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1.
DANIEL VERES ELISABETH LALLIER-VERGÈS BARBARA WOHLFARTH TERRI LACOURSE DIDIER KÉRAVIS SVANTE BJÖRCK FRANK PREUSSER VALéRIE ANDRIEU-PONEL LINDA AMPEL 《Boreas: An International Journal of Quaternary Research》2009,38(2):230-243
A new set of geochemical data obtained from a long sediment sequence from the Les Echets basin provides a new record of palaeoenvironmental change for western Europe. The sequence covers the late part of Marine Isotope Stage (MIS) 3 and MIS 2 ( c . 46.1–15.0 cal. kyr BP) and extends over 30 m of sediment, allowing for high sampling resolution. Distinct cyclic fluctuations in aquatic productivity proxies suggest a tempo of environmental change at Les Echets that resembles the one established for Dansgaard-Oeschger cycles and Heinrich events. Increases in organic carbon are paralleled by high hydrogenous contents and enriched δ13 Corg and Corg /Ntot ratios, implying a mixture of aquatic and land-derived constituents. The stable isotope values are directly linked to primary aquatic productivity and the input of terrestrial organic matter, enriched during warm, productive, periods, and drastically depleted during cold periods, particularly Heinrich events. Phases of relatively high productivity correlate with Dansgaard-Oeschger interstadials 8–2, while Heinrich events 3 and 2 are also clearly delineated by distinct lithological horizons with very low organic contents, high dry densities and enhanced organic matter oxidation. A large hiatus occurring about the time of Heinrich event 4 suggests that the cold and dry climate reconstructed for this event in the North Atlantic region also greatly affected Les Echets and its catchment. 相似文献
2.
《Quaternary Science Reviews》2007,26(9-10):1369-1383
Paleoenvironmental records in Europe describing paleofires extending back to the Last Interglacial have so far been unavailable. Here, we present paleofire results from the combined petrographic and automated image analysis of microcharcoal particles preserved in marine core MD95-2042 retrieved off southwestern Iberia and covering the last climatic cycle. The variability of microcharcoal concentrations reveals that the variability of fire emissions is mainly imprinted by the 23 000 yr precessional cycle. A focus on the Last Glacial Period further shows that paleofires follow the variability of Dansgaard–Oeschger oscillation and Heinrich events and, therefore, parallel the variability of atmospheric temperatures over Greenland detected in ice cores. There is no evidence for fire increase related to human activity. The variability of fire emission by-products for the Last Glacial Period is interpreted in terms of changes in biomass availability. Low fire activity is associated with periods of drought which saw the development of semi-desert vegetation that characterised stadial periods. Fire activity increased during wetter interstadials, related to the development of open Mediterranean forests with more woody fuel availability. 相似文献
3.
Orbital- and sub-orbital-scale climate impacts on vegetation of the western Mediterranean basin over the last 48,000 yr 总被引：1，自引：0，他引：1
High-resolution pollen analysis of Alborán Sea core MD95-2043 provides a 48-ka continuous vegetation record that can be directly correlated with sea surface and deep-water changes. The reliability of this record is supported by comparison with that of Padul (Sierra Nevada, Spain). Marine Isotope Stage (MIS) 3 was characterised by fluctuations in Quercus forest cover in response to Dansgaard-Oeschger climate variability. MIS 2 was characterised by the dominance of semi-desert vegetation. Despite overall dry and cold conditions during MIS 2, Heinrich events (HEs) 2 and 1 were distinguished from the last glacial maximum by more intensely arid conditions. Taxon-specific vegetation responses to a tripartite climatic structure within the HEs are observed. In MIS 1, the Bölling-Allerød was marked by rapid afforestation, while a re-expansion of semi-desert environments occurred during the Younger Dryas. The maximum development of mixed Quercus forest occurred between 11.7 and 5.4 cal ka BP, with forest decline since 5.4 cal ka BP. On orbital timescales, a long-term expansion of semi-desert vegetation from MIS 3 into MIS 2 reflects global ice-volume trends, while Holocene arboreal decline reflects summer insolation decrease. The influence of precession on the amplitude of forest development and vegetation composition is also detected. 相似文献
4.
