东昆仑造山带花岗岩类Pb-Sr-Nd-O 同位素特征

本文报道了东昆仑造山带三叠纪辉长岩、花岗岩类及其包裹体的Pb、Sr、Nd和O同位素组成.东昆仑造山带花岗质岩石全岩和长石Pb同位素组成相差不大,具明显的造山带Pb同位素特征;Sr同位素初始值(ISr)变化于0.70144~0.70972之间,暗示幔源成因;εNd值变化于-4.49939~-9.19258之间,具壳源成因特点;Nd同位素模式年龄(tDM)在1.38~1.761Ga之间,与中元古代变质岩相当;O同位素组成变化范围7.8~9.5,表明花岗岩类成岩物质主要来自地壳.综合岩石的同位素组成,结合矿物学、岩石地球化学的研究,表明花岗岩浆主要起源于地壳,但与来自地幔的基性岩浆曾发生过混合作用,从而导致同位素组成趋于一致.     

近百年来长江水下三角洲高分辨率洪水沉积记录及其控制机理

夏季洪涝灾害对长江流域社会经济造成了严重的影响,急需开展多时空尺度流域洪水发生规律和控制机理的研究,但因洪水器测数据年限短和缺少有效的古洪水沉积记录研究方法而难以实现。选取长江水下三角洲YEC1701柱状样顶部100 cm进行高分辨率XRF岩心连续扫描（XRFCS）,粒度、有机碳、N元素、δ13C和210Pb定年分析,并与流域洪水器测或历史记录等进行对比研究,以期建立高效的古洪水沉积记录代用指标。结果表明,长江水下三角洲沉积物中Zr/Rb峰值通常对应粒度粗组分高值和较高的C/N值、偏负的δ13C值,所在层位的沉积年龄与流域洪水事件发生年份有很好的对应关系。由此判断,Zr/Rb值可作为判别长江古洪水沉积的重要代用指标。长江流域于1930—2017年间共发生22次洪水事件,利用XRFCS获得的10 mm和2 mm间隔Zr/Rb值可分别识别出其中的11次和18次,识别率为50%和80%。由此推荐XRFCS样品测试间隔要小于年沉积速率一半以内,以提高古洪水事件的识别率。多源洪水和降雨数据分析表明,长江洪水年际至千年尺度发生规律主要受厄尔尼诺-南方涛动和东亚夏季风、南亚夏季风活动的共同影响。但早期长江洪水资料分辨率较低,长江水下三角洲有较连续的洪水沉积记录,运用XRFCS毫米级分辨率的Zr/Rb值可重建全新世高分辨率的长江古洪水发生历史,更精细地分析气候变化对洪水发生规律的控制机理,为预测全球变化背景下长江洪水演变趋势提供依据。     

潜源划分进展及我国海域和邻近海域区划潜源划分问题研究

对于陆域地区,我国已进行5次全国范围大面积地震区划研究工作,获得了丰富研究成果。但对于海域地区地震区划的研究较薄弱,较少涉及海域潜源划分模型。随着经济发展,涉及海域地区的经济活动日益频繁,对海域地区潜源划分研究及进一步地震区划研究工作的需求越来越强烈。为此,详细介绍代表性国家在潜源划分方面采取的原则和方法,总结我国海域地区地震地质背景及相应的研究现状,并在此基础上提出我国海域地区潜源划分可考虑的原则和基本思路,为后续我国海域地区区划研究提供方案。     

Understanding the relative impacts of natural processes and human activities on the hydrology of the Central Rift Valley lakes,East Africa

