Permafrost at the time of the Last Glacial Maximum (LGM) in North America

This paper presents three maps that summarize current knowledge as to the extent of Past permafrost and Relict permafrost in North America at approximately the time of the Last Glacial Maximum (LGM; c. 25–17 ka BP) and during subsequent deglaciation until c. 10 ka BP. Analysis of the post‐1983 literature suggests that the extent of Past permafrost south of the LGM limit was broader in eastern North America and slightly narrower in the Interior Great Plains than previously mapped. The recognition and dating of Relict permafrost in the nonglaciated terrain of the northwestern Arctic suggests that permafrost may be of great antiquity and can persist under changing climatic conditions. The formation of permafrost features during deglaciation suggests that ice‐proximal climatic conditions remained cold at least long enough for short‐lived permafrost aggradation; a latitudinal gradient is evident in the timing of its development as the Laurentide Ice Sheet retreated.     

青藏高原末次冰期最盛时的冰川与环境

在１６－３２ｋａＢｐ的末次冰期最盛时，青藏高原较现代降温７℃左右，降水为现代的０３－７０％。极地型冰川广泛分布，高原内部平衡线较下降值减至５００－３００ｍ以内，高原东部，南缘及西缘可能以亚极地型冰川为主，并有小部分温冰川，平衡线下降８００ｍ以至１００－１２００ｍ。初步统计，包括周围高山在内冰川面积在３５×１０＾４ｋｍ＾２左右，为现代冰川的７．５倍，冰储量相当于全海平面变化２４．２ｃｍ。其时，多年冻     

Radiocarbon constraints on Antarctic Peninsula Ice Sheet retreat following the Last Glacial Maximum (LGM)

We present marine sedimentologic and radiocarbon data for the timing of retreat of the largely marine-based Antarctic Peninsula Ice Sheet since the Last Glacial Maximum (LGM). Our findings indicate minimum estimates of deglaciation between 18,000 and 9000 calibrated years before present (cal yr BP), roughly in phase with the Northern Hemisphere deglaciation and eustatic sea-level rise. Our findings show this retreat occurred progressively from the outer, middle, and inner continental shelf regions, as well as progressively from the north to the south. Retreat initiated on the outer shelf of the northern Peninsula by 18,000 cal yr BP and continued southward by 14,000 cal yr BP on the outer shelf of Marguerite Bay, several thousand years earlier than estimated by numeric models. While individual cores yield estimates of glacial retreat that may vary up to ±1100 years, we note steps in the data occur at 14,000 and possibly 11,000 cal yr BP, coincidental to rapidly rising (eustatic) sea level, including the well documented melt water pulses (MWP 1a and 1b). These data support the hypothesis that rapidly rising sea level is associated with marine ice sheet destabilization, although additional dates are necessary to substantiate this finding. This study highlights problems with radiocarbon dating acid insoluble organic (AIO) matter in proximal Lateglacial sediments as well as the need for more accurate dating techniques.     

Last Glacial Maximum and Hypsithermal in the Southern Hemisphere

A synthesis of the two contrasting climates of the upper Quaternary in the Southern Hemisphere, based on continental geological indicators, suggests that the Antarctic Anticyclone is the most important climatic system in the hemisphere. According to glaciological and oceanographic studies, the Antarctic Anticyclone covered an area in the LGM that was double of that during the Hypsithermal. This phenomenon produced a consequent shifting of the climatic belts by approximately 10° of latitude to the north in the LGM and a migration to the south during the Hypsithermal. Oceanic and continental anticyclones were active systems in shaping climates in South America, Australasia, and Southern Africa. These structures were enhanced throughout the LGM (provoking generalized droughts), and weakened at the Hypsithermal (permitting more rains in tropical latitudes). The results presented here were obtained by integrating our own results with regional and continental syntheses of other authors. The paleoclimatic proposals are amply validated by more than 1500 dates in the four continents. Geological and geomorphological features, such as dunefields, paleosols, fluvial terraces and lake levels were the main tools employed in the work.     

