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1.
泥炭沉积物和泥炭地演化过程可以提供植被和气候变化历史的丰富信息.为了重建青藏高原东部全新世泥炭地发育、植被和气候变化,我们对若尔盖盆地一支泥炭岩芯进行了高分辨率的孢粉、烧失量和碳沉积速率分析.研究结果显示,当地泥炭发育起始于距今10.3ka,在早、中全新世繁盛,之后开始退化.若尔盖盆地全新世植被以高山草甸为主,周边山地针叶林在10.5~4.6ka曾数次扩张,之后迅速退缩.泥炭性质、孢粉组合主成分分析等揭示了研究区10~5.5ka气候温暖湿润,晚全新世气候相对冷干.其中,10.2~10、9.7~9.5、8.7~8.5、7.7~7.4、6.4~6、5.5~5.2、4.8~4.5、4~3.6、3.1~2.7、1.4~1.2和0.8~0.6ka时段,若尔盖地区发生了多次快速的泥炭地退化、针叶林扩张和气候变冷等事件.青藏高原东部地区全新世植被与气候的长期变化受控于太阳辐射及其主导的温度与亚洲夏季风强度的变化,而百年尺度的快速变化事件可能受到了季风减弱事件和北半球高纬度地区温度异常的调制作用.  相似文献   

2.
通过对比中国东部沙漠/沙地典型地层序列的年代和古环境代用指标,文章揭示了中国东部沙漠-沙地全新世以来的地表环境变化特征及其对古气候变化的响应.风沙-古土壤沉积序列中一系列的古环境代用指标和光释光测年数据显示:(1)库布齐沙漠大规模现代沙丘景观形成于全新世时期;并在4~2ka期间普遍发育古土壤,指示了该时段区域降水量或有效湿度增加并促进了植被生长,风沙活动减弱,进而导致有机质累积、土壤发育;最近2ka沙丘大规模的扩张除了受自然因素影响,还与人类活动密不可分,丰富的沙源和人类活动共同促成了该沙漠现代景观的形成.(2)浑善达克沙地现代沙丘景观可能形成于12ka左右,而在此之前浑善达克沙地西部应是一个大湖;在9.6~3ka期间,浑善达克沙地比现代明显湿润,普遍发育古土壤,然而风沙活动并未完全停止;全新世湿润期在该沙地可能具有穿时性,沙地东部气候条件的转好早于西部.(3)呼伦贝尔沙地的古土壤早在14.5ka便开始发育,可能一直延续到最近2ka.中国东部各个沙地的古土壤发育具有高度的空间异质性,甚至各个沙地内部不同地点的古土壤发育时间也不一致,但是总体上中全新世(尤其是在7.5~3.5ka)各个沙地趋于固定,风沙活动强度显著减弱.近十年来中国东部沙地的古环境记录数量迅速增长,但是已经发表的数据数量与中国东部沙地广大的空间范围仍然不匹配,要全面理解中国北方风沙活动与气候变化的关系还需对更多的风沙沉积剖面进行深入研究.  相似文献   

3.
吉林向海沼泽湿地典型剖面沉积及年代序列重建   总被引:12,自引:0,他引:12  
沼泽湿地发育过程中堆积的各类沉积物真实地记录下区域环境演变与沼泽湿地发育过程。本文以无尾河下游漫流区——向海沼泽湿地为研究对象,对其典型沉积剖面结构、沉积物容重、年龄指标、沉积速率等多项沉积记录进行了综合剖析。结果表明:沼泽沉积物的层序关系可以揭示沼泽的形成途径及环境变化;溪边沼泽接受更多的矿质沉积物;1880-1885年该区域出现河道变迁的痕迹;向海沼泽湿地沉积速率与典型的河口三角洲类似,体现了河口尾端湿地的特点;近50年来,向海沼泽湿地沉积速率急剧上升,其原因可能与解放后该流域人类活动增强、植被破坏、水土流失严重有关,在时间上,与流域上游大型露天煤矿开采时段有较好的耦合性。  相似文献   

