A Late Quaternary Climate Record Based on Multi-Proxies Analysis from the Jiaochang Loess Section in the Eastern Tibetan Plateau, China

We compared the stable carbon isotopic records from a loess transect of the Jiaochang in the eastern Tibetan Plateau, spanning the last ~21,000 years, with multiproxy data for pedogenesis, including magnetic susceptibility, clay fraction, Fed/Fet ratio, carbonate and total organic carbon content, in order to probe the mechanisms of δ13C values of organic matter and Late Quaternary climate variations in the eastern Tibetan Plateau. Our results indicate that there is no simple relationship between δ13C of organic matter and summer monsoon variations. The change in δ13C values of organic matter (in accordance with the ratios of C3 to C4 plants) results from the interaction among temperature, aridity and atmospheric pCO2 level. Drier climate and lower atmospheric pCO2 level contribute to positive carbon isotopic excursion, while negative carbon isotopic excursion is the result of lower temperature and increased atmospheric pCO2 level. Additionally, our results imply that the Tibetan monsoon may play an important role in climate system in the eastern Tibet Plateau, which specifically reflects frequently changing climate in that area. The results provide new insights into the forcing mechanisms on both the δ13C values of organic matter and the local climate system.     

16 ka以来黄土高原东亚夏季风变化的环境磁学记录

末次冰消期以来的气候变化是第四纪古气候研究的重要内容。本文对黄土高原西部和平镇剖面16 ka以来的黄土沉积序列（厚度为3.5 m）进行了高分辨率环境磁学研究。结果表明：该黄土序列的磁性颗粒主要由细颗粒磁铁矿主导。其磁化率和频率磁化率具有相同的变化特征,与黄土高原中部和东部的黄土磁化率变化机制一致,即黄土高原西部和平镇黄土的磁化率和频率磁化率仍然受成土作用形成的细颗粒磁铁矿控制,因此其磁化率和频率磁化率仍然可以反映季风降雨的变化特征,并且其反映的16 ka以来季风降雨变化与南方石笋氧同位素记录的季风变化特征一致。通过详细的海陆综合对比,本文认为16 ka至11 ka间东亚季风降雨的变化受到北半球太阳辐射和北半球区域温度的共同影响,而11 ka之后的夏季风降雨减少主要受太阳辐射降低的影响。     

若尔盖盆地河流古洪水沉积及其对黄河水系演变问题的启示

青藏高原东部若尔盖盆地古湖泊消亡、黄河贯穿盆地、黄河源区现代水系格局形成,是黄河发育演变史上的重要事件,也是青藏高原东部水文环境变化的转折点。关于其发生年代问题,目前尚无确切结论。本文根据野外考察所获资料和实验室测试分析数据,结合历年来前人多方面研究的结果,针对若尔盖盆地古湖泊消亡与黄河贯穿盆地的年代问题,进行比较全面的分析论述与展望。其中在玛曲—欧拉秀玛河段的最新研究,发现由古洪水沉积物记录的黄河特大洪水事件,发生在OSL年龄(13590±1200)~(12980±1090) a期间,其洪水主要来自于若尔盖盆地上游广泛分布的高山冰川的冰雪融水。这证明在末次冰消期Bolling-Allerod全球性相对温暖阶段,黄河就已经贯通若尔盖盆地,流经玛曲—欧拉秀玛断陷谷地,并且发生了若干次特大洪水事件。可见从河流古洪水沉积学、年代学与水文学新途径的研究,将会为解决黄河贯通若尔盖盆地的年代问题提供直接的证据。     

近百年东亚冬季气温及其大气环流变化型态

利用最新20世纪近百年再分析气象资料,研究近百年东亚冬季气温变化型及其相关的大气环流型态.结果表明近百年内东亚冬季气温主要有两种变化型:第一是东亚西南与东北相反气温变化型,表现在40°N以南及105°E以西地区(西南地区)气温变化与40°N以北及105°E以东地区(东北地区)变化相反;第二是40°N以南气温一致变化型.与第一种气温变化型耦合的大气模态是500hPa欧亚型遥相关、西伯利亚高压及北大西洋涛动.当欧亚型遥相关负位相,北大西洋涛动正位相及西伯利亚高压减弱时,有利于蒙古和我国105° E以东的区域增温而我国西南地区和青藏高原降温,反之亦然.第二种气温变化型耦合大气模态是500hPa西太平洋型遥相关,北太平洋涛动.当西太平洋型遥相关及北太平洋涛动处于正位相时(北太平洋北负南正),东亚40°N以南地区增温,东亚40°N以北地区降温.耦合的大气模态的型态差异,影响各阶段气温的年际变化.近一百年中,欧亚型遥相关和北大西洋涛动在1984～2010期间的型态最显著,是20世纪80年代东亚显著增暖的原因之一.研究还发现20世纪中期后东亚气温的年际变化与极地环流的变化联系紧密,表现在西伯利亚高压范围东扩并与极地环流联系,也是近百年气温趋势上升的一个原因.     

