青藏高原末次冰消期气候演化特点及其与格陵兰、欧洲的异同

根据生物、湖泊及冰川地层记录,分析了青藏高原末次冰消期的气候演化特点,并将其与格陵兰、欧洲气候演化序列进行了对比分析.结果表明,末次冰消期的气候演化大致可分为两个阶段:前一阶段为暖期,但波动频繁;格陵兰、欧洲在经历了H1事件后,迅速转暖,Bolling期比Allerod期气候更为适宜;而青藏高原渐趋回暖,夏季风降水逐渐增加,存在由冰融水与降水增加所形成的高湖面,气候温湿,进入一次湖泊扩涨期;大部分记录指示Allerod期比Bolling期气候更为适宜.后一阶段为冷期,格陵兰、欧洲气候恶化并显示出有回返冰期的气候特点;青藏高原气候严酷、荒漠扩展、冰流推进、湖面下降.气候演化的这种异同性表明:格陵兰、欧洲与青藏高原气候系统彼此存在联系,特别是在冷期;而在暖期,气候演化表现出各自的特点.气候演化格局所呈现的可比性,可能是通过冷期的一致而体现的.     

European Climatic Response to Millennial-Scale Changes in the Atmosphere–Ocean System during the Last Glacial Period

Pollen, foraminifer, dinocyst, and coarse lithic high-resolution analyses and δ¹⁸O measurements have been carried out for the last-glacial section of marine core MD95-2042 located near the southwestern margin of the Iberian Peninsula. The pollen data indicate a high frequency of vegetational changes on the adjacent continent during this period, suggesting a climatic variability very similar to that of the Dansgaard-Oeschger cycles recorded by the Greenland ice cores. The detailed direct correlation of the terrestrial and marine proxy data from core MD95-2042 indicates a three-phase pattern of Heinrich events in land and ocean environments. The first and last phases of the H5 and H4 events are characterized by a mild and humid climate in southwestern Europe, probably associated with the European origin of the ice-rafted detritus. The middle phase exhibits a cold and dry climate in Iberia linked with the maximum input of ice-rafted detritus. This phase seems to correspond with the Laurentide ice-sheet surges. Between the Heinrich events, several cold and dry periods on land are correlated with stades of the Dansgaard-Oeschger cycles. The impact of the Dansgaard-Oeschger stades in southwestern Europe seems to be preferentially connected to the cold winter air masses reaching this mid-latitude region.     

Glacial-interglacial changes in the surface water characteristics of the Andaman Sea: Evidence from stable isotopic ratios of planktonic foraminifera

Stable carbon and oxygen isotopic analyses of the planktonic foraminifera (Globigerinoides ruber) from a deep sea sediment core (GC-1) in the Andaman Sea show high glacial-to-Holocene δ¹⁸O amplitude of 2.1%o which is consistent with previously published records from this marginal basin and suggest increased salinity and/or decreased temperature in the glacial surface waters of this region. A pulse of¹⁸O enrichment during the last deglaciation can be attributed to a Younger Dryas cooling event and/or to a sudden decrease of fresh water influx from the Irrawady and Salween rivers into the Andaman Sea. High δ¹³C values observed during the isotopic stages 2 and 4 are probably due to the enhanced productivity during glacial times in the Andaman Sea.     

近50a来科尔沁地区沙漠化土地的动态监测结果与分析

在明确了沙漠化土地的程度分级及其指标、监测方法的基础上,对科尔沁地区近50 a来的沙漠化土地进行了遥感动态监测和分析。结果表明:科尔沁地区20世纪50年代未至70年代中期,是沙漠化土地扩展速度最快的一个时期,总面积增加了9 084 km²。从70年代中期到80年代后期,沙漠化土地继续呈快速增长之势,增加了9 624 km²;进入90年代,沙漠化过程呈现出逆转的趋势,沙漠化土地总面积由1987年的61 008 km²,减少到2000年的50 142 km²,减少了10 866 km²。就近50 a来沙漠化土地变化的整体而言,经历了发展-再发展-逆转的过程。到2000年,科尔沁地区的沙漠化态势依然是严峻的。但从整个发展过程来看,沙漠化已呈现逆转的趋势。整个区域的生态环境在改善,环境容量在提高,继续发展下去,有望进入良性循环以保障生态环境与社会经济的可持续发展。     

末次冰期以来黄河变迁

本文认为黄河在末次冰期时代解体消亡，在晚更新世末期贯通，贯通后下游经历了漫流，填淤泻湖，堤坝束可决口演化阶段。     

中国东部陆架海对"新仙女木"事件的响应

新仙女木（Younger Dryas）事件是末次冰消期持续升温过程中的一次突然降温的典型非轨道事件,对于研究古气候、古环境的快速突变事件和短周期现象,合理评估现今气候一环境条件并做出气候变化的预测有着重要的意义。它是一个全球性的事件,中国东部陆架海也普遍发现了“新仙女木”事件的沉积记录。由于中国东部陆架位于欧亚大陆和太平洋之间,受季风的强烈影响,因此有着独特的响应。在“新仙女木”事件发生时,海平面在-50m水深位置稍微下降或振荡徘徊,在-50m线上则以湖泊沼泽、埋藏河床、风沙沉积记录为主,-50m以下则以海洋沉积记录为主,这条线的附近则存在沼泽泥炭和古潮流沙脊。     

