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Monsoon variations inferred from high-resolution geochemical records of the Linxia loess/paleosol sequence, western Chinese Loess Plateau
No full textChinese eolian deposits have been investigated intensively to reconstruct East Asian monsoon changes at tectonic to millennial timescales. However, high-resolution elemental proxies sensitive to rapid monsoon changes remains sparse. Here we present multiple elemental ratios of the Linxia loess sequence generated by scanning and conventional X-ray fluorescence (XRF) to assess East Asian monsoon variability at glacial-interglacial to sub-orbital timescales. The results show that 11 elements (Al, Si, K, Ca, Ti, Mn, Fe, Rb, Sr, Zr and Ba) can be reliably measured by XRF scanning of loess cores, albeit with relatively lower precision and increased noise levels (due to variable water content and matrix effects) when compared to XRF scanning of dry and homogenized powder samples. Seven elements (Ca, Fe, Ti, Mn, Zr, Rb and Sr), measured by XRF scanning of the core face and powder samples show high correlation (R-2 > 0.7, n = 100) with those measured by conventional XRF methods, and thus can be considered as robust indicators for chemical weathering and grain-size sorting. We employ element ratios of Ca/Ti and Rb/Sr to reflect precipitation-induced weathering intensity, and the Zr/Rb ratio and mean grain size to infer the sorting effects related to winter-monsoon winds. These element ratios exhibit significant glacialinterglacial fluctuations, similar to records of magnetic susceptibility and mean grain size. Precessional- to millennial-scale monsoon changes are also persistent in our high-resolution elemental proxies, consistent with those in Gulang loess elemental ratios and Hulu/Sanbao speleothem d18O records. Our results suggest that high resolution XRF scanning elemental ratios of Chinese loess have great potential for evaluating co-evolution of orbital- and millennial-scale monsoon variations
Provenance of sub-aerial surface sediments in the Tarim Basin, Western China
No full textProvenance of surface sediments in the Tarim Basin is important for understanding the aridification of the Asian interior and the interplay between the Westerlies and the Asian monsoon. Although the desert sands in the Taklamakan Desert have been studied intensively, there is no consensus regarding their provenance, namely, the dispute exists between various sand sources in different parts of the desert and homogenization of the sands in the entire desert. Moreover, other surface sediments in the basin are poorly investigated. Here we examine the particle-size-specific rare earth element (REE) and trace element characteristics of various surface sediments from different regions of the basin. The results reveal that the 63 mu m fraction are dominated by regional-derived materials, mainly from the adjacent mountains (e.g. Pamirs, Kunlun, Kuruktag, Altun, Tianshan Mountains), and the fluvial systems are an important additional transport mechanism. Our findings potentially provide an improved understanding of the dust cycle and atmospheric circulation patterns in Central Asia, and of the provenance of loess in North China
Nitrate-nitrogen transport in streamwater and groundwater in a loess covered region: Sources, drivers, and spatiotemporal variation
No full textWater quality is an increasing concern in the dry regions of the world as it affects and reduces the quantity of available water. Our objective was to investigate the sources, drivers, spatiotemporal patterns of nitrate-nitrogen (NO3-N) transport in the streamwater and groundwater in a dry and a wet season in seven large rivers located in the Loess Plateau of China (640,000 km(2), 100 million population), which is a region with marked influence of human activities on streamflow and groundwater. We collected 510 streamwater and groundwater samples and found that NO3-N was significantly lower in the dry season ( 5.0 mg L-1). In the wet season, NO3-N was lower in the streamwater than groundwater; however, the spatial variation in the NO3-N was greater in streamwater, with higher concentrations in two rivers (Wei and Fen). The source characterization using stable isotopes of NO3 from the Wei River showed that chemical N fertilizers and soil organic N contributed similar to 75% of NO3 to streamwater and that soil organic N was the greatest contributor of NO3 to groundwater (similar to 60%) than streamwater (< 40%). The spatial pattern of NO3-N was dominated by fertilizer application and varied seasonally with rainfall-runoff and streamflow-groundwater connectivity. Our results showed the complicated patterns and sources of NO3 pollution in streamwater and groundwater and highlight that more emphasis should be placed to prevent and restore the degraded water quality in the dry regions. (C) 2020 Elsevier B.V. All rights reserved
Effect of source variation on the size and mixing state of black carbon aerosol in urban Beijing from 2013 to 2019: Implication on light absorption
No full textBlack carbon (BC) is the most important aerosol light-absorbing component, and its effect on radiation forcing is determined by its microphysical properties. In this study, two microphysical parameters of refractory BC (rBC), namely, size distribution and mixing state, in urban Beijing from 2013 to 2019 were investigated to understand the effects of source changes over the past years. The mass equivalent diameter of rBC (Dc) exhibited bimodal lognormal distributions in all seasons, with the major modes accounting for most (>85%) of the rBC masses. The mass median diameter (MMD) was obviously larger in winter (209 nm) than in summer (167 nm) likely due to the contribution of more rBC with larger Dc from solid fuel combustion and enhanced coagulation of rBC in polluted winter. More rBC particles were thickly coated in winter, with the number fraction of thickly coated rBC (fcoatBC) ranging within 29%-48% compared with that of 12%-14% in summer. However, no evidential increase in BC