青藏高原东部末次冰期最盛期气候的花粉证据

青藏高原许多湖泊钻孔、泥炭剖面等所揭示的花粉记录为重建当时的古气候提供了可靠的证据．应用这些资料探讨青藏高原东部末次最大盛冰期植被和气候．大约２５～１５ｋａＢＰ前后西藏东南部、川西若尔盖及青海柴达木和可可西里地区,气候寒冷干燥,年均气温比现今低６℃左右,植被以荒漠草原为主;在青海湖地区森林退缩演变为草原植被;甘肃临夏气候冷湿,年均温比现在低５～６℃,发育山地暗针叶林     

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     

末次冰盛期以来冲绳海槽古海洋环境研究进展

冲绳海槽处于东海与西太平洋边缘的交界处,不仅对全球气候变化响应敏感,其环境变化也影响着东亚边缘海,乃至东亚大陆的环境,是研究古海洋环境的理想区域。该区域的古海洋环境研究多集中于末次冰盛期以来,因此本文以冲绳海槽为主体,总结了该区域末次冰盛期以来古海洋环境变化的相关研究,主要包括3个方面：古海平面、温度和盐度等;沉积物来源及其演化;黑潮及其对海洋环境的影响。该区域末次冰盛期以来的环境变化可大致分为,主要由海平面控制为主的末次冰盛期-早全新世和由黑潮、季风等因素控制的早全新世-现代两个主要的阶段。沉积物主要来自古黄河、长江、日本、台湾岛以及火山喷发物质等,但不同区域、不同时间的物质来源存在差异。另外,黑潮是该区域最主要的海流,其路径和强度末次冰盛期以来经历多次变化,并对其他海洋环境要素产生重大的影响。综合上述研究,提出未来应该系统建立冲绳海槽海洋环境演化历史、加强黑潮对周边流系的影响和陆源物质源-汇过程的系统研究。

     

Glaciers and climate in Pacific Far NE Russia during the Last Glacial Maximum

A combined geomorphological–physical model approach is used to generate three‐dimensional reconstructions of glaciers in Pacific Far NE Russia during the global Last glacial Maximum (gLGM). The horizontal dimensions of these ice masses are delineated by moraines, their surface elevations are estimated using an iterative flowline model and temporal constraints upon their margins are derived from published age estimates. The equilibrium line altitudes (ELAs) of these ice masses are estimated, and gLGM climate is reconstructed using a simple degree–day melt model. The results indicate that, during the gLGM, ice masses occupying the Pekulney, Kankaren and Sredinny mountains of Pacific Far NE Russia were of valley glacier and ice field type. These glaciers were between 7 and 80 km in length, and were considerably less extensive than during pre‐LGM phases of advance. gLGM ice masses in these regions had ELAs of between 575 ± 22 m and 1035 ± 41 m (above sea level) – corresponding to an ELA depression of 350–740 m, relative to present. Data indicate that, in the Pekulney Mountains, this ELA depression occurred because of a 6.4°C reduction in mean July temperature, and 200 mm a^?1 reduction in precipitation, relative to present. Thus reconstructions support a restricted view of gLGM glaciation in Pacific Far NE Russia and indicate that the region's aridity precluded the development of large continental ice sheets. Copyright © 2011 John Wiley & Sons, Ltd.     

末次冰盛期与全新世青藏高原松属植被分布及其演变

史前人类与其生存环境,特别是与植被之间的相互作用一直是人们关注的焦点。气候变化与人类活动对植被覆盖格局的塑造均有重要影响,厘清植被分布及其植被变化背后的气候或人为因素,有助于更好地认识人类活动对植被环境的影响程度与范围。本研究对青藏高原松属（Pinus spp.）植被适生区分布动态历史进行了物种分布模型模拟,并结合环境考古学、古生态学等多学科方法,探究青藏高原松属植被分布变化历史及其驱动因素。结果表明,基于最大熵（MaxEnt）算法并结合R语言包ENMeval来优化参数设置的模型性能表现良好且稳健,较为准确模拟松属在青藏高原地区不同时期的适生区分布动态。高原上松属适生区在末次冰盛期（LGM）分布最小,仅在东缘的河谷局地;在全新世早、中期分布达到最大值,到全新世晚期部分区域分布缩小,高原东北部高度适生区向2500 m a. s. l.上下的低海拔谷地收缩,整体上与高原气候变化趋势大体一致。结合化石花粉、木炭等证据表明,全新世中晚期以前,人类对高原松属植被影响总体尚不显著;进入全新世晚期,农业技术的进步促使高原东北部人口快速增加,高原上现已发现的古遗址也高度集中在此。结合多项考古证据表明,人类对松属为代表的林木资源规模化开发行为开始显著干扰了当地植被,人类对松属等针叶林木材资源的利用可能是该地区树种向阔叶林树种演替的重要驱动因素之一。

