若尔盖盆地黄河第一湾河岸沉积地层序列及其成因研究

经过在若尔盖盆地进行全面野外考察,在黄河第一弯岸边发现了沉积序列清晰的、具有代表性的完整沉积地层剖面。通过沉积学和地层学特征和沉积相的观测分析,结合实验室粒度分析、数据处理和测年断代,其结果表明：该剖面底部蓝灰色古湖相沉积层反映出盆地内部在OSL年龄35 ka之前为较深的湖泊。其上覆盖的风沙与泥炭互层,反映出在该区域湖水消失之后,在30 ka之前古湖底出现泥炭沼泽,同时风沙作用盛行。而浊黄橙色古洪水沉积层（OFD1）则反映出在30~27 ka之间,曾经有来自于黄河源区流域的规模巨大的洪水进入若尔盖盆地,在古湖底泛滥并且将其携带的分选良好的细沙与粉沙质泥沙堆积下来。该剖面中部厚度达5~7 m的河漫滩-风沙层,沿着河岸追索,则可见其表现为高低起伏的古沙丘。这表明在末次冰期盛期和冰消期,气候干旱寒冷,黄河已经下切形成其河槽,其河漫滩沉积物被强劲的风力吹扬,形成连绵起伏的沙丘。该层之上所覆盖的浊黄橙色古洪水沉积层（OFD2）,则反映出在全新世初期9.86~8.28 ka之间,来自于黄河源区流域的大洪水再次进入盆地,在黄河第一湾两岸的古湖底沉积了分选良好的细沙质与粉沙质的泥沙。到了全新世中期后,若尔盖盆地风沙作用依然盛行,黄河河槽深切,第一湾两岸接受沙尘暴沉积。在全新世中期的相对温暖湿润气候条件之下,沙尘暴沉积物被改造为亚高山草甸黑土类土壤,成熟度极高。到了全新世晚期以来,风沙作用与沙尘暴沉积过程持续,沙尘暴沉积物也被改造为亚高山草甸黑土层。本文研究对于深入理解黄河源区末次冰期以来环境变化与地表过程演变,以及晚更新世以来的气候水文变化规律具有重要的科学意义。     

末次盛冰期西太平洋海温差异对亚洲夏季风影响的数值模拟

文章利用Zhao等的模拟结果,进一步研究了在末次盛冰期(LGM)情景下汪品先和CLIMAP两种重建海洋表面温度(SST)资料差异对亚洲夏季风的影响。模拟结果表明:在LGM情景下西太平洋海域SST资料的不同对模拟的亚洲夏季风有着十分重要的作用。夏季,与CLGM方案相比,在WLGM方案中,当热带西太平洋SST较暖时,印度地区的大气热量出现显著增加,大气热量的这种变化,使得南非高压、南印度洋经向Hadley环流加强,伴随着索马里越赤道气流加强,也导致了印度季风区纬向季风环流的加强,从而造成了印度夏季风增强、降水增多;与较暖的热带西太平洋相对应,澳大利亚高压和120°E附近越赤道气流减弱,东亚季风区20°N以南经向季风环流加强、20°N以北经向季风环流减弱,指示着一个强的南海夏季风和较弱东亚副热带大陆夏季风。     

Tessellons,topography, and glaciations on the Qinghai-Tibet Plateau

The Qinghai-Tibet Plateau has developed into a vast fortress-like structure that has recently presented a barrier limiting the egress of moisture-bearing air masses. Lower sea levels also affected the climate. This paper examines their effects on the current evidence for the timing of past glaciations, and the development and evolution of permafrost. There are two theories regarding glaciation on the Qinghai-Tibet Plateau(QTP). Kuhle suggested that there was a major, unified ice-cap during the Last Glacial Maximum(LGM), whereas major Chinese glaciologists and others have not found or verified reliable evidence for this per se. There have been limited glaciations during the last 1.1 Ma B.P. but with increasing dominance of permafrost including both primary and secondary tessellons infilled with rock, sand or loess. The East Asia Monsoon was absent in this area during the main LGM, starting at 30 ka B.P. on the plateau, with sufficient precipitation reappearing about 19 ka B.P. to produce ice-wedges. A weak Megathermal event took place between 8.5 and 6.0 ka B.P., followed by Neoglacial events exhibiting peak cold at 5.3–4.7 ka, 3.1–1.5 ka, and the Little Ice Age(LIA) after 0.7 ka. Subsequently,mean annual air temperature has increased by 4 °C.     