light-absorption capability was observed in winter. This finding was likely related to the lower absorption efficiency of larger rBC in winter, which partly offset the coating-induced light enhancement. Two stage of decreases in MMD and fcoatBC were observed, accompanied with a persistent decrease in rBC loading, thereby reflecting the discrepant effects of source control measures on rBC loading and physical properties. The control measures in the earlier stage before 2016 was more efficient to reduce the rBC loading but slightly influenced the microphysical properties of rBC. As of 2016, the reduction in rBC concentration slowed down because of its low atmospheric loading. However, rBC showed a more obvious decrease in its core size and became less coated. The decrease in fcoatBC may have weakened the BC absorption and accelerated the decrease in light absorption resulting from the reduction in rBC loading. (C) 2020 Elsevier Ltd. All rights reserved
Water depth variation and its impact on carbonate content and oxygen isotopes: A study from a satellite lake near Lake Qinghai over the past 7.6 kyr
No full textThe oxygen isotopic composition of sedimentary carbonate (delta O-18(carb)) provides information on the regional water balance between precipitation and evaporation in a lacustrine system. A volume effect was proposed to explain the abnormally low delta O-18(carb) values in Lake Qinghai on the northern Tibetan Plateau, under the conditions of high evaporation and low water levels, as observed during the early Holocene. Volume effect theory states that the small volume of the lake and its sensitivity to isotopic signals from freshwater discharge control the delta O-18(carb) values. In this study, we present 7.6-kyr records of carbonate content and oxygen isotopes from Lake Gahai, a small and saline satellite lake near Lake Qinghai. The records demonstrate that the water level and lake size of Lake Gahai considerably changed over the past 7.6 kyr, and the volume effect was responsible for the delta O-18(carb) variations. The records also suggest contrasting responses of carbonate precipitation to water depth across different timescales. For example, over the past 7.6 kyr, the carbonate content decreased with increasing lake water levels. This can be explained by gradual water freshening under low evaporation conditions and enhanced connection between Lake Qinghai and Lake Gahai. On the centennial scale, however, the carbonate content varied significantly and was positively correlated with Lake Gahai's water level. Such a variation is probably due to the periodically lower lake water levels and a stronger influence of terrestrial elastic material, which contributed to the dilution of the carbonate content under centennial cool and dry periods. Therefore, in order to advance our understanding of past hydroclimatic variations in the climatically sensitive region, information across different timescales should be separated
Water depth variation and its impact on carbonate content and oxygen isotopes: A study from a satellite lake near Lake Qinghai over the past 7.6 kyr
No full textThe oxygen isotopic composition of sedimentary carbonate (delta O-18(carb)) provides information on the regional water balance between precipitation and evaporation in a lacustrine system. A volume effect was proposed to explain the abnormally low delta O-18(carb) values in Lake Qinghai on the northern Tibetan Plateau, under the conditions of high evaporation and low water levels, as observed during the early Holocene. Volume effect theory states that the small volume of the lake and its sensitivity to isotopic signals from freshwater discharge control the delta O-18(carb) values. In this study, we present 7.6-kyr records of carbonate content and oxygen isotopes from Lake Gahai, a small and saline satellite lake near Lake Qinghai. The records demonstrate that the water level and lake size of Lake Gahai considerably changed over the past 7.6 kyr, and the volume effect was responsible for the delta O-18(carb) variations. The records also suggest contrasting responses of carbonate precipitation to water depth across different timescales. For example, over the past 7.6 kyr, the carbonate content decreased with increasing lake water levels. This can be explained by gradual water freshening under low evaporation conditions and enhanced connection between Lake Qinghai and Lake Gahai. On the centennial scale, however, the carbonate content varied significantly and was positively correlated with Lake Gahai's water level. Such a variation is probably due to the periodically lower lake water levels and a stronger influence of terrestrial elastic material, which contributed to the dilution of the carbonate content under centennial cool and dry periods. Therefore, in order to advance our understanding of past hydroclimatic variations in the climatically sensitive region, information across different timescales should be separated
Application of Ecosystem Service Bundles and Tour Experience in Land Use Management: A Case Study of Xiaohuangshan Mountain (China)
No full textWith the deterioration of human-terrestrial relations and the intensification of global warming, development in all countries is facing difficulties. Whether in highly urbanized countries or in rapidly urbanizing developing countries such as China, the research on ecosystem services (ES) and land use management has attracted increasing attention. The general management of land use unilaterally pursues economic benefits and neglects ecological benefits, which aggravates the disparity between ecological development and the economic benefits of land resources. How to strike up a balance between ecologic protection and economic development remains a difficult problem during urbanization. It may be a better choice to formulate regional development strategies by combining natural conditions with humanistic and social tendencies. Identifying regional cultural ecosystem services (CES) and other important ES while performing zoning planning for regional land use can be a viable approach in land use management. Here, our study quantitatively evaluates the tourism experience of Xiaohuangshan Mountain (XHSM) and various ES, including recreation, biodiversity, history, aesthetics, soil conservation, surface water regulation, and soil nutrition. All ES were classified into four bundles for XHSM. Different ES bundles generated are suitable for different land use management methods and development forms according to their outstanding ES. The results show that quantifying and mapping regional ES bundles can provide the necessary information to support a win-win solution and provide decision support for land and spatial planning in areas with different social and ecological characteristics