Progressive glacial retreat in the Southern Altiplano (Uturuncu volcano, 22°S) between 65 and 14 ka constrained by cosmogenic He dating

This work presents the first reconstruction of late Pleistocene glacier fluctuations on Uturuncu volcano, in the Southern Tropical Andes. Cosmogenic ³He dating of glacial landforms provides constraints on ancient glacier position between 65 and 14 ka. Despite important scatter in the exposure ages on the oldest moraines, probably resulting from pre-exposure, these ³He data constrain the timing of the moraine deposits and subsequent glacier recessions: the Uturuncu glacier may have reached its maximum extent much before the global LGM, maybe as early as 65 ka, with an equilibrium line altitude (ELA) at 5280 m. Then, the glacier remained close to its maximum position, with a main stillstand identified around 40 ka, and another one between 35 and 17 ka, followed by a limited recession at 17 ka. Then, another glacial stillstand is identified upstream during the late glacial period, probably between 16 and 14 ka, with an ELA standing at 5350 m. This stillstand is synchronous with the paleolake Tauca highstand. This result indicates that this regionally wet and cold episode, during the Heinrich 1 event, also impacted the Southern Altiplano. The ELA rose above 5450 m after 14 ka, synchronously with the Bolling–Allerod.     

The spatio-temporal variations of frost-free period in China from 1951 to 2012

The frost-free period(FFP)first frost date(FFD) and last frost date(LFD) have been regard as the important climate variables for agricultural production. Understanding the spatio-temporal variations of the FFPFFD and LFD is beneficial to reduce the harmful impacts of climate change on agricultural production and enhance the agricultural adaptation. This study examined daily minimum temperatures for 823 national-level meteorological stationscalculated the values of FFDLFD and FFP for station-specific and region-specific from 1951 to 2012estimated the gradients of linear regression for station-specific moving averages of FFDLFD and FFPand assessed station-specific time series of FFP and detected the abrupt change. The results as follows: at both the station level and the regional levelthe FFP across China decreases with the increase of latitude from south to northand with the increase of altitude from east to west generally. At the station levelthe inter-annual fluctuations of FFDLFD and FFP in south and west agricultural regions are greater than those in north and east. At the regional levelexcluding the QT regiontemporal changes of FFP are relatively small in both the low-latitude and the high-latitude regionsbut for the mid-latitude regions. According to the linear trend gradients of the moving average values of station-specific FFDLFD and FFPFFD was delayedLFD advancedand FFP extended gradually over the 80% of China. Furthermorethe change magnitudes for FFDLFD and FFP in the north and east agricultural regions are higher than that in the southern and western. Among the 659 station-specific time series of FFP examined by the Mann-Kendall test341 stationslocated mainly in the north regionhave one identifiable and significant abrupt change. And at the 341 stations with identified abrupt changesmost(57%) abrupt changes occurred during 1991–2012followed by the periods of 1981–1990(28%)1971–1980(12%)and 1951–1970(3%). The spatio-temporal variations of FFDLFD and FFP would provide important guidance to agricultural practices.     

苦海沉积物有机质反映的过去840年来青藏高原东部环境变化

青藏高原对全球气候变暖响应敏感,研究青藏高原近千年来环境演化过程、规律与驱动机制对预测其未来气候可能发生的变化有重要参照意义。通过位于青藏高原东部的苦海沉积物总有机质相关指标[总有机碳(TOC)、总氮(TN)、总有机碳与总氮比值(TOC/TN)和总有机碳同位素(δ¹³C_org)]的研究重建了该区域过去840年来的环境演化过程。研究结果表明,苦海沉积物中的有机质主要来自于湖泊内源水生植物。由于暖期(冷期)时黄河上游径流量较高(低),苦海水位随之升高(降低),湖泊水动力增强(减弱),浅水区沉水植物对研究岩芯中有机质的贡献率提高(降低),导致沉积物TOC、TN、TOC/TN升高,δ¹³C_org值正(负)偏。人类活动导致的青藏高原近50年气候异常变暖可能是～1950 AD之后δ¹³C_org反映的黄河上游径流量变化与重建的中国温度记录之间的关系发生转变的原因。苦海沉积物δ¹³C_org记录与万象洞石笋δ¹⁸     

近千年全球温度变化研究的新进展

结合国内外有关研究,综合评述了美国国家科学院国家研究理事会的报告 --"近两千年地面温度的重建"。重点介绍了气候变暖的新证据,3个特征时期即20世纪气候变暖、小冰期（LIA）、中世纪暖期（MWP）和近千年温度变化模拟的结果。     

Lateglacial and Holocene palaeoenvironments at Sierra La Madera,northwestern Mexico: Sharp signals of Younger Dryas and North American monsoon

During the last glacial termination, the climate system experienced intense global variations whose causes and impacts are not fully defined, particularly for low latitudes. The northwestern Mexico Sky Islands present a climate-sensitive ideal setting to record palaeoecological and palaeoclimatic changes due to their physiographic complexity and location in the ecotone between temperate and tropical ecosystems. High-resolution pollen analysis and a detailed sedimentological study were conducted at the Ciénega Tonibabi tropical thorn scrub site. The 15 540–0 cal a bp nearly continuous record shows that the North Atlantic Ocean did have a cold and humid climatic influence during the glacial stages of the end of the Pleistocene, including a sharp pulse during the Younger Dryas. However, a shift to the Pacific Ocean influence occurred during the Holocene, which led to the development of the El Niño conditions prevailing today. Colder and warmer phases follow one another with higher or lower winter precipitation, including a sharp Bølling–Allerød and development and intensification of the North American monsoon. They are reflected in hydrological changes as well as in the advances, retreats and intermingling of coniferous forests and tropical thorn scrub.