千年尺度气候突变事件是第四纪冰期普遍存在的气候现象。这些事件可以被分为两类,一类为Dansgaard-Oeschger Event (DO事件),另一类为海因里希(Heinrich Stadial,HS)事件,后者有时也被认为是一种特殊的DO事件,因此也被称为 HS-DO事件。HS事件期间北大西洋冰架的融化一般对应DO振荡的冷相位,这与通常认为的冰架在较冷气候下体积增加并不相符。这两类事件在北大西洋重建数据中表现得最为明显,但其气候影响具有全球性。由于没有显著的外强迫驱动这两类气候突变事件,自20世纪90年代首次被确认以来,HS-DO事件一直是古气候界关注的重点,且人们对其触发机理仍没有定论。本文基于目前对这两类千年事件的研究现状,集中总结了目前已有的可反映千年事件的重建数据,利用已有的模拟工作,重点回顾了现有的机制理论,评述了目前研究DO事件以及HS-DO事件的局限性,并对其后续工作,尤其是模拟部分,进行了展望。 相似文献
5.
Pollen and dinoflagellate cyst assemblages from Core SU 81-18 recovered off Portugal (37°46′N, 10°11′W; 3135-m water depth) have been used to document the short-term environmental changes that occurred in southwest Europe since 25,000 yr B.P. The relationship between the oceanic and continental environments has been further examined by the use of other marine proxies (coarse sedimentary fraction, foraminifera) and by comparison with proximal land pollen records. Heinrich 2 (H2) and Heinrich 1 (H1) events were the most extreme parts of the highly variable last glacial period, with the maximum extension of dry steppe on land and the occurrence of cool and dilute waters at the core site. Our study shows that H1 and H2 are divided in two distinct phases: one with Neogloboquadrina pachyderma left coiling associated with the maximum input of ice rafted debris, reflecting the in situ release of icebergs and the occurrence of cool and dilute seawater at the core site; the other with dinoflagellate cysts of subpolar affinity, Bitectatodinium tepikiense, reflecting a seasonal control marked by warm summer SST and cold winter SST. 相似文献
6.
Saharan Dust Transport and High-Latitude Glacial Climatic Variability: The Alboran Sea Record 总被引：1，自引：0，他引：1
Ana Moreno Isabel Cacho Miquel Canals Maarten A. Prins María-Fernanda Snchez-Goi Joan O. Grimalt Gert Jan Weltje 《Quaternary Research》2002,58(3):318
Millennial to submillennial marine oscillations that are linked with the North Atlantic's Heinrich events and Dansgaard–Oeschger cycles have been reported recently from the Alboran Sea, revealing a close ocean-atmosphere coupling in the Mediterranean region. We present a high-resolution record of lithogenic fraction variability along IMAGES Core MD 95-2043 from the Alboran Sea that we use to infer fluctuations of fluvial and eolian inputs to the core site during periods of rapid climate change, between 28,000 and 48,000 cal yr B.P. Comparison with geochemical and pollen records from the same core enables end-member compositions to be determined and to document fluctuations of fluvial and eolian inputs on millennial and faster timescales. Our data document increases in northward Saharan dust transports during periods of strengthened atmospheric circulation in high northern latitudes. From this we derive two atmospheric scenarios which are linked with the intensity of meridional atmospheric pressure gradients in the North Atlantic region. 相似文献
7.
Sidney R. Hemming Gerard C. Bond Wallace S. Broecker Warren D. Sharp Mieczyslawa Klas-Mendelson 《Quaternary Research》2000,54(3):372
The abundance and lithic content of ice rafted detritus in glacial North Atlantic sediment cores vary abruptly on millennial time scales that have been correlated to Dansgaard-Oeschger cycles in the Greenland ice cores. There is growing evidence that various ice sheet outlets contributed increased iceberg fluxes at multiple discrete intervals, and the relative timing of iceberg discharges from different sources is important for understanding interactions between oceans and ice sheets. We present a provenance study based on 40Ar/39Ar dates of individual hornblende grains from 20 samples taken at 600 to 700 yr spacing between 10,500 and 22,000 yr B.P., from Orphan Knoll core EW9303-GGC31. Heinrich layers are characterized by a dominant Paleoproterozoic hornblende provenance consistent with published studies. A change in provenance between Heinrich events H2 and H1 indicates contributions of iceberg calving from the Newfoundland and southern Labrador margins. Between H1 and the Younger Dryas interval, Paleoproterozoic ice rafted grains remained dominant. The dominance of Baffin Island (or Greenland?) sources to the ice rafted detritus is ascribed to the retreat of the southern Laurentide ice sheet at about the time of H1—a retreat that isolated Newfoundland and southern Labrador ice from the shelf-slope boundary. 相似文献
8.
