末次冰消期带湖光岩玛珥湖古季风变化记录

末次冰消期热带湖光岩玛珥湖沉积物高分辨率的生物硅、总有机碳、总氮和决氢等有机地化指标记录显示了一系列百年至升年尺度的快速变化,表明季风环流系统运行的强烈不稳定性,这种不稳定性变化与格陵兰冰芯记录的气候事件相比较,表现出一定的遥相关,但也表现出了末交肖期初始转暖低纬度区超前高纬度区的显著不同,这种变化可能与低纬度区热带水文循环的驱动作用相关。     

我国中低纬度末次冰消期气候转暖 与高纬度气候变化的关系*

末次冰消期转暖的过程和机制一直是古气候研究的热点,然而对于末次冰消期全球气候在时间、空间上的变化以及热带低纬度地区在其中发挥的作用仍不明确。文章根据我国中低纬度地区的湖光岩玛珥湖、渭南黄土剖面和东海DGKS9603孔沉积物中的植硅体等环境指标的分析,研究了末次冰消期在这些地区的变化特点,并结合古里雅冰芯和南京葫芦洞石笋氧同位素记录与南极BYRD冰芯、北极格陵兰GRIP冰芯氧同位素记录进行了对比。结果表明,各地区转暖的时间并不同步,明显受印度洋季风或东南季风影响的古里雅、湖光岩地区是气候转暖较早的地区,格陵兰地区的快速转暖滞后于我国中低纬度转暖1.5~2.0ka以上。如何理解高纬度和热带低纬度地区气候转暖的差异性问题及其原因和机制有待于更多高分辨率气候记录研究和模型的检验。     

末次冰消期冲绳海槽中部表层和温跃层海水温度演化的脱耦现象

解读末次冰消期全球水文气候演变过程对于理解气候系统对内外强迫的响应具有重要意义. 以冲绳海槽中部OKI02岩心为材料,通过浮游有孔虫Globigerinodes ruber和Pulleniatina obliquiloculata壳体Mg/Ca比值分别重建了19 ka BP以来海槽中部表层和温跃层海水温度（SST和TWT）,结合浮游有孔虫群落组成变化重点恢复了末次冰消期（~18~11.7 ka BP）上层水体温度变化的特征和过程. 结果显示SST在LGM显著偏低,末次冰消期表现为显著的千年尺度变化,清楚地记录了HS1、B/A、YD等快速气候波动事件. 19 ka BP以来重建的TWT整体呈明显的上升趋势,但波动频繁而剧烈,末次冰消期相对较低,未显示显著的千年尺度变化. 对比北半球高纬和热带太平洋的记录发现,末次冰消期冲绳海槽中部SST开始上升的时间基本与前者相当,但明显滞后于热带西太平洋;冰消期其变化模式明显区别于热带西太平洋持续稳定的升温过程,而更类似于北半球高纬区的变化. 与SST明显不同,海槽区温跃层的升温（~18 ka BP）明显早于北半球高纬变暖,却接近于热带西太平洋海表温度开始上升的时间;且TWT的上升和波动方式也更接近于热带太平洋海温的变化模式. 对末次冰消期SST和TWT差异化演变的分析表明,AMOC对中低纬大气环流的影响可能通过东亚冬季风强度的变化控制了海槽区SST的演变,而热带太平洋ENSO过程则可能通过黑潮强度的变化决定了区域TWT的演化. 末次冰消期冲绳海槽中部SST和TWT演化存在明显的脱耦现象,显示了其与高、低纬海洋和气候变化之间的密切联系.      

我国末次冰消期古气候时空演化特征初探

为探讨我国末次冰消期古气候时空演化特征,从北到南、从西到东分别选取8个和6个已发表的持续时间较长和分辨率相对较高的古气候记录,对比分析了我国末次冰消期气候演化(以Younger Dryas和Bφlling/Allerφd 事件为主)随纬度和海拔高度变化所表现出的趋势和规律.结果显示,末次冰消期的主要事件在我国基本均有显...     