Exploring the Influences of Temperature on "H-Shaped" Glycerol Dialkyl Glycerol Tetraethers in a Stratigraphic Context: Evidence From Two Peat Cores Across the Late Quaternary
No full textUnusual "H-Shaped" branched and isoprenoidal glycerol monoalkyl glycerol tetraethers (GMGTs, or H-GDGTs) have been found in peat, lake, and ocean sediments. A survey of recent samples from a modern global peat database suggested that there is a relationship between the abundance of H-GDGTs relative to regular GDGTs and temperature. However, this relationship has not been widely explored, including in a historical, stratigraphic or geological context. Here, we report the abundance and distribution of H-iso- and H-brGDGTs in two (Hani and Gushantun) peat cores from northeastern China through the late Quaternary (last 15 kyr) to examine whether the relationship between temperature and the relative abundance of H-GDGTs is preserved downcore. The results indicate that high relative abundances of H-brGDGTs are associated with high (or increasing) reconstructed mean annual air temperature (MAAT(peat)), albeit with considerable divergence in some intervals. On the other hand, high relative abundances of H-isoGDGTs are generally associated with low (or decreasing) MAAT(peat). These findings are partly inconsistent with the observations from the modern database of globally distributed peats, which showed that the abundance of both (br- and iso-) H-GDGTs is positively correlated with temperature. The deviation in the relationship between H-isoGDGTs and temperature suggests that additional factors, for example pH and shifts in archaeal community related to hydrology, exert an influence on the abundance of H-isoGDGTs on the long-term
Rapid warming has resulted in more wildfires in northeastern Australia
No full textWildfires, or bushfires, are one of the most destructive natural disasters in Australia, which can cause many deaths of stock, native animals, sometimes humans, and huge impacts on infrastructure. Reconstructing past wildfires and exploring the links between wildfires and climate are essential for understanding the dynamics of wildfires and for predicting future risks. In this study, the frequency of wildfires in northeastern Australia over the past 25,000 years was reconstructed from the charcoal records preserved in peat and lake sediments. The results showed that the frequency of wildfires were relatively low during the cool last glacial period and the warm mid Holocene, indicating that the stable mean climate conditions, whether cool or warm, would not independently initiate increased wildfires in northeastern Australia. The most frequent wildfires occurred during the last deglaciation period, when Earth's climate warmed and the warming rate was the highest over the last 25,000 years, before recent anthropogenic warming. It suggested that the rapid global warming may greatly increase the likelihood of dangerous wildfires in northeastern Australia during the last deglaciation. The wildfires reactivated over the most recent 4000 years, coinciding with amplified climate variability and probably an expansion of human activity. The rapid warming of global climate during the last deglaciation period is an ideal analogue for current anthropogenic global warming. The comparison between fire count and temperature changes in Australia since 2003 also showed that the fire frequency in Australia in recent years is more closely correlated with the warming amplitude, rather than mean temperature. Our results implied that the wildfire risk in northeastern Australia may increase further under the expected accelerating global warming, if human management systems does not intrude. Wildfire modeling could benefit greatly by considering the relationship of fires with dimate variability rather than only with stable climate scenarios. (C) 2021 Elsevier B.V. All rights reserved
Biodegradation of Crude Oil Under Low Temperature by Mixed Culture Isolated from Alpine Meadow Soil
No full textPetroleum hydrocarbons have been worldwide concern contaminants because of their mutagenicity and carcinogenicity. The potential biodegradation of petroleum hydrocarbons at low temperatures is important for petroleum contamination remediation in cold region. In this study, a mixed cold-adapted bacteria flora JY, including seven petroleum-degrading strains (B1, H1, H2, H3, R1, R2, and S), was isolated from Alpine Meadow soil. Based on their 16S rRNA sequence analysis, B1, R1, and H3 were identified as Arthrobacter sp.; R2, S, H1, and H2 were identified as Rhodococcus sp., Pseudomonas sp., Stenotrophomonas sp., and Sphingobacterium sp., respectively. The mixed flora demonstrated 53.68% of total petroleum hydrocarbons (TPH) removal of the contaminated water (1 g oil L-1) after 30 days of incubation under 10 degrees C. In the degradation process, alkanes were more preferred to be degraded by JY than polycyclic aromatic hydrocarbons (PAHs) and other polar component. During this period, the abundant bacteria in the flora were transformed from alkane degraders of Rhodococcus sp. and Sphingobacterium sp. to PAH degraders of Pseudomonas sp. and sheltered Arthrobacter sp. This study verified that a cold-adapted mixed culture JY isolated from alpines meadow soil was capable in degrading TPH under low temperature through flora cooperation