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1.
青藏高原与黄土高原过渡带的甘肃武都万象洞位于现代夏季风的边缘区, 对气候变化极为敏感.通过洞内一支石笋WX40D的6个高精度TIMS-U系定年数据和616个样品的氧同位素测定, 建立了28.3~23.0 ka B.P., 分辨率约为10年的亚洲季风气候变化序列. 石笋δ18O记录揭示Marine Isotope Stage 2 (MIS2)早期东亚季风气候具有10~100 a尺度高频震荡特征, 从中识别出北大西洋Heinrich 2 (H2)特强冷事件, 且记录显示该事件开始于24.6 ka B.P., 呈突发式降温之后持续跌宕式降温变化. 对比研究发现, 万象洞石笋δ18O记录H2事件与葫芦洞、天鹅洞的石笋记录有差别, 但是与湖南金滩湾洞穴石笋δ18O记录、33°N太阳辐射强度以及极地GRIP冰心记录变化趋势一致, 表明季风边缘区气候变化主要受北半球中纬度太阳辐射能背景、北大西洋冰漂碎屑带的扩张以及低纬太平洋海表温度变化等因素的控制, 同时万象洞特殊的地理位置使得区域气候更易受到与极地气候有密切联系的亚洲冬季风和西风环流变化的影响.   相似文献   

2.
Few terrestrial Holocene climate records exist from south‐eastern Europe despite its important geographical position as a transitional climatic zone between the Mediterranean and mainland continental Europe. Here we present new petrographic and stable isotope data for two Holocene speleothems from Modri? Cave, Croatia (44°15′N, 15°32′E), a coastal Adriatic site (120 m inland). Modern meteorological and cave conditions have been monitored for 2 years to understand the links between climate variability and stable isotope time‐series records in speleothems. Typical of a Mediterranean‐type climate, a negative water balance exists between April and September, so that recharge of the aquifer is restricted to the winter months. The weighted mean δ18O of the rainfall is ?5.96‰ (2σ = 2.83), and the weighted mean D/H rainfall value is ?36.83‰ (2σ = 19.95), slightly above the Global Meteoric Water Line, but well below the Mediterranean Meteoric Water Line. Modern calcite from the tops of each stalagmite exhibits δ18O values that are close to isotopic equilibrium with their respective drip water values. Unfortunately, the relatively young ages and low uranium contents (ca. 50 p.p.b.) of both stalagmites hamper the use of U‐series dating. Radiocarbon dates have been used instead to constrain their chronology using a dead carbon correction. Apart from some Isotope Stage 3 material (ca. 55 ka), both stalagmites were deposited during the late Holocene. Climatic conditions during the late Holocene are inferred to have been sufficiently wet to maintain stalagmite growth and any hiatuses appear to be relatively short lived. Inferred changes in the stalagmite diameters during deposition are linked to δ13C and δ18O variations, indicating alternating periods of drier and wetter conditions. Drier conditions are inferred for the late Roman Ages warm period and the mid‐Medieval Warm Period. Wetter conditions are associated with the Little Ice Age. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

3.
位于青藏高原与黄土高原过渡带的甘肃武都万象洞石笋WXSM51和WXSM52提供了MIS 5(118~79kaB.P.)高分辨率的δ18 O记录。研究表明, 万象洞石笋δ18 O值与夏季风强度呈负相关关系, 与我国西南部的贵州董歌洞石笋δ18 O记录有良好的对应关系, 并与高纬度的格陵兰NGRIP冰芯δ18 O记录和65°N太阳辐射强度有很好的一致性, 说明万象洞石笋δ18 O记录了118~79kaB.P.期间亚洲季风强度的变化, 同时也说明东亚季风强度的变化和全球气候变化同步, 而且主要受控于北半球太阳辐射强度的变化。同时它与地中海碳酸盐记录有很好的相似性, 和巴西石笋δ18 O记录在千年尺度上表现出相反的变化趋势, 说明东亚季风区、地中海地区以及巴西季风区之间存在密切的联系, 指示了南北半球气候在千年尺度上存在"跷跷板"(seesaw)现象。万象洞石笋δ18 O记录的MIS 5b与MIS 5a突发性转换, 与NGRIP冰芯δ18 O记录相似, 而与神农架记录存在差异, 说明万象洞地区对亚洲季风强度的响应更为敏感。  相似文献   