GEOMORPHOLOGICAL CHARACTERISTICS AND SIGNIFICANCE OF LATE QUATERNARY PARAGLACIAL ROCK-SLOPE FAILURES ON SKIDDAW GROUP TERRAIN, LAKE DISTRICT, NORTHWEST ENGLAND

ABSTRACT. Eight relict rock-slope failures (RSFs) on Skiddaw Group terrain in the Lake District, northwest England, are described. Five of the failures are rockslides, one is a product of slope deformation, and two are compound features with evidence for sliding and deformation in different sectors. As none appears to have been overrun and modified by glacier ice it is concluded that they all post-date the Last Glacial Maximum (LGM ; c. 21 ± 3 cal. ka bp ). Slope stress readjustments resulting from glacial and deglacial influences are considered to have weakened the slopes, and application of the term paraglacial is appropriate. Permafrost aggradation and degradation, seismic activity and fluvial erosion are among processes that may have contributed to failure at certain sites. The failures are significant as potential debris sources during future ice advances, contributing to valley widening and cirque enlargement and, possibly, for acting as sites of cirque initiation. Previously, Skiddaw Group rocks have been regarded as homogeneous and of limited resistance to the weathering and erosion associated with Quaternary glacial, periglacial and fluvial processes. These characteristics and processes have been used to explain the steep smooth slopes and rounded hills that dominate Skiddaw Group terrain. Rock-slope failure has also helped shape this terrain and should be incorporated in future interpretations of landscape development.     

中全新世和末次盛冰期北大西洋涛动变化及其与亚洲降水的联系:基于MPI-ESM模拟试验

本文利用古气候模式比较计划第三阶段(PMIP3)中MPI-ESM模式模拟输出, 采用主分量分析、回归分析、多窗谱分析等方法, 探讨了中全新世(MH)和末次盛冰期(LGM)北大西洋涛动(NAO)变化及其与亚洲降水的关系。结果表明:MH冬季NAO较现代有轻微增大, 南部高压中心东移; 而LGM冬季NAO明显减弱, 南北气压活动中心转为西南-东北走向。MH冬季强NAO信号可通过海洋记忆效应持续至夏季, 并以准静止Rossby波形式传至东亚地区, 导致乌拉尔山和鄂霍次克海阻高增强、贝加尔湖低压加深, 这种倒"Ω"流场增强有利于冷空气南下, 并通过热成风原理使得副热带西风急流增强, 急流南侧产生上升异常, 有利于该区降水产生; 而LGM时NAO减弱引起夏季倒"Ω"流场减弱, 冷空气南下弱于现代, 使得副热带西风急流减弱, 其南侧产生下沉异常, 最终抑制降水。因此, MH和LGM两阶段的NAO引起大气环流的变化可能对亚洲夏季降水产生影响。     

Approximate General Solution Of The Two-Dimensional Duffing Dynamical System

This paper presents the approximate general solution of the triple well, double oscillator non-linear dynamical system. This system is non-integrable and the approximate general solution is calculated by application of the Last Geometric Theorem of Poincaré (Birkhoff, 1913, 1925). The original problem, known as the Duffing one, is a 1 degree of freedom system that, besides the conservative force component, includes dumping and external forcing terms (see details in the web site: http://www.uncwil.edu/people/hermanr/chaos/ted/chaos.html). The problem considered here is a 2 degree of freedom, autonomous and conservative one, without dumping, and of axisymmetric potential. The space of permissible motions is scanned for identification of all solutions re-entering after from one to nine oscillations and the precise families of periodic solutions are computed, including their stability parameter, covering all cases with periods T corresponding to 4osc/T. Seven sub-domains of the space of solutions were investigated in detail by zooming, an operation that proved the possibility to advance the accuracy of the approximate general solution to the level permitted by the integration routine. The approximation of the general solution, although impressive, provides clear evidence of the complexity of the problem and the need to proceed to larger period families. Nevertheless, it allows prediction of the areas where chaos and order regions in the Poincaré surfaces of section are to be expected. Examples of such surfaces of sections, as well as of types of closed solutions, are given. Two peculiar points of the space of solutions were identified as crossing, or source points from which infinite families of periodic solutions emanate. The morphology and stability of solutions of the problem are studied and discussed.     

天山末次冰期以来干旱化过程的冰川证据

依据天山7个有确切年代学资料的典型地区进行冰川面积和平衡线高度等重建,揭示天山地区末次冰期以来冰川经历的扩张和收缩过程。冰川规模在MIS 4~MIS 3大幅度扩张,形成大规模的复合型山谷冰川和山麓冰川;MIS 2冰川扩张显著,但远不及MIS 4~MIS 3,许多山区形成大型山谷冰川;全新世新冰期NG和小冰期LIA都略有扩张,冰碛垄分布在现代冰川外围,冰川类型与现在一致。冰川平衡线高度的降幅亦表现为MIS 4~MIS 3最大,MIS 2以后降幅递减。MIS 4~MIS 3天山冰川大规模扩张与欧亚冰盖演化,巨大冰前湖泊、广阔的湿地的形成为西风提供更多水气带到天山有关;MIS 2至今,随着欧亚冰盖减小到消失,西风带来的水气渐少,干冷的蒙古高压逐渐加强,制约了冰川规模扩张。     