     

渭河盆地末次冰盛期以来沉积环境变化研究

研究过去气候快速变化能为当前极端气候分析和未来环境预测提供自然背景理解。亚洲季风在北半球乃至全球的第四纪气候变化中扮演着重要角色,其演化是全球气候变化背景下的典型区域响应。然而,不同地质载体及不同指标所记录的亚洲冬、夏季风变化存在着较大差异,产生差异的原因及受到的动力机制是值得深入研究的科学问题。渭河盆地位于黄土高原和古三门湖沉积交叠的区域,是研究第四纪亚洲季风演化的理想场所。在盆地西南部西安市户县和长安县获取了两个黄土沉积钻孔,户县ZZC孔长4 m,长安县XFC孔长3 m,两孔的年代均超过25 ka。通过两钻孔的粒度和元素地球化学等代用指标研究,对比分析不同指标对气候变化的敏感度差异,反演了末次冰盛期（LGM）以来的区域沉积环境变化,并尝试探讨该时期发生的气候突变事件及反映的季风强度变化。结果表明,两钻孔的平均粒径从LGM到中全新世逐渐变细,中全新世之后少许变粗,空间上表现出一致性,总体反映了末次冰盛期以来的冬季风强度演化;Ca/Ti反映了与季风降水相关的淋溶强度,从LGM到全新世暖期夏季风逐渐减弱,并记录了若干次气候快速变化。粒度和元素比值变化表明,渭河盆地沉积良好地记录了末次冰盛期至全新世的大幅冷干-暖湿波动及若干次持续时间较短的快速水文变化事件,主要是受到太阳辐射和冰量等因素调控的影响。由于渭河盆地有上千米的新生代沉积,未来开展高分辨率研究有望揭示不同时间尺度季风变化特征及其与区域和全球变化的联系。

     

The PMIP3 Simulated Climate Changes over Arid Central Asia during the Mid‐Holocene and Last Glacial Maximum

In this study, the climate changes over Arid Central Asia(ACA) during the mid-Holocene(approximately 6,000 calendar years ago, MH) and the Last Glacial Maximum(approximately 21,000 calendar years ago, LGM) were investigated using multimodel simulations derived from the Paleoclimate Modelling Intercomparison Project Phase 3(PMIP3). During the MH, the multimodel median(MMM) shows that in the core region of ACA, the regionally averaged annual surface air temperature(SAT) decreases by 0.13°C and annual precipitation decreases by 3.45%, compared with the preindustrial(PI) climate. The MMM of the SAT increases by 1.67/0.13°C in summer/autumn, whereas it decreases by 1.23/1.11°C in spring/winter. The amplitude of the seasonal cycles of the SAT increases over ACA due to different MH orbital parameters. For precipitation, the regionally averaged MMM decreases by 5.77%/5.69%/0.39%/5.24% in spring/summer/autumn/winter, respectively. Based on the analysis of the aridity index(AI), compared with the PI, a drier climate appears in southern Central Asia and western Xinjiang due to decreasing precipitation. During the LGM, the MMM shows that the regionally averaged SAT decreases by 5.04/4.36/4.70/5.12/5.88°C and precipitation decreases by 27.78%/28.16%/31.56%/27.74%/23.29% annually and in the spring, summer, autumn, and winter, respectively. Robust drying occurs throughout almost the whole core area. Decreasing precipitation plays a dominant role in shaping the drier conditions, whereas strong cooling plays a secondary but opposite role. In response to the LGM external forcings, over Central Asia and Xinjiang, the seasonal cycle of precipitation has a smaller amplitude compared with that under the PI climate. In the model-data comparison, the simulated MH moisture changes over ACA are to some extent consistent with the reconstructions, further confirming that drier conditions occurred during that period than during the PI.     

末次盛冰期以来中国东部陆架层序地层研究现状

本文中笔者总结了多年来国内外中国东部陆架晚更新世地层结构研究的主要认识,系统阐述了层序地层与沉积环境演化.中国东部陆架沉积物输运量高、沉积作用受海平面变化影响强烈,是分析晚更新世沉积演化史的理想场所.末次盛冰期(22 ka BP)之前,海面的持续下降形成以浅海、三角洲及海陆交互沉积为主的强制海退体系域.进入盛冰期后,一个新的旋回开始,在海退体系域之上,相继形成了包括低位体系域、海侵体系域及高位体系域在内新的4级层序:22~15 ka BP盛冰期时期,海面降至最低,形成低位体系域,包括陆架深切河湖沉积及风成沉积,以及陆架边缘三角洲和潮流砂体等;盛冰期结束的15~7 ka BP时期,全球海平面快速上升,形成含河道充填、湖泊、盐沼、潮坪、潮流砂体及浅海沉积的退积型海侵体系域;约7 ka BP以后,海面与现今海面位置基本相当,形成高位体系域,主要为三角洲和潮流砂等近岸陆架的沉积.     

