10 research outputs found
Human activity and its impact on the landscape at the Xishanping site in the western Loess Plateau during 4800–4300 cal yr BP based on the fossil charcoal record
The taxonomic identification of fossil charcoal can be a useful archaeobotanical tool, as it can reveal information about prehistoric humans' use of plant resources and other factors. In this study, we quantify the fossil charcoal in a cultural sequence from Xishanping in the western Loess Plateau of China representing 4800–4300 cal yr BP to consider aspects of humans' impact on this landscape. The fossil charcoal assemblages reveal that the relative abundances of Picea, Betula, Acer, Ulmus and Quercus decreased markedly after 4600 cal yr BP. This suggests a marked decline in the mixed coniferous-broadleaved forest after this time. Concurrently, an increasing abundance of Bambusoideae charcoal has been suggested to reflect the expansion of the bamboo forest. The marked changes in the vegetation after 4600 cal yr BP were not obviously influenced by climate; they may be a better reflection of the results of human activity. Furthermore, other genera that provide important resources to humans also increased after 4600 cal yr BP, including Castanea, Cerasus, Padus and Diospyros. It is nearly certain that nuts and berries were an important food resource and that fruit trees were managed by prehistoric humans in the late Neolithic. This work suggests that the scale of prehistoric human impact on the western Loess Plateau landscape during the late Neolithic was much greater than was previously believed.</p
Moisture dynamics in central Asia for the last 15 kyr: new evidence from Yili Valley, Xinjiang, NW China
Based on high resolution palynological investigations and AMS(14)C dating, the continuous lacustrine sediments contained in Yili Valley, Xinjiang provide an opportunity to reconstruct the effective moisture changes for the last 15 kyr in central Asia. The relatively warm and humid climate of the Bolling-Allerod (15-12.9 cal kyr BP) is a generalization, but it seems to show some fluctuations. The time of the Younger Dryas (YD) interrupted the increasing trend of effective moisture in the study region, the climate was cold and relatively dry in the early YD period (12.9-12.0 cal kyr BP), whereas the desert vegetation community appeared around 11.8 cal kyr BP, almost the driest time since the 15 cal kyr BR A sharp increase in effective moisture marked the beginning of the Holocene in the Yili Valley. The early Holocene (10.6-7.6 cal kyr BP) was the wettest time with a developed temperate steppe. A dry climate with desert vegetation arose in the early mid-Holocene (7.6-6.5 cal kyr BP), spanning 1100 years. A second humid phase emerged between 6.5 and 5.2 cal kyr BP, whose vegetation community was represented by temperate steppe. Moisture was reduced again and the climate became drier between 5.2 and 3.3 cal kyr BP when vegetation was dominated by desert steppe in the Yili Valley. Regional comparisons indicate that the moisture changes in Yili Valley were mainly influenced by the North Atlantic Ocean SSTs through the westerlies. The mean position of the Siberian High Pressure cell probably made a great contribution to the drought between 7.6 and 6.5 cal kyr BP. The climate changes were generally consistent between the westerly-dominant central Asia and Asian monsoon regions since the last deglaciation, possibly forced by summer insolation conditions in the Northern Hemisphere.</p
Climate instability during the last deglaciation in central Asia, reconstructed by pollen data from Yili Valley, NW China
An extended pollen record with grain size analysis and AMS C-14 dating is provided for a palaeolake section which is located in an intermountain basin in Yili Valley, Xinjiang, NW China. Covering the late MIS 3, early MIS 2 and the last deglaciation, vegetation variations and climate events are discussed in relation to changes in pollen assemblages and Artemisia/Chenopodiaceae (A/C) ratios. The presence of montane forest-steppe dominated by Picea and Taraxacum indicates a relative humid climate in the study area during late MIS 3 (before 31.5 cal kyr BP). Picea forest disappeared and the vegetation dominated by Chenopodiaceae shows the climate became dry from 31.5 to 14.7 cal kyr BP. The sediments of Last Glacial Maximum (LGM) period are absent in the section probably. Betula-Picea mixed forest occurred at 14.7 cal kyr BP and corresponds to the onset of the warm Bolling period in the North Atlantic. A long dry period was detected from 14.5 to 13.6 cal kyr BP on the basis of the occurrence of Chenopodiaceae desert. A subalpine meadow community dominated by Geranium covered the area during 13.6-13.4 cal kyr BP, suggesting lower temperatures at this time. This may coincide with the Older Dryas (OD). The most humid period in the record occurred between 13.4 and 12.9 cal kyr BP, which coincides with the warm Allerod period. Dry conditions prevailed from similar to 12.9 to 11.7 cal kyr BP in the area, coinciding with the Younger Dryas (YD) in the North Atlantic. Within this period a three-phase climate fluctuation was detected, which can be summarized as follows: a dry early YD (12.9-12.6 cal kyr BP), a slightly moister mid-YD (12.6-12.0 cal kyr BP) and a very dry late YD (12.0-11.7 cal kyr BP). These millennial to century-scale climatic events in Yili Valley correlate well with other palaeoclimate records in North Hemisphere, suggesting that these events probably originate from same mechanisms.</p
