太湖14000年来古环境演化的湖泊记录

Two sediment cores, one 396 cm long from west Taihu Lake, another 246 cm long from east Taihu Lake, are interpreted from the analysis of their magnetic susceptibility, total organic carbon, total nitrogen, total pigments, organic carbon isotope, hydrogen index, saturated hydrocarbons, ¹⁴C dating and surficial sediment conditions. The west Taihu Lake core is the longest one studied in this lake so far, and has provided us the most complete environmental and climatic information for this lake. The results from the west Taihu lake core indicate that Taihu Lake has undergone the following stages:from ca.14 300 to 13 300 aB.P. Taihu Lake was in low lake-level, and there existed exposed features from the proxies reflecting arid paleoclimate. From ca.13 300 to 12 400 aB.P. an arid transitional stages occurred with a slightly warmer and wetter climate. From ca. 12 400 to 10 900 aB.P. a period of large climatic fluctuation occurred and from 10900-10 000 aB.P. a warm period developed with deep water and strongly reducing sediments. During ca.10 000-7 200aB.P., a cool transitional period alternating with a warm climate occurred. It was warm and wet during 7 200-5 700aB.P.; some proxies changed violently in 5 050aB.P., reflecting obvious changes in material source and a probable interruption of sedimentation. The east Taihu Lake history from ca. 6 550 to 6 450 aBP, the climate was cold and dry, and gradually turned warm and wet in ca. 6 450-6 050 aBP. It was warm and wet in ca. 6 050-5 800 aBP and had a cold tendency in 5 800-ca. 5 000 aBP. An abrupt change occurred at ca. 5 000 aBP, and the lake sediment in the uppmost part was disturbed by wave action indicating shallow water conditions.     

可可西里库赛湖KS-2006孔矿物组成揭示的青藏高原北部晚全新世气候变迁

通过对可可西里库赛湖KS-2006孔矿物组合的分析表明:库赛湖沉积的碳酸盐为以文石为主的自生碳酸盐,其含量的高低能够指示温度的变化;盐类矿物只是在2150 cal aBP以来才出现,表明湖水盐度增高,与此同时,石英含量的持续增高可能同冷干气候条件下该区风成活动的加强有关.青藏高原北部晚全新世的气候环境演化过程为:377...     

可可西里库赛湖揭示的青藏高原北部近4000年来的干湿变化

通过青藏高原北部可可西里库赛湖KS-2006孔(深637cm)沉积岩芯总有机碳、总氮含量及沉积物粒度变化的研究,恢复了该地区近4000年来的干湿变化历史.结果表明,该地区近4000年来经历了显著的干湿变化,干旱时段出现在3900-3590cal aBP、3320-2630cal aBP、1720-1420cal aBP及1100-840cal aBP期间:湿润时段出现在3590-3320cal aBP、2630-1720cal aBP、1420-1100cal aBP以及840cal aBP之后小冰期有效降水升高的相对湿润时期.区域对比分析表明库赛湖地区近4000年来的干湿变化受亚洲季风影响;同时,该地区存在明显的中世纪暖期及小冰期的三次降温事件记录.     

青海湖全新世硬水效应随时间变化性及其对沉积物~(14)C年龄的校正

通过研究青海湖全新世硬水效应变化与大气~(14)C浓度(X_(atm))之间的关系,确定了湖水溶解无机碳(DIC)与大气~(14)C浓度之比值(X_(DIC)/X_(atm))约为0.790.利用已知X_(atm)随时间变化曲线重建了青海湖全新世的硬水效应,并对沉积物年龄作了相应校正.结果表明,青海湖全新世沉积物(有机质)~(14)C年龄偏老主要缘于湖泊硬水效应,从全新世早期的1000a左右升高到核爆近前的2300a左右,核爆效应之后2005AD又降至1500a左右,其变化至少在很大程度上受控于X_(atm)的波动(对应于以上3个时期,根据X_(atm)所恢复的硬水效应分别为1100a、2150a、1313a).在此基础上,利用硬水效应校正表对青海湖全新世沉积物~(14)C年龄进行了分阶段校正,基于此校正年龄的红度曲线较好地响应了9000-8000cal aBP、6000-5000cal aBP、4200-3800cal aBP、3500-2500cal aBP、1200-1000cal aBP和600-150cal aBP等全球性冷事件.     