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。     

Ice stream influence on West Greenland Ice Sheet dynamics during the Last Glacial Maximum

This paper investigates the processes governing bedrock bedform evolution in ice sheet and ice stream areas in central West Greenland, and explores the evidence for a cross‐shelf ice stream at the Last Glacial Maximum (LGM). To the east of Sisimiut the formation of streamlined bedforms with high elongation ratios and high bedform density has been controlled by geological structure and topography in slow‐flowing ice sheet areas. At the coast, the effects of regional flow convergence, caused by coastal fjord orientation, routed ice into the Sisimiut/Itilleq area where it formed an ice stream onset zone. This funnelled ice into an offshore trough (Holsteinsborg Dyb), resulting in a southwesterly regional ice flow direction and the formation of a topographically routed ice stream (Holsteinsborg Isbrae). To the south of this, striae and bedform evidence show that local valley glaciers initially flowed east to west across the coast, but were later redirected by the Itilleq Fjord ice which turned southwestward due to diffluent flow and deflection by Holsteinsborg Isbrae. Roches moutonnées in this area have low elongation ratios and high bedform density, but do not provide unequivocal support for ice streaming, as they are a product of both bedrock structure and changes in ice flow direction, rather than enhanced flow velocities. Cosmogenic surface exposure ages limit maximum ice sheet surface elevation to ca. 755–810 m above sea level in this region. Such ice thickness enabled Holsteinsborg Isbrae to reach the mid/outer continental shelf during the LGM, and to contribute to the formation of a trough mouth fan and the Outer Hellefisk moraines. Initial deglaciation across this region was driven by rising sea level and increasing air temperatures prior to the Bølling Interstadial at ca. 14.5 cal. ka BP. Between 12 and 10 cal. ka BP both increased air and ocean temperatures post the Younger Dryas, and peak sea‐level rise up to the marine limit, caused accelerated thinning and marginal retreat through calving, although dating evidence suggests ice streams remained along the inner shelf/coast boundary until at least ca. 10 cal. ka BP, their longevity maintained by increased ice thickness and ice discharge. Copyright © 2009 John Wiley & Sons, Ltd.     

Use of environmental magnetic measurements to validate the vertical extent of ice masses at the Last Glacial Maximum

Analysis of soil samples from above and below trimlines representing the upper limit of glacial erosion at the Last Glacial Maximum demonstrates that soils with prolonged weathering histories above such trimlines yield significantly different mineral magnetic signatures from soils below trimlines. The nature of the contrast is conditioned by lithology. Basalt soils above the trimline yield significantly higher values of concentration‐dependent magnetic parameters (χ, χ_arm, IRM_3T, soft IRM and hard IRM) than those below the trimline, due probably to transformation of non‐magnetic iron‐bearing minerals into magnetic forms. Conversely, for sandstone soils most magnetic parameters yield significantly lower values for above‐trimline samples, probably reflecting loss of ferrimagnetic minerals by dissolution and oxidation to aniferrimagnetic forms. These significant contrasts represent a new approach to validating high‐level weathering limits as periglacial trimlines cut at the Last Glacial Maximum. Copyright © 2002 John Wiley & Sons, Ltd.     

NAO在末次冰盛期和全新世对AMOC影响的对比研究

大西洋经向翻转环流(AMOC)的年代际变率对气候变化起着重要的调制作用。在现代气候背景下, 北大西洋涛动(NAO)加强能使AMOC增强, 但这种关系在更长时间尺度上是否成立尚不清楚。本研究利用TraCE-21ka模拟资料, 对比分析末次冰盛期(LGM)和全新世时期NAO对AMOC影响的异同。结果表明, LGM时期较全新世时期经向温度梯度偏强, NAO位置偏南, 这导致NAO与AMOC关系的不同: NAO的增强在LGM时期可以使AMOC增强, 而在全新世使AMOC减弱。具体地, 在LGM时期NAO的加强使北大西洋副极地气旋性环流增强, 其南支导致向北的高盐海水输送增加, 从而使北大西洋副极地区域密度升高, AMOC增强。与此同时, NAO正位相还能在中纬度激发异常的Ekman下沉流使AMOC加强。相反, 在全新世时期, NAO正位相导致北大西洋副极地地区气旋性环流减弱, 这导致中纬度向高纬度输送的高盐度海水减少, AMOC减弱。本研究表明NAO与AMOC的关系在很大程度上取决于不同气候背景下NAO的位置。

     

