A minimal lag time and continuous sedimentation in alpine lakes near Mount Rainier, Cascade Range, Washington, USA

Alpine lakes near Mount Rainier are dammed by late-glacial moraines. Multiple cores show that sedimentation started less than 350 years after deglaciation. Numerous tephra layers provide excellent marker horizons that allow comparison of the stratigraphy without the errors associated with radiocarbon dating. Cores from different locations within a lake display the same stratigraphy and basal sediments. Core location therefore is not crucial to obtaining the oldest sediments. Continuous sedimentation in all cores is interpreted as evidence for stable lake levels throughout the Holocene. The cores are valuable tools for reconstruction and dating of glacier advances and volcanic activity.     

东海陆架浙-闽沿岸泥质沉积研究进展

比较全面的回顾了关于东海浙-闽沿岸泥质体以及其形成前的沉积演化历史、泥质沉积的物质来源及其东亚季风/古气候记录等方面的研究进展。分析了目前关于浙-闽沿岸沉积研究中所存在的问题,即,泥质体的物质来源与形成,长江入海历史的陆架沉积物记录,8.2 ka冷事件,年代框架调整及区域对比,代用指标指示意义等多方面问题。提出在东海浙-闽沿岸泥质区,我们需要更多高分辨率的钻孔进行综合研究,其中应该特别加强对泥质沉积物的研究,以期对海陆交界敏感地带的"源到汇"以及全球变化研究取得突破性进展。     

GLACIER RETREAT IN THE MARITIME ALPS AREA

In the southernmost tract of the Alps (Italian‐French Maritime Alps), extensively covered by glaciers during the Last Glacial Maximum, about 30 small glaciers were present by the end of the Little Ice Age. The aim of this paper is to document the progressive decrease towards exhaustion of these glaciers, located at the latitude of 44° N, highlighting the factors affecting their retreat. All available data sources were investigated for this work including: the annual glaciers fluctuations record, comparative analyses of historical maps and multi‐temporal oblique photographs and direct surveys in the field. The history of the Maritime Alps glaciers fluctuations was thoroughly reconstructed. Stationary conditions were observed from 1896 up to the beginning of the 1930s; since then they underwent phases of withdrawal with variable intensity. In the early 1990s, only six glaciers were still present, the extent of which were all was dramatically reduced. In the past two decades, the Maritime Alps glacier fronts experienced a global retreat of about 100 m, with a sharp acceleration after 2002. Currently ice patches along cirque walls and/or semi‐buried lenses of ice are still present; morphological evidence of permafrost creeping in the glacier forefield accounts for the incipient transition to periglacial landforms (i.e. rock glaciers). The main factors controlling glaciers retreat seem to have been their original extent at the beginning of the current regressive phase and their distance from the main chain divide. From a climatic point of view unfavourable factors for glaciers persistence have been in the last decades a remarkable and sharp temperature increase, a decrease in winter snowfall and a shift of the rainfall peak from autumn to spring.     

Geomorphology and style of plateau icefield deglaciation in fjord terrains: the example of Troms‐Finnmark,north Norway

In spite of a widespread distribution, the way in which plateau icefields affect the glaciation and deglaciation of adjacent terrains is not particularly well‐known. This paper aims to identify how the deglaciation of the fjord and plateau terrain of north Norway has influenced the glacial geomorphology and relative sea‐level history of both local and adjacent areas and so serve as a model for interpreting similar areas along the continental margins of northwest Europe and elsewhere. The identification of moraines and their relationships with the Main shoreline of northern Norway allows the margins of the Øksfjordjøkelen, Svartfjelljøkelen and Langfjordjøkelen plateau icefields to be identified in the adjacent terrains. In locations where ice margins are uncertain, it is also possible to reconstruct ice limits by means of glacier models appropriately constrained by known local conditions and dates. Earlier glacier margins, characterised in north Norway by ice shelves floating in the local inlets of major fjords, also can be related to known regional shorelines. The distribution of high shoreline fragments, augmented by radiocarbon dates, helps show the extent to which inter‐island channels and outermost parts of fjords can become deglaciated relatively early in comparison with published maps of regional deglaciation. Plateau‐icefield‐centred glaciation became important sometime after 14 000 ¹⁴C yr BP and was characterised by glacier readvances up to, and in some locations beyond, earlier moraines and raised marine features. Although overlooked until recently, the identification of the influence of plateau icefields on local glaciation, and their interaction with local and regional marine limits, is of great importance in accurate palaeoenvironmental reconstruction. Copyright © 2002 John Wiley & Sons, Ltd.     

Morphology, distribution and formation of relict marginal moraines in the Swedish mountains

Relict marginal moraines are commonly used landforms in palaeoglaciological reconstructions. In the Swedish mountains, a large number of relict marginal moraines of variable morphology and origin occur. In this study, we have mapped 234 relict marginal moraines distributed all along the Swedish mountains and classified them into four morphological classes: cirque‐and‐valley moraines, valley‐side moraines, complex moraines and cross‐valley moraines. Of these, 46 moraines have been reclassified or are here mapped for the first time. A vast majority of the relict moraines are shown to have formed during deglaciation of an ice‐sheet, rather than by local mountain glaciers as suggested in earlier studies. The relict marginal moraines generally indicate that deglaciation throughout the mountains was characterised by a retreating ice‐sheet, successively damming glacial lakes, and downwasting around mountains. The general lack of moraines indicating valley and cirque glaciers during deglaciation suggests that climatic conditions were unfavourable for local glaciation during the last phase of the Weichselian. This interpretation contrasts with some earlier studies that have reconstructed the formation of local glaciers in the higher parts of the Swedish mountains during deglaciation.     