内蒙古东乌珠穆沁旗乌拉盖高毕湖泊沉积记录的5万年来环境演变

中国北方季风边缘区的湖泊对环境的反应很敏感,乌拉盖高毕是位于内蒙古高原东北部的一个已干涸的内陆封闭湖泊.研究剖面总厚度为405 cm,根据取得的9个AMS¹⁴C及光释光测年数据,建立了51.9 ka BP以来的年代序列.结合岩性的变化、粒度组分分析、粒度参数(标准偏差、偏度、峰度等)及Rb/Sr比值特征进行了详细的分析,恢复了乌拉盖高毕湖泊沉积记录的5万年来的环境演化过程.将0~405 cm的剖面划分为4个较大的气候阶段:51.9-44.1 ka BP(405~343 cm),气候为干冷期,各环境指标显示为滨湖沉积,湖泊水位较低;44.1-28.5 ka BP(343~130 cm),气候为温湿期,湖泊逐渐扩张,湖泊水位升高;28.5-11.38 ka BP(130~35 cm),气候转冷,湖面萎缩,并在盛冰期出现砂楔,该阶段后期湖泊干涸;11.38 ka BP至今(35~0 cm),气温回升.     

太湖晚冰期—全新世气候、环境变化的沉积记录

本文根据西太湖３．９６ｍ长湖泊岩芯沉积物的地球化学、微体古生物的综合分析,讨论了太湖距今１４００多年来的演化过程,结果表明：１４３００－１３０００ａＢＰ气候干旱,西太湖尚未形成：１３００－１１０３０ａＢＰ降水增加,湖泊形成,但气候偏凉;１１０３０－１０２００ａＢＰ是一个较显著的冷偏湿期,湖泊水位相对较深;１０２００－９５００ａＢＰ为一温干时期;９５００－７２００ａＢＰ是偏暖湿的过渡阶段,内部波动剧     

Holocene vegetational and climatic variation in westerly-dominated areas of Central Asia inferred from the Sayram Lake in northern Xinjiang,China

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.     

巢湖悬浮物中稀土元素(REE)的物源精确示踪作用

通过巢湖南灵钻孔(ACN)的植硅体化石的系统研究,划分出六个植硅体组合带．并根据各植硅体组合带主要成分所反映的生态特征,结合主成分分析法(PCA),恢复了该区中全新世以来的古气候与古环境变化:自5600 aBP以来气候划分为3个相对寒冷期(5600-5200 aBP、4600-3600 aBP、2500-2100 aBP)和3个相对温暖时期(5200-4600 aBP、3600-2500 aBP、2100-1800 aBP);并讨论了各个时期巢湖流域的环境变化．     

黄河下游南四湖地区黄河河道变迁的湖泊沉积响应

黄河下游地区湖泊演化多与黄河河道变迁密切相关,进行高分辨率的湖泊沉积环境的研究,可揭示历史时期黄河下游的河道变迁,本文以南四湖ＤＳ孔为例,探讨河道变迁的湖泊沉响应。     

青海湖QH-2000钻孔沉积物粒度组成的古气候古环境意义

据孢粉记录所划分的气候演化阶段,研究了青海湖QH—2000孔沉积物粒度组成的变化．结果表明,冷干和暖湿气候条件下沉积物的粗颗粒组分明显增多;介于二者之间的气候条件下,沉积物的粒径变化相对较平缓．QH—2000孔沉积物粒度的波动特征表明：晚冰期冰川的消融开始于14300aBP左右;博令(Boelling)暖期是冰川大量消融的时期,冰融水对青海湖的补给结束于博令暖期的晚期,即12000aBP左右;新仙女木冷事件和8200aBP左右的冷事件具有突变性的特点．全新世大暖期结束后,气候在转型过程中具有相对冷暖和干湿的快速波动特征;2100—0aBP间,沉积物粒度的变化特征同人类活动有关．     

西藏扎布耶盐湖水位Winters和ARIMA模型分析

由于温室效应,气温加速上升,我国西部干旱一半干旱盐湖区盐湖水位出现加速下降或上升等变化．藏北高原湖泊众多,但都缺少湖水位的人工观测记录．中国地质科学院盐湖中心自1990年始在西藏扎布耶盐湖建立了长期科学观测站,进行水位动态观测,积累了连续13年珍贵的数据．如何根据湖泊水位历史记录数据,准确的定量预测水位中短期变化,是关系着盐湖资源开发命运的大事．本文用Winters线性和季节性指数平滑法、ARIMA乘积季节模型两种时间序列分析方法,根据西藏扎布耶盐湖1991年1月-2003年12月水位变化的时间序列数据,探讨了两种时间序列数据的预测方法在盐湖水位动态变化预测中的应用．     

