乌鲁木齐东道海子剖面的硅藻记录与环境演变

通过分析乌鲁木齐河尾闾湖泊东道海子剖面的硅藻记录,结合孢粉、磁化率、烧失量和粒度分析资料,以^14C测年数据为基础,讨论了天山北麓古尔班通古特沙漠南部边缘的环境演变。研究认为：东道海子地区在4900aBP～3120aBP这一时段气候较稳定,3120aBP以来,有几次波动;湖泊的高湖面期与气候的冷期对应,湖泊的盐碱度较低,硅藻以及水生、沼生植物生长较繁盛;湖泊的中湖面期与气候的暖期对应,湖泊的盐碱度较高,硅藻以及水生、沼生植物生长较稀少。     

小冰期气候的研究进展

小冰期是近2ka来的一个重要气候事件,又是目前全球变暖的背景事件,已成为古气候和古环境研究的热点。对此,科学工作者已经做了大量的研究。本文广泛综合前人研究的成果,介绍了小冰期的概况,认为1450-1890年是小冰期的时限,在此期间有三次冷期和两次暖期。冷期发生在1450-1510年、1560-1690年和1790-1890年,其中第二次冷期表现最甚;暖期发生在1510-1560年和1690-1790年。太阳活动和火山活动是小冰期气候变化的主要因素。并重点从冰芯、树轮、湖泊沉积、历史文献和沙漠地层等方面综述了近年来国内外对小冰期气候变化的研究现状。     

烧失量分析在湖泊沉积与环境变化研究中的应用

烧失量分析是一种便捷的测定湖泊沉积物有机碳与碳酸盐含量的方法。由于沉积物烧失量主要受区域气温、有效降水等气候环境条件的控制,因此烧失量反映湖泊气候环境特征,成为指示区域气候环境变化的重要指标,该项指标在环境变化研究中具有重要作用。     

豫西渑池盆地湖泊沉积特征与古环境

对渑池盆地池底村古湖泊沉积剖面进行连续采样,在粒度组成和有机碳含量分析的基础上,结合¹⁴C年代测定(校正为日历年龄),重建了盆地区末次冰盛期以来的气候环境演化进程:19543~9240cal.aB.P.,气候比较干燥,古湖泊尚未形成;9240~8039cal.aB.P.,气候由干冷向暖湿化方向转变,古湖泊开始形成;8039~3473cal.aB.P.期间,气候温暖湿润,湖泊水位最高;3439~2931cal.aB.P.期间,气候波动剧烈,总体上气候较前一段干旱,湖泊水位下降;2931~2423cal.aB.P.期间,气候干旱,古湖泊干涸。盆地区的人类文化演进对气候环境变化的响应十分明显,二者之间存在一定的耦合关系。     

中国热带第四纪气候波动特征

中国热带早更新世气候波动以高频率小幅度为特征。“中更新世革命”发生在MIS20／MIS21之交。中更新世气候波动一般为三大旋回。晚更新世为两大旋回,但有变暖事件D／01～21及变冷事件H1～H6的表现。可以识别末次间冰期MISS及其阶段5a～5e。末次亚间冰期有4～7次冷暖波动。末次冰期温度一般比今低1～2℃或3～5℃。终止点Ⅰ为15000～13670aB．P．。终止点Ⅱ为0．135～0．130MaB．P．。新冰期Ⅰ、Ⅱ、Ⅲ都有表现。历史时期出现南北朝冷期、北宋冷期、明清小冰期。近200a的气候,前百年升温,后百年降温。     

近2000年都兰树轮10年尺度的气候变化及其与中国其它地区温度代用资料的比较

据高分辨率的青海都兰树轮年表 ,将过去 2 0 0 0年的气候变化划分为 2 30’S以前的高温期 ,2 40’S～ 80 0’S冷暖波动强烈的低温期 ,810’S～ 10 70’S显著高温期 ,即中世纪暖期 ,10 80’S～ 1880’S的低温期 ,其中包括 142 0’S～1870’S的小冰期 ,以及 1890’S后的升温期。统计发现 11次极端高温或低温事件 ,以及几次大的突变事件全部出现于中世纪之前 ,指示 15 0’S～ 110 0’S期间气候运行的高度不稳定性。和中国东部、古里雅冰芯和青藏高原南部温度代用资料比较后发现 ,公元初至 3世纪前期的东汉暖期 ,3世纪后期至 7世纪初的魏晋南北朝冷期 (期间约380’S～ 46 0’S暖 ) ,中世纪暖期以及小冰期等几次重大的气候事件在中国东部、都兰和青藏高原南部序列中均存在。古里雅冰芯仅记录了前两次重要事件 ,中世纪暖期以及小冰期在该序列中表现微弱。 2 0世纪的升温在古里雅冰芯最显著 ,都兰、中国东部次之 ,而高原南部似乎不明显。     

