白令海盆17ka以来的古海洋与古气候记录

通过白令海盆08BR02钻孔(57°0.06'N,174°29.97'E,水深3 805 m)的AMS14C测年数据、颜色反射率b*与NGRIP(North Greenland Ice Core Project)氧同位素曲线及白令海4个钻孔颜色反射率b*记录作对比,建立该孔的地层年代框架,顶、底部沉积物年龄分别为4.2 ka和17.0 ka。该孔自17 ka以来,IRD(ice-rafted detritus:冰筏碎屑)、粒度的砂组分以及敏感组分中的33—63μm组分百分含量在全球性冷事件H1(Heinrich event 1)、B/A(Blling/Allerd)中期和YD(Younger Dryas)期间明显增加。IRD和有孔虫丰度在H1、B/A和YD期间同步增加,可能反映海冰融化为表层水提供营养物质,促使表层钙质生产力勃发并将有机质进一步输送至海底,为底栖生物提供营养物质。     

Sedimentary characteristics of relict deposits on the western South Yellow Sea

Integrated studies of vertical sedimentary sequences, grain sizes, and benthic foraminifera and ostracoda, in combination with AMS 14C dating, and 210Pb and 137Cs analysis were carried out in three vibracores taken from the area of relict deposits on the western South Yellow Sea. The relict sands, which are about 0.4 m thick, overlie on the Early Holocene coastal marsh or tidal flat deposits with an evident erosional interface in between. The middle and upper parts or sometimes the whole of the relict sands have been reworked under the modern dynamic environment. The sedimentation rate varies between 0.20–0.30 cm year-1. The relict sands show a bimodal grain-size distribution pattern in frequency curves, with a sharp peak in the coarse fraction between 3Φ and 4Φ and a secondary peak in the fine fraction of about 7Φ. Of the benthic foraminiferal and ostracod assemblages, the reworked relict sands are characterized by the mixing of the nearshore euryhaline shallow-water species and deeper water species. The erosional interface at the bottom of the relict sands is considered as a regional ravinement surface formed during the transgression in the Early Holocene due to shoreface retreating landwards. The relict sands were accumulated on the ravinement surface during the transgression in the deglaciation period as lag deposits after winnowing and reworking by marine dynamic processes. And the secondary peak of fine fraction in the frequency curve for the relict sands suggests the input of fine-grained sediments during the reworking process. As the conclusion, the relict sands in the study area are interpreted as a type of reworked relict sediments.     

EVIDENCE FOR ABRUPT CLIMATIC CHANGES ON NORTHWESTERN MARGIN OF EAST ASIAN MONSOON REGION DURING LAST DEGLACIATION

Based on investigations of the Zhongwei Nanshan aeolian section situated in the southeastern margin of Tengger Desert, carbon-14 and TL (thermoluminescence) dating results and paleoclimatie proxies such as magnetic susceptibility and grain size, we inferred that the northwestern margin of East Asian monsoon region experienced abrupt climatic changes during the last deglaciation. Six oscillation events were identified: Oldest Dryas, Bφlling, Older Dryas, Allerφd, Intra-Allerφd Cold Period (IACP) and Younger Dryas (YD). The summer monsoon was weaker during Oldest Dryas and Younger Dryas when the winter monsoon was stronger. However, during the B/A (Bφlling/Allerφd) period, the summer monsoon strengthened, reflected by magnetic susceptibility, when the winter monsoon also became strong, which is different from the paleoclimatic pattern established in the East Asian monsoon region. Furthermore, the summer monsoon was nearly in phase with the climate changes inferred from the oxygen isotopic records of     

Wisconsinan Late-glacial environmental change in Nova Scotia: A regional synthesis

A synthesis of the interpreted vegetational and climatic history of Nova Scotia during the Wisconsinan Late-glacial period (14-9 ka BP) is presented and described in 500-year intervals. The concomitant regional deglaciation history of the region is also described. A synthesis chart is provided which includes a qualitative curve of temperature reconstructions for the Lateglacial period.     