河西走廊4200年以来青铜冶炼的元素地球化学记录

金属的使用与冶炼是人类社会发展过程中一项革命性事件。河西走廊地区全新世条湖湖相沉积元素地球化学记录显示,10500-9500cal aBP和8000-7200cal aBP时段Cu、Pb、Zn、Ni元素含量高值区,分别对应了早全新世增温期冰川融水量增加和全新世适宜期季风降水的增强。Cu、As、Pb、Zn、Ni含量在4200-3700cal aBP时段出现最高峰值,另外Cu、Pb、Zn、Ni4种元素在3000-2700和2100-1900cal aBP时段出现较高峰值。4200-3700cal aBP时段元素异常记录了我国西北地区最早的青铜冶炼,As元素是这一时期青铜合金的主要成份。另外,西周时期(3000-2700cal aBP)和汉代(2100-1900cal aBP)Cu、Pb、Zn、Ni元素峰值,可能是先民青铜冶炼的结果。元素地球化学记录不仅可以判定早期青铜冶炼的起迄时间,也提供了甄别不同时代青铜合金元素组成变化的信息。     

黄河中游北洛河宜君段全新世特大洪水及其气候背景研究

通过对黄河中游北洛河的野外考察,在宜君基岩峡谷全新世风成黄土-土壤剖面中发现三层古洪水滞流沉积物(SWD).野外观察和室内实验分析,证明它们是北洛河特大洪水悬移质泥沙在高水位滞流环境下的沉积物.这些古洪水滞流沉积层夹在全新世中期古土壤之内,其每一层记录了一期特大洪水事件.利用古水文学方法恢复了古洪水洪峰水位和流量,确定...     

A case study of the role of climate,humans, and ecological setting in Holocene fire history of northwestern Europe

We present the major results from studies of fire history over the last 11000 years(Holocene) in southern Sweden, on the basis of palaeoecological analyses of peat sequences from three small peat bogs. The main objective is to emphasize the value of multiple, continuous sedimentary records of macroscopic charcoal(macro-C) for the reconstruction of local to regional past changes in fire regimes, the importance of multi-proxy studies, and the advantage of model-based estimates of plant cover from pollen data to assess the role of tree composition and human impact in fire history. The chronologies at the three study sites are based on a large number of 14 C dates from terrestrial plant remains and age-depth models are achieved using Bayesian statistics. Fire history is inferred from continuous records of macro-C and microscopic charcoal counts on pollen slides. The Landscape Reconstruction Algorithm(LRA) for pollen-based quantitative reconstruction of local vegetation cover is applied on the three pollen records for plant cover reconstruction over the entire Holocene. The results are as follows:(1) the long-term trends in fire regimes are similar between sites, i.e., frequent fires during the early Holocene until ca. 9 ka BP, low fire frequency during the mid-Holocene, and higher fire frequency from ca. 2.5 ka BP;(2) this broad trend agrees with the overall fire history of northwestern and western Europe north of the Mediterranean area, and is due to climate forcing in the early and mid-Holocene, and to anthropogenic land-use in the late Holocene;(3) the LRA estimates of plant cover at the three sites demonstrate that the relative abundance of pine played a primordial role in the early and mid-Holocene fire history; and(4) the between-site differences in the charcoal records and inferred fire history are due to local factors(i.e., relative abundance of pine, geomorphological setting, and anthropogenic land-use) and taphonomy of charcoal deposition in the small peat bogs. It is shown that continuous macro-C records are most useful to disentangle local from regional-subcontinental fire history, and climate-induced from human-induced fire regimes, and that pollen-based LRA estimates of local plant cover are more adequate than pollen percentages for the assessment of the role of plant composition on fire history.     

湖泊沉积物14C年龄硬水效应校正初探——以青海湖为例

在深入探讨湖泊硬水效应成因和变化规律的基础上,借鉴海洋碳库效应校正方法,首次利用湖水和大气14C放射性比度之间关系的方法对青海湖沉积物14C年龄进行硬水效应校正,并重建了青海湖硬水效应在过去8 ka中的变化过程.笔者认为,青海湖表层沉积物有机质14C年龄不老于1549 aBP,青海湖硬水效应在7000-1000 aBP期间是逐渐增强的.     