LGM热带西太平洋硅藻席古生产力定量评估

巨型"树荫种"硅藻在成层化大洋中通过"秋季倾泻"勃发模式向深部大洋输出的有机碳通量等于甚至超过"春季勃发"硅藻, 其在第四纪全球气候转型、大洋碳储库演变中的重要地位最近才予以重视.作为大洋碳循环系统的重要参数, 生产力无疑成为探索这一作用的有效窗口.以东菲律宾海的Ethmodiscus rex硅藻席(LDM, laminated diatom mats)岩心WPD-03为材料, 以opal、TOC、bio-Ba等生源组分数据为基础, 运用前人建立的各种生产力经验公式, 试图估算LGM(last glacial maximum)热带西太平洋LDM的古生产力状况.结果显示, LDM沉积期初级生产力、有机碳雨率和埋藏生产力估算合理, 平均分别为248.42 g·m-2·a-1、61.93 g·m-2·a-1和5.27 g·m-2·a-1.估计的初级生产力与代表高生产力的世界大洋各上涌海区可比, 纠正了成层化大洋生产力低下的传统观点, 支持巨型"树荫种"硅藻对大洋有机碳生产与输出的充分贡献.然而, 估算的输出生产力明显不合理, 表明利用基于真光层建立的生产力模型评估次表层水中的巨型"树荫种"硅藻时应格外谨慎, 加强了区别对待"深部"生产力和"表层"生产力的重要性.LGM热带西太平洋LDM的高生产力状况与风尘硅输入的E. rex勃发条件以及还原的沉积环境相一致.      

末次盛冰期华北平原古气候古环境演化

华北平原宁晋泊南王庄剖面的^14C和光释光年代测定表明宁晋泊地区在末次盛冰期有连续的湖相沉积。依据孢粉、碳酸盐、有机碳含量（TOC）及C／N值的高分辨率分析与综合判识，末次盛冰期并不是一个持续的干冷时期，而是存在从凉湿-冷偏湿-冷干的波动变化过程。其中早期明显降温事件，可以与Heinrich事件2（H2）对比，说明全球降温的同步性。本研究说明末次盛冰期（20-16ka BP），在全球气候变冷的背景下，存在一个冬季风不断加强夏季风逐渐变弱的过程。     

末次盛冰期以来河北平原第四系地下水流系统的演变

以区域自然地理及地质历史分析为基础,以环境同位素及大陆盐化咸水后期变化为实证依据,重塑了末次盛冰期以来河北平原第四系地下水流模式演变。研究发现,末次盛冰期以来河北平原第四系地下水流系统经历3个演变阶段:(1)距今18～15ka的低海平面时期,接受持续补给,地下水得到充分交替,发育穿透达到或接近第四系底界的区域水流系统;(2)距今15～12ka的海平面急剧抬升期,地形势差减弱,发育穿透第三含水层组的早期中间水流系统,与此同时区域水流系统趋于停滞;(3)距今2.5ka以来,现代河流地貌成形,高位河床与低位河床及河间低地的势差成为主要驱动力,发育穿透第一及第二含水层组的晚期中间水流系统。随着海平面抬升,后期发育的水流系统切割前期水流系统的一部分并叠置其上。因此,现今河北平原第四系的地下水流系统乃是不同演变时期地下水流系统的时空四维集合体。其他濒海平原,乃至侵蚀强度随时间减弱的内陆盆地,都有可能出现类似图景。距今12ka前后形成的大陆盐化咸水,由上升水流带到浅部,导致浅层咸水以及土地盐渍化,乃是河北平原水资源利用及生态与环境保护的关键性不利因素。     

The Last Glacial Maximum in the North Sea Basin: micromorphological evidence of extensive glaciation