4.
通过研究四会地下古森林沉积剖面总有机碳及细根的碳同位素组成,揭示珠江三角洲地区在中晚全新世4.5~0.6ka BP期间的气候和地理环境变化特征.研究结果表明:在4.5—0.6ka BP期间,该地区的主要植被类型为C3植被.古森林在4ka BP左右于湿地环境中开始发育,在3ka BP左右与湿地同时消失,表明在3ka BP左右该地区的气候可能发生过急剧的变化.模拟结果显示:在3.5-3ka BP期间,该地区大气CO2浓度上升,气候有变暖的趋势;3~1.2ka BP期间的地层^14C年代呈现大的跨度,这可能与新构造运动过程中地层抬升并遭到强烈剥蚀有关.在1.2~0.6ka BP期间,该地区为陆相沉积环境,植被的生物量日渐减少.古森林的消失可能与在3ka BP左右研究区域气候变干有关,热带辐合带的南移可能是导致气候变化的主要机制.  相似文献   

5.
理解过去生态系统对气候变化的响应是评估未来气候变化影响的关键.在全新世气候逐渐变化背景下,萨赫勒-撒哈拉生态系统经历了由萨瓦拉到荒漠的突变.这样的非线性响应现象是否具有普遍意义仍需深入研究.本研究基于38个高质量的化石孢粉记录,系统分析了全新世中亚地区植被与气候的关系.结果显示全新世中亚地区的植被发生了两次大的突变,一次在早全新世(突变Ⅰ,"建立式"突变),另一次在晚全新世(突变Ⅱ,"崩溃式"突变),全新世中期则较稳定.然而这些植被突变无法与任何已知的气候突变事件相关联,并且不同区域发生植被转型的时间表现出异步性,显示出与当地降水量变化密切相关.这些植被突变可归因于植被响应轨道驱动的气候渐变的阈值效应.早全新世在轨道驱动下降水量增加,较湿润的区域首先达到植被"建立"的阈值,而在较干旱的区域明显较晚才达到该阈值.与之相反,晚全新世时在轨道驱动下降水量降低,首先在较干旱的区域达到阈值,导致植被"崩溃",而在较湿润地区延后达到阈值.另外,4.2kyr BP左右的干旱事件以及人类活动干扰对植被的崩溃退化也起到了一定的作用.上述认识得到了现代孢粉-气候关系分析以及生态系统模拟结果的支持.这些结果暗示未来气候变化一旦达到阈值将导致干旱生态系统产生突变.  相似文献   

6.
吉兰泰盐湖沉积物孢粉记录的季风边缘区全新世气候演化   总被引:1,自引:1,他引:1  
全新世气候具有不稳定性,且存在着区域差异,在季风边缘区尤为显著.因此,本研究选取季风边缘区吉兰泰盐湖沉积物的孢粉记录并结合AMS14C测年结果,对该地区全新世的古植被演化及古气候变化历史进行了重建.结果表明,在全新世阶段,该地区植被类型未发生变化,以干旱的荒漠植被为主.早全新世(10.5 8.5 cal ka BP),以蒿属孢粉为主,伴随出现少量藜科、禾本科及麻黄属孢粉,蒿藜比(A/C比值)相对稳定(4.11左右),指示全新世早期气候逐步转湿的过程,在8.5 cal ka BP,蒿属孢粉数量下降且被藜科孢粉取代,指示一次明显气候干旱事件;中全新世(8.5 3.5 cal ka BP),蒿属孢粉含量增加及藜科孢粉含量降低,A/C比值在7.1 cal ka BP左右达到峰值,指示该地区中全新世气候最为湿润;晚全新世(3.5 cal ka BP至今),藜科孢粉含量增加且超过早全新世,A/C比值低至3.66,区域呈现明显的干旱化趋势.此外,结合吉兰泰盐湖沉积物矿物组成结果,发现中全新世湖泊沉积物中,钙芒硝大量出现,一定程度上指示降水量增多所带来的淡水注入,与孢粉指标指示该阶段湿润的结果一致.通过区域对比,发现吉兰泰地区在全新世时期的气候演化模式与东亚季风区具有较好的一致性,表明该地区受到东亚夏季风的影响较大,尤其是在中全新世,东亚夏季风增强,带来较多的降水,气候湿润.  相似文献   