冲绳海槽北部陆坡4.4万年以来古海洋环境演化的地质记录

利用AMS^14 C年代测试、氧同位素分析和浮游有孔虫分析重建了冲绳海槽北部陆坡DOC-42孔约44cal．kaBP以来的古海洋环境演化记录。DOC-42孔沉积速率整体较低，呈明显的阶段性变化：在氧同位素3期和LGM期间沉积速率相对较大，分别为7．3和14cm／ka；末次冰消期以来的沉积速率则显著降低，与冲绳海槽冰后期沉积速率高于末次冰期明显不同；自约6．4cal．kaBP以来，沉积物堆积作用基本可以忽略，表明了受黑潮入侵引起的中国东部陆架环流体系的改变，岩心所在区域的沉积格局发生了重大变化。浮游有孔虫氧碳同位素、转换函数古温度和低温、低盐特征种Globigerina quinqueloba等一致反映了冲绳海槽北部在氧同位素3期早期约37．5～44cal．kaBP期间存在明显的低温、低盐阶段，表明该期间冲绳海槽北部的沿岸冲淡水影响明显加强，而在氧同位素3期晚期该区可能受到了黑潮暖流的影响。此外，浮游有孔虫Pulleniatina obliquiloculata与氧同位素记录有很好的对应关系，表明它是冲绳海槽末次冰期以来的一个可靠的海洋环境指标。     

Identification of last interglacial deposits in eastern Beringia: a cautionary note from the Palisades,interior Alaska

Last interglacial sediments in unglaciated Alaska and Yukon (eastern Beringia) are commonly identified by palaeoecological indicators and stratigraphic position ～2–5 m above the regionally prominent Old Crow tephra (124 ± 10 ka). We demonstrate that this approach can yield erroneous age assignments using data from a new exposure at the Palisades, a site in interior Alaska with numerous exposures of last interglacial sediments. Tephrochronology, stratigraphy, plant macrofossils, pollen and fossil insects from a prominent wood‐rich organic silt unit are all consistent with a last interglacial age assignment. However, six ¹⁴C dates on plant and insect macrofossils from the organic silt range from non‐finite to 4.0 ¹⁴C ka BP, indicating that the organic silt instead represents a Holocene deposit with a mixed‐age assemblage of organic material. In contrast, wood samples from presumed last interglacial organic‐rich sediments elsewhere at the Palisades, in a similar stratigraphic position with respect to Old Crow tephra, yield non‐finite ¹⁴C ages. Given that local permafrost thaw since the last interglaciation may facilitate reworking of older sediments into new stratigraphic positions, minimum constraining ages based on ¹⁴C dating or other methods should supplement age assignments for last interglacial sediments in eastern Beringia that are based on palaeoecology and stratigraphic association with Old Crow tephra. Copyright © 2011 John Wiley & Sons, Ltd.     

The lacustrine depression at Annecy (France), geological setting and Quaternary evolution

The Annecy lacustrine depression lies in a tectonic transverse valley of structural origin, linking the present day towns of Annecy and Ugine and bounded by the Bauges and Bornes massifs. Only the last two major glacial periods are represented in the stratigraphic and geomorphic evidence from the area, but its successive glaciations that have been largely responsible for the form of the valley within which the present day lake lies. Of particular importance were the lobes of the Arve glacier, one shaping the depression from the south-east; the other from the north. The retreat of the glaciers left behind a more extensive precursor of the present day Lac d'Annecy, which latter constitutes the residual body of open water after lake level lowering, partial infilling and drainage diversions within the catchment. The drainage basin of the extended lake formed shortly after the last glacial maximum (LGM) in the region. Its extent can be determined from field sampling and coring and its elevation can be established at 460 m above present day sea level. The present day lake is more isolated, since the Fier river, to the north, no longer drains into it. To the southeast, the course of the Chaise river has also been diverted, leaving the lake's drainage basin reduced to half its post-LGM size. The major paleogeographical events in the Late-Quaternary evolution of the basin are described in chronological sequence.     

Preliminary study on the mineral magnetic properties of sediments from Kůlna Cave (Moravian Karst), Czech Republic

Summary Magnetic property variations in marine, lacustrine and loess-paleosol sequences have proved to be useful proxies in climate change studies. However in order to correctly interpret the record of the magnetic property variations it is absolutely necessary to have a good understanding of the cause of the observed variations. Most of the ambiguity in loess-paleosol studies is in distinguishing the role of pedogenesis from other climatic factors. Studying the mineral magnetic properties of the protected cave sediments which have not undergone pedogenesis allows us to determine the degree to which detrital input is climatically driven. These results will help us better understand the variations observed in the surficial loess-paleosol sequences. This study reports mineral magnetic data collected from entrance facies sediments deposited during the early Wurmian glacial stage in the Kůlna Cave. The entrance facies sediments consist of loess-like silts with varying amount of talus. The magnetic susceptibility record from these sediments shows higher values in layers originating in colder climates which is different to that commonly observed in surficial loess deposits. Higher values of magnetic susceptibility in Kůlna sediments are probably due to higher concentrations of ferromagnetic minerals (magnetite and maghemite) and due to an increased proportion of superparamagnetic grains. The magnetic mineralogy and the grainsize distribution (grains larger than superparamagnetic) appear not to change throughout the studied profiles. Higher magnetic susceptibility accompanied by an increase in the superparamagnetic fraction observed in the sediments deposited during colder periods can be explained by an increased input from a pedogenic source when the vegetation cover was reduced and the erosion rate increased.