Evidence of Younger Dryas and Neoglacial cooling in a Late Quaternary palaeotemperature record from a speleothem in eastern Victoria,Australia

A calcitic stalagmite collected from a limestone cave in the Buchan area of eastern Victoria has been dated by three mass-spectrometric uranium series analyses. Two growth phases are represented: the older from 13.4 to 10.6 ka and the younger from 3.2 to 2.1 ka. Oxygen isotope analysis reveals that temperatures were below present-day values at all times, but particularly cool conditions are indicated between 12.3 and 11.4 ka, and Neoglacial conditions occurred at about 3 ka. The older cold climate event is clearly synchronous with the Younger Dryas in Europe and this is the first time that strong evidence for this event has been found in Australia. Carbon isotope variations are interpreted as indicating changes in plant productivity on the surface and are most likely controlled by variations in summer rainfall. They indicate particularly high levels of plant productivity from 11.5 to 11.0 ka. © 1996 John Wiley & Sons, Ltd.     

Calendar year age estimates of Allerød–Younger Dryas sea‐level oscillations at Os,western Norway

A detailed shoreline displacement curve documents the Younger Dryas transgression in western Norway. The relative sea‐level rise was more than 9 m in an area which subsequently experienced an emergence of almost 60 m. The sea‐level curve is based on the stratigraphy of six isolation basins with bedrock thresholds. Effort has been made to establish an accurate chronology using a calendar year time‐scale by ¹⁴C wiggle matching and the use of time synchronic markers (the Vedde Ash Bed and the post‐glacial rise in Betula (birch) pollen). The sea‐level curve demonstrates that the Younger Dryas transgression started close to the Allerød–Younger Dryas transition and that the high stand was reached only 200 yr before the Younger Dryas–Holocene boundary. The sea level remained at the high stand for about 300 yr and 100 yr into Holocene it started to fall rapidly. The peak of the Younger Dryas transgression occurred simultaneously with the maximum extent of the ice‐sheet readvance in the area. Our results support earlier geophysical modelling concluding a causal relationship between the Younger Dryas glacier advance and Younger Dryas transgression in western Norway. We argue that the sea‐level curve indicates that the Younger Dryas glacial advance started in the late Allerød or close to the Allerød–Younger Dryas transition. Copyright © 2004 John Wiley & Sons, Ltd.     

福建仙云洞石笋记录的新仙女木突变事件结束时的缓变特征

新仙女木（Younger Dryas,简称YD）事件是发生在末次冰消期升温过程中北半球的一次急剧降温事件。文章基于福建西部仙云洞石笋（编号：XYⅣ-14）9个高精度²³⁰Th年龄和233个氧同位素分析,建立了12.68~11.25 ka B.P.时段平均分辨率达7 a的东亚夏季风强度的演变序列。该石笋氧同位素记录最为显著的特征是在11.89~11.51 ka B.P.时δ¹⁸O在380±95 a内偏负约1.3‰,指示了YD事件缓慢的结束过程。与基于年层时标的我国北方苦栗树洞、南京葫芦洞和神农架青天洞石笋记录对比发现,仙云洞记录的YD结束过程的时间（380±95 a）明显比苦栗树洞、葫芦洞和青天洞记录（38 a、10 a和11 a）长300多年。仙云洞石笋所记录的YD事件缓慢结束的特征与低纬菲律宾Palawan洞穴石笋记录十分相似。分析结果表明,受热带西太平洋海气耦合的影响,低纬水文循环过程的变化比高纬的气候突变要缓慢的多。

     

Stomatal evidence for a decline in atmospheric CO2 concentration during the Younger Dryas stadial: a comparison with Antarctic ice core records

