西藏特提斯喜马拉雅白垩纪中期Cenomanian-Turonian期碳同位素偏移

过去大量关于白垩纪中期Cenomanian-Turonian晴期的古海洋及其界线时期缺氧事件研究的高分辨率碳氧同位素的实际材料绝大多数都来自深海钻探(DSDlP)、大洋钻探(0DP)和欧美的一些较深水盆地．通过对西藏南部地区(位处特提斯洋东南)同一层位高分辨率碳同位素分析,目的在于为Cenomanian-Turonian古海洋及全球事件的碳同位素响应提供西藏地区的对比材料,并试图就浅海相的变化情况进行探讨．西藏定日和岗巴地区的高分辨率碳同位素分析结果显示．δ^13C值在Cenomanian中晚期稳定,Cenomanian-Turonian界线时期快速高幅正偏,Turonian期持续负偏,这种长期变化趋势在特提斯甚至全球可以对比．深入研究还发现,Turonian中后期存在2个较大幅度的负偏凹陷区,与来自欧洲的相关资料在偏移时间和幅度方面惊人相似．对比分析表明,岗巴地区δ^13C值长期变化和短期波动幅度及步调与定日及全球其他地区存在一定差别,幅度差异可能与样品制备和成岩改造有关,步调不一致则可能受生物地层定位的影响．研究区近海一半远洋环境Cenomanian-Turonian界线时期未出现典型富有机质黑色页岩,说明δ^13C值极度正偏与黑色页岩的出现并非一对应．     

利用GPS与GRACE监测陆地水负荷导致的季节性水平形变：以喜马拉雅山地区为例

地表陆地水负荷变化是引起重力场和地壳形变呈现季节性特征的主要因素,并且能够利用地表及空间大地测量技术对其进行有效的监测.本文通过对质量负荷形变效应的理论模拟,描述了水平分量的形变指向以及垂直与水平分量的幅值比可以提高对负荷区域的辨别程度,并且联合GPS坐标时间序列及GRACE模型对喜马拉雅山地区的季节性负荷形变进行了详细对比分析,研究结果显示两者垂直分量的季节性变化具有较好的一致性,且GPS周年项幅值要大于GRACE.而由GRACE解算得到的水平分量结果表明该地区季节性形变主要受东南亚及印度东北部地区的陆地水负荷控制,位于喜马拉雅山地区多数GPS台站的垂直分量及北向分量的初相位与GRACE模型解算结果相近,而部分GPS台站的东向分量与GRACE模型存在明显不同,由此导致GPS与GRACE监测到的形变指向存在差异.通过对GRACE估算精度以及GPS垂直与水平分量幅值比的深入分析,发现GPS对局部周边地区的河流、谷地及农田灌溉等负荷变化造成的形变效应较为敏感,而GRACE由于截断阶次及平滑滤波等影响因素,不仅造成在水平分量上的分辨率远低于垂直分量,而且整体估算精度要低于GPS观测得到的形变信息.     

Visualizing Patterns of Genetic Landscapes and Species Distribution of Taxus wallichiana (Taxaceae), Based on GIS and Ecological Niche Models

The Chinese yew (Taxus wallichiana), which is widely distributed in the Himalayas and in southern China, is now on the edge of extinction. In order to understand the evolutionary processes that control the current diversity within this species at the genetic and ecological levels, its genetic patterns and range dynamics must first be identified and mapped. This knowledge can then be applied in the development of an effective conservation strategy. Based on molecular data obtained from 48 populations of T. wallichiana, we used GIS-based interpolation approach for the explicit visualization of patterns of genetic divergence and diversity, and a number of potential evolutionary hotspots have been specifically identified within the genetic landscape maps. Within the maps of genetic divergence and diversity, five areas of high inter-population genetic divergence and six areas of high intra-population genetic diversity have been highlighted in a number of separate mountain regions, and these evolutionary hotspots should have the priority to be protected. Furthermore, four geographical barriers have been identified: the eastern Himalayas, the Yunnan Plateau, the Hengduan Mountains and the Taiwan Strait. According to ecological niche modeling (ENM), the populations of T. wallichiana within the Sino-Himalayan Forest floristic subkingdom experienced westward expansion from the periods of Last Inter-glacial to Last Glacial Maximum (LGM). Following the LGM, the distribution range overall became reduced and fragmented. These findings challenge the classic mode of contraction-expansion in response to the last glaciation. In conclusion, our findings suggest that the changes in geographical landscapes and climate that occurred during the Quaternary resulted in current genetic landscape patterns.     