Wisconsinan Late-glacial environmental change on the southeast Baffin shelf,southeast Baffin Island and northern Labrador

The importance of the Baffin-Labrador region is explained in terms of the channelling through this area of the mass flux of meltwater from the Laurentide Ice Sheet and the probable effects of this on the thermohaline circulation of the North Atlantic. The chronology of glaciation and deglaciation in the region is summarised. Reference is made to recent marine records from the Baffin Shelf. Isotopic changes recorded in foraminiferal assemblages obtained from marine sediments in the Baffin Shelf-Labrador Sea area indicate the timing and possible magnitude of meltwater fluxes during the period 14.0-11.0 ka BP.     

A continuous stable isotope record from the penultimate glacial maximum to the Last Interglacial (159–121 ka) from Tana Che Urla Cave (Apuan Alps,central Italy)

Relatively few radiometrically dated records are available for the central Mediterranean spanning the marine oxygen isotope stage 6–5 (MIS 6–5) transition and the first part of the Last Interglacial. Two flowstone cores from Tana che Urla Cave (TCU, central Italy), constrained by 19 U/Th ages, preserve an interval of continuous speleothem deposition between ca. 159 and 121 ka. A multiproxy record (δ¹⁸O, δ¹³C, growth rate and petrographic changes) obtained from this flowstone preserves significant regional-scale hydrological changes through the glacial/interglacial transition and multi-centennial variability (interpreted as alternations between wetter and drier periods) within both glacial and interglacial stages. The glacial stage shows a wetter period between ca. 154 and 152 ka, while the early to middle Last Interglacial period shows several drying events at ca. 129, 126 and 122 ka, which can be placed in the wider context of climatic instability emerging from North Atlantic marine and NW European terrestrial records. The TCU record also provides important insights into the evolution of local environmental conditions (i.e. soil development) in response to regional and global-scale climate events.     

菲律宾海北部19cal.kaBP以来表层海水温度变化

对菲律宾海北部E-2岩心柱(29.62°N、131.14°E,水深3 877m)进行了浮游有孔虫δ18 O分析、AMS14 C测年以及U3k7表层海水温度(U3k7-SST)的测试。结果表明,E-2岩心记录了约19cal.kaBP以来U3k7-SST变化过程,其末次冰消期整体变化过程与北大西洋高纬地区相似,记录了Heinrich 1(H1)、Blling/Allerd(B/A)和Younger Dryas(YD)等快速气候事件,同时也识别出发生于19.4～19.2和18.5～18.0cal.kaBP的2次变冷事件,说明了研究区与北大西洋气候存在遥相关;在B/A和YD阶段中发现的百年尺度气候波动及变化过程,可能反映了热带过程对研究区域的影响;E-2岩心柱末次冰消期变暖存在阶段性,其变暖时间开始于19.4cal.kaBP,而大幅升温阶段则从15.3cal.kaBP开始。     

Post‐Younger Dryas deglaciation of the Greenland western margin as revealed by spatial analysis of lakes

Lake shapes and their spatial distribution are important geomorphological indicators in previously glaciated areas. Their shapes are influenced by the underlying geological structure and processes of glacial sediment deposition or erosion. Since these processes act on large areas, distribution of lakes can reflect the intensity of glacial erosional/depositional processes and their spatial extent. Landsat imagery was used to extract lake outlines from a selected pilot‐study area on the widest ice‐free coastal margin of the south‐western Greenland north of Kangerlussuaq. Analysis included image classification and spatial analysis of lakes with elevation data using geographic information system (GIS) tools. A morphometric index was applied to extract kettle lakes as indicators of a specific glacial process – ice stagnation. Analysis of their spatial distribution helped in the reconstruction of glacial dynamics in formerly glaciated terrain. Our results show that spatial lake distribution combined with elevation analysis can be used to identify zones of glacial erosion and deposition. The highest concentrations of lakes within the study area occupy the elevation range between 164 and 361 m above sea level (a.s.l.). This zone can be identified as an area where intensive glacial erosion took place in the past. The widespread distribution of modeled kettle lake features within the same elevation range and across the study area suggests that the last deglaciation process was accompanied by abandonment of blocks of stagnant ice. This conclusion is supported by surface exposure ages obtained in the same study area and published elsewhere. Copyright © 2009 John Wiley & Sons, Ltd.