Paleolimnological evidence of limnetic nutrient concentration equilibrium in a shallow, macrophyte-dominated lake

: Paleolimnological techniques were used to infer long-term changes in trophic status of Lake Opinicon (Ontario), a mesotrophic, shallow, macrophyte-dominated lake, and to assess whether these patterns support the hypothesis of 'alternative equilibria' proposed for shallow lake systems. Analysis of the diatom assemblages indicated cold, oligotrophic to mesotrophic, alkaline conditions during the period shortly following deglaciation (>11000 yr BP). With the establishment of an open spruce-woodland (ca. 11000 yr BP), benthic diatoms dominated, indicating shallow waters and the presence of macrophytes. Pieces of aquatic macrophytes also became common in the core. An increase in lake productivity to mesotrophic levels (diatom-inferred [TP] of 23 7g/L) occurred following the transition to a deciduous forest in the catchment ca. 7500 yr BP. Paleolimnological data did not indicate any significant change in limnetic nutrient concentrations resulting from the hemlock decline (ca. 4800 yr BP) or from extensive flooding with the construction of the Rideau Canal (1828-1832). Modest nutrient enrichment of the lake has occurred more recently with increasing agricultural and residential/recreational activities, with a diatom-inferred [TP] increase to 32 7g/L. However, compared to other, similarly-disturbed deep lakes in the area, Lake Opinicon showed much smaller changes in lakewater conditions, still maintaining a clear-water, mesotrophic state and a large macrophyte community.¶The apparent inertia of Lake Opinicon to changes in trophic status, as compared to other deep, near-by, stratifying lakes in southeastern Ontario, supports the 'alternative equilibria' hypothesis. Paleolimnological evidence suggests that Lake Opinicon has been in a clear-water, equilibrium state dominated by macrophytes since early in its development, and has displayed hysteresis to nutrient enrichment. These results may provide lake managers with important information for effective management strategies of shallow water systems in southeastern Ontario.     

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

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.     

全新世镜泊湖粒度特征记录的该地区古降水变化历史

在湖泊沉积与环境演变研究中,粒度参数通常用来反映湖泊水动力条件的变化,进而反映湖面波动状况以及湖区环境有效湿度的变化．镜泊湖JPH-1钻孔沉积物粒度分析表明:全新世以来镜泊湖沉积物粒度的变化呈现明显的粗细交替变化的规律性．结合14C测年,镜泊湖沉积物粒度特征有效地指示了历史时期镜泊湖水动力变化的情况．进而揭示了该地区古降水的变化历史．9300-8540cal aBP,是一个降水较少的偏干旱时期;8540-6350 cal aBP,降水颇丰的湿润时期; 6350-3120cal aBF,气候波动频繁,前期(6350-4800 cal aBP)由湿润向干旱过渡,后期(4800-3120cal aBP左右)又由于早转向湿润,31 20-1 580 cal aBP,降水较多,气候湿润;1 580 cal aBP至今,降水变化波动剧烈,这阶段粒度特征的变化除了与降水的自然变化有关外,还与人类活动的剧烈影响有关系．湖区周围人类活动破坏了原始植被,大量地表裸露,降水冲刷地表作用明显增大,陆源物质被携带人湖,粗颗粒含量显著增多．     

The chronology and stratigraphy of the alluvial terraces of the river Dane Valley,Cheshire, N.W. England

Three groups of alluvial terraces together with the modern floodplain mark the Postglacial development of the middle part of the Dane Valley, Cheshire. These are a High terrace group of late Pleistocene age, a Middle terrace group of late Pleistocene to early Holocene age, a Low terrace of mid–late Holocene age, and a modern (post ca. 1840 AD) floodplain. A chronology of erosion, deposition, and landform development since mid-Holocene times is established in this paper on the basis of terrace morphology, stratigraphy, sedimentology, soil analysis, magnetic mineral analysis, and four radiocarbon dates. After dissection of the Middle terrace during the early to mid-Holocene, a long period of lateral activity by the river was followed by a major aggradation phase, which formed the Low terrace surface. This was followed by dissection during the last ca. 300 years and the development of the modern floodplain since ca. 1840 AD. Various explanations for the changes during the Holocene are considered; the Low terrace aggradation appears to be related to a major phase of mediaeval soil erosion.     

龙感湖地区近3000年来的气候环境变迁

本文通过分析龙感湖沉积物中的色素、孢粉、硅藻研究结果,探讨该区近３０００年来环境气候波动特点,结果表明：３２００－２４００ａＢＰ,色素含量较高,与温度条件较好有关。该带孢粉浓度也最高,阔叶乔木绎种花粉丰富,湿生及水生植物经常出现。总体上为相对暖湿阶段,其中仍有凉湿波动。２４００－１６００ａＢＰ,具体分为两个阶段,前期约２４００－２０００ａＢＰ,ＣＤ、ＴＤ、Ｍｙｘ含量明显较低,水生、湿生草本减少,气