4.
Interhemispheric anti-phasing of rainfall during the last glacial period   总被引：1，自引：0，他引：1  
We have obtained a high-resolution oxygen isotopic record of cave calcite from Caverna Botuverá (27°13′S, 49°09′W), southern Brazil, which covers most of the last 36 thousand years (ka), with an average resolution of a few to several decades. The chronology was determined with 46 U/Th ages from two stalagmites. Tests for equilibrium conditions show that oxygen isotopic variations are primarily caused by climate change. We interpret our record in terms of meteoric precipitation changes, hence the variability of South American Monsoon (SAM) intensity. The oxygen isotopic profile broadly follows local insolation changes and shows clear millennial-scale variations during the last glacial period with amplitudes as large as 3‰ but with smaller centennial-scale shifts (<1‰) during the Holocene. The overall record is strikingly similar to, but strongly anti-correlated with, a number of records from the Northern Hemisphere.We compared our record to other precisely dated contemporaneous records from Hulu Cave eastern China. Minima in δ18O (wet periods, intense SAM) at our site are synchronous with maxima in δ18O (dry periods, weak East Asian Monsoon, EAM) in eastern China (within precise dating errors) and vice versa. This anti-phased precipitation relationship between two low-latitude locations may be interhemispheric in extent, based on comparison with records from other sites. Precipitation anti-phasing may be related to north–south shifts in the mean position of the intertropical convergence zone (ITCZ) and asymmetry in Hadley circulation in two hemispheres, associated not with seasonal changes as observed today, but with millennial-scale climate shifts. The millennial-scale atmospheric see-saw patterns that we observe could have important controls and feedbacks on climate within hemispheres because of water vapor's greenhouse properties.  相似文献   

5.
To understand oxygen and carbon stable isotopic characteristics of aragonite stalagmites and evaluate their applicability to paleoclimate, the isotopic compositions of active and fossil aragonite speleothems and water samples from an in situ multi-year (October 2005-July 2010) monitoring program in Furong Cave located in Chongqing of China have been examined. The observations during October 2005-June 2007 show that the meteoric water is well mixed in the overlying 300-500-m bedrock aquifer, reflected by relatively constant δ18O, ±0.11-0.14‰ (1σ), of drip waters in the cave, which represents the annual status of rainfall water. Active cave aragonite speleothems are at oxygen isotopic equilibrium with drip water and their δ18O values capture the surface-water oxygen isotopic signal. Aragonite-to-calcite transformation since the last glaciation is not noticeable in Furong stalagmites. Our multi-year field experiment approves that aragonite stalagmite δ18O records in this cave are suitable for paleoclimate reconstruction. With high U, 0.5-7.2 ppm, and low Th, 20-1270 ppt, the Furong aragonite stalagmites provide very precise chronology (as good as ±20s yrs (2σ)) of the climatic variations since the last deglaciation. The synchroneity of Chinese stalagmite δ18O records at the transition into the Bølling-Allerød (t-BA) and the Younger Dryas from Furong, Hulu and Dongge Caves supports the fidelity of the reconstructed East Asian monsoon evolution. However, the Furong record shows that the cold Older Dryas (OD) occurred at 14.0 thousand years ago, agreeing with Greenland ice core δ18O records but ∼200 yrs younger than that in the Hulu record. The OD age discrepancy between Chinese caves can be attributable to different regionally climatic/environmental conditions or chronological uncertainty of stalagmite proxy records, which is limited by changes in growth rate and subsampling intervals in absolute dating. Seasonal dissolved inorganic carbon δ13C variations of 2-3‰ in the drip water and 5-7‰ in the pool and spring waters are likely attributed to variable degrees of CO2 degassing in winter and summer. The variable δ13C values of active deposits from −11‰ to 0‰ could be caused by kinetically mediated CO2 degassing processes. The complicated nature of pre-deposition kinetic isotopic fractionation processes for carbon isotopes in speleothems at Furong Cave require further study before they can be interpreted in a paleoclimatic or paleoenvironmental context.  相似文献   