Significant changes have been observed in the hydrology of Central Rift Valley (CRV) lakes in Ethiopia, East Africa as a result of both natural processes and human activities during the past three decades. This study applied an integrated approach (remote sensing, hydrologic modelling, and statistical analysis) to understand the relative effects of natural processes and human activities over a sparsely gauged CRV basin. Lake storage estimates were calculated from a hydrologic model constructed without inputs from human impacts such as water abstraction and compared with satellite‐based (observed) lake storage measurements to characterize the magnitude of human‐induced impacts. A non‐parametric Mann–Kendall test was used to detect the presence of climatic trends (e.g. a decreasing or increasing trends in precipitation), while the Standard Precipitation Index (SPI) analysis was used to assess the long‐term, inter‐annual climate variability within the basin. Results indicate human activities (e.g. abstraction) significantly contributed to the changes in the hydrology of the lakes, while no statistically significant climatic trend was seen in the basin, however inter‐annual natural climate variability, extreme dryness, and prolonged drought has negatively affected the lakes. The relative contributions of natural and human‐induced impacts on the lakes were quantified and evaluated by comparing hydrographs of the CRV lakes. Lake Abiyata has lost ~6.5 m in total lake height between 1985 and 2006, 70% (~4.5 m) of the loss has been attributed to human‐induced causes, whereas the remaining 30% is related to natural climate variability. The relative impact analysis utilized in this study could potentially be used to better plan and create effective water‐management practices in the basin and demonstrates the utility of this integrated methodology for similar studies assessing the relative natural and human‐induced impacts on lakes in data sparse areas. Copyright © 2015 John Wiley & Sons, Ltd.     

A diatom‐inferred record of lake variability during the last 900 years in Lützow–Holm Bay,East Antarctica

Decadal–centennial‐scale climate variability in coastal Antarctica remains poorly understood due to the limited number of highly resolved, well‐dated records. We present a 900‐year, decadal‐scale reconstruction based on sedimentary diatoms from Lake Abi in Lützow–Holm Bay, East Antarctica. Hydrological change is inferred from diatom ecological preferences in conjunction with an existing regional training set and implies that lake water specific conductivity, depth and nitrogen availability are the key drivers of diatom assemblage change. Lake Abi underwent a series of subtle environmental changes related to these environmental variables, possibly driven by changes in catchment snow melt and the duration of seasonal ice cover. Ordination is used to trace the major patterns of change in the diatom community, with notable shifts identified between 470 and 400 and at ～350 cal a BP (where present = CE 1950). The frequency of environmental variability at Lake Abi is broadly consistent with a record of the Interdecadal Pacific Oscillation during the last millennium, but contrasts with the apparent climate stability elsewhere in eastern Antarctica. Further research is required to constrain the limnological and ecological responses of lakes in coastal Antarctica to obtain more rigorous palaeoclimate reconstructions from these sites of immense potential.     

Phase transition of the Pacific decadal oscillation and decadal variation of the East Asian summer monsoon in the 20th century

This paper focuses on the relationship between the phase transition of the Pacific decadal oscillation (PDO) and decadal variation of the East Asian summer monsoon (EASM) in the twentieth century. The first transition occurred in the 1940s, with an enhanced SST in the North Pacific and reduced SST in the tropical eastern Pacific and South Indian Ocean. In agreement with these SST changes, a higher SLP was found in most parts of the Pacific, while a lower SLP was found in the North Pacific and most parts of the Indian Ocean. In this case, the EASM was largely enhanced with a southerly anomaly in the lower troposphere along the east coast of China. Correspondingly, there was less rainfall in the Yangtze River valley and more rainfall in northern and southern China. An opposite change was found when the PDO reversed its phase in the late 1970s. In the tropical Indian Ocean and western Pacific, however, the SST was enhanced in both the 1940s and 1970s. As a result, the western Pacific subtropical high (WPSH) tended to extend westward with a larger magnitude in the 1970s. The major features were reasonably reproduced by an atmospheric general circulation model (IAP AGCM4.0) prescribed with observed SST and sea ice. On the other hand, the westward extension of the WPSH was exaggerated in the 1970s, while it was underestimated in the 1940s. Besides, the spatial pattern of the simulated summer rainfall in eastern China tended to shift southward compared with the observation.