U–Pb zircon chronostratigraphy of early-Pliocene ignimbrites from La Pacana, north Chile: implications for the formation of stratified magma chambers     

Axel K Schmitt  Jan M Lindsay  Shan de Silva  Robert B Trumbull 《Journal of Volcanology and Geothermal Research》2003,120(1-2):43-53

High spatial resolution U–Pb dates of zircons from two consanguineous ignimbrites of contrasting composition, the high-silica rhyolitic Toconao and the overlying dacitic Atana ignimbrites, erupted from La Pacana caldera, north Chile, are presented in this study. Zircons from Atana and Toconao pumice clasts yield apparent ²³⁸U/²⁰⁶Pb ages of 4.11±0.20 Ma and 4.65±0.13 Ma (2σ), respectively. These data combined with previously published geochemical and stratigraphic data, reveal that the two ignimbrites were erupted from a stratified magma chamber. The Atana zircon U–Pb ages closely agree with the eruption age of Atana previously determined by K–Ar dating (4.0±0.1 Ma) and do not support long (>1 Ma) residence times. Xenocrystic zircons were found only in the Toconao bulk ignimbrite, which were probably entrained during eruption and transport. Apparent ²³⁸U/²⁰⁶Pb zircon ages of 13 Ma in these xenocrysts provide the first evidence that the onset of felsic magmatism within the Altiplano–Puna ignimbrite province occurred approximately 3 Myr earlier than previously documented.  相似文献   

PREDICTION AND VERIFICATION OF THE 1997-1999 EL NINOAND LA NINA BY USING AN INTERMEDIATE OCEAN-ATMOSPHERE COUPLED MODEL^*          下载免费PDF全文

LI Qingquan  ZHAO Zongci  DING Yihui 《Acta Meteorologica Sinica》2001,15(2):144-159

The numerical simulations,hindcasts and verifications of the tropical Pacific sea surface temperature anomaly(SSTA) have been conducted by using a dynamical tropical Pacific ocean-atmosphere coupled model named NCCo.The results showed that the model had performed reasonable simulations of the major El Nino episodes in the history,and the model forecast skill in 1990s had been significantly improved.NCCo model has been used to predict the tropical Pacific SSTA since January 1997.The comparisons between predictions and observations indicated that the occurrence,evolution and ending of the 1997-1998 El Nino episode have been predicted fairly well by using this model.Also,the La Nina episode that began in the autumn of 1998 and the developing tendency of the tropical Pacific SSTA during the year 1999 have been predictedsuccessfully.The forecast skills of NCCo model during the 1997-1999 El Nino and La Nina events are above 0.5 at 0-14 lead months.  相似文献   

Deconstructing the best case scenario: lessons from water politics in La Paz-El Alto, Bolivia     

Nina Laurie  Carlos Crespo 《Geoforum》2007,38(5):841-854

For nearly a decade the La Paz-El Alto concession in Bolivia was heralded by donor organizations, the state and the commercial water industry alike as an emblematic ‘pro-poor’ water concession under the private sector model. Managed by one of the largest water multinationals in the world (the French company Suez), the network was extended beyond the new connections required by the original ‘pro-poor’ contract, acclaimed as a pioneer of new pro-poor technologies and frequently disseminated internationally as an example of best practice. This paper analyses the La Paz-El Alto concession’s pro-poor image focusing on issues of social exclusion and network extension, contract negotiation, participation and transparency. It documents the rise of social protest about the concession and critiques the failure of neoliberal regulatory systems to promote accountability to the poor. In the context of the continued transnationalisation of the water industry the paper highlights the need for new mechanisms and delivery models to ensure greater national control over private companies and the development of a framework for international water governance.  相似文献   

流感世界大流行的气候特征     

杨冬红  杨学祥 《沙漠与绿洲气象(新疆气象)》2007,1(3):1-8

流感爆发与气候的剧烈变化有关。本文揭示了拉马德雷冷位相、拉尼娜、太阳黑子极值年、厄尔尼诺、低温冷害、沙尘暴、潮汐南北震荡异常与流行性感冒世界大流行相互对应的关系及其物理机制,对气候及其相关灾害的预测有重大科学意义。规律表明,在拉马德雷冷位相时期,全球强震、低温、飓风伴随拉尼娜、全球性流感伴随厄尔尼诺将越来越强烈。面对日益增大的全球灾害,长期气候预报意义重大。  相似文献   

潮汐和地震对全球气候变化的影响   总被引：1，自引：0，他引：1  

杨冬红  杨学祥 《沙漠与绿洲气象(新疆气象)》2007,1(4):5-12

2004年12月26日印尼地震海啸后,全球低温冻害和暴雪灾害频繁发生。"潮汐调温说"和"深海巨震降温说"是一种合理的解释。根据"潮汐调温说"和"深海巨震降温说"理论,2005年全球气温将因为印尼地震海啸和强潮汐南北震荡而降低。美国国家航空航天局(NASA)的科学家认为,一个较弱的厄尔尼诺现象和人类排放的温室气体将使2005年成为人类有记载以来最热的一年。事实上,2005年的温度低于1998年。现在,西方科学家也承认了2005—2007年自然气候的变化抵消了全球气候变暖效应这一客观事实。  相似文献   