中国喜马拉雅山地区冰川1999—2015年期间动态变化遥感调查

根据完成的青藏地区基于1999年ETM、2014/2015年GF-1/OLI两期遥感调查的冰川编目数据,对1999-2015年期间中国喜马拉雅山地区的冰川变化进行分析。结果显示,从1999-2015年间,中国喜马拉雅山地区的冰川普遍退缩,冰川数量减少了85条,面积减少了42.00 km^2,冰储量减少了2.385 km^3,分别占其减少变化率的1.53%、0.67%和0.50%。沿山脉由东向西冰川变化不一,其中东段的冰川数量减少多,西段的冰川面积和冰储量减少多,并且东段的数量减少变化率远大于西段,西段的面积、冰储量减少变化率大于东段,中段的冰川相对稳定。喜马拉雅山地区的冰川在北、北东和东等方向上发生退缩,且减少量依次减少,其中东向的数量减少变化率最大,北东向的面积减少变化率最大,而北向的减少变化率最小。冰川在不同坡度退缩程度不一,在坡度10°~15°范围冰川面积退缩最多、变化率最大,在坡度30°~35°范围数量减少最多、变化率最大。冰川在高程5 500~6 000 m区间数量和面积退缩量最多,其次是在高程5 000~5 500 m区间;在高程3 500~4 000 m区间的退缩变化率最大,而在高程6 000~6 500 m区间的退缩变化率最小。不同流域中冰川变化差异较大,在雅鲁藏布江流域(5O2)冰川数量和面积减少最多,其次是朗钦藏布等流域(5Q2)和朋曲等流域(5O1),而扎日南木措流域(5Z3)的冰川减少量最小,但是变化率最大。总之,小冰川的大规模退缩或者消失,较大冰川也普遍退缩,是喜马拉雅山地区冰川变化的特点。喜马拉雅山地区冰川退缩与气候变化关系密切。根据多年年平均气温和年降水量分析,自1961年以来,该地区年平均气温显著上升,年降水量有增有减,但气温上升、降水量减少是导致冰川消融原因之一。     

Using MaxEnt Model to Predict Suitable Habitat Changes for Key Protected Species in Koshi Basin,Central Himalayas

Because of its landscape heterogeneity, Koshi Basin (KB) is home to one of the world’s most abundant, diverse group of species. Habitat change evaluations for key protected species are very important for biodiversity protection in this region. Based on current and future world climate and land cover data, MaxEnt model was used to simulate potential habitat changes for key protected species. The results shows that the overall accuracy of the model is high (AUC > 0.9), suggesting that the MaxEnt-derived distributions are a close approximation of real-world distribution probabilities. The valley around Chentang Town and Dram Town in China, and Lamabagar and the northern part of Landtang National Park in Nepal are the most important regions for the protection of the habitat in KB. The habitat area of Grus nigricollis, Panax pseudoginseng, and Presbytis entellus is expected to decrease in future climate and land cover scenarios. More focus should be placed on protecting forests and wetlands since these are the main habitats for these species.     

Atmospheric methane over the past 2000 years from a sub-tropical ice core,central Himalayas

A high-resolution 2000-year methane record has been constructed from an ice core recovered at 7200 m a.s.l. on the Dasuopu Glacier in the central Himalayas. This sub-tropical methane record reveals an increasing trend in the concentration of methane during the industrial era that is similar to observations from polar regions. However, we also observed the differences in the atmospheric methane mixing ratio between this monsoon record and those from polar regions during pre-industrial times. In the time interval 0-1850 A.D., the average methane concentration in the Dasuopu ice core was 782±40 ppbv and the maximum temporal variation exceeded 200 ppbv. The difference gradient of methane concentration in Dasuopu ice core with Greenland and Antarctica cores are 66±40 ppbv and 107±40 ppbv, respectively. This suggests that the tropical latitudes might have acted as a major global methane source in pre- industrial times. In addition, the temporal fluctuation of the pre-industrial methane records suggests that monsoon evolution incorporated with high methane emission from south Asia might be responsible for the relatively high methane concentration observed in the Dasuopu ice core around A.D. 800 and A.D. 1600. These results provide a rough understanding of the contribution of tropical methane source to the global methane budget and also the relationship between atmospheric methane and climate change.     