湖泊碳酸盐在过去环境变化研究中的应用

国内外的研究成果表明,湖泊沉积碳酸盐矿物及其微量元素、同位素分布特征记录了全球或区域古气候环境演变历史,可以从中提取大量定量化的古气候参数。因此,可以根据湖泊碳酸盐矿物的含量和碳、氧同位素变化等信息推知其形成时期的气候环境,重建古环境,揭示气候环境演变的规律。湖泊碳酸盐是一种研究古环境演化重要的代用指标,在过去气候环境变化研究中有广阔的应用前景。     

内蒙古岱海气候环境演变的沉积记录

根据对岱海湖泊岩芯沉积物的有机碳同位素、碳酸盐和磁化率等指标的综合分析,讨论岱海近１０００ 年来的气候环境演化过程,结果表明：９８０ａ Ｂ Ｐ～７３０ａ Ｂ Ｐ,气候以暖湿为主,岱海为高湖面期;７３０ａ Ｂ Ｐ～４８０ａ Ｂ Ｐ,以冷偏干气候为主;４８０ａ Ｂ Ｐ～２７０ａ Ｂ Ｐ,湖面急剧下降,气候冷偏湿转冷干气候;２７０ａ Ｂ Ｐ～１１０ａ Ｂ Ｐ,湖泊收缩,以温干气候为主;１１０ａ Ｂ Ｐ以来,有效降水略有增加,以凉偏湿气候为主。同时分析近年来气候向温干变化的总趋势。     

艾比湖Ash浅孔沉积信息揭示的环境演变过程

通过对艾比湖西南湖底1．8m浅孔的沉积特征、粒度组成、有机地化分析结合^14C测年数据重建湖泊沉积时代的环境面貌。研究显示近3000年来艾比湖地区的环境总体上是相对稳定的，全球的气候波动曾引起艾比湖水位和周边环境发生一定的变化。其中艾比湖在2600～2450aBP年问湖水相对较浅，气候相对冷干。2300a BP年左右湖泊深度变浅，剖面处受到河流的影响。2300～440a BP年间是艾比湖的高水位时期,气候温暖湿润，水陆生植物繁茂。440a BP以来湖泊变浅。气候变得更加干旱。艾比湖作为一内陆干旱区封闭型湖泊，对全球环境变化的响应较为敏感，艾比湖的形成演变具有典型的干旱区代表性。     

北极巴罗苔原区湖泊沉积的地球化学特征及其气候意义

应用地球化学元素、地球化学淋溶系数及环境温度指标,研究了北极阿拉斯加巴罗热融湖Ｉｋｒｏａｖｉｋ钻孔岩芯ＡＢ－３２连续的高分辨环境记录。结合２１０Ｐｂ测年数据,指出巴罗地区气候、环境变化的历史状况是：１６００～１７３５年为寒冷、干燥时期;１７５０～１８３０年,气候变暖、变湿;１８３０年出现明显的地球化学转折界限,１８３０～１９９４年,气候较湿润温暖。１９６９～１９７０年前后,巴罗地区有一变冷阶段。ＡＢ－３２钻孔岩芯１８３０年左右表现的古地球化学特征与现代Ｉｋｒｏａｖｉｋ湖泊环境地球化学特征相吻合,并且和Ｅｌｓｏｎ泻湖ＡＢ－６７沉积岩芯反映的气候环境变化基本一致。     

