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101.
Liquid chromatography–mass spectrometry (LC–MS) analysis of glycerol dialkyl glycerol tetraethers (GDGTs) from sediment and soil samples has become a widely adopted approach for reconstructing past ocean and continental climate variables such as temperature and pH. The LC–MS data used for constructing these GDGT climate proxies are taken directly from the peak area values of individual GDGT [M+H]+ ions, often determined from manual peak integration due to unreliable computer integrators in commercial software, particularly in cases of complex baselines, asymmetric peak shapes and peak coelution. Manual integration is not only time consuming, but also prone to user induced inconsistency when individuals utilize different criteria for peak/baseline definition. To overcome these problems, we have developed a user friendly, graphical user interface (GUI) programmed in the MATLAB environment, allowing users to efficiently and reproducibly perform batch processing and peak integration of LC–MS data. The program, “TEXPRESS” v1.0 (“tetraether index express”), incorporates modern chemometric based techniques for baseline definition and deconvolution of complex chromatographic peaks and we show that LC–MS data processed using the TEXPRESS toolbox are in strong agreement with results obtained from manual peak integration. We provide a general overview of the concepts and architecture of the TEXPRESS toolbox and discuss the advantages of chemometric based peak integration methods for processing branched and isoprenoid GDGT LC–MS data. 相似文献
102.
In the present study, Eastern Inner Mongolia (EIM) and the North China Plain (NCP) during the Qing Dynasty (1644–1911) were selected as study areas. Based on records of agricultural exploitation, settlement expansion, and revolts obtained from the Veritable Records of the Qing Dynasty (a collection of official records), a collection of proxy data reflecting historical social change in EIM was gathered. The social response in EIM to the immigrants from the NCP, who were mainly destitute and homeless refugees and came into EIM under the acquiescence or even with the encouragement of the government in and after a severe flood or drought, was analysed by comparing the data on climatic factors as well as changes in governmental policy. The results indicated that social response was significantly dependent on phase changes. In the 18th century, immigrants from the NCP promoted the reclamation of EIM, which was a pastoral region throughout the 17th century and displayed agricultural prosperity, settlement expansion, and positive regional interactions. However, from the beginning of the 19th century, agriculture declined and settlement slowed. Immigrants intensified local social contradictions in EIM, which led to a series of armed revolts and collapse in the late 19th century. This transformation was affected by both natural and human factors, especially periodic fluctuations in temperature, which significantly affected land use and environmental capacity in EIM by controlling the location of the agro-pastoral transitional zone, and the implementation and repeal of quarantine policy, which immediately affected the extent of immigration in EIM. 相似文献
103.
M. Rodrigo-Gámiz F. Martínez-Ruiz F.J. Jiménez-Espejo D. Gallego-Torres V. Nieto-Moreno O. Romero D. Ariztegui 《Quaternary Science Reviews》2011,30(15-16):2018-2034
Eolian input fluctuations and paleoceanographic conditions in the western Mediterranean have been reconstructed by using a multi-proxy approach to infer climate variability for the last 20,000 yr. A sediment core from the East Alboran Sea basin provides high-resolution geochemical, mineralogical and grain size distribution records from the Last Glacial Maximum onward. The accurate chronology obtained, closely related with the North Greenland Ice core Project, has provided a detailed paleoclimate reconstruction at the centennial–millennial time scale. Mineral and chemical compositions as well as sediment grain size distribution have been used to establish both fluvial and eolian input variations, deep-water current intensity, and ventilation and productivity conditions at the time of deposition. During the cold period Greenland Stadial-2a, the analyzed proxies evidence significant climate oscillations. Redox proxies, showing marked Mn/Al and Fe/Al peaks, as well as granulometric parameters, support major changes in thermohaline circulation, with active circulation triggered by the Western Mediterranean Deep Water formation. Ba/Al ratios and the presence of authigenic barite point to high productivity during the Last Heinrich event. At this time, Zr/Al, Si/Al and Ti/Al ratios as well as quartz and palygorskite contents also corroborate dryer conditions in the Alboran borderlands, with a major reorganization of atmospheric circulation at the beginning of the deglaciation and during the Last Heinrich event. In contrast, a decreasing trend in the Zr/Al ratio and increasing Mg/Al, K/Al and illite + chlorite/kaolinite ratios would indicate enhanced river runoff and supporting lower eolian dust input and wetter periods during the Bölling–Alleröd. Short-term and abrupt climate oscillations such as the Intra-Alleröd Cold Period are likewise reflected by minor yet conspicuous changes in eolian proxies. During the Younger Dryas, we distinguish an initial cold and dry phase, with major westerlies intensity, thermohaline reactivation, and high productivity levels, and a second wetter phase characterized by sporadic rainfalls over poorly vegetated surrounding continental areas. Then, during the Holocene, alternating phases of major humidity and aridity were recorded by major fluctuations in detrital input. These are also correlated with recurrent forest cover declines reported from pollen records, with a noteworthy early decline in the African Humid Period. During the Holocene, an initial demise of the Last Organic-Rich Layer is also evidenced, tentatively associated with aspiration forces promoted by intense thermohaline circulation through the Gibraltar Strait. 相似文献
104.
