巢湖杭埠河流域湖相沉积物多指标揭示的全新世以来环境演变

在巢湖杭埠河流域中的古湖盆中心——三河圩区获取28.6 m长的湖相岩芯（SZK1507孔）,利用AMS¹⁴C测年技术建立可靠的地层年代序列,通过对SZK1507孔738 cm以上段湖相沉积物平均粒径、磁化率、总氮（TN）、总有机碳（TOC）及C/N的综合分析,高分辨率重建了巢湖杭埠河流域全新世以来的古环境演变过程.结果表明,本区域的环境变化过程可以分为4个阶段,阶段Ⅰ（约10050—9700 cal.a B.P.）与阶段Ⅲ（约9250—5300 cal.a B.P.）气候较为湿润,巢湖水位较高,平均粒径、磁化率值较低,TN、TOC、C/N也偏低;阶段Ⅱ（约9700—9250 cal.a B.P.）与阶段Ⅳ（约5300 cal.a B.P.以来）气候干燥,巢湖水量减少,水位降低,平均粒径、磁化率值、TN、TOC、C/N均较高.一些全球范围内显著发生的气候突变事件在SZK1507孔沉积记录中也有体现,如9.3、8.2和4.2 ka B.P.事件等.将巢湖杭埠河流域10000 cal.a B.P.以来的平均粒径、磁化率、TN、TOC、C/N沉积记录与全新世以来的北纬30°夏季太阳辐射量、太阳黑子数、火山喷发对大气中硫酸盐含量贡献率等进行对比,发现巢湖杭埠河流域全新世气候突变事件主要受控于北半球夏季太阳辐射量变化、太阳活动以及火山活动等因素,并与它们之间复杂的响应机制有关.     

青藏高原中部全新世气候变化的湖泊沉积地球化学记录

通过青藏高原中部兹格塘错湖泊沉积物总碳(TC)、总有机碳(TOC)、总氮(TN)、总硫(TS)、氢指数(HI)、氧指数(OI)和有机质的碳同位素(δ¹³C_org)等多项指标的综合分析, 在判断沉积物中有机质来源的基础上, 根据各指标的变化特征阐明了各自的气候指示意义, 建立了兹格塘错全新世以来的古气候演化序列. 10100 cal a BP兹格塘错地区进入全新世, 全新世早中期为暖湿气候特征, 在8600~8400和7400~7000 cal a BP发生两次强烈冷事件; 中晚全新世以来气候变冷变干. 这一气候演化过程与其邻近的错鄂的研究结果相近, 代表了青藏高原中部全新世的气候演化特点. 青藏高原中部全新世气候变化主要受太阳辐射控制.     

太阳辐射驱动气候变化的泥炭氧同位素证据

已证明太阳辐射水平变化的历史可从树轮14 C含量变化的历史来认识 .所报道的 5 0 0 0a高分辨的泥炭植物纤维素氧同位素 (δ18O)气候代用记录所指示的气候变化对太阳辐射变化的响应关系 .结果表明 ,过去 5 0 0 0a中 34次急速的气候冷暖变化 ,以及气候变化的 86 ,1 0 1 ,1 1 0 ,1 2 7,1 32 ,1 40 ,1 5 5 ,2 0 7,2 45 ,31 1 ,82 0和 1 0 5 0a等周期 ,都与太阳辐射变化和太阳辐射变化的周期有比较好的一对一的响应 .因此 ,结果为数十年至百年尺度的太阳辐射变化驱动气候变化的假说提供了新的证据     