Climate fluctuation on a kiloyear scale during the Late Last Glacial in Mu Us Desert,China: evidence from Rb and Sr contents and ratios 总被引：1，自引：0，他引：1
Yuejun Si Baosheng Li David Dian Zhang Xiaohao Wen Fengnian Wang Shuhuan Du Dongfeng Niu Yihua Guo 《Environmental Earth Sciences》2014,72(11):4521-4530
The MGS2 segment of the Milanggouwan stratigraphical section in China’s Salawusu River Valley records 5.5 sedimentary cycles consisting of dune sands alternating with fluviolacustrine facies or/and palaeosols. The high Rb and Sr contents and low Rb/Sr ratios in the fluviolacustrine facies indicate the presence of a warm and humid climate, and vice versa for a dry and cold climate. Rb and Sr appeared to have 5.5 element cycles that are consistent with the sedimentation changes, and each cycle lasts about 2 ka on average. This study suggests that the observed cycles mainly resulted from variations in the strength of the East Asian winter and summer monsoons, and the MGS2 segment experienced six cold-dry winter monsoons and five warm-humid summer monsoons during the OIS2. In addition, the millennial-scale monsoonal climate fluctuations revealed by the element cycles corresponded well with the Dansgaard–Oeschger cycles recorded in the Greenland ice cores and Heinrich events in the North Atlantic marine sediments. Therefore, the monsoonal climate fluctuations revealed by the Rb and Sr in the MGS2 segment were likely triggered by global climate change. 相似文献
9.
末次间冰期以来地球气候系统的突变 总被引：14，自引：0，他引：14
地球气候系统的突然变化是近年来地学研究的热点。取自极地冰芯、海洋沉积物和陆地的古气候记录表明,末次间冰期以来全球经历了一系列数百年—千年时间尺度的气候突变事件,证明了在末次冰期—间冰期旋回大尺度气候变化背景下,全球气候存在较大不稳定性这一基本事实。尽管末次间冰期以来这些数百年—千年时间尺度气候突变事件的成因和影响范围还存在明显的不确定性,但已从诸如末次间冰期(MIS 5e)中期的干冷事件、末次冰期的Dansgaard-Oeschger旋回、Heinrich事件和Younger Dryas事件以及发生在全新世冰后期的一些降温事件的研究中,获得对过去130 ka来气候变化过程总体上的认识和理解。综述了近年来的主要研究成果,介绍了有关末次间冰期以来全球气候突变事件发生的时间、过程和机制等最新的研究进展。 相似文献
10.
Guan Qing Yu Pan Bao Tian Li NaLi Qiong Zhang JundiGao Hongshan Liu Jia 《Comptes Rendus Geoscience》2010,342(3):189-196
Records of two loess sections located in mid-eastern and western margins of the East Asian Monsoon area captured 20 Dansgaard-Oescher events and six Heinrich events. All these suggested that the climate in the East Asian Monsoon area fluctuated rapidly on millennial to century timescales during the whole Last Glacial. We found that these loess-based events of rapid climate fluctuations were generally synchronous with those of GRIP records, but that there were differences between the Shagou loess section in the west and the Wangguan loess section in the east: the former was more sensitive to climate change than the latter. Compared with earlier studies on loess records covering the Last Glacial from neighboring areas, we discovered that the magnitude of Dansgaard-Oeschger cycles decreased gradually from west to east and we suggest that it resulted from the combined effect of the Westerlies and the East Asian Monsoon. 相似文献
11.
Grant R. Bigg Richard C. Levine Chris D. Clark Sarah L. Greenwood Haflidi Haflidason Anna L. C. Hughes Atlé Nygård Hans Petter Sejrup 《第四纪科学杂志》2010,25(5):689-699
Ice‐rafted debris (IRD) seeded into the ocean from Northern Hemisphere ice sheets is found in ocean cores along the southwestern European margin through the last glacial period. It is known that the origin of this IRD, especially off Iberia, can vary between North America and western Europe during short‐lived episodes of greatly enhanced iceberg flux, known as Heinrich events, although in most Heinrich events the IRD has a North American source. During the longer times of much lower IRD fluxes between Heinrich events, use of an intermediate complexity climate model, coupled to an iceberg dynamic and thermodynamic model, shows that background levels of IRD most likely originate from western Europe, particularly the British–Irish Ice Sheet. Combining modelling with palaeoceanographic evidence supports reconstructions of a short‐lived, but substantial, Celtic and Irish Sea Ice Stream around 23 ka. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
12.