Despite a long history of investigation, critical issues regarding the last glacial cycle in northwest Europe remain unresolved. One of these refers to the extent, timing and dynamics of Late Devensian/Weichselian glaciation of the North Sea Basin, and whether the British and Scandinavian ice sheets were confluent at any time during this period. This has been the result of the lack of the detailed sedimentological data required to reconstruct processes and environment of sediments recovered through coring. This study presents the results of seismic, sedimentological and micromorphological evidence used to reconstruct the depositional processes of regionally extensive seismic units across the North Sea Basin. Thin section micromorphology is used here to provide an effective means of discriminating between subglacial and glacimarine sediments from cored samples and deriving process‐based interpretations from sediment cores. On the basis of micromorphology, critical formations from the basin have been reinterpreted, with consequent stratigraphic implications. Within the current stratigraphic understanding of the North Sea Basin, a complex reconstruction is suggested, with a minimum of three major glacial episodes inferred. On at least two occasions during the Weichselian/Devensian, the British and Scandinavian ice sheets were confluent in the central North Sea. Whilst micromorphology can provide much greater confidence in the interpretation of Late Quaternary offshore stratigraphic sequences, it is noted that a much better geochronology is required to resolve key stratigraphic issues between the onshore and offshore stratigraphic records. Copyright © 2006 John Wiley & Sons, Ltd.     

The extent of permafrost in China during the local Last Glacial Maximum (LLGM)

Recent investigations into relict periglacial phenomena in northern and western China and on the Qinghai–Tibet Plateau provide information for delineating the extent of permafrost in China during the Late Pleistocene. Polygonal and wedge‐shaped structures indicate that, during the local Last Glacial Maximum (LLGM, between ～35 and 10.5 ka BP), the southern limit of latitudinal permafrost in northern China advanced southward at least to ～38–40°N in the east and to ～37–39°N in the west. This represents an advance of about 5–10° of latitude beyond present‐day permafrost limits. The lower limits of elevationally controlled permafrost on the Qinghai–Tibet Plateau and its peripheries were about 1000 m lower: this permafrost was largely continuous during the LLGM. This suggests a cooling of between 4 and 10°C, or more. This paper discusses the extent of permafrost during the LLGM and presents maps that have been constructed on the basis of extensive and integrative analysis of all reliable and pertinent data. The results indicate that the extent of LLGM permafrost in China was between ～3.8 and 4.3×10⁶ km². This is 80 to 100% more than that of ～2.15×10⁶ km² in the 1970s, and 120 to ～150% more than that of ～1.75×10⁶ km² today.     

末次盛冰期以来长江河口段河道演变研究综述

末次盛冰期以来,由于海面发生大幅度的变化,长江河口段经历了深切古河谷形成—古河谷充填—三角洲发育的河床演变过程。海陆相互作用是河口段河道演变的主要影响因素。综合分析了对河口段河道研究的成果,着重对长江河口段古河谷的形成与充填、最大海侵以来的河床演变、古河谷的沉积层序与沉积相及研究的方法进行了综述。过去对古河谷宏观的趋势研究及单个钻孔的研究较多,宏观与微观结合的不够,专门研究古河谷河形的成果很少。今后应注重宏观与微观研究的结合;根据系列钻孔剖面,分析、恢复古河谷河型;根据河型、沉积物特征等,估算古长江流速、流量;加强高分辨率研究、定性与定量研究相结合,探讨环境变化与河道演变的关系和规律。     

漓江流域末次冰期以来气候环境变化研究进展

为更好地认识漓江流域过去气候环境变化,更好服务于漓江流域未来气候环境预测、生态环境建设及资源环境可持续发展,本文对漓江流域末次冰期以来的气候环境研究现状进行了总结和综述。总结了年代学、现代过程研究、古气候环境重建和古人类演化方面的进展及存在的问题,并对下一步的研究方向进行了分析和探讨。希望能促进华南地区过去气候环境变化研究,并对经济社会可持续发展提供借鉴和参考,助力桂林可持续发展创新示范区建设。     