"空中调水"设想的可行性研究

"空中调水"设想是改变雅鲁藏布大峡谷及其以北地形来改善向北水汽输送.根据气候资料和新建立的南亚季风指数,选择历史上最强的季风年,通过简便可行的计算方案来讨论这个设想在气象学上的可行性.初步诊断分析表明,在制约印度洋暖湿水汽通过雅鲁藏布大峡谷通道继续向北输送的因素中,地形阻碍固然重要,但与青藏高原地形有关的大尺度环流的辐合作用更为重要;而要改变大尺度环流则比改变局地地形更为困难.从气象学条件来看,即使改变了雅鲁藏布大峡谷及其以北地区的地形,也很难实现"空中调水"的设想.     

Impact of subgrid scale scheme on topography and landuse for better regional scale simulation of meteorological variables over the western Himalayas

An attempt is made to integrate subgrid scale scheme on the work of Dimri and Ganju (Pure Appl Geophys 167:1–24, 2007) to understand the overall nature of surface heterogeneity and landuse variability along with resolvable finescale micro/meso scale circulation over the Himalayan region, which is having different altitudes and orientations causing prevailing weather conditions to be complex. This region receives large amount of precipitation due to eastward moving low-pressure synoptic weather systems, called western disturbances, during winter season (December, January, February—DJF). Surface heterogeneity and landuse variability of the Himalayan region gives rise to numerous micro/meso scale circulation along with prevailing weather. Therefore, in the present work, a mosaic type parameterization of subgrid scale topography and landuse within a framework of a regional climate model (RegCM3) is extended to study interseasonal variability of surface climate during a winter season (October 1999–March 2000) of the work of Dimri and Ganju (Pure Appl Geophys 167:1–24, 2007). In this scheme, meteorological variables are disaggregated from the coarse grid to the fine grid, land surface calculations are then performed separately for each subgrid cell, and surface fluxes are calculated and reaggregated onto the coarse grid cell for input to the atmospheric model. By doing so, resolvable finescale structures due to surface heterogeneity and landuse variability at coarse grid are subjected to parameterize at regular finescale surface subgrid. Model simulations show that implementation of subgrid scheme presents more realistic simulation of precipitation and surface air temperature. Influence of topographic elevation and valleys is better represented in the scheme. Overall, RegCM3 with subgrid scheme provides more accurate representation of resolvable finescale atmospheric/surface circulations that results in explaining mean variability in a better way.     

珠穆朗玛峰北坡局地环流日变化的观测研究

青藏高原地-气间的物质/能量交换是高原与全球大气系统相联系的重要纽带.陡峭的地形和强烈的地表差异在高原山区形成特殊的局地大气环流系统,在地气交换中起着重要作用.为研究珠峰北坡的局地环流系统,于2006年5～6月间在珠峰北坡绒布河谷实施强化观测实验HEST2006,对该地区的局地环流以及辐射和热力状况进行观测,分析了该地区局地环流的日变化过程,包括:(1)地面风场的分布和变化;(2)风场垂直结构;(3)垂直运动及可能的驱动机制.研究表明,该地区局地大气环流是由地形与地表状态调整的大气辐射加热和冷却所驱动,包含多种不同的山地环流成分,与典型山谷风环流不同,具有很强的特殊性,对地气问的交换有重要影响.     

喜马拉雅山北坡奥陶纪—古近纪构造古地磁新数据

在喜马拉雅山北坡奥陶系-古近系近乎连续的沉积地层中系统采集古地磁样品3791件,其中测试统计样品数为2920件,基本获取了统级年代古地磁数据,绘制出喜马拉雅地块奥陶纪-古近纪古地磁极移曲线和古纬度变化曲线.喜马拉雅地块在向北漂移过程中曾发生了多次旋转,最后一次约28°的顺时针旋转发生在始新世,可能与西喜马拉雅构造结形成有关;晚三叠世和晚侏罗世曾发生了纬度为2°和3.8°的向南回返,可能与雅鲁藏布新特提斯洋弧后扩张有关.根据古纬度数据推算:中白垩世雅鲁藏布新特提斯洋盆的宽度至少为2200km;始新世以来的喜马拉雅陆-陆碰撞造山运动导致印度地块-喜马拉雅褶冲带-拉萨地块之间的地壳缩短量至少为1000km.