近800年来内蒙古岱海地区古气温的定量重建

根据对现代湖水、现生介形类壳体以及湖泊沉积岩芯中同一种属介形类壳体的Sr/Ca分析,利用现代湖水Sr/Ca与湖水盐度的关系,确定了不同沉积时期湖水盐度;其次,在室内模拟实验,建立了湖水盐度与湖水氧同位素的函数关系;结合²¹⁰Pb测定沉积速率和¹⁴C测年资料,利用沉积剖面的自生碳酸盐氧同位素及由湖水盐度推算的湖水氧同位素组成,定量恢复了不同时期的湖水温度,进而根据碳酸盐结晶时水温与年均气温关系推测了古气温。结果表明:在近800年内蒙古岱海地区的气温变化序列中,中世纪暖期、现代小冰期以及近百年增温均有明显表现。研究时段内,岱海地区中世纪暖期比当代30年的年均气温高1℃以上;在公元1240年左右突然降温过程表现特别突出,在其后约60年的时段内气温下降1.8℃;小冰期最大降温幅度2℃以上,大于华北其它地区。不同于我国西部古里雅冰芯的记录,岱海地区近百年增温程度仍没有达到中世纪暖期水平,预示气候变暖对我国西部地区的影响将大于东部。     

The Little Ice Age recorded in sediments of a small dystrophic mountain lake in southern Poland

We inferred the temperature and environmental conditions of Smreczynski Staw Lake in the Tatra Mountains, southern Poland, from a sediment record covering the last 1,500 years. Paleobiological methods (cladocera, chironomid, and diatom analyses) were used together with sedimentological analysis and dating. These studies provide new information about the timing and character of climate fluctuations during the Little Ice Age (LIA). The Medieval Warm Period ended in the Tatra region at the beginning of the thirteenth century, followed by the first episode of the LIA. The LIA was a relatively long but unstable period. The first part of the LIA was cold in the Tatra Mountains, without evidence of increasing precipitation, while the second part, after AD 1540, was cold and humid. The LIA terminated in the Tatra Mountains at the beginning of the twentieth century, although some aspects of its climatic and sedimentological regime continued until the 1920s. We also found some evidence of warming and acidification during the twentieth century.     

A comparison of climate changes between Arctic and China in the last 600 years

A compilation of paleoclimate records from lake sediments, trees, ice cores, and historical documents provide a view of China and Arctic environmental changes in the last 600 years. Many of these changes have also been identified in sedimentary and geochemical signatures in deep-sea sediment cores from the North Atlantic Ocean, Arctic and Greenland and ice cores from the Qinghai-Tibet Plateau, confirming the linkage of environmental changes of different time scales between the Arctic and China. It is shown that the changes of precipitation, temperature and sea ice cover in Arctic were correlated with climate changes in China. This paper also developed a comparative research on the climate changes between Arctic and China both during the Little Ice Age (LIA) and the instrumental observation period. Cycles and trend of temperature variations during LIA and temperature and precipitation during the instrumental observation period are performed. We found some similarities and differences of environmental changes between Arctic and China.     

近600年来北极与中国气候变化的对比

A compilation of paleoclimate records from lake sediments, trees, ice cores, and historical documents provide a view of China and Arctic environmental changes in the last 600 years. Many of these changes have also been identified in sedimentary and geochemical signatures in deep-sea sediment cores from the North Atlantic Ocean, Arctic and Greenland and ice cores from the Qinghai-Tibet Plateau, confirming the linkage of environmental changes of different time scales between the Arctic and China. It is shown that the changes of precipitation, temperature and sea ice cover in Arctic were correlated with climate changes in China. This paper also developed a comparative research on the climate changes between Arctic and China both during the Little Ice Age (LIA) and the instrumental observation period. Cycles and trend of temperature variations during LIA and temperature and precipitation during the instrumental observation period are performed. We found some similarities and differences of environmental changes between Arctic and China.     