6.
基于豫西老母洞LM2石笋8个高精度230Th年龄,449个氧碳同位素,建立了达十年际分辨率的8.2~10.9 ka B.P.亚洲季风变化的δ18O记录序列.老母洞石笋δ18O值最为偏负达-12.0‰,最偏正为-8.2‰,振幅达3.8‰.早全新世10.13~10.9 ka B.P.时段内,河南西部老母洞石笋和东石崖石笋,陕西九仙洞C996-2石笋δ18O曲线揭示该时段内季风稳定,而中国南方的衙门洞石笋、三宝洞石笋和极地冰芯GRIP记录揭示该时段季风逐渐增强;同时季风达到顶峰的时期也不相同,进一步说明中国南北方早全新世10.13~10.9 ka B.P.时段季风演变过程的差异,可能与中国南北方气候的响应机制有关.从早全新世平均分辨率10年的LM2石笋记录中识别出8.2 ka,9.5 ka,10.2 ka和10.9 ka显著弱季风事件,尤其是8.2 ka和9.5 ka事件.对比分析老母洞与已发表的高分辨率石笋δ18O记录发现:石笋所揭示的某些冷事件发生时间在亚洲季风区存在差异,主要表现在事件内部变化特征及趋势上.LM2石笋δ18O曲线并没有明显记录9.3 ka弱季风事件,而是在9.3~9.6 ka B.P.左右记录了一个弱季风事件,与DSY09(2009)、Y1、HS-4记录相似,表明在该时段内存在季风的减弱事件,但是氧同位素传输的复杂性,使其在南北方表现不同.此外,在LM2石笋δ18O的8.2 ka B.P.开始时段,氧同位素曲线阶段性下降,且变幅达3‰,与Zhang等研究万象洞石笋提出的“中国8 200阶段”吻合,表明中国北方地区的8.2 ka事件是阶段性的事件,而南方的石笋氧同位素记录揭示的8.2 ka事件并未表现出阶段性特征,其原因有待于更多北方高精度石笋记录来进一步研究.LM2石笋氧同位素记录进行功率谱分析发现:在短尺度上季风变化与太阳活动密切相关,这与近年来对早全新世极端气候变化研究的驱动机制是一致的,早全新世亚洲季风的演化与太阳活动变化引起的太阳辐射能量的变化和北半球高纬气候的变化状况有关.  相似文献   

7.
The isotopic compositions of oxygen and carbon and trace concentrations of magnesium and strontium in speleothems formed in limestone caves respond to climate changes outside the caves. Measurements of these properties on a stalagmite from Shihua Cave near Beijing, China, allowed reconstruction of the regional changes in precipitation, temperature and nature of vegetation. Over the last ∼ 500 years, there were fourteen precipitation cycles with a periodicity of 30–40 years, which may well reflect fluctuations in the strength of the East Asian summer monsoons reaching northeastern China. Relative to the mean temperature of this time interval, the period 1620–1900 AD was cold and periods 1520–1620 and 1900–1994 were warm. Over the last ∼ 3000-years, about eight wet/cool-dry/warm climatic cycles of 300–400 years duration occurred, the latest wet/cool half cycle corresponding to the Little Ice Age. The δ13C record registers the anthropogenic activities of fossil fuel CO2 combustion in recent decades and regional deforestation between 13 and 16 centuries when Beijing was bustling with palatial constructions and being developed into the world’s most populated city.  相似文献   