A recent high‐resolution record of Late‐glacial CO₂ change from Dome Concordia in Antarctica reveals a trend of increasing CO₂ across the Younger Dryas stadial (GS‐1). These results are in good agreement with previous Antarctic ice‐core records. However, they contrast markedly with a proxy CO₂ record based on the stomatal approach to CO₂ reconstruction, which records a ca. 70 ppm mean CO₂ decline at the onset of GS‐1. To address these apparent discrepancies we tested the validity of the stomatal‐based CO₂ reconstructions from Kråkenes by obtaining further proxy CO₂ records based on a similar approach using fossil leaves from two independent lakes in Atlantic Canada. Our Late‐glacial CO₂ reconstructions reveal an abrupt ca. 77 ppm decrease in atmospheric CO₂ at the onset of the Younger Dryas stadial, which lagged climatic cooling by ca. 130 yr. Furthermore, the trends recorded in the most accurate high‐resolution ice‐core record of CO₂, from Dome Concordia, can be reproduced from our stomatal‐based CO₂ records, when time‐averaged by the mean age distribution of air contained within Dome Concordia ice (200 to 550 yr). If correct, our results indicate an abrupt drawdown of atmospheric CO₂ within two centuries at the onset of GS‐1, suggesting that some re‐evaluation of the behaviour of atmospheric CO₂ sinks and sources during times of rapid climatic change, such as the Late‐glacial, may be required. Copyright © 2002 John Wiley & Sons, Ltd.     

The Younger Dryas Event and Holocene Climate Fluctuations Recorded in a Stalagmite from the Panlong Cave of Guilin

Comprehensive studies on a stalagmite from the Panlong cave, Guilin, have shown that the isotopic records and sedimentary characteristics can reflect the changes of both palaeotemperatures and palaeorainfall, that is to say, it is possible to get some information about the changes in climate of the area from the speleothem. The results suggest that: (1) the Younger Dryas event might have persisted in the area from 11 300 to 10 800 a B.P.; (2) from 9000 to 7000 a B.P., the climate got warmer and wetter, and the summer monsoon was gradually enhanced; (3) from 7000 to 4500 a B.P., the climate was warm and wet, and the summer monsoon prevailed; and (4) from 4500 a B.P. on, the summer monsoon was weakened and the modern climate pattern appeared, but there were several cold and dry periods, namely, from 4000 to 2500 a B.P., ca. 2400 a B.P. and < 1000 a B.P.     

新仙女木(YD)事件区域特征及动力机制研究新进展

新仙女木事件(Younger Dryasevent,YD事件)为末次冰消期发生的快速降温事件,作为典型突变气候事件,它一直是国际古气候关注热点,其研究的开展促进和深化了科学界对千年尺度突变气候事件的理解和认识。近年来,随着高分辨率地质记录涌现,YD事件时空差异性日益突出。对比和认识这些区域之间事件细节结构及转型模式异同有助于甄别其相位关系,探讨不同环境快速重组对高、低纬突变气候事件的响应方式,进而验证早期驱动—响应假说,为其动力学机制建立及未来相似边界条件下气候预测提供基本地质证据和理论模型。本文从YD事件区域响应方式入手,通过总结和对比模拟研究及地质记录,对YD事件已有研究存在的争议进行回顾,提出有待加强的研究区域和未来研究方向。     

新仙女木事件在罗布泊湖相沉积物中的记录

通过对罗布泊CK-2钻孔湖相沉积物磁化率、粒度、碳酸盐和有机质含量的测定以及地球化学元素的多元统计分析, 探讨了我国西北极端干旱区域的环境对全球气候变化的响应.结果显示各代用指标均一致揭示了发生在12.8~11.6kaBP间非常明显的低温期, 且降温幅度大, 变化迅速.这次冷事件在时间坐标以及发生特点上都与格陵兰冰心记录的末次冰消期中的新仙女木事件相对应, 为新仙女木事件的全球性特征提供了新的证据.这说明在我国新疆的极端干旱区, 其气候与环境的变化也与北半球高纬度地区有着密切的联系; 由主成分分析结果, 揭示了我国西北地区的西风气候区有别于东南季风气候区的水热配置特点, 即冷期湿润, 暖期干旱, 并提出了该事件信号从北大西洋传送到罗布泊地区的潜在机制.      