漓江流域末次冰期以来气候环境变化研究进展

为更好地认识漓江流域过去气候环境变化,更好服务于漓江流域未来气候环境预测、生态环境建设及资源环境可持续发展,本文对漓江流域末次冰期以来的气候环境研究现状进行了总结和综述。总结了年代学、现代过程研究、古气候环境重建和古人类演化方面的进展及存在的问题,并对下一步的研究方向进行了分析和探讨。希望能促进华南地区过去气候环境变化研究,并对经济社会可持续发展提供借鉴和参考,助力桂林可持续发展创新示范区建设。     

Chronology of the Last Glacial Maximum in the Salzach palaeoglacier area (Eastern Alps)

A chronostratigraphy based on luminescence data was established at a key loess profile (Duttendorf) in the northern alpine foreland of Austria. The data help to constrain the timing and duration of the Last Glacial Maximum (LGM) in the area of one of the largest east Alpine piedmont glaciers, the Salzach palaeoglacier. Climate deterioration and maximum advance of this glacier were coeval with the beginning of the main loess accumulation phase in the glacier forefield at ～29–30 ka. A late LGM‐outwash gravel layer deposited on top of the loess profile marks the end of the LGM glacier activity at ～20 ka. The geomorphological setting around the loess profile provides evidence of a major glacier oscillation during the course of the LGM, a phenomenon qualitatively known from other alpine palaeoglaciers but never interpreted in terms of palaeoclimate. A LGM glacier oscillation similar to that of the Salzach palaeoglacier was reported recently from the south Alpine Tagliamento palaeoglacier, suggesting a common forcing. The onset of loess deposition at Duttendorf and the tentatively contemporal advance of the Salzach palaeoglacier reflect, as do other data, the drastic cooling in Europe as a result of Heinrich event 3. The first glacier maximum is not well constrained in the study area but a correlation with the better dated Tagliamento amphitheatre suggests a possible response to Heinrich 2. The second re‐advance occurred synchronously (within dating uncertainties) in both palaeoglaciers forefields (at ～21 ka) but the forcing mechanism remains unknown. Copyright © 2011 John Wiley & Sons, Ltd.     

北京平原区永定河冲洪积扇地下水水化学特征与演化规律

本文以北京市平原区永定河冲洪积扇地下水化学场的演化机理及地下水水循环规律为研究目的,根据水化学特征的水平分布及典型剖面上的演化过程研究,得到以下结论:1)从永定河冲洪积扇顶部补给区到扇缘排泄区,地下水水化学类型呈现水平分带性,潜水水化学类型由Ca-HCO3过渡到Ca·Mg-HCO3、Mg·Na-SO4,局部因人类活动影...     

北京平原区永定河地下水系统地下水化学和同位素特征

北京平原区永定河地下水系统位于北京市的西部.在该区采集了一个水文年的大气降水样,并对其中的D和18O组成作了分析;于旱季在该地下水系统中采集了大量地下水样,并对其中的八大离子浓度、D和18O组成、Sr浓度以及87Sr/86Sr比值作了分析.研究结果表明,研究区地下水的水化学类型较为单一;研究区地下水主要来源于大气降水入...     

黄河上游末次冰盛期古洪水事件的初步研究

洪水的发生规律是洪灾预报的前提，已有的人类洪水记录时间尺度，不足以认识和把握洪水的出现规律。因此，利用地质记录延长洪水序列，探讨地球特征气候期的洪水特点，就显得非常重要的必要。黄河上游兰州－银川段的洪水地质记录表明，在末次冰盛期的20－18ka，该区共发生了106次大洪水漫滩事件，其中有18次为多次洪峰叠加的复合型大洪水，洪水的发生频率达53次/ka。发生于末次冰盛期的大洪水可能属冰凌洪水，与末次冰盛期强烈的气候波动和不稳定有关。这些大洪水的频发与中国西部的末次冰盛期出现的高湖面相对应，既不符合一般的季风气候理论，也不同于我国东部广大地区末次冰盛期以冷干为主的气候特点，表明中国西部气候的独特性和复杂性。     