Climatic variations over the last 4000 cal yr BP in the western margin of the Tarim Basin, Xinjiang, reconstructed from pollen data
The nature of Holocene climate patterns and mechanisms in central Asia are open areas of inquiry. In this study, regional vegetation and climate dynamics over the last ca. 4000 years are reconstructed using a high resolution pollen record from the Kashgar oasis, on the western margin of the Tarim Basin, central Asia. Ephedra, Chenopodiaceae and Cannabaceae dominate the pollen assemblages, and Chenopodiaceae/Ephedra ratios and percentages of long-distance transported pollen taxa are used to infer regional variations in moisture and vegetation density. Three periods of increased humidity are identified, from ca. 4000-2620 cal yr BP, ca. 1750-1260 cal yr BP and ca. 550-390 cal yr BP and these periods coincide with the respective Holocene Bond Events 2,1 and 0, which are reported in the North Atlantic. Any increase in strength, or southward migration, of the mid-latitude westerlies would result in more precipitation and meltwater on mountains surrounding the study site. Warm and dry conditions are detected between ca.1260 and 840 cal yr BP (AD 690-1110), and cool and wet conditions are detected between ca. 840 and 680 cal yr BP (AD 1110-1270), during the Medieval Warm Period (ca. AD 800-1200). The climate variations in the Kashgar region over the last 4000 years appear to have been dominated by changes to the westerly circulation system and glacier dynamics on surrounding mountains. However, the question of whether the Asian monsoon delivers precipitation to the western Tarim Basin, a region that is influenced by several climate systems, is still open to debate.</p
Vegetation characteristics in the western Loess plateau between 5200 and 4300 cal. BP based on fossil charcoal records
Understanding terrestrial vegetation dynamics is a crucial tool in global change research. The Loess Plateau, an important area for the study of Asian monsoons and early agriculture, poses a controversial question on the potential vegetation and its pattern. Fossil charcoal as direct evidence of wood provides precision in species identification and hence vegetation reconstruction. Charcoals from the Dadiwan and Xishanping sites suggest a great variety of plants between 5200 and 4300 cal. b.p. in the valley area of the western Loess Plateau. The deciduous broad-leaf wood from Quercus, Ulmus, Betula, Corylus and Acer is very frequent and makes up almost half the total abundance ratio of the represented taxa. Meanwhile, some typical subtropical taxa such as Liquidambar formosana, Eucommia ulmoides, Toxicodendron and Bambusoideae, are present at the two study sites. The high abundance of Picea appearing between 5200 and 4300 cal. b.p. suggests the development of Picea forests in the valley of the western Loess Plateau. The assemblages of charcoal indicate that the mixed forest of evergreen deciduous and conifer-deciduous broadleaved trees developed in the valley of the Loess Plateau during the Holocene optimum. Precipitation is the main controlling factor for forest development. The increasing precipitation is the probable reason for the appearance of north-subtropical forests between 5200 and 4300 cal. b.p.</p
Land degradation during the Bronze Age in Hexi Corridor(Gansu, China)
Pollen and charcoal analysis, with high resolution AMS C-14 dating, on two sediment sections in the Hexi Corridor track the process of settlement development and abandonment during the Bronze Age. The evidence shows that agricultural activity during the Bronze Age caused an increase in farmland and a decrease in the abundance of Artemisia grassland in the Hexi Corridor. Land degradation is probably the main cause for decreased agricultural activity and settlement abandonment. Agriculture- induced soil fertility loss and land salinization contributed to the process of land degradation. However, increasing climate aridity around 4000-3500 cal BP is probably the main initiating cause for the contraction of arable land and vegetation degradation in the Hexi Corridor.</p
Subsistence and the isotopic signature of herding in the Bronze Age Hexi Corridor, NW Gansu, China