Younger Dryas事件与北黄海泥炭层的形成

形成于海平面变化处于停滞阶段和湿润气候条件下的泥炭层是古环境变化信息的重要载体。对北黄海4个含泥炭层的沉积剖面进行研究后发现,其均集中在渤海海峡入口处,水深变化在50～54m。泥炭层的AMS14C年龄在10650～1010014 CaBP,与发生在11000～1000014 CaBP间的末次冰消气候回冷事件——Younger Dryas(YD)事件在年代上非常吻合,表明北黄海泥炭层的形成可能与YD事件的全球效应密切相关,可作为YD事件在北黄海陆架响应的一个重要证据。泥炭层在北黄海的集中出现说明,冰后期的海平面上升过程中在YD事件期间存在停滞阶段,这一时期海面已经达到渤海海峡外侧,并可能在此徘徊了近千年。此外,泥炭层的大量出现和孢粉记录表明YD事件发生期间约为10600～1020014 CaBP,此时北黄海可能处在寒冷而湿润的环境。这一发现与全球范围内大部分YD事件的海陆记录存在明显差异,说明不同地区对YD事件的响应存在差异,不能简单地利用单一的干冷模式来分析YD事件在区域上的响应特征和过程。     

The glacial geomorphology of the Loch Lomond (Younger Dryas) Stadial in Britain: a review

This paper systematically reviews the glacial geomorphological evidence of the Loch Lomond Stadial (LLS; Younger Dryas) glaciation in Britain (12.9–11.7 ka). The geomorphology of sub‐regions within Scotland, England and Wales is assessed, providing the most comprehensive synthesis of this evidence to date. The contrasting nature of the evidence at the local scale is reviewed and conceptual themes common to multiple sub‐regions are examined. Advancements in glaciological theory, mapping technologies, numerical modelling and dating have been applied unevenly to localities across Britain, inhibiting a holistic understanding of the extent and dynamics of the LLS glaciation at a regional scale. The quantity and quality of evidence is highly uneven, leading to uncertainties regarding the extent of glaciation and inhibiting detailed analysis of ice dynamics and chronology. Robust dates are relatively scarce, making it difficult to confidently identify the limits of LLS glaciers and assess their synchroneity. Numerical models have allowed the glacier–climate relationships of the LLS to be assessed but have, thus far, been unable to incorporate local conditions which influenced glaciation. Recommendations for future research are made that will allow refined reconstructions of the LLS in Britain and contribute to a more comprehensive understanding of glacier–climate interactions during the Younger Dryas.     

Atlantic surface water inflow to the Nordic seas during the Pleistocene–Holocene transition (mid–late Younger Dryas and Pre‐Boreal periods, 12 450–10 000 a BP)

The inflow of Atlantic Water to the Nordic seas from mid–late Younger Dryas to earliest Holocene (12 450–10 000 a BP) is reconstructed on the basis of a high‐resolution core (LINK14) from 346 m water depth on the east Faroe shelf. We have analysed the distribution of planktic and benthic foraminifera, stable isotopes and ice‐rafted debris (IRD), and calculated absolute temperatures and salinities by transfer functions. During the investigated time period there was almost continuous inflow of Atlantic Water to the Nordic seas. Deposition of IRD during the mid–late Younger Dryas and Pre‐Boreal coolings indicates the presence of melting icebergs and that summer sea surface temperatures were low. The east–west temperature gradient across the Faroe–Shetland Channel was much steeper than today. The cold conditions around the Faroe Islands are attributed to stronger East Greenland and East Icelandic currents than at present. The near‐continuous inflow of Atlantic Water is consistent with published evidence suggesting that deep convection took place in the Nordic seas, although the convection sites probably had shifted to a more easterly position than at present. Around the time of deposition of the Saksunarvatn Tephra c. 10 350 a BP, sea surface temperatures increased to the present level. Copyright © 2011 John Wiley & Sons, Ltd.     