105.
本文在关联度定义的基础上,利用测井资料,依据测井地质评价方法和准则,提出了关联分析评价砾岩储层的方法、技术和软件。通过二连哈南油田夫特构造上10多口井的评价处理,论述了这一分析技术在砾岩储层上的评价方法、处理实例及应用效果。 相似文献
106.
107.
通过实地考察和对收藏标本的细致研究,以获取第一手资料的方式,文章客观地评价了中国古人类学研究者的工作业绩和历史局限,认为在中国发现的东亚早期人类的新证据为探讨人类起源的单极和多极理论提供了新的可能;东亚人的古老性是目前科研工作的关键问题,必须利用各种手段,对此予以尽可能准确的界定。与中国学者合作研究人字洞遗址、龙骨坡遗址和东谷坨遗址的结果说明中国的考古遗址具有多样性,各遗址的石器相互间差异性很大,与同一时期非洲的模式不同,在这里可以找到更加有趣的材料来认识早期人类的方方面面,因此,应以最严谨的态度和最高的注意力对待中国的考古发现。此外,结合中国古人类、旧石器遗址和古气候学的研究资料,文章从宏观地理学的角度阐述了旧石器时代阿舍利和勒瓦娄哇两个典型的文化现象及其发展脉络,探讨了旧石器时代东亚和西亚之间的关系,对中国旧石器文化的发展模式及其与西亚乃至全球的关系提出了个人的独到见解;着眼于研究早期工业技术的发现地、创新地及其传播地点等问题认为,中国同西欧一样,在地理环境和人类生存方面都处于孤立无援的境地,其技术的发展亲历了在本土发明、从境外引进和向外输出等不同阶段,它们不愧是穿越时空来追随技术变革的两大实验场。文章 相似文献
108.
《Quaternary Science Reviews》2007,26(17-18):2247-2264
In the semiarid loess regions, slackwater deposition of overbank flooding over the piedmont alluvial plains was episodic and alternated with dust accumulation and soil formation throughout the Holocene. The records of past hydrological events are therefore preserved within the architecture of loess and soils and are protected from subsequent erosion and destruction. Several Holocene loess–soil sequences with the deposits of overbank flooding over the semiarid piedmont alluvial plains in the southeast part of the middle reaches of the Yellow River drainage basin were investigated by field observation, OSL and C14 dating, measurement of magnetic susceptibility, particle-size distribution and chemical elements. This enables the reconstruction of a complete catalog of Holocene overbank flooding events at a watershed scale and an investigation of hydrological response to monsoonal climatic change as well. During the Holocene, there are six episodes of overbank flooding recorded over the alluvial plain. The first occurred at 11,500–11,000 a BP, i.e. the onset of the Holocene. The second took place at 9500–8500 a BP, immediately before the mid-Holocene Climatic Optimum. After an extended geomorphic stability and soil formation, the third overbank flooding episode came at about 3620–3520 a BP, i.e. the late stage of the mid-Holocene Climatic Optimum, and the floodwater inundated and devastated a Bronze-age town of the Xia Culture built on the alluvial plain, and therefore the town was abandoned for a period of ca 100 years. During the late Holocene, the alluvial plain experienced three episodes of overbank flooding at 2420–2170, 1860–1700 and 680–100 a BP, respectively. The occurrence of these overbank flooding episodes corresponds to the anomalous change in monsoonal climate in the middle reaches of the Yellow River drainage basin when rapid climate change or climatic decline occurs. During at least the last four episodes, both extreme floods and droughts occurred and climate departed from its normal condition, which was defined as a balanced change between the northwestern continental monsoon and southeastern maritime monsoon over time. Great floods occurred as a result of extreme rainstorms in summers caused by rare intensive meridianal airflows involving northwestward moving tropical cyclone systems from the Pacific. These results could be applied to improve our understanding of high-resolution climatic change, and of hydrological response to climatic change in the semiarid zones. 相似文献
109.
110.