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。     

青海喇家遗址齐家文化时期黍粟农业的植硅体证据

齐家文化时期的农业经济状况是学术界关心的问题.喇家遗址是一处具有中心聚落性质的齐家文化遗址,已有的研究认为喇家遗址齐家文化时期的经济形态是以粟为主的粟黍旱作农业,但在具体的认识上还存在一些不同看法,仍需系统的植物考古学研究进一步验证.对喇家遗址土样的植硅体分析结果显示,齐家文化时期种植的农作物为粟和黍,而且以黍为主,没有发现麦类遗存.以黍为主的种植结构可能与所在区4.5ka B.P.以来气候趋于干冷有关.植硅体和浮选结果在黍粟含量对比上存在差异,我们对这种差异的产生原因进行了探讨.这一结果为重新认识喇家遗址乃至齐家文化的农业生产状况提供了新的参考资料.     

Modern pollen distributions in Qinghai-Tibetan Plateau and the development of transfer functions for reconstructing Holocene environmental changes

This study investigates the distribution of modern pollen assemblages in the Qinghai-Tibetan Plateau, China, based on surface soil samples collected at 1202 sites along an altitudinal gradient of 10–5500 m asl, where mean annual precipitation (MAP) ranges from 12 to 1840 mm and mean annual temperature (MAT) from ?7 to 21.5 °C. A total of 153 pollen taxa were found with relative abundances greater than 1% in at least two samples. Canonical correspondence analysis (CCA) was used to determine the main environmental variables influencing pollen distributions. The results reveal that MAP is the most significant dominant variable. However, MAT, altitude (ALT), July temperature (MT7), and relative humidity (HHH) are also significant variables that clearly follow the gradients in the CCA ordination, suggesting that pollen assemblages probably not only reflect a single climatic parameter, but also a variety of other climatic inter-related parameters.Transfer functions, based on locally weighted weighted averaging (LWWA), were developed for MAP (R²-boot = 0.89, RMSEP = 109 mm), MAT (R²-boot = 0.78, RMSEP = 2.3 °C), ALT (R²-boot = 0.73, RMSEP = 597 m), HHH (R²-boot = 0.82, RMSEP = 4.5%), and July mean precipitation (MP7) (R²-boot = 0.87, RMSEP = 23 mm). Overall, our results confirm that pollen can provide reliable estimates of the primary climatic parameters. The application of the LWWA model to the fossil records of Chen Co Lake allowed quantitative inferences to be made about Holocene climatic changes in the southern Tibetan Plateau, suggesting that LWWA is a robust calibration method for quantitative palaeo-environmental reconstruction based on pollen data in the regions.     

A ~30,000-year record of environmental changes inferred from Lake Chen Co,Southern Tibet

Climatic and environmental changes since the last glacial period are important to our understanding of global environmental change. There are few records from Southern Tibet, one of the most climatically sensitive areas on earth. Here we present a study of the lake sediments (TC1 core) from Lake Chen Co, Southern Tibet. Two sediment cores were drilled using a hydraulic borer in Terrace 1 of Lake Chen Co. AMS ¹⁴C dating of the sediments showed that the sequence spanned >30,000 years. Analyses of present lake hydrology indicated that glacier melt water is very important to maintaining the lake level. Sediment variables such as grain size, TOC, TN, C/N, Fe/Mn, CaCO₃, and pollen were analyzed. Warm and moderately humid conditions dominated during the interval 30,000–26,500 cal year BP. From 26,500 to 20,000 cal year BP, chemical variables and pollen assemblages indicate a cold/dry environment, and pollen amounts and assemblages suggest a decline in vegetation. From 20,000 to 18,000 cal year BP, the environment shifted from cold/dry to warm/humid and vegetation rebounded. The environment transitioned to cold/humid during 16,500–10,500 cal year BP, with a cold/dry event around 14,500 cal year BP. After 10,500 cal year BP, the environment in this region tended to be warm/dry, but exhibited three stages. From 10,500 to 9,000 cal year BP, there was a short warm/humid period, but a shift to cold/dry conditions occurred around 9,000 cal year BP. Thereafter, from 9,000 to 6,000 cal year BP, there was a change from cold/dry to warm/humid conditions, with the warmest period around 6,000 cal year BP. After 6,000 cal year BP, the environment cooled rapidly, but then displayed a warming trend. Chemical variables indicate that a relatively warm/dry event occurred around 5,500–5,000 cal year BP, which is supported by time-lagged pollen assemblages around 4,800 cal year BP. Our lake sediment sequence exhibits environmental changes since 30,000 cal year BP, and most features agree with records from the Greenland GISP2 ice core and with other sequences from the Tibetan Plateau. This indicates that environmental changes inferred from Lake Chen Co, Southern Tibet were globally significant.     