新疆巴里坤湖全新世气候环境变化与高低纬间气候变化的关联

选择位于新疆东北部的封闭湖泊-巴里坤湖作为研究对象,采用常规14C测年建立了该湖一剖面约9400 cal a BP以来的时间序列,对该剖面沉积自生碳酸盐碳（δ13Ccar）、氧同位素（δ18Ocar）、有机碳（TOC）等多代用指标进行了连续小波变换、奇异谱分析.结果表明,全新世以来巴里坤湖地区的气候变化模式具有明显的阶段性变化：9400～8000 cal a BP期间气温偏低且较干旱;8000～6000 cal a BP期间气候环境温凉湿润;6000～2700 cal a BP期间,气候环境在总体上较为暖干,在向全新世晚期演变过程中呈现出降温、增湿的趋势;2700～800 cal a BP期间气温降低,湿润状况有所改善;800 cal a BP以来气候环境偏干.巴里坤湖全新世气候变化过程与周边区域古气候记录具有较好地一致性.研究发现,全新世以来研究区的气候环境不仅可能受到了北大西洋地区气候变化的影响,同样可能与来自热带低纬过程的海-气相互作用有关,特别是自全新世中期以来,逐渐增强的El Nio/La Nia-South Oscillation（ENSO）活动对研究区的气候环境变化可能具有一定的影响.研究还发现,在全新世期间,新疆东北部地区的气候演变可能并非简单地遵循某种单一的气候变化模式,不同气候系统（如西风、季风）在该地区的强弱对比状况可能对此地区气候环境变化模式有重要影响.     

青藏高原东部若尔盖盆地全新世泥炭地发育和植被变化

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.     

孢粉-气候定量重建方法体系的建立及其应用——以青藏高原东部全新世温度重建为例

长时间尺度气候变化的定量重建结果可为理解气候自然变率及其机制提供参考,并为气候模拟提供边界条件与验证.然而,由于已有定量重建方法体系并不完善,许多重建结果的可信度存在很大不确定性.本研究建立了一个基于高质量现代孢粉数据库的定量重建方法体系:包括现代孢粉数据筛选、训练集选择、主控气候因子分析、最优模型建立、评估检验和生态解释等多个步骤.将该方法体系应用于青藏高原东部若尔盖盆地的三个高分辨率孢粉记录,定量重建了研究区全新世温度变化.结果表明,全新世早期最暖月温度(MT_(wa))约为10.4℃,随后温度逐步升高,在8.5～6ka BP达到全新世最高(约11℃).经历了早、中全新世的温暖气候后,温度持续降低1.2℃,在新冰期期间达到全新世温度最低值.除全新世整体变冷趋势外, MT_(wa)还具有明显的500年周期波动,其信号强度随时间有所波动.温度的高(低)值与太阳活动的最大值(最小值)同相位变化,这表明青藏高原东部地区百年尺度气候波动很可能受到了太阳活动的影响.     

晚冰期以来青海湖沉积物多指标高分辨率的古气候演化

通过青海湖沉积物孢粉、碳酸盐、有机C, N和有机δ¹³C等多项指标的综合分析, 建立了青海湖晚冰期以来的高分辨率古气候演化序列. 结果表明, 18.2 cal. ka BP左右为末次冰期盛冰阶进入晚冰期的界限, 自15.4 cal. ka BP起气候开始向暖湿化发展, 7.4 cal. ka BP时达到了暖湿组合的鼎盛期, 4.5 cal. ka BP以后气候又逐步转入冷干. 晚冰期向全新世转换期间气候的冷暖干湿波动十分频繁, 其特征与北大西洋深海沉积、格陵兰冰芯、欧洲地区湖泊沉积以及中国黄土、古里雅冰芯等记录的古气候具有一定的可对比性. 青海湖地区晚冰期以来的古气候演化特征揭示了万年尺度上东亚季风的源驱动力同太阳辐射有关.     

广东湖光岩玛珥湖沉积物漫反射光谱数据反映的全新世以来古环境演化

利用漫反射光谱技术得到湖光岩玛珥湖沉积物的叶绿素a浓度.通过与TOC、Sr/Rb比值和磁化率的对比发现,叶绿素a浓度能够忠实地反映湖泊初级生产力的变化,较高的叶绿素a浓度代表季风较强、降雨量较高,反之亦然.湖光岩玛珥湖沉积物多环境代用指标分析结果显示,湛江地区早全新世季风强盛,中全新世季风迅速衰退.这种全新世季风演化模式与北半球季风区的很多地质记录以及北纬30°变化趋势相似,反映了太阳辐射是湛江地区千年尺度季风演化的主要驱动因素,但是湛江地区的季风演化滞后于太阳辐射变化大约2200 a.叶绿素a浓度记录显示6000 a BP左右季风迅速减弱,这与其他记录显示的季风渐变模式不同.一方面,太阳辐射渐变激发了湛江地区植被-大气圈的负反馈作用,这可能是造成6000 a BP左右气候迅速变干的原因之一;另一方面,沉积速率增加导致的稀释作用放大了叶绿素a浓度下降的趋势.3600 a BP以来的沉积环境可能受到了人类活动的影响.     