Climate change inferred from aeolian sediments in a lake shore environment in the central Tibetan Plateau during recent centuries

Studies of the past climate variation on the Tibetan Plateau(TP) are currently limited in number and low in density and temporal resolution. We investigated the climate condition from about 400 years before present(B.P.) in the central TP at the shore of Co(means "lake") Nag using aeolian sediments. A 2.7-m sand profile with 57 sediment samples and six optically stimulated luminescence(OSL) samples were studied through grain-size analysis, geochemical elements and parameters, and depositional rate estimation. A previous assumption was verified that sand deposition at the shore of Lake Co Nag originated from hills to the east. Two significant wet periods between 90–140 and about 380 years B.P. were indicated by the variation of element profiles and sediment depositional rates. Aeolian activity is sensitive to variations from different seasonal changing patterns of climate factors in the study area, and aeolian sediments respond differently to climate conditions during the cold little ice age(LIA) and the warm 20 th century. Present day dry seasons of winter and spring might be much warmer and drier compared to seasons of 400 years ago although summer precipitation has increased, resulting in significantly more aeolian activity and higher depositional rate(about 6 times compared to 380–240 years ago) of sandy sediments. Aeolian problems like blown-sand deposition and desertification may be worse in a projected warming future in the central TP as well as other cold and high altitude regions. Our results suggest an agreement with environmental evolution during the little ice age and the 20 th century in a broader scale on the TP.     

Environmental impacts of Little Ice Age cooling in central Mexico recorded in the sediments of a tropical alpine lake

The Little Ice Age (LIA), AD 1350–1850, represents one of the most recent, persistent global climate oscillations. In Mexico, it has been associated with temperature decreases of 1.5–2 °C and mountain glacier advances, which are not accurately dated. We present new information about the nature of the LIA in central Mexico based on a decadal-resolution sediment sequence from high-altitude, tropical Lake La Luna, in the Nevado de Toluca volcano. We inferred past climatic and environmental changes using magnetic susceptibility, charcoal particles, palynomorphs, diatoms, cladoceran remains and multivariate statistics. The onset of the LIA corresponds with the beginning of a long-term trend to colder and drier climate ca. AD 1360–1910. The coolest and driest episode, ~AD 1660–1760, which corresponds with the Maunder Minimum in solar activity, was characterized by a cladoceran assemblage that showed the greatest dissimilarity to the modern one (no modern analogue), with the presence of cold-water species and Daphnia ephippia. The beginning of a warming trend ca. AD 1760, was identified by a diatom assemblage dominated by species with affinities for higher pH values (>6) and the greatest dissimilarity to the modern assemblage. This less cold, but still dry period, corresponds with historical reports of cattle and crop losses that predated the Mexican wars of Independence (AD 1810–1821) and Revolution (1910–1924). Modern conditions, established around AD 1910, resemble those during the Medieval Climate Anomaly (ca. AD 1200). No clear evidence of modern, human-induced environmental change was recorded, indicating that Lake La Luna is an ideal site in Mexico to monitor future impacts of global change.     

Late Holocene change in climate and atmospheric circulation inferred from geochemical records at Kepler Lake, south-central Alaska

Climate records during the last millennium are essential in placing recent anthropogenic-induced climate change into the context of natural climatic variability. However, detailed records are still sparse in Alaska, and these records would help elucidate climate patterns and possible forcing mechanisms. Here we present a multiple-proxy sedimentary record from Kepler Lake in south-central Alaska to reconstruct climatic and environmental changes over the last 800?years. Two short cores (85 and 101?cm long) from this groundwater-fed marl lake provide a detailed stable isotope and sediment lithological record with chronology based on four AMS ¹⁴C dates on terrestrial macrofossils and ²¹⁰Pb analysis. The ??¹⁸O values of inorganic calcite (CaCO₃) range from ?17.0 to ?15.7???, with the highest values during the period of 1450?C1850 AD, coeval with the well-documented Little Ice Age (LIA) cold interval in Alaska. The high ??¹⁸O values during the cold LIA are interpreted as reflecting shifts in atmospheric circulation. A weakening of the wintertime Aleutian low pressure system residing over the Gulf of Alaska during the LIA would have resulted in ¹⁸O-enriched winter precipitation as well as a colder and possibly drier winter climate in south-central Alaska. Also, elevated calcite contents of >80?% during the LIA reflect a lowering of lake level and/or enhanced seasonality (warmer summer and colder winter), as calcite precipitation in freshwater lakes is primarily a function of peak summer temperature and water depth. This interpretation is also supported by high ??¹³C values, likely reflecting high aquatic productivity or increased residence times of the lake water during lower lake levels. The lower lake levels and warmer summers would have increased evaporative enrichment in ¹⁸O, also contributing to the high ??¹⁸O values during the LIA. Our results indicate that changes in atmospheric circulation were an important component of climate change during the last millennium, exerting strong influence on regional climate in Alaska and the Arctic.     