8.
A 7-cm long aragonite stalagmite, FR0510-1, from Furong Cave, Chongqing, was dated by 210Pb and 230Th methods, revealing a-2000-year record of climate history under the influence of the East Asian Monsoon. The FR0510-1 record resembles Dongge Cave DA record on 10–100-year scales, but quite different from the Wanxiang Cave WX42B record, indicating that while stalagmite δ18O record represents local/regional moisture change, spatial variability of the monsoonal rainfall over eastern China must take into account. During the past 2000 years, climate in Chongqing was relatively wet in the intervals of 50 BC–AD 250, AD 1150–1450 and AD 1600–1950, and relatively dry during the periods of AD 250–1150 and AD 1450–1600. Dry conditions were prevailing over the Medieval Warm Period, whereas wet climates were dominant during the most time of the Little Ice Age in Chongqing area.  相似文献   

9.
We present the updated Holocene section of the Sofular Cave record from the southern Black Sea coast (northern Turkey); an area with considerably different present-day climate compared to that of the neighboring Eastern Mediterranean region. Stalagmite δ13C, growth rates and initial (234U/238U) ratios provide information about hydrological changes above the cave; and prove to be more useful than δ18O for deciphering Holocene climatic variations. Between ～9.6 and 5.4 ka BP (despite a pause from ～8.4 to 7.8 ka BP), the Sofular record indicates a remarkable increase in rainfall amount and intensity, in line with other paleoclimate studies in the Eastern Mediterranean. During that period, enhanced summertime insolation either produced much stronger storms in the following fall and winter through high sea surface temperatures, or it invoked a regional summer monsoon circulation and rainfall. We suggest that one or both of these climatic mechanisms led to a coupling of the Black Sea and the Mediterranean rainfall regimes at that time, which can explain the observed proxy signals. However, there are discrepancies among the Eastern Mediterranean records in terms of the timing of this wet period; implying that changes were probably not always occurring through the same mechanism. Nevertheless, the Sofular Cave record does provide hints and bring about new questions about the connection between regional and large scale climates, highlighting the need for a more extensive network of high quality paleoclimate records to better understand Holocene climate.  相似文献   

10.
The oxygen and carbon stable isotope compositions of cave speleothems provide a powerful method for understanding continental climate change. Here, we examine the question of the regionality of this isotopic record and its linkage with the marine isotopic record in the Eastern Mediterranean (EM) region. The study presents a new, accurately dated 250-kyr δ18O and δ13C record determined from speleothems of the Peqiin Cave, Northern Israel. Its comparison with the continuous 185-kyr isotopic record of the Soreq Cave speleothems from Central Israel reveals striking similarities. Thus, a strong regional climatic signal, brought about by variations in temperature and rainfall amount, is reflected in both cave records. Low δ18O minima in the Peqiin profile for the last 250- to 185-kyr period (interglacial marine isotopic stage 7) match the timing of sapropels 9 to 7 and are indicative of high rainfall in the EM region at these times. The combined Soreq and Peqiin δ18O record for the last 250 kyr excellently matches the published Globigerinoides ruber (G. ruber) marine δ18O record for the EM Sea, with the isotopic compositional difference ΔG.ruber-speleothems remaining relatively constant at −5.6 ± 0.7‰, thus establishing for the first time a robust, exploitable link between the land and the marine isotopic records. The correspondence of low δ18O speleothem values and high cave water stands with low G. ruber δ18O values during interglacial sapropel events indicates that these periods were characterized by enhanced rainfall in the EM land and sea regions. By use of sea surface temperatures derived from alkenone data as a proxy for land temperatures at the Soreq Cave, we calculate the paleorainfall δ18O values and its amounts. Maximum rainfall and lowest temperature conditions occurred at the beginning of the sapropel events and were followed by decrease in rainfall and increase in temperatures, leading to arid conditions. The record for the last 7000 yr shows a trend toward increasing aridity and agrees well with climatic and archeological data from North Africa and the Middle East.  相似文献   