末次冰消期以来赛里木湖沉积记录的气候突变

末次冰消期以来的气候突变事件的时空变化特征及其区域响应是古气候环境变化研究的重要内容,然而亚洲中部干旱区末次冰消期以来的气候突变记录较少,尤其缺少末次冰消期期间快速转暖过程的区域响应.本研究通过对位于亚洲中部干旱区的新疆西天山中部亚高山湖泊赛里木湖湖心采得的长300 cm的SLM2009钻孔沉积物的碳酸盐含量和粒度变化特征的分析,在 14 个 AMS 14C测年数据的基础上,探讨了末次冰消期约23. 4 cal. ka B. P.以来亚洲中部干旱区的气候突变事件记录及其区域响应过程.结果表明:赛里木湖湖心钻孔沉积物完整记录了 H1 ( 17. 5 ~ 15. 2 cal. ka B. P.)、 YD ( 12. 6 ~ 11. 7 cal. ka B. P.)冷事件以及 B-A ( 15. 2 ~12. 9 cal. ka B. P.)暖事件等末次冰消期气候突变事件以及全新世以来的10. 5 ka、 8. 2 ka、 5. 5 ka、 4. 2 ka、 2. 8 ka和小冰期冷事件,这与亚洲中部干旱区已有的气候突变事件记录相吻合,表明末次冰消期以来亚洲中部干旱区具有相似的气候突变演化模式.同时这些气候突变事件与高纬冰芯以及低纬石笋氧同位素记录的一致性则表明气候突变具有全球性影响,受相同的成因机制因素控制.     

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.     

西太平洋暖池核心区新不列颠海沟有机质来源及碳酸盐含量变化

深海有机质的来源与演化及其碳酸盐含量变化是碳循环的重要环节之一。通过分析新不列颠海沟水深3908 m采集的柱状沉积物总有机碳(TOC)和总氮(TN)的含量、有机碳的δ¹³C值和AMS-¹⁴C定年以及CaCO_3含量变化,探讨该海区的有机质来源与演化及碳酸盐含量变化与控制因素。研究发现:(1)该地区的有机质主要来源于海洋自生有机质,但受到陆源有机质输入的影响,其中在末次冰消期和全新世早期,海平面相对较低,但海平面逐渐上升会带来部分侵蚀的陆源土壤输入,而且作为降水带的赤道辐合带(ITCZ)位置偏南引起的陆源剥蚀物质输入增强,使陆源有机质贡献比例较高,主要来自巴布亚新几内亚森林土壤的有机质贡献;(2)该地区的CaCO_3含量在末次冰消期以来呈现出末次冰消期和全新世中晚期较低,而全新世早中期较高的特征,其变化主要受海平面变化和ITCZ迁移引起的陆源碎屑物质输入强弱的影响。     

岗日嘎布玉东曲末次冰消期冰川演化及其10Be暴露测年研究

末次冰盛期（Last Glacial Maximum, LGM）结束后,全球经历末次冰消期进入全新世,这代表了过去十万年以来最为显著的气候转型事件。末次冰消期的开始在全球范围内近乎同步,但其背后的气候驱动机制仍不明确。中低纬度,如青藏高原及其周边地区的山地冰川对气候变化响应敏感,准确限定LGM结束前后冰川地貌的时代可为上述问题的解决提供可靠的古冰川信息。然而,目前青藏高原仍缺乏足够有针对性的研究。本文选取位于青藏高原东南部的岗日嘎布作为研究区,对该区格泥峰东侧的玉东曲谷口分布的冰碛垄序列进行了详细的地貌调查和宇宙成因核素¹⁰Be暴露测年研究。采自玉东曲谷口附近6道冰碛垄中地貌相对年代较老的4道冰碛垄的14个冰川漂砾¹⁰Be暴露年龄介于（13.3±1.0）~（19.3±1.4） ka。利用累积概率密度和简化卡方等统计分析方法排除异常值后,将这4道冰碛垄中地貌相对年代较年轻两道的形成时代限定为（17.0±0.5） ka和（18.4±1.0） ka,分别对应末次冰消期和LGM后期。与气候记录进行对比后,我们认为这两次冰川波动响应可能受控于印度洋-太平洋暖池海表温度的夏季气温变化。     

LATE QUATERNARY HIGH LAKE LEVELS AND ENVIRONMENTAL CHANGES SINCE LAST DEGLACIAL IN DALIANHAI,GONGHE BASIN IN QINGHAI PROVINCE

干旱区晚第四纪已有较多高湖面与湖泊演化的报道和研究,对于认识区域环境变化有重要意义,但高湖面出现的时间尚存争议,高分辨率的气候环境记录仍相对缺乏.本文通过青海共和盆地达连海湖岸地貌考察和AMS 14C年代学研究,讨论达连海古湖晚第四纪高湖面出现的可能时间;并通过达连海DLH99孔岩芯年代和高分辨率代用指标,讨论高原东北缘末次冰消期以来的气候环境变化.达连海周围存在6级高湖面岸线或台地,14C测年结果显示,最低的两级湖岸堤形成于全新世,其余湖岸台地年代均老于44cal.kaB.P.,当时在达连海地区形成一个较大的古湖泊.DLH99孔显示达连海近15cal.kaB.P.沉积了40.92m的湖相沉积物,平均沉积速率高达2.7mm/a.孢粉资料揭示出,现代干旱的共和盆地在末次冰消期以来存在两个山地针叶林发育阶段,分别位于末次冰消期和全新世早中期.全新世早中期是适合山地针叶林植被发育的气候最宜期,而晚全新世山地森林植被整体衰退.粒度分析结果显示,达连海全新世低水位时期对应于岩芯中部山地森林植被发育的晚期,出现较强烈干旱事件(岩芯深13～15m段),这种湖泊水位与植被所指示的气候变化不一致现象(即低水位时期盆地内耐旱植物和山地乔木花粉同时增加),可能揭示出干旱区山地与盆地环境对区域气候不同响应.达连海存在的系列高湖面和冰消期以来的完整气候记录,为理解晚第四纪季风边缘区气候变化过程及其机制提供了条件.     