Dietary patterns at two Bronze Age sites in the Hexi Corridor are investigated by the analysis of stable carbon and nitrogen isotopes in faunal bone collagen. The findings are compared with archaeobotanical remains from one of the sites which include high proportions of millet (Panicum miliaceum and Setaria italica) as well as the western derived cereals wheat (Triticum aestivum), barley (Hordeum vulgare) and oat (Avena sativa). The isotopic data indicate domestic omnivores (Canis and Sus) had diets dominated by millet. Minimally offset delta(15)N values between herbivore and omnivore fauna suggest low consumption of animal protein by omnivores. Diets of herded animal (Bos and Caprinae) included only low proportions of C4 foods, suggesting that these animals were not regularly foddered with millet plants, and that their grazing areas were mostly beyond the agricultural zone. The wide range in delta(15)N values amongst herbivore fauna (4.1 parts per thousand-11.8 parts per thousand) suggests grazing occurred in a variety of ecological zones, and this would be consistent with the occurrence of long-distance transport of livestock in the region.</p
Plant diversity of the Tianshui Basin in the western Loess Plateauduring the mid-Holocene e Charcoal records from archaeological sites
Assessing the potential impact of increased temperature needs examination of robust palaeorecords that contain analogues. The fossil charcoal (anthracological) records from the mid-Holocene archaeological sites can provide palaeo-analogues on the impacts of climate change. The Xishanping and Dadiwan sites were continuously developed during the Neolithic Culture in the Tianshui Basin, western Loess Plateau. A total of 24 samples of fossil charcoal were recovered using a floatation method. At least 100 fragments were examined from each sample, and these fragments were identified following standard procedures, and the results were used to reconstruct the vegetation and plant diversity between 5200 and 4300 cal BP, which was a warm period for the region. The charcoal evidence from the Xishanping and Dadiwan sites confirm that woody plants were widely available, including temperate taxa such as Betula, Ulmus, Quercus, Carpinus, Acer, Corylus and Padus, and typical subtropical taxa such as Bambusoideae, Liquidambar formosana, Castanopsis, Pseudotsuga sinensis, and Eucommia ulmoides. The assemblages of fossil charcoal show that mixed forests of north-subtropical evergreen and deciduous broadleaved trees existed. This is a broader range of woody plants than at present in the Tianshui Basin. This leads to the conclusion that the warmer and increasing monsoon precipitation resulted in a northward shift in the southern vegetation zones. And that the natural botanical diversity between 5200 and 4300 cal BP was also greater than at present in the Tianshui Basin, western Loess Plateau.</p
The impact of early smelting on the environment of Huoshiliang in Hexi Corridor, NW China, as recorded by fossil charcoal and chemical elements
Recent research has greatly increased our knowledge of early human impacts on the environment. Records of fossil charcoal and chemical elements from a bronze smelting site at Huoshiliang, in the Hexi corridor of northwest China, provide material with which to estimate the extent of smelting activity and its impact on the environment. Analysis of the microstructure of wood fossil charcoal is used to identify the types of charred wood and to reconstruct the local vegetation present during the period of smelting. Four wood types were used as firewood for smelting: Tamarix, Populus, Salix, and Polygonaceae. The assemblages of fossil charcoal showed that Tamarix was the most dominant shrub and was widely used as firewood, as a percentage of charcoal it increased from 89% to 97% over the smelting period.</p
Towards sustainable energy. Generation ofhydrogen fuel using nuclear energy
The increasing demand for sustainable energy results in the development of new technologies of energy generation. The key objective of hydrogen economy is the introduction of hydrogen as main energy carrier, along with electricity, on a global scale. The key goal is the development of hydrogen-related technologies needed for hydrogen generation, hydrogen storage, hydrogen transportation and hydrogen distribution as well as hydrogen safety systems. It is commonly believed that hydrogen is environmentally clean since its combustion results in the formation of water. However, the technology currently employed for the generation of hydrogen from natural gas, does in fact lead to the emission of greenhouse gases and climate change. Therefore, the key issues in the introduction of hydrogen economy involve the development of environmentally clean hydrogen production technology as well as storage and transport. The clean options available for hydrogen generation using nuclear energy; such as advanced nuclear fission and, ultimately, nuclear fusion, are discussed. The latter, which is environmentally clean, is expected to be the primary approach in the production of hydrogen fuel at the global scale. The present work considers the effect of hydrogen on properties of TiO2 and its solid solutions in the contexts of photocatalytic energy conversion and the effect of tritium on advanced tritium breeders.</p