11.
石笋氧同位素记录具有明显的2万年周期,其他记录中广泛存在的10万年周期是否在石笋中有所表现目前还鲜有报道。通过对湖北三宝洞20支石笋的铀同位素数据的分析研究发现,石笋初始234U/238U值在序列连续性较好的640.3~299.6 ka B.P.时间段有强烈的10万年周期特征。在间冰期和冰期时,初始234U/238U值分别呈增大和减小状态。初始234U/238U值的10万年周期与全球冰量、黄土磁化率、黄土平均粒度和大气CO2变化有良好的对应关系。这些对应关系表明全球冰量、大气CO2对喀斯特区地球化学元素富集和迁移作用有重要影响。石笋氧同位素的显著岁差周期独立于石笋微量元素、高纬冰量和全球温室气体变化,暗示了太阳辐射变化对中低纬水汽环流的直接影响。石笋初始234U/238U与氧同位素、太阳辐射在冰消期时的对应变化支持北半球太阳辐射能量变化对冰期-间冰期旋回的调控作用。  相似文献   

12.
Speleothem carbon and oxygen isotopic records from Onondaga Cave, south-central Missouri, and Beckham Creek Cave, north-central Arkansas, are compared with the Cupola Pond and Oldfield Swamp pollen series from southeastern Missouri and the Rodgers Shelter and Modoc Shelter vertebrate biostratigraphic sequences from central Missouri and southwestern Illinois. Similar, and roughly contemporaneous, shifts between deciduous forest and steppe indicators throughout the Holocene are revealed in each database. These independent proxies record steppe conditions between approximately 9000 and 1500 cal yr B.P. A shift toward lighter speleothem carbon may reflect a change from warm and dry to cool and dry conditions between 4500 and 3000 yr B.P. The sensitive response of speleothem δ13C to changes in vegetation emphasizes their importance as paleoclimate records in an area containing few other millenial-scale climate proxies.  相似文献   

13.
米兰科维奇冰期旋回理论:挑战与机遇   总被引：7，自引：6，他引：7       下载免费PDF全文
丁仲礼 《第四纪研究》2006,26(5):710-717
米兰科维奇理论认为,北半球高纬夏季太阳辐射变化是驱动第四纪冰期旋回的主因。这个理论的核心是单一敏感区的触发驱动机制,即北半球高纬气候变化信号被放大、传输进而影响全球。最近,由于大量高分辨率及精确定年的气候变化记录的获得,从以下4个方面构成了对米氏理论的挑战:1)一些低纬地区并没有明显的10万年冰量周期,而是以2万年岁差周期为主,表明北半球冰盖的扩张、收缩变化并没有完全控制低纬区的气候变化;2)在最近几次冰消期时,南半球和低纬区的温度增高,要早于北半球冰盖的融化,表明冰消期的触发机制并非是北半球高纬夏季太阳辐射;3)大气CO2浓度在第2冰消期的增加同南极升温相一致,表明该时大气CO2浓度增加亦有可能早于北半球冰盖消融;4)南半球的末次冰盛期有可能早于北半球。这就说明单一敏感区触发驱动机制已难以圆满解释所有观察事实,天文因素控制下轨道尺度气候变化机制研究正面临理论突破的新需求和新机遇。  相似文献   

14.
利用树轮稳定碳同位素组成（δ１３Ｃｔ）序列可以较为灵敏地记录降水变化的特性，以长白山树轮δ１３Ｃｔ序列为降水变化的自然记录体，探讨太阳活动对长白山乃至东北季风气候区降水变化的影响。研究指出：１）２００年来长白山及东北季风气候区降水变化有准２２年的周期性波动；２）东北季风气候区里，东南季风强弱变化具有准２２年的周期性振荡；３）直接控制东南季风强弱变化的西太平洋副热带高压的活动可能具有相应的准２２年周期  相似文献   