人类生存与环境演变

人类进化与环境演变几乎同步发生,人类与环境的相互关系大体经历了萌发、原始、冲击和协调四个时期。人类起源和生存与全球环境演变密切相关,他在环境剧变中产生,在适应环境变化中成长。当他向自然环境过分索取时,就要造成环境恶化;而恶化的环境又会给人类带来各种各样的灾难,促使人类迁移,引起民族战争和社会动荡,摧毁人类文明。人类只有协调好与环境的相互关系才能得以生存和发展。     

Grey characteristics of microbanding of stalagmite in Shihua Cave, Beijing and its climatic signification(I)

Grey microstructure of microbanding in thin sections of stalagmite T9501 from Shihua Cave, Beijing was studied. The types of grey and the morphologic features of organic material were classified. The signification of microbanding and annual layer was discussed. The standard distinguishing the false annual layer and the multi-year layer is set up, which provides the theoretic fundaments for paleoclimatic study. Project supported by the National Natural Science Foundation of China (Grant No. 49672134).     

渤海东侧海岸带黄土中的放射虫

阐述了海岸带黄土中放射虫的种类及组合特征，并对其来源进行了探讨。 初步认为：放射虫最初是在间冰期高海面时被黄海暖流带入渤海的，后来在冰期低 海面时，裸露的海底受强大的西北向低空气流作用，致使一些放射虫壳体伴随沙尘 而沉降到附近海岸黄土之中。     

Fifty years of Quaternary palynology in the Tibetan Plateau

Science China Earth Sciences - Quaternary palynology in the Tibetan Plateau (TP) was initiated in the 1960s to meet the needs of economic development in western China. Pollen analysis was conducted...     

西准噶尔和布克赛尔古洋盆的厘定——来自和布克赛尔蛇绿混杂岩的锆石U-Pb年代学及地球化学证据

本文对西准噶尔北部先前较少报道的和布克赛尔蛇绿混杂岩进行了系统的野外填图与室内分析测试研究。该套蛇绿混杂岩总出露面积约4km2,岩石组分主要包括蛇纹石化橄榄岩、辉石岩、辉长岩、辉绿岩、玄武岩、硅质岩、大理岩及火山碎屑岩围岩。蛇纹石化橄榄岩作为基质,其它蛇绿混杂岩组分均以断块或断片形式与基质呈不规则的断层接触,为典型的基质包裹团块接触关系。围岩、基质和团块均发生不同程度变形和蚀变,围岩和基质中劈理较为发育。对蛇绿混杂岩中辉长岩团块进行地球化学分析,显示上凸型稀土配分模式,(La/Yb)N为0.48~0.65,具有轻微的Eu负异常,高场强元素(Zr-Lu)以几乎不分异并贴近于MORB为特征,显示该蛇绿岩应为洋中脊(MOR)型。辉长岩团块的LA-ICP-MS锆石U-Pb定年结果为484±3 Ma,说明古洋壳形成于早奥陶世。和布克赛尔蛇绿混杂岩时代与属性的最新厘定,一方面暗示了博什库尔-成吉斯弧与扎尔玛-萨吾尔弧之间应发育一个至少在早奥陶世已经存在的古洋盆,可为西准噶尔北部构造演化研究提供重要线索;另一方面,该蛇绿混杂岩可以与邻区已报道的库吉拜、洪古勒楞等蛇绿混杂岩做很好的对比连接,而与查干陶勒盖蛇绿混杂岩在各项特征上存在某些差异,可以为西准噶尔北部构造缝合带的划定提供新的约束。