing of the Holocene Thermal Maximum (HTM) in high-elevation sites lagged that in low-elevation sites. We also find that the warming rate in early Holocene was faster at a higher elevation site, by comparing with another MAT reconstruction using the same archive and the same proxy. We hypothesize the delayed HTM at high-elevation areas was probably caused by the offset of remaining regional glaciers and/or snow cover on the Tibetan Plateau. The enhanced warming with elevation can be ascribed to snow albedo and latent heat release. Our new results may imply a faster high-elevation temperature rise with an on-going global warming, considering the disappearing regional glaciers on the Tibetan Plateau
Global distribution of oxygenated polycyclic aromatic hydrocarbons in mineral topsoils
No full textHazardous oxygenated polycyclic aromatic hydrocarbons (OPAHs) originate from combustion (primary sources) or postemission conversion of polycyclic aromatic hydrocarbons (PAHs) (secondary sources). We evaluated the global distribution of up to 15 OPAHs in 195 mineral topsoils from 33 study sites (covering 52 degrees N-47 degrees S, 71 degrees W-118 degrees E) to identify indications of primary or secondary sources of OPAHs. The sums of the (frequently measured 7 and 15) OPAH concentrations correlated with those of the sigma 16EPA-PAHs. The relationship of the sigma 16EPA-PAH concentrations with the sigma 7OPAH/sigma 16EPA-PAH concentration ratios (a measure of the variable OPAH sources) could be described by a power function with a negative exponent 400 ng g(-1), there was a nearly constant sigma 7OPAH/sigma 16EPA-PAH ratio (0.08 +/- 0.005 [SE], n = 80) determined by their combustion sources
Simulated Sensitivity of Ozone Generation to Precursors in Beijing during a High O-3 Episode
No full textThis study uses the WRF-Chem model combined with the empirical kinetic modeling method (EKMA curve) to study the compound pollution event in Beijing that happened in 13-23 May 2017. Sensitivity tests are conducted to analyze ozone sensitivity to its precursors, and to develop emission reduction measures. The results suggest that the model can accurately simulate the compound pollution process of photochemistry and haze. When VOCs and NOx were reduced by the same proportion, the effect of O-3 reduction at peak time was more obvious, and the effect during daytime was more significant than at night. The degree of change in ozone was peak time > daytime average. When reducing or increasing the ratio of precursors by 25% at the same time, the effect of reducing 25% VOCs on the average ozone concentration reduction was most significant. The degree of change in ozone decreased with increasing altitude, the location of the ozone maximum change shifted westward, and its range narrowed. As the altitude increases, the VOCs-limited zone decreases, VOCs sensitivity decreases, NOx sensitivity increases. The controlled area changed from near-surface VOCs-limited to high-altitude NOx-limited. Upon examining the EKMA curve, we have found that suburban and urban are sensitive to VOCs. The sensitivity tests indicate that when VOCs in suburban are reduced about 60%, the O-3-1h concentration could reach the standard, and when VOCs of the urban decreased by about 50%, the O-3-1h concentration could reach the standard. Thus, these findings could provide references for the control of compound air pollution in Beijing
Seasonal Variation of the Westerly Jet over Asia in the Last Glacial Maximum: Role of the Tibetan Plateau Heating
No full textThe westerly jet (WJ) is an important component of atmospheric circulation, which is characterized by prominent seasonal variations in intensity and position. However, the response of the WJ over Asia during the Last Glacial Maximum (LGM) is still not clear. Using general circulation model experiments, the seasonal behaviors of the WJ over central Asia and Japan are analyzed in this paper. The results show that, compared to the present day (PD), the WJ presents a complicated response during the LGM, both in intensity and position. Over central Asia, it becomes weaker in both summer and winter. But over Japan, it is enhanced in summer but becomes diminished in winter. In terms of position, the WJ over central Asia shifts southward in both summer and winter, whereas the WJ over Japan moves southward in summer but does not change obviously relative to PD in