The Last Glacial Maximum and Heinrich Event 1 in terms of climate and vegetation around the Alboran Sea: a preliminary model-data comparison

The Heinrich Event 1, the most recent of the glacial North Atlantic large iceberg discharges, is well documented in continental and marine records, but this large perturbation of the climate system has rarely been simulated. Here we propose a preliminary model-data comparison for this period, which we compare to the Last Glacial Maximum state. The pollen record from one specific core from the western Mediterranean Sea (ODP site 976) is analysed both in terms of vegetation distribution and climatic implication. The climate and vegetation of both periods are then simulated and compared to the pollen-based data. To cite this article: M. Kageyama et al., C. R. Geoscience 337 (2005).     

Lower and Middle Pleistocene human settlements recorded in fluvial deposits of the middle Loire River Basin,Centre Region,France

This paper records the findings from c. 80 prehistoric sites that have been discovered in the alluvial deposits of the rivers Creuse, Cher, and Loir, tributaries of the middle Loire River, over the period since 1981. These deposits comprise river terrace aggradations formed during successive glacial–interglacial cycles which have recorded climate and environment during Quaternary time. The systematic dating of these river deposits by Electron Spin Resonance (ESR) applied to optically bleached sedimentary quartz has resulted in the establishment of a chronological framework for the evolution of these rivers during Lower and Middle Pleistocene (between 1.7 Ma and 130 ka). Evidence for Early Palaeolithic (Mode 1) industries with an in situ context (workshops, soils) in the highest aggradations indicates that Hominins were present in the study area, near the geographical centre of France (47°N), around 1.1 Ma. Examination of the sites indicates that Human occupations were located along valley bottom sites during temperate episodes. Subsequently, after a gap of several hundred thousand years industries with handaxes appear in the Middle Loire Basin in the interval between 700 and 600 ka, and then continuously from 400 ka. These two phases of settlement produced industrial assemblages with clear differences in their responses to the supplies of raw materials and in the modes of making flakes.     

末次盛冰期以来青藏高原东北部共和盆地气候与环境变化研究进展

青藏高原东北部共和盆地气候与环境变化文献分析认为:末次盛冰期(14 C年龄14ka BP或16cal ka BP之前)地层沉积主要为风成砂和黄土,冰缘地貌发育,气候寒冷干燥,植被可能为干旱荒漠或荒漠草原;末次冰消期(14 C年龄14ka BP或16 cal ka BP-Younger Dryas,缩写YD事件)地层发育古土壤,湖泊水位明显上升,并显著的捕捉到冷暖事件(Blling-Allerd,缩写B/A、YD)的信息,气候趋于温暖湿润,对应植被为荒漠草原;全新世8.5ka BP(14 C年龄)之前区域温度和湿度不同程度增加,湖泊水位较高,地层发育古土壤,植被为荒漠草原或干草原;8.5～7.0ka BP(14 C年龄)风成砂出现,古土壤发育中断,气候寒冷干燥,为全新世新冰期第一期;7.0～3.0ka BP(14 C年龄)古土壤显著发育,高水位湖面出现,水热组合达到全新世最佳,植被向干草原方向演化,但期间也存在千–百年尺度的冷事件(全新世新冰期第二期);3.0ka BP(14 C年龄)以来气候向温凉(寒冷)干燥方向发展.太阳辐射等外部因素变化并触发地球系统内部各个圈层之间相互作用是区域气候、环境变化的主要驱动力.同时,对研究现状进一步剖析,阐明其存在的问题,并提出气候、环境变化研究的发展方向.