7.
新疆艾比湖地区湖泊沉积记录的早全新世气候环境特征   总被引:29,自引:0,他引:29  
通过干旱区封闭湖泊艾比湖沉积物的多环境代用指标分析, 重点对全新世早期气候环境演化特征进行了研究. 孢粉组合及地球化学指标表明, 研究时段(8.0 ~ 11.5 cal kaBP)温度总体偏低, 初期(11.5 ~ 10.6 cal kaBP) 温度较高且降水较多; 早全新世向中全新世转换时期(8.9 ~ 8.0 cal kaBP )气候波动显著. 尤其是, 3层泥炭沉积显示了艾比湖地区早全新世气候的强烈不稳定性. 泥炭的发育程度及其同位素、孢粉分析数据都暗示, 8.2 cal kaBP, 8.6 cal kaBP, 10.5 cal kaBP的气候状况具有显著的冷湿特征, 可视为早全新世的3次冷湿事件.  相似文献   

8.
全新世初期气候的数值模拟研究   总被引:1,自引:1,他引:1       下载免费PDF全文
本文尝试用一个完全耦合的大气-海洋-植被模式(Atmosphere-Ocean-Vegetation General Circulation Model, AOVGCM)模拟全新世初期的地球气候.模拟结果表明,耦合模式成功地再现了全新世初期复杂气候条件下的基本特征,为研究这一时期的气候状况提供了重要的模型支持.就全球平均而言,11ka BP冬季地表气温比现代约低1.6 K,夏季比现代低约0.3 K;大气温度从低层到高层有不同的表现,高层反映了太阳辐射的重要作用,而低层气候对下垫面(如冰川、植被和海洋等)的影响比较敏感.从区域分布来看,11 ka BP冬季大部地区比现在偏干,但热带太平洋和南半球少部地区降水偏多;夏季大部地区比现在偏湿,亚洲和非洲季风偏强,主要的季风区降水偏多.  相似文献   

9.
浑善达克沙地的光释光年代序列与全新世气候变化   总被引:4,自引:0,他引:4  
浑善达克沙地具有对气候变化响应敏感和生态环境脆弱的特点,是研究环境变化的理想地区.相对于黄土而言,沙质沉积是近源、在沉积期堆积速率快,有可能记录了某些时间段千年时间尺度的干旱事件.应用光释光测年技术,对浑善达克沙地东北.西南断面上具代表性的10个沙丘和沙/黄土剖面进行了年代测试,获得了35个样品的光释光年龄;结合野外地层观察分析和粒度、磁化率等测试,得到了浑善达克沙地全新世干旱事件和相对湿润期的气候变化记录:在距今9.9~8.2ka期问,沙地发育厚层粗砂层,沙丘处于活动状态,气候干燥,植被覆盖度低;在距今8.0~2.7ka期间,沙地发育有多层浅灰一灰黑色砂质土壤,沙丘总体上处于固定.半固定状态(也含有短时段的沙丘活化的干旱事件),指示气候较之前明显湿润,植被相对茂密;2.3ka以来,沙地沉积物以粗砂堆积为主,沙丘又重新活化,气候总体上为干旱.通过对沙丘沉积记录和沉积产状的分析,发现浑善达克沙地在全新世早期、8.2ka前后以及小冰期时期,气候较为干旱,植被盖度小,沙丘活化;在“隋唐暖期”和“中世纪温暖期”,气候较湿润,植被发育良好,沙丘固定.具有绝对释光年龄控制的沙丘沉积记录表明,全新世浑善达克沙地多次千年时间尺度的气候事件可能是全球气候变化的区域响应.  相似文献   

10.
河西走廊花海古湖泊全新世白云石的发现及其环境意义   总被引:4,自引:3,他引:1  
通过对河西走廊花海古湖泊沉积物的X衍射分析发现,全新世期间有明显的白云石沉积.岩性、沉积过程、石膏以及Fe3+含量的变化表明,花海湖全新世白云石沉积环境以还原环境为主,即还原环境利于白云石的形成,为白云石的成因研究提供了新的证据.白云石作为碳酸盐矿物,可以反映湖水盐度,但并非直接指示了湖水的咸化.随着湖水盐度的进一步增加,在硫酸盐型湖泊中,白云石含量随盐度的增加而相应减少,表明利用白云石分析湖水盐度时需要结合其他矿物进行分析.结合石膏含量的变化,花海湖全新世时期白云石含量的变化可以揭示该区域湖水盐度的变化.在10.478.87 cal ka B.P.早全新世时期,湖水的盐度较高,气候由干向湿转变;8.87 cal ka B.P.时期,有大量石膏沉积,显示了湖水盐度的进一步升高,气候干旱;随后湖水相对淡化,气候湿润;5.50 cal ka B.P.至今,沉积出现间断,气候逐渐干旱.  相似文献   

