Temporal and spatial variations of δ18O in precipitation of the Yarlung Zangbo River Basin

This paper reveals the temporal and spatial variations of stable isotope in precipita-tion of the Yarlung Zangbo River Basin based on the variations of δ18O in precipitation at four stations (Lhaze, Nugesha, Yangcun and Nuxia) in 2005. The results show that δ18O of pre-cipitation has distinct seasonal changes in the Yarlung Zangbo River Basin. The higher value of δ18O occurs in spring prior to monsoon precipitation, and the lower value occurs during monsoon precipitation. From the spatial variations, with the altitude-effect and rainout process during moisture transport along the Yarlung Zangbo River Valley, 18O of precipitation is gradually depleted. Thus, δ18O of precipitation decreases gradually from the downstream to the upstream, and the lapse rate of δ18O in precipitation is approximately 0.34‰/100m and 0.7‰/100km for the two reasons. During monsoon precipitation, spatial variation of δ18O in precipitation is dominated by the amount effect in the large scale synoptic condition.     

丽江7.0级地震短临异常特征及震源硬化模型

重点讨论了丽江地震短临预报中识别继承性异常、继承性新异常及新异常的形态特征。同时讨论了判断丽江地震进入短临阶段的判据,如中期趋势异常的结束,巨变异常及异常同步转折等特征。最后,在讨论短临异常时空演化的基础上,结合震中区小震活动的异常平静,短临阶段定点前兆由外向震中迁移,异常外围幅度大、数量多等事实,作者提出了新的震源孕青模型——震源硬化模型。按此模型预测,震源区（余震展布区或地表宏观裂缝展布区）在中短期阶段应出现中小地震的异常平静,元或很少有定点前兆异常显示,但当强震孕育发展到破裂成核时——不可逆失稳阶段,某些地震震源区可能会出现明显的宏观破裂,即地表可见喷沙冒水或前震活动。     

雅鲁藏布江流域降水中氧稳定同位素的时空变化

This paper reveals the temporal and spatial variations of stable isotope in precipita-tion of the Yarlung Zangbo River Basin based on the variations of δ18O in precipitation at four stations (Lhaze,Nugesha,Yangcun and Nuxia) in 2005. The results show that δ18O of pre-cipitation has distinct seasonal changes in the Yarlung Zangbo River Basin. The higher value of δ18O occurs in spring prior to monsoon precipitation,and the lower value occurs during monsoon precipitation. From the spatial variations,with the altitude-effect and rainout process during moisture transport along the Yarlung Zangbo River Valley,18O of precipitation is gradually depleted. Thus,δ18O of precipitation decreases gradually from the downstream to the upstream,and the lapse rate of δ18O in precipitation is approximately 0.34‰/100m and 0.7‰/100km for the two reasons. During monsoon precipitation,spatial variation of δ18O in precipitation is dominated by the amount effect in the large scale synoptic condition.     

Stable Isotope in Precipitation in the Southern Tibetan Plateau Revealing Strong Signal of Monsoon Precipitation

STABLE ISOTOPE IN PRECIPITATION IN THE SOUTHERN TIBETAN PLATEAU REVEALING STRONG SIGNAL OF MONSOON PRECIPITATION     

贵州关岭地区中——上三叠统海参骨片化石的首次发现

报道了贵州关岭地区中——上三叠统竹杆坡组发现的海参骨片化石5属6种及2个属种未定的形态类型。分析了海参化石属种的历史分布特征，上述化石指示竹杆坡组为晚三叠世沉积产物。这一发现进一步丰富了关岭生物群的内容，为探讨中国三叠纪海参骨片化石的分类及演化增加了新的资料。     

三峡地区震旦系碳酸盐岩碳氧同位素特征

本文对三峡地区秭归庙河陡山沱组第一段至第三段，宜昌棺材崖陡山沱组第三段上部至灯影组底部以及四溪灯影组石板滩段和白马沱段碳酸盐岩碳氧同位素组成特点的研究结果表明，三峡地区震旦系碳同位素组成与全球新元古代广布的后Martinoan冰期地层δ^13C的分布模式基本一致，本文还讨论了地层中碳同位素组成与生物演化和地层层序发展的关系，指出陡山沱组一段白云岩中δ^13C的负异常可以作为震旦系底界划分的标志，最晚Varanger冰期在三峡地区由陡山沱组三段上部出现的三级层序界面所替代，震旦系内部陡山沱组一段和三段可能形成于Marinoan冰期之后，伊迪卡拉生物分异发展之前，而陡山沱组四段及上覆灯影峡组则大致与国外伊迪卡拉期地层对比。     