Advances in Palaeoclimatic Research Recorded by Peat in China since the Last Deglaciation

泥炭记录的环境演变是过去全球变化（PAGES）研究的重要领域之一,分析了中国泥炭记录的古气候演化研究的区域范围,当前主要以东北哈尼、青藏高原的红原、神农架大九湖以及华南定南大湖四个位于东部季风区的研究工作最为集中。泥炭沉积高分辨率综合信息揭示了末次冰消期以来中国气候变化的时空特征：冷暖干湿变化既有一致性又表现出区域差异,末次冰消期东北地区、东部山地、华南地区都表现出冷偏湿的气候特点,而青藏高原却为冷偏干或凉偏干;Younger Dr-yas（YD）事件之后,全新世早期和中期青藏高原、东部山地、华南地区气候总体以温湿为主要特征,而东北地区有效降水减少,到全新世晚期,呈现出干旱的变化趋势。并对B～A事件,YD事件,8.2ka以及4.2 ka等重大气候突变事件研究工作进行了综述。最后指出今后应拓展与重建更多区域古气候环境变化序列的对比,加强泥炭沉积及环境指标的基础理论,重视和提高大气沉降泥炭档案以及气候变化背景下泥炭地碳循环机制等研究工作。     

Controls on the East Asian monsoon during the last glacial cycle,based on comparison between Hulu Cave and polar ice-core records

Previous studies have suggested a sound chronological correlation between the Hulu Cave record (East Asian monsoon) and Greenland ice-core records, which implies a dominant control of northern hemisphere climate processes on monsoon intensity. We present an objective, straightforward statistical evaluation that challenges this generally accepted paradigm for sub-orbital variability. We propose a more flexible, global interpretation, which takes into account a broad range of variability in the signal structures in the Hulu Cave and polar ice-core records, rather than a limited number of major transitions. Our analysis employs the layer-counted Greenland Ice-Core Chronology 2005 (GICC05), which was developed for Greenland records and has since been applied – via methane synchronisation – to the high-resolution δ¹⁸O_ice series from EPICA Dronning Maud Land (EDML). The GICC05 chronology allows these ice-core records to be compared to the U–Th dated Hulu Cave record within relatively narrow (～3%) bounds of age uncertainty. Following previous suggestions, our proposed interpretation suggests that the East Asian monsoon is influenced by a combination of northern hemisphere ‘pull’ (which is more intense during boreal warm periods), and southern hemisphere ‘push’ (which is more intense monsoon during austral cold periods). Our analysis strongly suggests a dominant control on millennial-scale monsoon variability by southern hemisphere climate changes during glacial times when the monsoon is weak overall, and control by northern hemisphere climate changes during deglacial and interglacial times when the monsoon is strong. The deduced temporally variable relationship with southern hemisphere climate records offers a statistically more plausible reason for the apparent coincidence of major East Asian monsoon transitions with northern hemisphere (Dansgaard–Oeschger, DO) climate events during glacial times, than the traditional a priori interpretation of strict northern hemisphere control.     

Paleohydrological Changes in the Western Tibetan Plateau over the Past 16,000 years Based on Sedimentary Records of n‐Alkanes and Grain Size

Both monsoons and westerlies have exerted influence on climate dynamics over the Tibetan Plateau (TP) since the last deglaciation, producing complex patterns of paleohydroclimatic conditions. Diverse proxy records are essential to forge a robust understanding of the climate system on the TP. Currently, there is a general lack of understanding of the response of inland lakes over the TP to climate change, especially glacier‐fed lakes. Paleohydrological reconstructions of such lakes could deepen our understanding of the history of lake systems and their relationship to regional climate variability. Here we use records of n‐alkanes and grain size from the sediments of Bangong Co in the western TP to reconstruct paleohydrological changes over the past 16,000 years. The Paq record (the ratio of non‐emergent aquatic macrophytes versus emergent aquatic macrophytes and terrestrial plants) is generally consistent with the variations in summer temperature and precipitation isotopes. The changes in grain‐size distributions show a similar trend to Paq but with less pronounced fluctuations in the early‐middle Holocene. The new data combined with previous results from the site demonstrate that: 1) Bangong Co experienced relatively large water‐level fluctuations during the last deglaciation, with a steadily high lake‐level during the early‐middle Holocene and a decreasing lake‐level in the late Holocene; 2) The lake level fluctuations were driven by both high summer temperatures via the melting water and monsoon precipitation. However, the dominant factor controlling lake level changed over time. The lake‐level history at Bangong Co deduced from the n‐alkanes and grain‐size records reveals the past hydrological changes in the catchment area, and stimulates more discussion about the future of glacier‐fed lakes under the conditions of unprecedented warming in the region.     