11.
Large numbers of peatlands were developed in volcanic landform regions, which would provide valuable long-term records of lake–mire ecosystem shifts and act as significant carbon pool in regional carbon cycle. To investigate lake–mire ecosystem transformations and driving mechanisms in volcanic landform regions, the developmental history of Gushantun peatland in northeast China was reconstructed in this study. Results indicate that Gushantun peatland initiated in the deepest portions of the basin, and subsequently experienced expansions outward. Peat initiated from approximately 12 ka cal. bp to present. The developmental patterns of Gushantun peatland can be divided into four stages: the stable stage 1 (12–10 ka cal. bp ), maximum stage (10–7 ka cal. bp ), stable stage 2 (7–4 ka cal. bp ) and stable stage 3 (4–0 ka cal. bp ). The possible forcing mechanisms for the development of Gushantun peatland were different during different periods. From 12 ka cal. bp to 10 ka cal. bp , autogenic process was probably the major controlling factor for the expansion of this peatland. From 10 to 7 ka cal. bp , flat basin morphology was the major influence factor for fast expansion. However, the development of Gushantun peatland was probably controlled by the dual effects of high moisture and autogenic process during the period of 7 to 4 ka cal. bp . From 4 ka cal. bp to present, steep basin morphology was the major influence factor, while moisture might be the secondary factor for development of Gushantun peatland. These features indicate that lake–mire ecosystem transforms in volcanic landform regions of Changbai Mountains were probably triggered by the complex effects of autogenic process, hydroclimate and underlying basin morphology. © 2020 John Wiley & Sons, Ltd.  相似文献   

12.
龙陵-瑞丽断裂(南支)北段晚第四纪活动性特征   总被引:5,自引:0,他引:5       下载免费PDF全文
遥感影像解译和野外地质地貌调查表明,龙陵-瑞丽断裂(南支)北段是以左旋走滑为主兼张性正断的区域性活动断裂。根据一些断错地貌点的大比例尺填图、实地测量及其年代学分析,确定了该断裂为全新世活动断裂,断裂晚更新世以来的平均水平滑动速率为2.2mm/a,平均垂直滑动速率为0.6mm/a;全新世以来的平均水平滑动速率为1.8~3.0mm/a,平均垂直滑动速率为0.5mm/a。断裂晚更新世以来的滑动速率在不同的时间尺度上变化不大,反映了该断裂晚更新世以来的活动强度比较平稳  相似文献   

13.
Changes in the vegetation and climate of the westerly-dominated areas in Central Asia during the Holocene were interpreted using pollen-assemblages and charcoal data from a 300-cm-long sediment core of the Sayram Lake,northern Xinjiang.Accele-rator Mass Spectrometry(AMS) radiocarbon dating methods were applied to bulk organic matter of the samples.Artemisia spp./Chenopodiaceae ratios and results from principal component analysis were used to infer that the lake basin was dominated by desert vegetation before ca.9.6 cal.ka BP,which suggests a warm and dry climate in the early Holocene.Desert steppe/steppe expanded during 9.6-5.5 cal.ka BP,indicating a remarkable increase both in the precipitation and temperature during the mid-Holocene.Desert vegetation dominated between 6.5 and 5.5 cal.ka BP,marking an extreme warmer and drier interval.The steppe/meadow steppe recovered,and temperatures decreased from 5.5 cal.ka BP in the late Holocene,as indicated by the increased abundance of Artemisia and the development of meadows.Holocene temperatures and moisture variations in the Sayram Lake areas were similar to those of adjacent areas.This consistency implies that solar radiation was the main driving factor for regional temperature changes,and that the effect of temperature variations was significant on regional changes in humidity.The evolution of climate and environment in the Sayram Lake areas,which were characterized as dry in the early Holocene and relatively humid in the middle-late Holocene,are clearly different from those in monsoonal areas.Dry conditions in the early Holocene in the Sayram Lake areas were closely related to decreased water vapor advection.These conditions were a result of reduced westerly wind speeds and less evaporation upstream,which in turn were caused by seasonal changes in solar radiation superimposed by strong evaporation following warming and drying local climate.  相似文献   