Paleoproductivity evolution off central Chile from the Last Glacial Maximum to the Early Holocene

A geochemical and paleontological reconstruction of paleoproductivity, upwelling intensity and sea surface temperature (SST) off central Chile at 35°S (GeoB3359-3) reveals marked changes from the Last Glacial Maximum (LGM) through the Early Holocene. Surface-water productivity was determined by the interaction between the atmospheric (the Southern Westerlies) and oceanographic (the Antarctic Circumpolar Current, ACC) systems from the LGM through early Termination I (TI). The northward shift of the climate zones during the LGM brought the ACC, as the main macronutrient source, closer to the GeoB3359-3, SST lowered, and surface water productivity and accumulation rates of biogenic components enhanced. With the poleward return of the Southern Westerlies and the ACC, the subtropical high-pressure system became the dominant atmospheric component southward till 35°S during the late TI and Early Holocene and caused surface water productivity to increase through enhanced upwelling.     

Wetter or colder during the Last Glacial Maximum? Revisiting the pluvial lake question in southwestern North America

Well-preserved shorelines in Estancia basin and a relatively simple hydrologic setting have prompted several inquiries into the basin's hydrologic balance for the purpose of estimating regional precipitation during the late Pleistocene. Estimates have ranged from 86% to 150% of modern, the disparity largely the result of assumptions about past temperatures. In this study, we use an array of models for surface-water runoff, groundwater flow, and lake energy balance to examine previously proposed scenarios for late Pleistocene climate. Constraints imposed by geologic evidence of past lake levels indicate that precipitation for the Last Glacial Maximum (LGM) may have doubled relative to modern values during brief episodes of colder and wetter climate and that annual runoff was as much as 15% of annual precipitation during these episodes.     

Malaco temperature reconstructions and numerical simulation of environmental conditions in the southeastern Carpathian Basin during the Last Glacial Maximum

We investigate the glacial climate conditions in the southeastern Carpathian Basin (Vojvodina, Serbia) based on the reconstruction of malacological palaeotemperatures and results from a high-resolution regional climate simulation. Land snail assemblages from eight loess profiles are used to reconstruct July temperatures during the Last Glacial Maximum (LGM). The malacological reconstructed temperatures are in good agreement with the simulated LGM July temperatures by the Weather Research and Forecast model. Both methods indicate increasing temperatures from the northwestern towards the southeastern parts of the study area. LGM aridity indices calculated based on the regional climate model data suggest more arid conditions in the southeastern parts compared with more humid conditions in the northwestern parts. However, for present-day conditions, the moisture gradient is reversed, exhibiting more humid (arid) conditions in the southeast (northwest). An explanation for the reversed LGM aridity pattern is provided by an analysis of the prevailing wind directions over the South Banat district (Serbia). The prevailing moist northwesterly winds during summer are not able to compensate for the annual lack of moisture induced by the dry winds from the southeast that are more frequent during the LGM for the other seasons.     

Late Pleistocene(MIS 2) climate change on the Northern Tibetan Plateau inferred from pollen and geochemical records from Lake Gomo Co

正Introduction A 405-cm sediment section GM02 from Gomo Co salt lake in the northern Tibetan Plateau was used to reconstruct climate changes during marine isotope stage(MIS)2,including the Last Glacial Maximum(LGM)and last     

Carbonate dissolution revealed by silt grain-size distribution: comparison of Holocene and Last Glacial Maximum sediments from the pelagic South Atlantic

The current issue of global warming and the role of the ocean in global exchange of CO₂ increases the interest in solid budgets of marine carbonate production and dissolution. The present study utilizes grain‐size composition of pelagic sediments in order to trace spatial and temporal variability of carbonate sedimentation in the South Atlantic for the Holocene and Last Glacial Maximum (LGM, 19–23 cal kyr BP). A decrease in grain size (e.g. sand content, mean grain size of coarse carbonate silt) indicates increased carbonate dissolution as a result of increased fragmentation of calcareous microfossils. The spatial grain‐size pattern suggests a threshold water depth below which a gradual grain‐size decrease becomes increasingly rapid. This water depth is considered as the sedimentary lysocline. For the Holocene time slice, a constant, gradual decrease of foraminifer carbonate of about 5–10% per 1000 m water depth above the lysocline gives evidence for supra‐lysoclinal dissolution. The water depth of the lysocline for the Holocene is tied to the interface of North Atlantic Deep Water and Antarctic Bottom Water (AABW) (ca 4100 m). Submarine ridges which restrict intrusion of AABW into the Angola Basin cause an asymmetry in carbonate preservation across the Mid‐Atlantic Ridge. The lysocline was reconstructed at ca 3100 m for the LGM. These data suggest that the ca 1000 m rise of the lysocline eradicated the Holocene east–west asymmetry.     

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。