江汉—洞庭地区与黄广—九江地区更新统划分与对比

为进一步厘清长江中游江汉—洞庭地区与黄广—九江地区更新统划分与对比,在区域地质调查基础上,识别出区内早更新世砾石层与上覆网纹红土之间的不整合关系,辅以年代学研究,开展了长江中游江汉—洞庭地区与黄广—九江地区第四系研究,建立了区域地层划分与对比格架。研究表明: 白沙井砾石层、阳逻砾石层、宜昌砾石层、九江砾石层等是区内短程河流的冲洪积相沉积,时代为早更新世晚期(Qp₁),而上覆网纹红土则形成于中更新世(Qp₂),二者之间为不整合接触,并以此为基础构建了区内第四纪更新世地层格架; 白沙井砾石层、阳逻砾石层、宜昌砾石层、九江砾石层与上覆网纹红土所代表的水动力条件和沉积环境的重大调整是长江三峡续接贯通的环境响应,暗示了长江上游“川峡二江”续接贯通的时限为早—中更新世之交。     

Estimating the criterion for determining water vapour sources of summer precipitation on the northern Tibetan Plateau

According to the precipitation and δ¹⁸O data obtained during the GEWEX Asian Monsoon Experiment–Tibet Intensive Observation Period, based on the knowledge that δ¹⁸O is lower in precipitation formed from ocean air mass vapour than that from local evaporation vapour, the water vapour sources can be identified from the δ¹⁸O values in precipitation. We attempt to give the identification criterion of δ¹⁸O values in precipitation. The threshold values chosen to distinguish between ocean and local sources are δ¹⁸O < ?20‰ and δ¹⁸O > ?13‰ respectively. According to this criterion, the proportion of local evaporation‐formed precipitation and ocean air‐mass‐formed precipitation in total precipitation was estimated. The average value of precipitation at three sites (NODA, Amdo and AQB) is 249·76 mm. Among this, precipitation formed directly by the ocean air mass vapour is 80·08 mm at most. Precipitation formed by water vapour evaporated from local places is 117·05 mm at least. That is to say that precipitation formed directly by the ocean air mass vapour accounts for 32·06% of the total precipitation at most. Precipitation formed by water vapour evaporated from local places accounts for 46·86% of the total precipitation at least. At least 21·8% of the total precipitation came from water vapour that was evaporated on the way and transported by the monsoon circulation. Copyright © 2005 John Wiley & Sons, Ltd.     

Relation between stable isotope in monsoon precipitation in southern Tibetan Plateau and moisture transport history

The moisture transport history to the south of the Tibetan Plateau was modeled using the meteorological data provided by NCEP in this paper, and the modeled results were compared with the measured δ¹⁸O in the south of the Tibetan Plateau. The relation between δ¹⁸O in precipitation in the south of the Tibetan Plateau and moisture trajectories was discussed. The results show that the extremely low δ¹⁸O in precipitation in the south of the Tibetan Plateau is always related to the moisture from the low-level sea surface evaporation. The long-distance transport of moisture also contributes to low δ¹⁸O in precipitation probably due to the rainout process during moisture transport. It is also found that low δ¹⁸O in precipitation is also related with deep layer transport of moisture, and with intensive condensation in the upper layers of the atmosphere, resulting in low δ¹⁸O because of depletion of heavy isotopes in deep condensation. However, high δ¹⁸O in precipitation whether in monsoon period or not is always companied with moisture coming from the upper layers, and the moisture is from northern or western sides of the plateau. The interpretation of the modeled results is in agreement with the isotope fractionation processes.

     

A study of cross-shore maximum upwelling intensity along the Northwest Africa coast

Satellite images of sea surface temperature (SST) show that the location of cross-shore SST minimum (LCSM) stretches along the isobaths in the Northwest Africa Upwelling System. To understand and interpret these observations better, we set up a two-dimensional analytical model that takes into account the surface and bottom Ekman transport and the alongshore geostrophic current, as well as bottom friction and variations in bottom topography. The structure of vertical velocity with a realistic topography clearly illustrates the variations of SST drop in a sample cross-shore section. Some idealized theoretical model experiments are carried out to examine the effects of eddy viscosity, Coriolis force, and cross-shore wind on the location of the cross-shore maximum upwelling intensity. The results show that the cross-shore wind largely impacts on the location where the coldest water outcrops to the surface through an adjustment of the cross-shore pressure gradient. This is also verified by the remotely sensed data, which indicate that the maximum correlation coefficient between cross-shore wind stress and the depth of LCSM is ?0.65 with a lag of approximately 1 day.