15.
The oxygen isotope signature (δ18O) of stalagmite SI3 collected from Shizi Cave in north‐east Sichuan Province provides an Asian Summer Monsoon (ASM) record in Central China for the period 54–46 ka. The SI3 δ18O record clearly shows a negative δ18O excursion centred around 49.4 ka, which was reported in Hulu Cave in East China but not identified in the speleothem records from South‐west China. As a whole, this record displays a higher coherence with the two Hulu records from East China than with the speleothem δ18O records from South‐west China, suggesting that at 54–46 ka, Central China was influenced more by the East Asian Summer Monsoon than by the Indian Summer Monsoon. It also displays a significant negative δ18O excursion at 47.5–46.6 ka, which is not clearly documented in two other speleothem δ18O records previously reported from South‐west China. This suggests that details of the Greenland interstadial 12 warrant further investigations in future in monsoonal China. The SI3 δ18O record displays more significant centennial‐scale variations than the other four speleothem δ18O records from East and South‐west China, which may be due to the fact that the study site is closer to the north‐west boundary of the ASM and more sensitive to variations of the ASM than East and South‐west China. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

16.
There has been much recent debate about Holocene climate variation in the monsoon region of China, especially the temporal pattern of variations in precipitation, the time-transgressive nature of the Holocene precipitation maximum, and the extent to which variations in regions influenced by the Indian Summer Monsoon (ISM) and the East Asian Summer Monsoon (EASM) have been synchronous. We summarize and compare carbonate oxygen-isotope records (δ18Ocarb) from ten lakes within the present-day ISM region. We discuss their paleoclimate significance considering the present-day moisture source, isotopic composition of precipitation and the hydrological setting. The δ18Ocarb records are controlled mainly by the isotopic composition of lake water, which in turn is a function of regional Precipitation/Evaporation (P/E) balance and the proportion of precipitation that is monsoon-derived. We normalized the δ18Ocarb data and used these records to generate an integrated moisture index. This index, along with oxygen-isotope records from speleothems and carbon-isotope records (δ13Corg) from peats within the monsoon region, suggests that Holocene climate was broadly synchronous across the monsoon region and, within the limits of accuracy of the existing age models, provides no strong evidence for previously-proposed anti-phasing of the ISM and the EASM. Stable-isotope records from lake sediments and peat bogs have excellent potential for providing high-quality paleoclimate data for monsoon Asia, and complement high-resolution speleothem sequences, which are only found in certain localities.  相似文献   

17.
Variations in speleothem δ13C values can reflect changes in overlying surface vegetation, which, over historical time scales, may represent the influence of human activities. Here, we examined δ13C variations in two stalagmites growing for the last 2200 years in Shennong Cave, Jiangxi Province, SE China. The two δ13C records corroborate well one another and show a prominent 6‰ enrichment of the δ13C values from AD 700 to 1100. The isotopic equilibrium for modern calcite and negative correlation between δ18O and δ13C values along the growth axis suggest that the influences of kinetic fractionation are negligible. Varied correlations between Mg/Ca and Sr/Ca ratios and divergent changes between δ13C values and Mg/Ca and Sr/Ca ratios from AD 700 to 1100 reveal that the prior calcite precipitation (PCP) and water–rock interaction did not dominate the increase of δ13C values. It is plausible that the obvious δ13C variation was largely influenced by the changes in vegetation cover overlying the cave. Our δ13C results, together with the records of climate and human activity from historical documentary records, suggest that: (i) prior to AD 700, small fluctuations in relatively light δ13C values reflect the presence of lush forest coverage above the cave, which was minimally disturbed by human activities; (ii) during AD 700–1100, the drastic increase in δ13C values indicates persistent and massive deforestation associated with large‐scale immigration into northern Jiangxi after the Rebellion of An & Shi (AD 755–763) in the Tang Dynasty and the subsequent development of agriculture and economic activity; and (iii) since AD 1100, fluctuations in relatively high δ13C values suggest that local vegetation during the last millennium has been sparse. Since the Rebellion of An & Shi, southeastern China was progressively developed, coincident with deforestation and vegetation deterioration caused by human disturbance in the form of deforestation and cultivation.  相似文献   