14.
High-resolution peat humification records were obtained from Dajiuhu of the Shennongjia Mountains and Qianmutian of the Tianmu Mountains to study climate changes in East China. The analyses of pollen, organic matters, TOC, and Rb/Sr indicate a high degree of peat humification and thus strong decomposition of organic matter when climate was dry. Conversely, when climate was humid, the degree of humification is low because peat was preserved in a waterlogged condition. Peat humification from Dajiuhu occurred not only during the Younger Dryas (about 11.4–12.6 cal ka BP), the Bølling-Allerød Warm Period (12.6–15.2 cal ka BP), and the Oldest Dryas (about 15.2–16.0 cal ka BP), but also during the early Holocene (about 11.4–9.4 cal ka BP), the 8.2 cal ka BP cold event, and the Holocene Optimum (about 7.0–4.2 cal ka BP). Both peat humification records since nearly 5 ka BP are consistent, showing that mountain peatland has synchronous responses to the East Asia monsoon-induced precipitation. The LOI data confirm the above observation. The monsoon precipitation since nearly 5 ka BP recorded in these two peat profiles can be divided into three phases. During 4.9–3.5 ka BP, precipitation amount was high but fluctuated greatly. During 3.5–0.9 ka BP, precipitation amount was low. During 0.9–0 ka BP, degree of humification reduced gradually, indicating the increase of monsoon precipitation. Contrast to other high-resolution records from East China monsoon region shows that the monsoon precipitation records of the two peat profiles since nearly 16 ka BP are controlled by a common forcing mechanism of summer solar radicalization in the Northern Hemisphere.  相似文献   

15.
在青藏高原东北隅发育一系列向北东凸出的弧形断裂带.其中最主要的三条断裂带从北到南分别为牛首山-罗山断裂带、香山-天景山断裂带和天祝一海原断裂带。香山-天景山断裂带从上世新以来一直有过活动,并在1709年发生了中卫南7t/2级地震。近期,宁夏地震局在孟家湾村南开挖了一个探槽.揭露出石炭纪的煤系地层逆冲于晚更新世风成沙之上.根据风成沙光释光测年结果表明。此探槽显示的断裂活动时代在距今约26.14±1.08ka.极有可能为22.09±0.4ka与26.14±1.08ka之间.  相似文献   

16.
The dune system in Otindag sand field of northern China is sensitive to climate change, where effective moisture and related vegetation cover play a controlling role for dune activity and stability. Therefore, aeolian deposits may be an archive of past environmental changes, possibly at the millennial scale, but previous studies on this topic have rarely been reported. In this study, thirty-five optically stimulated luminescence (OSL) ages of ten representative sand-paleosol profiles in Otindag sand field are ob-tained, and these ages provide a relatively complete and well-dated chronology for wet and dry varia-tions in Holocene. The results indicate that widespread dune mobilization occurred from 9.9 to 8.2 ka, suggesting a dry early Holocene climate. The dunes were mainly stabilized between 8.0 and 2.7 ka, implying a relatively wet climate, although there were short-term penetrations of dune activity during this wet period. After ~2.3 ka, the region became dry again, as inferred from widespread dune activity. The "8.2 ka" cold event and the Little Ice Age climatic deterioration are detected on the basis of the dune records and OSL ages. During the Medieval Warm Period and the Sui-Tang Warm Period (570-770 AD), climate in Otindag sand field was relatively humid and the vegetation was denser, and the sand dunes were stabilized again. These aeolian records may indicate climate changes at millennial time scale during Holocene, and these climatic changes may be the teleconnection to the climate changes elsewhere in the world.  相似文献   