云南雨季逐候降水量的低频振荡特征     

何华  陶云  段旭  孙绩华 《气象科技》2006,34(1):52-56

应用主分量方法分析了云南省84站1991~2000年雨季(5~10月)逐候降水量的主要时空特征,并用非整波技术分析了所提取的第1、第2主分量频谱分布的低频振荡特点,同时分析了低频振荡现象与El Nino(La Nina)事件及云南雨季降水多、少之间的关系。结果表明:①云南地区雨季降水主要低频振荡周期为6候(30天)、10候(50天)的月际振荡和15~17候(75~85天)的季节内振荡;②云南雨季的候降水每年都存在30天振荡周期,30天振荡是云南雨季固有的振荡;③当发生El Nino或La Nina异常气候事件时,云南雨季的候降水存在50天振荡周期;④当云南雨季存在75~85天振荡时,云南主汛期(6~8月)降水距平百分率为正(除2000年为零距平);当云南雨季不存在75~85天振荡时,云南主汛期降水距平百分率为负。  相似文献   

Anthropogenic iodine-129 in seawater along a transect from the Norwegian coastal current to the North Pole     

Alfimov V  Aldahan A  Possnert G  Winsor P 《Marine pollution bulletin》2004,49(11-12):1097-1104

Variation in the concentrations of iodine-129 (129I, T1/2=15.7 Myr), a low-level radioactive component of nuclear fuel waste, is documented in surface waters and depth profiles collected during 2001 along a transect from the Norwegian Coastal Current to the North Pole. The surface waters near the Norwegian coast are found to have 20 times higher 129I concentration than the surface waters of the Arctic Ocean. The depth profiles of 129I taken in the Arctic Ocean reveal a sharp decline in the concentration to a depth of about 300-500 m followed by a weaker gradient extending down to the bottom. A twofold increase in the 129I concentration is observed in the upper 1000 m since 1996. Based on known estimates of marine transient time from the release sources (the nuclear reprocessing facilities at La Hague, France, and Sellafield, UK), a doubling in the 129I inventory of the top 1000 m of the Arctic Ocean is expected to occur between the years 2001 and 2006. As 129I of polar mixed layer and Atlantic layer of the Arctic Ocean is ventilated by the East Greenland Current into the Nordic Seas and North Atlantic Ocean, further dispersal and increase of the isotope concentration in these regions will be encountered in the near future.  相似文献   

TYPHOON ACTIVITY IN NORTHWEST PACIFIC IN RELATION WITH EL NINO AND LA NINA EVENTS     

何敏  宋文玲  陈兴芳 《热带气象学报(英文版)》1999,5(2):153-162

Statistic and typical-year composition methods are used to study the northwest Pacific typhoon activities in relation with the EI Niño and La Niña events. The result indicates that the typhoon tends to be inactive in the EI Niño years and active in the La Niña years and it is also dependent on the onset and ending time and intensity of the events and areas of genesis of typhoons. With statistic features of the frequency of typhoon activity in the EI Niño and La Niña years and the time-lag correlation between the frequency and sea surface temperature(SST), useful information is provided for the prediction of typhoon occurrence. In addition, the singular values disassemble(SVD)method is applied to study the correlation between the geopotential field and SST field. The result shows that the air-sea coupling in the EI Niño years is unfavorable for the typhoon to develop. Which take place with a smaller number. Opposite situations are found with the La Niña years.  相似文献   

厄尔尼诺事件和拉尼娜事件的成因与预测   总被引：5，自引：0，他引：5  

杨冬红  杨学祥 《沙漠与绿洲气象(新疆气象)》2008,2(5):1-10

通过对南极气温资料、环南极海冰资料、臭氧变化资料、太平洋海温资料、地球自转速度变化资料、厄尔尼诺和拉尼娜资料的综合验证,发现了构造运动与厄尔尼诺因果关系。大气、海洋与岩石圈的角动量交换在南半球和北半球有不同的形式,这是由陆海分布的差异决定的。南极上空臭氧变化和环南极海冰变化是赤道海温和全球气候准两年振荡的原因。其中,德雷克海峡的海冰变化起主要作用。这个结论给出了作者提出的“海洋锅炉效应”、“臭氧洞漏能效应”、“德雷克海冰气候开关效应”和“大洋地壳跷跷板运动”的相互关系,证明构造运动对厄尔尼诺的重要影响。强潮汐准4a周期的发现,表明南极海冰变化、东太平洋海温变化、地球自转变化和厄尔尼诺都具有4a准周期变化的原因。海温和海冰开关的准2a周期和日食-厄尔尼诺系数理论有较好的预测效果。  相似文献   

Chemical contamination in southwest Puerto Rico: an assessment of trace and major elements in nearshore sediments     

Pait AS  Whitall DR  Jeffrey CF  Caldow C  Mason AL  Lauenstein GG  Christensen JD 《Marine pollution bulletin》2008,56(11):1953-1956

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