18.
Asynchronous Holocene climatic change across China   总被引：1，自引：0，他引：1  
A review of Holocene climatic variations in different parts of China shows that they were asynchronous. Proxy data from ice cores, pollen, loess, lacustrine sediments, and changes of sea and lake levels demonstrate that many warm and cold oscillations have occurred in China during the Holocene, including a most important climatic event known as the “Holocene optimum,” a milder and wetter period, and that the duration and amplitude of the optimum period, as well as its start and end times, differed in different parts of China. Uplift of the Tibetan plateau over the past millions of years led to the development of the monsoon climate and to complex atmospheric circulation over continental China during the Holocene. As a result, the Holocene optimum began and terminated earlier in high-altitude regions of western China than at lower elevations in eastern China, and the amplitude of the variations was lower in the east. This suggests that the western higher-altitude areas were more sensitive to climatic change than were the eastern lower-altitude areas. Holocene climatic records in the Dunde and Guliya ice cores do not correspond. Inverse δ18O variations between the two cores indicate that the effects of climate and atmospheric processes on the stable isotopes at the two sites differed. The correlation between the isotopic composition of carbonates in lake deposits in western China and climatic variations is similar to that in the ice cores. The climatic resolution in ice cores and lake sediments is higher than that in other media. The lack of precise correspondence of climatic records constructed on the basis of proxy data from different parts of China is a result of the different locations and elevations of the sampling sites, the different resolutions of the source material, and the varied climatic conditions within China. Further work is needed to confirm both the conclusions and the inferences presented here.  相似文献   

19.
The low-latitude hydrological cycle is a key climate parameter on different timescales, as it contributes to various feedback processes. Modelling studies suggest that the interhemispheric insolation contrast is the major factor controlling the cycle, although the influence of glacial conditions and the phase relationships relative to insolation forcing remain undetermined. In this work, we studied precipitation variability over Papua New Guinea (PNG, 3°S) for the past 400 ka using terrigenous fractions transported by the Sepik River to the Western Pacific Warm Pool (WPWP). A multi-decadal to centennial resolution of the elemental content was obtained using X-ray fluorescence scanning of a marine sediment core using an age model based on 14C dates and benthic foraminiferal δ18O. Indicators of the coarse river particulate fraction (bulk and CaCO3-free basis Ti concentrations, the log intensity ratios of Ti/K and Ti/Ca) displayed a dominant 23 ka periodicity without a clear glacial–interglacial trend. Our precipitation records showed a tight relationship with local summer insolation (3°S, January) with time-dependent lag of 0 to 4 ka. They were generally in anti-phase for U–Th dated Chinese speleothem δ18O records. Based on an analogy to modern climate, we propose that precipitation over PNG was primarily determined by interhemispheric insolation contrast, and the contribution of austral fall/winter precipitation added second-order variability that formed the lags. For the last four climate cycles, the WPWP hydrological cycle was closely associated with the eastern Asian monsoon, and the influence of glacial conditions on the low-latitude hydrological cycle was estimated to be limited.  相似文献   

20.
北京猿人洞堆积旋回与黄土和深海气候旋回对比   总被引：8，自引：0，他引：8       下载免费PDF全文
黄培华 《地质科学》1993,28(4):305-311
北京猿人洞13个堆积层可划分为7个堆积旋回。每个旋回早期的堆积层(砂、粉砂、粘土和钙扳层),含有暖温带气候特征的哺乳动物和孢粉组合;晚期的堆积层(洞穴角砾与巨砾层),含有温带较干冷气候特征的哺乳动物和孢粉组合。堆积层年代测定数据表明北京猿人洞7个堆积旋回形成于更新世中期,年代为128-730ka,与中国黄土层L2-S7,相当,可与深海氧同位素阶段6-19和气候旋回C-I对比。北京猿人在此洞断续生活了约35万年,即从距今约60万年的第5堆积旋回(δ18O第14阶段)至距今约25万年的第2堆积旋回(δ18O第8阶段)。  相似文献   

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