中亚东部晚全新世水文气候变化及可能成因

中亚东部水文气候变化对中纬大气环流非常敏感.为了查明该地区水文气候的长期变化及其与大气环流的关系,文章利用位于中天山深水湖泊——赛里木湖钻孔岩芯,在137Cs、210Pb和AMS14C定年基础上,对湖泊岩芯有机碳、有机氮、碳/氮比、碳酸盐含量和粒度等多指标进行了分析,重建了晚全新世以来该地区水文气候变化历史.结果显示,晚全新世以来共发生了4次降水显著增加时期(4000~3780、3590~3210、2800~2160和890~280cal a BP)和1次降水微弱增加时期(1700~1370cal a BP),这与中亚东部地区已有的降水/湿度记录相吻合,表明晚全新世以来该地区具有相似的水文气候变化模式.太阳活动减弱以及整个环北大西洋地区大气环流南移,特别是中纬西风主要路径的南移,可能是中亚东部地区晚全新世水文气候变化的最主要原因.此外,赛里木湖研究结果还揭示了该地区最近100年降水显著增加,但中亚地区未来水文气候如何变化仍需更多不同载体的深入研究.     

湛江湖光岩玛珥湖全新世粒度变化特征及古气候意义

对湖光岩玛珥湖沉积物全新世粒度参数、550℃烧失量和Ti元素含量的变化特征研究后认为:粒度频率特征曲线指示湖光岩玛珥湖沉积物的外源输入部分主要来自其小流域;沉积物粒径的变化主要受降雨量,而不是湖泊水位波动的控制;较粗的粒径指示降雨量增加,较细的粒径指示降雨量降低.湛江地区全新世早期季风强盛,6085 a B.P.以后,季风显著减弱.湖光岩沉积物记录的全新世中期季风迅速减弱的发生时间与全球很多地质载体记录的全新世中期季风迅速减弱时间都非常接近,体现了湛江地区全新世季风演化的全球性.湛江地区6085 a B.P.以后的季风迅速减弱、气候转干很可能与厄尔尼诺活动增强有关.2000 a B.P.以后,粒度参数、550℃烧失量和Ti元素含量的变幅明显增加与人类活动的影响有关,是人类活动和气候因素共同作用的结果.     

The Earth's Climate in the Next Hundred Thousand years (100 kyr)

One of the most striking features of the Quaternary paleoclimate records remains the so-called 100-kyr cycle which is undoubtedly linked to the future of our climate. Such a 100-kyr cycle is indeed characterised by long glacial periods followed by a short-interglacial (10–15 kyr long). As we are now in an interglacial, the Holocene, the previous one (the Eemian, which corresponds quite well to Marine Isotope Stage 5e, peaking at 125 kyr before present, BP) was assumed to be a good analogue for our present-day climate. In addition, as the Holocene is 10 kyr long, paleoclimatologists were naturally inclined to predict that we are quite close to the next ice age. Simulations using the 2-D climate model of Louvain-la-Neuve show, however, that the current interglacial will most probably last much longer than any previous ones. It is suggested here that this is related to the shape of the Earth's orbit around the Sun, which will be almost circular over the next tens of thousands of years. As this is primarily related to the 400-kyr cycle of eccentricity, the best and closest analogue for such a forcing is definitely Marine Isotopic Stage 11 (MIS-11), some 400 kyr ago, not MIS-5e. Because the CO₂ concentration in the atmosphere also plays an important role in shaping long-term climatic variations – especially its phase with respect to insolation – a detailed reconstruction of this previous interglacial from deep sea and ice records is urgently needed. Such a study is particularly important in the context of the already exceptional present-day CO₂ concentrations (unprecedented over the past million years) and, even more so, because of even larger values predicted to occur during the 21st century due to human activities.     