winter. Such WJ changes are well explained by meridional temperature gradients in high troposphere, which is closely linked to seasonal thermal anomalies over the Tibetan Plateau (TP). Despite cooler LGM conditions, the anomalous warming center over the TP becomes stronger in summer. Derived from the heat budget equation, the stronger heating center is mainly caused by the weaker adiabatic cooling generated from ascending motion over the area south of the TP. In winter, the cooling over the TP is also strengthened, mostly owing to the subsidence-induced weaker adiabatic heating. Due to the importance of the WJ, the potential role of TP thermal effects should be a focus when explaining the East Asian climate change during the LGM
Seasonal Variation of the Westerly Jet over Asia in the Last Glacial Maximum: Role of the Tibetan Plateau Heating
No full textThe westerly jet (WJ) is an important component of atmospheric circulation, which is characterized by prominent seasonal variations in intensity and position. However, the response of the WJ over Asia during the Last Glacial Maximum (LGM) is still not clear. Using general circulation model experiments, the seasonal behaviors of the WJ over central Asia and Japan are analyzed in this paper. The results show that, compared to the present day (PD), the WJ presents a complicated response during the LGM, both in intensity and position. Over central Asia, it becomes weaker in both summer and winter. But over Japan, it is enhanced in summer but becomes diminished in winter. In terms of position, the WJ over central Asia shifts southward in both summer and winter, whereas the WJ over Japan moves southward in summer but does not change obviously relative to PD in winter. Such WJ changes are well explained by meridional temperature gradients in high troposphere, which is closely linked to seasonal thermal anomalies over the Tibetan Plateau (TP). Despite cooler LGM conditions, the anomalous warming center over the TP becomes stronger in summer. Derived from the heat budget equation, the stronger heating center is mainly caused by the weaker adiabatic cooling generated from ascending motion over the area south of the TP. In winter, the cooling over the TP is also strengthened, mostly owing to the subsidence-induced weaker adiabatic heating. Due to the importance of the WJ, the potential role of TP thermal effects should be a focus when explaining the East Asian climate change during the LGM
In situ synthesis of micro-plastics embedded sewage-sludge co-pyrolyzed biochar: Implications for the remediation of Cr and Pb availability and enzymatic activities from the contaminated soil
No full textCareful designing of biochar (BC) employing biological and industrial waste materials has gained much attention to improve soil health via reducing the bioavailability of heavy metals (HMs) in the contaminated-soil. Herein, a forty-day pot experiment was conducted to explore the influence of micro plastic (MP) embedded sewage-sludge (SS). The effects of SS and MP dosage ratios (0e15%) on the physicochemical properties of the modified-biochars were also studied with slow-pyrolyzed (SBC-500 degrees C) and flash-pyrolyzed biochar (FSBC-70 0 degrees C). Our investigations found remarkable positive synergistic effects for the SBC-15% involving increased soil pH, CEC, high carbon contents, and alleviation in Cr and Pb leaching than control and FSBC-70 0 degrees C. Besides, SBC-15% containing high carbon functional groups can effectively mitigate the Cr and Pb availability stress by intensifying the adsorption or passivation in the amended-soil, thereby, significantly reducing the Cr and Pb EDTA-extractable contents. Chemical fractionation analyses further confirmed that SBC-15% addition was more helpful for Cr and Pb immobilization and ultimately reducing transfer-rate, bioconcentration-factor, and translocation-factor as compared to FSBC-15% and control due to its higher alkalinity, surface area/porosity, and available carbon functional groups. The maize biomass (root and shoot) increased by more than 50%, and the activities of soil enzymes such as urease, alkaline phosphatase, and glucosidase enzyme activities were also enhanced. This ecologically feasible strategy would pave an efficient way to make full use of the SS and MP for the biochar synthesis with excellent soil remediation performance. (C) 2021 Elsevier Ltd. All rights reserved