通过对位于东亚季风区中东部与西部边缘的两个高分辨率黄土剖面记录的对比研究，发现它们不仅捕捉到了20个Dansgaard Oeschger事件与6个Heinrich事件，而且黄土记录与GRIP冰芯记录的这些快速气候波动基本上是同步的。暗示在整个末次冰期，东亚季风气候同样存在千年—百年尺度上的快速波动。所不同的是，西面的沙沟剖面对这些快速气候波动的反应比东面的王官剖面敏感。结合末次冰期中国黄土记录的先前研究结果，我们发现，自西向东Dansgaard Oeschger旋回的幅度逐渐变小，推测这主要是由西风与东亚夏季风共同作用所造成的。 相似文献
13.
Alexandra Haase-Schramm Steven L. Goldstein Mordechai Stein 《Geochimica et cosmochimica acta》2004,68(5):985-1005
U-series dating can be an effective means to obtain accurate and precise ages on Quaternary carbonates. However, most samples require a correction for U and Th in admixed detritus. This complication is often addressed through generation of U-Th isochrons, requiring analyses of several coeval samples. In addition, presence of water-derived (hydrogenous) Th in the carbonate can cause inaccuracies in isochron ages.This study reports a high-resolution U-series chronology of sediments deposited by Lake Lisan, the last glacial precursor of the Dead Sea. The strategy employed combines multiple measurements from a few stratigraphic heights and fewer analyses from many heights in a single described and measured section. The resulting chronology is based on ages at 22 heights in a ∼40-m-thick section covering the interval of ∼70-14 calendar ka BP. The effects of admixed detritus are evaluated using trace elements. Nearly pure aragonite samples, indicated by very low abundances of insoluble elements such as Nb and Zr, were found to contain hydrogenous Th, which causes the uncorrected U-230Th age of a modern sample to be ∼2.5 ka. Nevertheless, accurate ages have been obtained by correcting for the detrital and aqueous interferences. The resulting ages are in stratigraphic order, and their accuracy is evidenced by consistency of Lisan Formation U-series and 14C ages with the coral-based calendar-radiocarbon age calibration.The U-Th ages provide a context to unravel the limnological history of Lake Lisan. Boundaries between the Lower, Middle, and Upper stratigraphic units correspond to the MIS 4/3 and 3/2 transitions, respectively. During MIS 2 and 4 the lake generally showed a stable two-layer configuration and a positive fresh-water balance, reflected by deposition of laminated aragonite-detritus. Dry intervals during MIS 2 and 4 are indicated by thick gypsum layers and an inferred depositional hiatus, which are temporally associated with Heinrich events H1 at ∼17 ka and H6 at ∼65 ka, respectively. During MIS 3 the lake level was unstable with intermittent dry periods indicated by abundant clastic layers and a significant hiatus between ∼43-49 ka. Clastic layers are associated with Dansgaard-Oeschger events during MIS 3, and indicate lake level declines during abrupt Northern Hemisphere warmings. Overall, the climate of the Eastern Mediterranean region shows a strong linkage to the Northern Hemisphere climate, with increasing lake size and stability during cold periods, and fluctuations and dessication during warmings and Heinrich events. 相似文献
14.
Two cores from the southwestern shelf and slope of Storfjorden, Svalbard, taken at 389 m and 1485 m water depth have been analyzed for benthic and planktic foraminifera, oxygen isotopes, and ice-rafted debris. The results show that over the last 20,000 yr, Atlantic water has been continuously present on the southwestern Svalbard shelf. However, from 15,000 to 10,000 14C yr BP, comprising the Heinrich event H1 interval, the Bølling-Allerød interstades and the Younger Dryas stade, it flowed as a subsurface water mass below a layer of polar surface water. In the benthic environment, the shift to interglacial conditions occurred at 10,000 14C yr BP. Due to the presence of a thin upper layer of polar water, surface conditions remained cold until ca. 9000 14C yr BP, when the warm Atlantic water finally appeared at the surface. Neither extensive sea ice cover nor large inputs of meltwater stopped the inflow of Atlantic water. Its warm core was merely submerged below the cold polar surface water. 相似文献
15.