17.
The depositional history of peat‐dominated wetlands can be used to understand palaeoclimate and palaeohydrology and also constrain the impacts of future climate change. However, in chalkland valleys, seasonal water table fluctuations and a high alkalinity have diminished key environment indicators such as pollen, and there is a need for alternative investigative techniques. The method of Rock‐Eval pyrolysis can track changes in organic matter source and degradation, potentially relating to historic changes in vegetation cover. This is the first Rock‐Eval on cores from a groundwater‐dependent riparian chalk valley wetland combined with radiocarbon dating. The dating showed that the cores represented approximately 4000 years of depositional history. Changes in hydrocarbon chemistry including normal alkane composition of the peat indicated shifts of around 500 to 1000 years between terrestrial and more aquatic species, relating to periods of climate wetness. These climatic shifts are broadly consistent with other evidence from ombrotrophic peatland and lacustrine sediments across northwest Europe. However, the connection between climate wetness and groundwater dependent chalkland wetlands is complicated by external anthropogenically driven factors relating to land use and vegetation cover changes in the catchment. Nonetheless, this study suggests that Rock‐Eval pyrolysis is a useful and cost‐effective tool that can provide evidence for long‐term Holocene groundwater fluctuations. Copyright © 2016 British Geological Survey.  相似文献   

18.
Wetlands of Northeast Asia and High Asia: an overview   总被引:3,自引:0,他引:3  
This review reports background information on wetlands in the Northeast Asia and High Asia areas, including wetland coverage and type, significance for local populations, and threats to their vitality and protection, with particular focus on the relationship of how global change influenced wetlands. Natural wetlands in these areas have been greatly depleted and degraded, largely due to global climate change, drainage and conversion to agriculture and silviculture, hydrologic alterations, exotics invasions, and misguided management policies. Global warming has caused wetland and ice-sheet loss in High Asia and permafrost thawing in tundra wetlands in Northeast Asia, and hence induced enormous reductions in water-storage sources in High Asia and carbon loss in Northeast Asia. This, in the long term, will exacerbate chronic water shortage and positively feed back global warming. Recently, better understanding of the vital role of healthy wetland ecosystems to Asia’s sustainable economic development has led to major efforts in wetland conservation and restoration. Nonetheless, collaborative efforts to restore and protect the wetlands must involve not only the countries of Northeast and High Asia but also international agencies. Research has been productive but the results should be more effectively integrated with policy-making and wetland restoration practices under future climatic scenarios.  相似文献   

19.
The stability of Earth's critical zone is intimately linked with erosion, weathering and vegetation type and density. Therefore, it affects global biogeochemical processes which in turn affect the global climate by absorbing and reflecting solar radiation, and by altering fluxes of heat, water vapour, carbon dioxide and other trace gases through various feedback mechanisms. However, there is a lack of knowledge about how Earth's critical zone processes have changed over time and their link with past monsoon variability, especially in Asia. The study of lake sediments, which contain a suite of inorganic elemental and isotopic proxies, may facilitate the understanding of the Earth's critical zone processes on millennial timescales. Here we reconstruct the history of erosion–weathering–vegetation interactions since ~14.7 ka using geochemical records from a radiocarbon‐dated sediment core from Lake Gonghai in the monsoon‐arid transitional zone of north China. Detrital (Al, Ti, K, Rb) and authigenic (Ca, Sr) elemental records reveal distinct, millennial‐scale, late deglacial‐Holocene erosion and weathering patterns and transitions with the former (latter) elements showing higher (lower) values in warm intervals and vice versa. Chemical Index of Alteration (CIA) molar, a humidity proxy, suggests low humidity during the late deglacial ~11.5–14.7 ka, high humidity during the early‐mid Holocene ~11.5–3.2 ka, and intermediate humidity during the late Holocene interval since ~3.2 ka. The results of cross‐spectral analysis and comparison of our records with other climate reconstructions also suggest a pattern of orbitally‐phased humidity changes in north China. Overall, our results provide evidence for the solar‐forcing of Earth's surface processes in mid‐latitude China under natural climatic conditions. Copyright © 2017 John Wiley & Sons, Ltd.  相似文献   

20.
精河入湖口湿地是新疆艾比湖湿地的重要组成部分.本文通过空间序列代替时间序列的方法,对艾比湖精河入湖口退化湿地不同恢复期的浮游植物群落特征进行分析,结果表明,恢复早期和中期硅藻种类最多,绿藻在密度上占明显优势,恢复近期硅藻为主要优势类群.恢复早期及自然区浮游植物群落结构较为稳定,中期和近期群落结构不够稳定,易受外界环境的...  相似文献   

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