SUR LA PUISSANCE DES CRUES AU JAPON A MADAGASCAR ET A LA REUNION

Abstract

Hydrological modelling has faced the problem of ungauged basins for many years: how does one estimate hydrological characteristics for a river for which there are no data? Whatever the kind of model, it needs at least hydroclimatic input data and discharge data for calibration. However, the Yates model does not need any discharge data for calibration: it is a pre-calibrated model from a vegetation—climate classification map. In the specific context of West and Central Africa, where data are often of poor quality and very scarce, it is interesting to compare the performance of such a model with those of calibrated models, and with observed data. For this study, a platform including different semi-global rainfall—runoff models which allow the estimation of monthly runoff at a spatial resolution of 0.5° × 0.5° was used. The performance of the Yates model is very close to those of calibrated models, so that one can say that this simple model, based simply on a vegetation—climate classification, can be a very useful prediction tool in regions of scarce and unreliable data, such as those of interest to the International Association of Hydrological Sciences (IAHS) initiative on prediction in ungauged basins (PUB). Therefore, this model was applied to a period covering the last 30 years, and to a data set covering the first decades of the 21st century, from a climatic scenario of doubling the CO₂ concentration in the atmosphere. The results show that, in West Africa, where drought conditions have now prevailed for 35 years, water resources should still be decreasing in the future, following the general decreasing trend of rainfall projected by the climatic scenarios.     

A sedimentological proxy indicator linking changes in loess and deserts in the Quaternary

From Yulin, which is located in the transitional zone between the Loess Plateau and the Mu Us desert, to Weinan in the southernmost part of the Loess Plateau, 9 loess sections were studied. Grain size analyses show that the advance-retreat changes of the deserts in northern China may be the most important factor controlling changes in the sand particle percentage of the loess-soil sequences during the last glacial-interglacial period. It is thus suggegted to use the sand grain content of loess deposits as a proxy indicator of desert variations. Applying this indicator to the last glacial loess deposits in the northwestern part of the Loess Plateau reveals that there were many millennial-scale cycles of the desert environments. Project supported by the National Natural Science Foundation of China (Grant No. 49525230)     

A test of a climatic index of dune mobility using measurements from the southwestern United States

The climatic index of dune mobility developed by Lancaster (1988) has been applied to a variety of different environments. The index is, however, untested and unverified. We tested the index by comparison of values of the dune mobility index calculated from climate data with rates of sand transport measured at three stations in Arizona and New Mexico over the period 1985 to 1997. Our results show that changes in measured rates of sand transport closely parallel temporal changes in the dune mobility index. The mobility index is, however, a relatively poor predictor of the magnitude of actual sand transport on a year‐to‐year basis. This discrepancy is probably due to the fact that sand transport rates at these sites are strongly influenced by vegetation cover, the state of which may lag changes in annual precipitation. There is, however, a good relation between the mean annual mobility index and mean annual rates of sand transport. This indicates that the dune mobility index is a valid predictor of the long‐term state of the aeolian system and can be used confidently for the purposes for which it was originally intended. Copyright © 2000 John Wiley & Sons, Ltd.     