尕海湖DG03孔碳酸盐含量及其环境意义

通过对尕海DG03孔岩芯碳酸盐含量的测定,表明碳酸盐含量指标较好地记录了尕海湖地区自冰消期晚期以来的气候环境变化。对阿勒罗德暖期和新仙女木期都有较好的反映,并揭示出早全新世气候变暖且波动明显,中全新世早期暖湿,后期温凉偏干,晚全新世气候明显变干,早期较为寒冷,后期偏暖。碳酸盐含量的变化反映了湖水的浓缩程度,与湖泊所处的沉积阶段相联系,同时与岩性特征所反映的环境也有关。在风成作用堆积的粉砂至中砂层,碳酸盐含量降至很低;在滨湖相沉积的细砂层,碳酸盐含量也较低,因此,碳酸盐含量指示的气候环境意义应与岩性及其他指标相结合进行分析,方可得到可信的结论。     

Climate changes and human activities recorded in the sediments of Lake Estanya (NE Spain) during the Medieval Warm Period and Little Ice Age

A multi-proxy study of short sediment cores recovered in small, karstic Lake Estanya (42°02?? N, 0°32?? E, 670 m.a.s.l.) in the Pre-Pyrenean Ranges (NE Spain) provides a detailed record of the complex environmental, hydrological and anthropogenic interactions occurring in the area since medieval times. The integration of sedimentary facies, elemental and isotopic geochemistry, and biological proxies (diatoms, chironomids and pollen), together with a robust chronological control, provided by AMS radiocarbon dating and ²¹⁰Pb and ¹³⁷Cs radiometric techniques, enabled precise reconstruction of the main phases of environmental change, associated with the Medieval Warm Period (MWP), the Little Ice Age (LIA) and the industrial era. Shallow lake levels and saline conditions with poor development of littoral environments prevailed during medieval times (1150?C1300 AD). Generally higher water levels and more dilute waters occurred during the LIA (1300?C1850 AD), although this period shows a complex internal paleohydrological structure and is contemporaneous with a gradual increase of farming activity. Maximum lake levels and flooding of the current littoral shelf occurred during the nineteenth century, coinciding with the maximum expansion of agriculture in the area and prior to the last cold phase of the LIA. Finally, declining lake levels during the twentieth century, coinciding with a decrease in human pressure, are associated with warmer climate conditions. A strong link with solar irradiance is suggested by the coherence between periods of more positive water balance and phases of reduced solar activity. Changes in winter precipitation and dominance of NAO negative phases would be responsible for wet LIA conditions in western Mediterranean regions. The main environmental stages recorded in Lake Estanya are consistent with Western Mediterranean continental records, and show similarities with both Central and NE Iberian reconstructions, reflecting a strong climatic control of the hydrological and anthropogenic changes during the last 800 years.     

Paleoclimatic evolution indicated by major geochemical elements from aeolian sediments on the east of Qinghai Lake

As the largest inland lake of China, along with its unique landscape and geographical location, Qinghai Lake has got much attention of the scientists for a long time. The precursors have done substantive researches by using the lake sediment, which deepen our understanding of the climate changes in this region. Although sand dunes and loess sediment are widely distributed around the lake, so far the researches on geochemical elements from aeolian sediment have been less reported. In this paper, we selected a typical aeolian profile on the east of Qinghai Lake. Based on systematic sampling and analysis of seven major geochemical elements, combined with OSL dating and previous researches, this paper discusses climate changes in the Qinghai Lake area since 12.5 ka B.P.. Our conclusions are: (1) Before 12.5 ka B.P., the climate in this region was dry, cold, and accompanied by strong wind-sand activities. (2) During 12.5–11.9 ka B.P., the climate became warm and wet. However, there was an abrupt climate cooling event during 12.2–11.9 ka B.P., which likely corresponded to the Younger Dryas event. (3) During 11.9–8.0 ka B.P., the climate fluctuated greatly and frequently from warm to cold, and three cooling events occurred. (4) During 8.0–2.6 ka B.P., the climate was warm and humid. (5) Since 2.6 ka B.P., similar to the modern climate, the climate was mainly dry and cold.