Short-term climate changes during the Last Glacial–Holocene transition: comparison between Mediterranean records and the GRIP event stratigraphy

This paper presents biostratigraphical and stable isotope data obtained from core CM92–43, which was recovered from the central Adriatic as part of a comprehensive investigation of the palaeoenvironmental history of the basin. The data span the period of the Last Glacial–Holocene (LG–H) transition (ca. 18000 to 8000 GRIP ice-core yr BP). Regional biozones are defined on the basis of characteristic assemblages of planktic Foraminifera, and these are compared with other foraminiferal biostratigraphical schemes from the southern Adriatic and the Tyrrhenian Sea. Variations in relative abundance of selected planktic Foraminifera and in selected pollen types are shown alongside variations in δ¹⁸O and δ¹³C obtained from Globigerina bulloides and relative abundance of Globigerinoides ex. gr. ruber. The data are compared with the GRIP ice-core record and the event stratigraphy scheme based on this record, and it is concluded that the climate forcing mechanisms that controlled climate variations in the North Atlantic region during the LG–H transition also extended their influence into the Mediterranean region over the same period. Copyright © 1999 John Wiley & Sons, Ltd.     

共和盆地末次冰消期以来的植被和环境演变

在青藏高原共和盆地中的内陆湖泊--达连海获取40.92 m长的湖泊岩芯(DLH钻孔),选用植物残体作为测年材料,利用AMS14C测年技术建立可靠的地层年代序列,对岩芯进行孢粉分析,重建该地末次冰消期以来的古植被和古环境。末次冰消期以来达连海周围山地在14.8～12.9Cal ka BP和9.4～3.9 Cal ka BP时段曾发育森林,气候较湿润,达连海附近盆地发育的荒漠草原盖度增加或演化为草原;在15.8～14.8 Cal ka BP、12.9～9.4 Cal ka BP 和3.9～1.4 Cal ka BP 时段该地气候比较干旱,依据干旱的程度周围山地森林退化或消失,盆地内发育盖度较低的荒漠草原或草原化荒漠。1.4 Cal ka BP以来湿度有所增加,发育草原植被类型。依据植被的演替历史推断该地气候的变化历程是15.8～14.8 Cal ka BP 干旱,14.8～12.9 Cal ka BP 湿润,12.9～9.4 Cal ka BP干旱,9.4～3.9 Cal ka BP湿润,3.9～1.4 Cal ka BP干旱,1.4～0 Cal ka BP湿润。达连海的孢粉记录与附近青海湖的孢粉结果对比,发现两地植被发育基本一致。末次冰消期Bølling-Allerød 时期,山地森林发育;新仙女木事件发生时森林萎缩;全新世中期两地针叶林发育达到鼎盛,之后逐渐减少至消失。早全新世达连海森林扩张的时间滞后于青海湖,主要与两地森林树种的不同和植被演替的时间差异有关。该区森林发育的全盛时期在中全新世,这与石笋记录到的亚洲季风强盛时期在早全新世不相一致,可能与植被复杂的响应机制有关。     

末次冰期40 ka以来阿拉善高原地区的环境演变与地貌演化

阿拉善高原末次冰期（40 ka）以来的环境演变研究是揭示中纬度沙漠的发展变化与物质来源的重要依据,为不同尺度区域乃至全球气候变化间的比较提供依据,进一步揭示气候要素的发展变化。目前已有大量的研究工作及成果见诸文献报道,但缺乏系统性的总结与对比分析,尤其是40 ka以来的环境演变过程及其原因。本文通过对中西方已有文献的系统总结和对比研究,从末次冰期、全新世早、中、晚期的古气候变化记录、地貌演化记录及环境变化的原因、可能存在的问题等方面,分析了阿拉善高原地区末次冰期以来的环境演变历史。指出约40 ka到末次盛冰期结束时的环境比现在湿润,之后至更新世结束环境普遍干旱,风沙活动增强;但是乌兰布和沙漠的环境演变与区域总体的变化结果不同,即整个末次冰期均表现为干旱的环境;全新世早期和中期环境普遍湿润,湖泊、植被等进一步发育,风沙活动弱,全新世晚期环境干旱,沙漠或进一步扩大。但是,腾格里沙漠全新世早期表现为干旱的环境,并且存在争议最大的是巴丹吉林沙漠全新世中期的干旱事件,这些问题仍需要进一步研究。此外,西风带、东亚季风在不同时期对研究区气候变化的影响不同,关于研究区与全球气候变化的具体关系的研究很少,缺少代表性事件的证据。沙源的研究结果存在不一致性,由于研究方法的局限性和地貌营力作用的复杂性,沙源的定性和量化分析具有一定的难度;沙丘的形态、分布与风的方向、能量具有相互指示性,适当的风能才是沙丘建造的关键;从气候变化的全球尺度分析,沙漠的形成普遍与冰期或者气候寒冷干燥时期相对应。