High resolution multiproxy analysis (microcharcoal, pollen, organic carbon, Neogloboquadrina pachyderma (s), ice rafted debris) of the deep-sea record MD04-2845 (Bay of Biscay) provides new insights for understanding mechanisms of fire regime variability of the last glacial period in western France. Fire regime of western France closely follows Dansgaard–Oeschger climatic variability and presents the same pattern than that of southwestern Iberia, namely low fire regime associated with open vegetation during stadials including Heinrich events, and high fire regime associated with open forest during interstadials. This supports a regional climatic control on fire regime for western Europe through fuel availability for the last glacial period. Additionally, each of Heinrich events 6, 5 and 4 is characterised by three episodes of fire regime, with a high regime bracketed by lower fire regime episodes, related to vegetational succession and complex environmental condition changes. 相似文献
16.
17.
We present new palynological information from the anoxic Cariaco Basin, off Venezuela, that provides insight into the response of northernmost South American vegetation to rapid climate changes between 68 and 28 ka, specifically during North Atlantic Heinrich events (HEs) and Dansgaard/Oeschger cycles. We defined three different vegetation modes: (1) an interstadial mode characterized by the highest pollen concentration and the maximum extension of semi-deciduous and evergreen forests; (2) a stadial mode characterized by increases of salt marshes, herbs, and montane forests; and (3) a Heinrich event mode characterized by the lowest pollen concentrations, abrupt increases of salt marshes, and decreased forest abundance. Similarly, indices of C4/C3 plants show increases during stadials with clear peaks during the onset of HEs, though grasslands did not become dominant during these periods. We alternatively propose that these expansions of C4 plants are associated with the expansion of coastal salt marshes. Our vegetation record suggests the prevalence of humid conditions during interstadials, dry and cold conditions during stadials, and dry and cold conditions together with changes in sea level during HEs. This new palynological evidence supports previous interpretations that main environmental changes in northernmost South America were driven by latitudinal displacements of the Intertropical Convergence Zone and sea-level changes. 相似文献
18.
Detailed reconstructions of the vegetation of Iberia during the last glacial inception are rare due to the limited number of terrestrial sites recording this period. Active retreat of El Asperillo cliff, located on the Atlantic coast of southwestern Iberia, has exposed a fossil organic level dating back to one of the early stades of the last glacial cycle. Pollen and macrofossil analyses from this site show that the Doñana area was covered mainly by steppic vegetation; temperate trees survived the coldest periods, albeit in reduced numbers. Mediterranean taxa are extremely reduced, in contrast with other dry areas of southern Iberia over this time span. This vegetation suggests cold and arid climatic conditions, in accordance with paleoclimatic reconstructions based on several Atlantic marine cores. 相似文献
19.
邯郸地区晚更新世以来植被波动特征及其对气候变化的响应 总被引：1，自引：0，他引：1
对河北邯郸HZ S孔沉积物进行孢粉分析,结果表明该地区晚更新世以来的气候演变形式既有与全球同步的特点,也有本区域独自的特征。古气候与古植被演变过程如下:（1）晚更新世末次间冰期气候温暖湿润(130～75 kaBP),植被为森林草原;末次冰期气候演化经历了寒冷干燥(75～55 kaBP)→温暖湿润(40～30 kaBP)→寒冷干燥(30～10 kaBP)的过程,植被演替过程相应为草原→森林草原→草原。（2）全新世气候演化经历了温凉略干(10～8 kaBP)→温暖湿润(8～3 kaBP)→温凉偏干(3～0 kaBP)的过程,植被演替过程相应为疏林草原→森林草原→疏林草原。（3）发生在25 kaBP左右,16 kaBP左右和11～10 kaBP的冷事件可能是Heinrich事件3、1和Younger Dryas事件在中国东部季风区的响应。 相似文献
20.
以南海北、西、南部3个沉积速率相对较高而且连续的沉积柱状样MD2904,MD2901和MD2897为基础,通过粒度、碳酸盐、有机地球化学和元素分析,并综合前人研究成果,对南海MIS3期进行探讨。结果显示,南海MIS3是末次冰期中的弱暖期,海水表层古温度比相邻的MIS2和MIS4期略高,但是明显比MIS1和MIS5期低。MIS3的最大特点就在于其气候的不稳定性,发生了多次气候快速变化事件。在格陵兰冰芯中记录的千年尺度快速气候变化事件（D/O事件和Heinrich事件）基本上在南海北、西、南部都有响应,具有与全球同步的特征。南海MIS3古生产力都显示出较高的特点,这与东亚季风有着密切的关系,北部主要受冬季风影响,西部和南部主要受夏季风影响。南海南部MIS3表现出比MIS5更高的古生产力和更强的夏季风强度,这一特点有待更进一步深入研究。 相似文献