Sub-millennial scale variations in East Asian monsoon systems recorded by dust deposits from the north-western Chinese Loess Plateau

Previous work has demonstrated that magnetic properties and sediment particle size of Chinese loess deposits provide information on past behaviour of Chinese summer and winter monsoons, respectively (Heller and Evans, 1995; Derbyshire et al, 1997). It has been suggested that the East Asian winter monsoon system in particular is teleconnected on earth orbital and sub-orbital timescales to climatic states and events in high northern latitudes, especially northern hemisphere ice volume and Heinrich events, (Porter and An, 1995; Chen et al., 1997). However, the majority of this research has been performed around the central part of the Chinese Loess Plateau where the rate of dust accumulation is relatively low, thus limiting the potential resolution of palaeoclimatic records. Here we present a high resolution (5mm / ~20 yr interval) magnetic susceptibility record from an thick loess deposit located at Caoxian in the north-western part of the Loess Plateau. The record spans the “Lateglacial” (last glacial / interglacial transition) and when placed on a palaeomagnetic chronology shows a relationship with the GISP2 proxy air temperature record from Greenland (Grootes et al., 1993; Meese et al., 1994; Stuiver et al 1995). The results demonstrate that several Lateglacial climatic fluctuations previously reported in the North Atlantic region and in Europe are also recorded in China. In addition, the apparent absence of a signal corresponding to the Bølling Interstadial in China during the early deglaciation suggests that, at certain times, the apparent North Atlantic — Asian monsoon teleconnection may have collapsed. The demonstrated ability of the loess deposits to resolve sub-millennial scale climate variations points to their potential as a previously unexplored archive for very high-resolution studies of terrestrial climate.     

The role of seasonality in abrupt climate change

A case is made that seasonality switches dominated by wintertime were instrumental in abrupt climate changes in the North Atlantic region during the last glaciation and into the Holocene. The primary evidence comes from mismatches between mean annual temperatures from Greenland ice cores in comparison with snowline changes in East Greenland, northern Europe, and North America. The most likely explanation is a shutdown (or reduction in strength) of the conveyor. This allows the spread of winter sea ice across the North Atlantic, thus causing the northern region to experience much colder winters. Because they mimic the Greenland temperature rather than the snowline signal, changes in the Atlantic Intertropical Convergence Zone and the Asian monsoon may also share a winter linkage with Greenland. Thus the paleoclimate record is consistent with the notion that a huge continental sector of the Northern Hemisphere, stretching from Greenland to Asia, was close to an extreme winter threshold during much of the last glaciation. Winter climate crossed this threshold repeatedly, with marked changes in seasonality that may well have amplified and propagated a signal of abrupt change throughout the hemisphere and into the tropics.     

Lake sediments from Store Koldewey, Northeast Greenland, as archive of Late Pleistocene and Holocene climatic and environmental changes

A 2.9 m long sedimentary record was studied from a small lake, here referred to as Duck Lake, located at 76°25'N, 18°45'W on Store Koldewey, an elongated island off the coast of Northeast Greenland. The sediments were investigated for their geophysical and biogeochemical characteristics, and for their fossil chironomid assemblages. Organic matter began to accumulate in the lake at 9.1 cal. kyr BP, which provides a minimum age for the deglaciation of the basin. Although the early to mid-Holocene is known as a thermal maximum in East Greenland, organic matter accumulation in the lake remained low during the early Holocene, likely due to late plant immigration and lack of nutrient availability. Organic matter accumulation increased during the middle and late Holocene, when temperatures in East Greenland gradually decreased. Enhanced soil formation probably led to higher nutrient availability and increased production in the lake. Chironomids are abundant throughout the record after 9.1 cal. kyr BP and seem to react sensitively to changes in temperature and nutrient availability. It is concluded that relative temperature reconstructions based on biogeochemical data have to be regarded critically, particularly in the period shortly after deglaciation when nutrient availability was low. Chironomids may be a suitable tool for climatic reconstructions even in those high arctic environments. However, a better understanding of the ecology of chironomids under these extreme conditions is needed.