Hydrological changes in the European midlatitudes associated with freshwater outbursts from Lake Agassiz during the Younger Dryas event and the early Holocene

Recent studies of lake-level fluctuations during the last deglaciation in eastern France (Jura Mountains and Pre-Alps) and on the Swiss Plateau show distinct phases of higher water level developing at the beginning and during the latter part of Greenland Stade 1 (i.e., Younger Dryas event) and punctuating the early Holocene period at 11,250-11,050, 10,300-10,000, 9550-9150, 8300-8050, and 7550-7250 cal yr B.P. The phases at 11,250-11,050 and 8300-8050 cal yr B.P. appear to be related to the cool Preboreal Oscillation and the 8200 yr event assumed to be associated with deglaciation events. A comparison of this mid-European lake-level record with the outbursts from proglacial Lake Agassiz in North America suggests that, between 13,000 and 8000 cal yr B.P., phases of positive water balance were the response in west-central Europe to climate cooling episodes, which were induced by perturbation of the thermohaline circulation due to sudden freshwater releases to oceans. This probably was in response to a southward migration of the Atlantic Westerly Jet and its associated cyclonic track. Moreover, it is hypothesized that, during the early Holocene, varying solar activity could have been a crucial factor by amplifying or reducing the possible effects of Lake Agassiz outbursts on the climate.     

A re-evaluation and spatial analysis of evidence for a Younger Dryas climatic reversal in Beringia

An objective classification of paleoclimatic proxies from 75 lake and peat records is used to re-evaluate data quality and inferred climatic patterns in Beringia during the Younger Dryas. Mapped data reveal coherent but spatially-complex regional patterns, suggesting the Younger Dryas was characterized by: (1) cooling in Southern Alaska, Eastern Siberia, and portions of Northeastern Siberia; and (2) uniform to warmer-than-present conditions through most of Central Alaska, Northeastern Siberia, and possibly the Russian Far East and Northern Alaska. The Beringian patterns correspond to distinctive large-scale climatic forcings, although in some locations further modified by more local influences, such as topography. General circulation models and modern synoptic climatology provide a conceptual framework for exploring possible mechanisms responsible for the observed changes. Forcings and associated climatic responses consistent with the proxy data include: (1) lowered sea-surface temperatures in the North Atlantic and Pacific reducing temperature and precipitation in Eastern Siberia; (2) intensified Aleutian low and lowered sea-surface temperatures causing cooler summers and higher winter precipitation in Southern Alaska; (3) stronger Pacific Subtropical High and an eastward shift of the East Asian Trough reducing summer temperatures in Southern Alaska and causing relative warmth in Northeastern Siberia; and (4) strong high pressure system producing warm, dry conditions in interior Alaska.     

Climate and environment during the Younger Dryas (GS‐1) as reflected by composite stable isotope records of lacustrine carbonates at Torreberga,southern Sweden

Climatic and environmental changes during the Younger Dryas stadial (GS‐1) and preceding and following transitions are inferred from stable carbon and oxygen isotope records obtained from the sediments of ancient Lake Torreberga, southern Sweden. Event GS‐1 is represented in the sediment sequence by 3.5 m of clay containing lacustrine carbonates of various origins. Comparison of isotopic records obtained on mollusc shells, ostracod valves, and Chara encrustations precipitated during specific seasons of the year supports estimates of relative changes in both lake water and mean annual air temperatures. Variations in soil erosion rates can also be estimated from a simple isotope–mass‐balance model to separate allochthonous and autochthonous carbonate contributions to the bulk carbonate content of the sediments. The well‐known, rapid climatic shifts characterising the Last Termination in the North Atlantic region are clearly reflected in the isotopic data, as well as longer‐term changes within GS‐1. Following maximum cooling shortly after the Allerød–Younger Dryas (GI‐1–GS‐1) transition, a progressive warming and a slight increase in aquatic productivity is indicated. At the Younger Dryas–Preboreal (GS‐1–PB) transition mean annual air temperature rapidly increased by more than 5°C and summer lake‐water temperature increased by ca. 12°C. The subsequent Preboreal oscillation is characterised by an increase in soil erosion and a slight decrease in mean annual air temperature. These results are in harmony with recent findings about large‐scale climate dynamics during the Last Termination. Copyright © 1999 John Wiley & Sons, Ltd.