若尔盖盆地河流古洪水沉积及其对黄河水系演变问题的启示

青藏高原东部若尔盖盆地古湖泊消亡、黄河贯穿盆地、黄河源区现代水系格局形成,是黄河发育演变史上的重要事件,也是青藏高原东部水文环境变化的转折点.关于其发生年代问题,目前尚无确切结论.本文根据野外考察所获资料和实验室测试分析数据,结合历年来前人多方面研究的结果,针对若尔盖盆地古湖泊消亡与黄河贯穿盆地的年代问题,进行比较全面...     

末次冰消期以来东海内陆架沉积物地球化学特征及其古环境意义

尝试对末次冰消期以来东海内陆架沉积物地球化学特征及其蕴含的古环境、古气候信息进行探讨。对位于浙-闽沿岸泥质沉积中心附近的EC2005孔岩性、粒度、常量元素、矿物以及AMS^14C测年数据进行了综合分析,得出以下主要结论：（1）东海内陆架沉积物不同常量元素与TiO2的比值具有不同的环境、气候意义,SiO2、Na2O与TiO2的比值可以用来反映沉积水动力条件的强弱,Al2O3、Fe2O3、MgO、K2O、MnO以及下部湖相沉积层中的CaO、P2O5与TiO2的比值则主要反映了沉积物源区的变化以及与风化程度相关的源区气候变化。（2）研究区自17．3k。BP以来沉积环境经历了剧烈变化,岩芯底部60．20m至41．00m（17．3～13．1kaBP）为湖泊三角洲沉积序列,海水自13．1kaBP开始侵入研究区,形成了41．00m的海相沉积地层。自12．3kaBP研究区受到沿岸流影响,7．3ka BP以来稳定的泥质沉积体开始形成。（3）自末次冰消期初期至末期,气候总体向暖湿方向发展,新仙女木事件、8．2k。冷事件在本孔中有明显的记录,显示出全球性重要气候事件在中纬度浅海陆架海域的区域性响应。     

16 ka以来黄土高原东亚夏季风变化的环境磁学记录

末次冰消期以来的气候变化是第四纪古气候研究的重要内容.本文对黄土高原西部和平镇剖面16 ka以来的黄土沉积序列(厚度为3.5 m)进行了高分辨率环境磁学研究.结果表明:该黄土序列的磁性颗粒主要由细颗粒磁铁矿主导.其磁化率和频率磁化率具有相同的变化特征,与黄土高原中部和东部的黄土磁化率变化机制一致,即黄土高原西部和平镇黄...     

南京葫芦洞石笋微量元素记录的末次冰消期气候变化

采用Avaatech型岩芯X射线荧光光谱扫描仪技术, 对发育有连续3900年纹层(18.3~14.4ka B.P.时段)的南京葫芦洞YT石笋进行了Sr, Ba和Pb微量元素分析。选择Sr/Ca, Ba/Ca 和Pb/Ca 作为代用指标, 研究了末次冰消期洞穴地点岩溶水文条件和气候变化特征。Ba/Ca 和Pb/Ca 值从大约17.5ka B.P. 开始呈现出减小的趋势变化, 而Sr/Ca 呈现出在大约16.1ka B.P. 发生转折的"V"型演化趋势。Sr/Ca 反映了岩溶水在上覆围岩中的滞留时间(与夏季降水相关), 而Ba/Ca 和Pb/Ca 指示了土壤及其基岩的本底值和淋滤作用强度。Sr/Ca 比值与纹层厚度、δ13C 记录在数百年-千年尺度上呈现一致的变化, 共同指示了南京葫芦洞地点有效湿度的变化过程, 与 δ18O的对应性表明葫芦洞石笋 δ18O可以指示当地季风降雨量的变化过程。此外, 石笋Ba/Ca 和Pb/Ca 与格陵兰粉尘和Ca2+记录在长期趋势上呈现一致变化, 表明该类元素比值主要反映与冬季风强度密切相关的粉尘活动强度变化。研究结果表明, 东亚冬、夏季风对神秘期内发生的冰漂碎屑事件(H1a, 16.1ka B.P. 和H1b, 17.5ka B.P.)具有不同的响应方式。Ba/Ca 和Pb/Ca 序列的功率谱分别呈现出66a、35a、23a、14a和61a、46a、22a、19a、17a、15a周期, 说明北大西洋涛动和太阳活动影响着冬季风强度的高频变化。     

末次冰消期以来赛里木湖沉积记录的气候突变

末次冰消期以来的气候突变事件的时空变化特征及其区域响应是古气候环境变化研究的重要内容,然而亚洲中部干旱区末次冰消期以来的气候突变记录较少,尤其缺少末次冰消期期间快速转暖过程的区域响应。本研究通过对位于亚洲中部干旱区的新疆西天山中部亚高山湖泊赛里木湖湖心采得的长300 cm的SLM2009钻孔沉积物的碳酸盐含量和粒度变化特征的分析,在14个AMS¹⁴C测年数据的基础上,探讨了末次冰消期约23.4 cal.ka B.P.以来亚洲中部干旱区的气候突变事件记录及其区域响应过程。结果表明：赛里木湖湖心钻孔沉积物完整记录了H1（17.5~15.2 cal.ka B.P.）、YD（12.6~11.7 cal.ka B.P.）冷事件以及B-A（15.2~12.9 cal.ka B.P.）暖事件等末次冰消期气候突变事件以及全新世以来的10.5 ka、8.2 ka、5.5 ka、4.2 ka、2.8 ka和小冰期冷事件,这与亚洲中部干旱区已有的气候突变事件记录相吻合,表明末次冰消期以来亚洲中部干旱区具有相似的气候突变演化模式。同时这些气候突变事件与高纬冰芯以及低纬石笋氧同位素记录的一致性则表明气候突变具有全球性影响,受相同的成因机制因素控制。