末次冰盛期中国气候要素定量重建

古气候定量化是古全球变化研究的核心目标之一.重建末次冰盛期时段((18±2)ka14C)气候变化特征,对理解冰期-间冰期地球气候演化规律具有重要的意义.以往古气候要素定量重建,主要基于现代气候条件下孢粉-气候的统计学方法,因难以有效区分过去气候季节性变化和大气CO2浓度降低对植物生长的影响,导致重建结果可能存在不确定性.本研究基于植物生理过程、新一代古气候定量重建的植被反演方法,考虑上述环境因子对植物生长的影响,利用新完善的中国第四纪孢粉数据库,重建了古气候的空间格局.结果表明,在末次冰盛期,大气CO2浓度降低对中国古气候要素重建结果影响不显著;全国年均温比现在低约(5.6±0.8)℃,最冷月温度和最热月温度分别降低约(11.0±1.6)℃和(2.6±0.9)℃,且中国南方降温幅度达到约(5.5±0.5)℃,接近平均值的水平,年均温变化主要归因于冬季温度的降低;全国年降水量比现在低约(46.3±17.8)mm,其中北方降水减少约(51.2±21.4)mm,年降水变化主要源于夏季降水的减少.与古气候模拟结果的对比揭示,虽然现有模式能较好模拟年均气候模态,但是在季节性变化上与重建结果还有较大的差距,指示未来在提高古气候重建精度的同时需进一步加强古气候模式的季节性气候模拟能力.     

The world's longest continued series of sea level observations

Sea level data from Stockholm, with the initial year 1774, have been recalculated using old information hitherto not taken into account. Since the resultant series of annual mean sea levels is the longest continued one in the world, and of very good reliability, it is published here. Also some results on eustatic changes of sea level, due to changes of climate, are given.     

Climatic variations in the past 140 ka recorded in core RM, east Qinghai-Xizang Plateau

The sequences of climatic evolution are reconstructed by the analyses of δ¹³C and δ¹⁸O of carbonate from core RM in the Zoige Basin since 140 kaB. P. During the Last Glaciation there existed at least seven warm climatic fluctuations and five cold events correlated with the records of ice core and deep sea, and during the preceding last interglacial period there were two cold climatic variations coinciding with the record of ice core GRIP. These results de-pict climatic instability in east Qinghai-Xizang Plateau over the last interglacial period. In addition, the environmental proxies of the carbonate content and pigments indicate the similar results to the stable isotope record from core RM. Project supported by the Chinese Climbing Project (85-029-02-01).     

中昆仑山区封闭湖泊湖面波动及其气候意义

封闭湖泊湖面波动是气候变化很敏感的指示器,其水量平衡特征对此可给予理论证明,进而可将这种灵敏度表示为Z=A_l/A_b=(P_b-E_b)/(E_l—P_l)。中昆仑山区的封闭湖泊自17000a B.P.以来曾经历了三次高湖面,即17000a B.P.前后、12000a B.P.前后及8000—6000a B.P.。其中第一期的高湖面与高山区冰体消融、西风带位置的变动及土壤湿度、太阳辐射值的变化有关,第二次的高湖面是湖泊总体收缩下降过程中出现的相对稳定或短暂回升,第三期的高湖面是全球性温湿气候的产物。理论探讨与实例分析均说明,封闭湖泊湖面波动不仅对无人类观测记录的地质历史时期的气候变化有着重要的指示性,而且可以弥补人类观测资料的不足,是研究气候变化的理想场所。     

鄱阳湖湖泊气候及其围垦后的变化

对鄱阳湖地区30多年的气候资料分析比较得出,鄱阳湖围垦后,年平均气温垦区上升0.11℃,湖区上升0．09℃,年平均最高气温垦区上升0．57℃,湖区上升0．07℃,口最高气温≥35℃的天数垦区年增加10天,湖区年增加4天,年平均最低气温垦区下降0．26℃,湖区上升0．06℃,水汽压和相对湿度,垦区减少0.05hpa和1％,湖区减少0.1hPa和1％,降水量垦区减少95mm,湖区变化不明显,因而,湖区有向干旱陆相盆地气候发展的趋势。     

浅钻岩芯揭示的固城湖4000年来环境演化

对固城湖6.2m深的现代沉积物柱状岩芯进行了放射性同位素、粒度、有机质含量、有机质σ~(13)C和孢粉分析。沉积记录巾各项环境指标的变化表明,4ka以来固城湖经历了高湖面—低湖面—高湖面的显著变化。气候变化是影响湖泊环境演化的重要自然因素,但2.5ka以来人类活动对湖泊演化的影响显得更为明显。特别是2.5ka和1.1ka两次人类对湖泊水系的改造是引起湖泊环境两次突变的主要因素。