Mechanism for enhanced diffusivity in the deep-sea perpetual salt fountain     

Xinrong Zhang  Shigenao Maruyama  Koutaro Tsubaki  Seigo Sakai  Masud Behnia 《Journal of Oceanography》2006,62(2):133-142

The mechanism of enhanced diffusivity occurring in the deep-sea perpetual salt fountain has been investigated experimentally and numerically. Some factors which possibly contribute to the enhanced diffusivity were found to be the pipe oscillation with ocean waves and its baffled wall surface. Field experiments in the ocean (Onagawa Bay of Miyagi, Japan) and numerical simulations were performed to study and confirm the dynamics of the flow and heat transport with enhanced diffusivity occurring in upwelling deep-sea water. The agreement between the field experimental data and the numerical solutions of an oscillating-wall boundary condition imposed on the baffled pipe is encouraging, and it indicates the baffled pipe surface subject to the oscillatory motion leads to the enhanced diffusivity. The buoyancy force and then upwelling velocity can be greatly increased by the enhanced diffusivity. The dominant mechanism is the occurrence of complicated vortices and vortex shedding leading to efficient mixing and enhanced diffusion.  相似文献   

台湾海峡生态系统对海洋环境年际变动的响应分析   总被引：13，自引：2，他引：13  

洪华生  商少凌  张彩云  黄邦钦  胡建宇  黄加祺  卢振彬 《海洋学报》2005,27(2):63-69

通过比较1985~2001年的海表温度与其间收集的现场营养盐、浮游植物和浮游动物丰度及群落结构变动信号,以及1971~1998年的中上层鱼类渔获量变动信息,发现了台湾海峡生态系统对物理环境年际变动产生的响应迹象.1997 年夏季台湾海峡处于偏冷状态,南部近岸上升流强度减弱;1997年冬季正值一个较强的暖事件发展到顶峰,北上入侵暖水强度增强、浙闽沿岸冷水强度减弱.导致这两个时期营养盐分布特征改变,发生了一系列从浮游植物到浮游动物,从生物量到群落结构的异常响应,暖水性中上层鱼类渔获量则似乎呈现出El Niño年偏高的趋势.根据有限的辅助证据推测,El Niño很可能不是控制台湾海峡海洋环境年际变动的强信号,而台湾海峡的气候海洋生态长期低频变动可能更多地受到东亚季风中国边缘海系统的控制.  相似文献   

普里兹湾水文特征与变化   总被引：2，自引：1，他引：2  

赵松鹤  陈明剑 《中国海洋大学学报(自然科学版)》1995,(Z1)

根据澳大利亚学者分别在１９８２年１２月和１９８７年２月普里兹湾的调查资料,并结合中国＂极地＂号南极考察船１９９０～１９９１年间的调查资料印证,提出在中国＂中山站＂所在地普里兹湾在初夏与晚夏期间的水文特征。  相似文献   

How does a generalist seabird species use its marine habitat? The case of the kelp gull in a coastal upwelling area of the Humboldt Current     

Villablanca  Roberto; Luna-Jorquera  Guillermo; Marin  Victor H.; Garthe  Stefan; Simeone  Alejandro 《ICES Journal of Marine Science》2007,64(7):1348-1355

  相似文献   

论多因复成矿床的形成机理     

许德如  周岳强  邓腾  王智琳  于亮亮  胡国成  邹少浩 《大地构造与成矿学》2015,(3)

结合现代大陆动力学与地球动力学最新理论与研究和应用进展,以及国内几个典型矿床的成矿实例分析,本文重新审视了地台活化区(即地洼区)多因复成矿床的形成机理。作者认为,陈国达先生所研究的地台活化区应特指中国东部或全球类似地区大地构造发展至中生代时期因发生强烈构造–岩浆活动和相关成矿作用而在大陆地壳的表现。由于成矿作用与大地构造发展和/或地球动力学事件具有密切的成因联系,以及由于地壳演化及其大地构造发展阶段还具有独特性或存在某些差异,成矿作用从而表现出多旋回性、特殊性或叠加改造和富化特点;特别是,地台活化区往往包含多大地构造发展阶段,并发生大规模构造变形、岩浆活动和变质作用等构造–岩浆–热(流体)事件,因而这种活化构造区内的成矿作用往往具有多因复成成矿特征,并形成了具有经济意义的、大而富的矿床。实质上,多因复成矿床是多地质过程包括沉积作用、构造变形、岩浆作用和变质作用及伴生的大规模流体事件等耦合的产物,其动力学机制可能来源于(多期或幕式)地幔(柱)对流和上涌及壳?幔相互作用或地幔柱–岩石圈板块相互作用。作者最后指出,多因复成矿床今后的研究重点仍应关注其成矿动力学机制与过程。  相似文献   

增生造山过程中大陆地壳的净生长——来自中亚造山带中段南缘岩浆岩的约束     

宋博  王宝文  许伟  牛亚卓  张乔  苟红光  闫全人 《岩石学报》2021,37(4):1044-1060

软流圈地幔上涌是大陆地壳净生长的重要方式,这种壳幔作用在增生造山作用过程的地质表现如何有待深入研究。内蒙古西部的居延海地区位于中亚造山带中段南缘,处于北山造山带与阿拉善地块北缘造山带的构造衔接部位。通过对居延海地区4口井所钻获的具壳幔作用特征的花岗质岩石的研究,本文深入剖析了增生造山过程中软流圈地幔物质贡献及其具体地质表现。首先,花岗质岩石中的闪长质暗色微粒包体(富含针状磷灰石微晶)指示了壳幔岩浆混合特征。再者,花岗质岩浆锆石结晶年龄为306～313Ma,具有正的εHf(t)值,平均值介于+13.0～+14.3之间,二阶段模式年龄tDM2平均值介于410～588Ma之间,揭示一次显著的大陆地壳净生长事件,锆石Hf同位素表明花岗质岩浆源区具有初生陆壳重熔和亏损幔源岩浆混合的特征。以上地质事实暗示居延海所在的中亚造山带中段南缘晚石炭世处于洋中脊俯冲或俯冲板片回卷的地球动力学过程中。  相似文献   

Co-development of Jurassic I-type and A-type granites in southern Hunan,South China: Dual control by plate subduction and intraplate mantle upwelling     

Hua Kong  Huan Li  Qian-Hong Wu  Xiao-Shuang Xi  Jeffrey M. Dick  Jillian Aira S. Gabo-Ratio 《Chemie der Erde / Geochemistry》2018,78(4):500-520

Two types of spatially and temporally associated Jurassic granitic rocks, I-type and A-type, occur as pluton pairs in several locations in southern Hunan Province, South China. This paper aims to investigate the genetic relationships and tectonic mechanisms of the co-development of distinct granitic rocks through petrological, geochemical and geochronological studies. Zircon LA-ICPMS dating results yielded concordant U–Pb ages ranging from 180 to 148 Ma for the Baoshan and Tongshanling I-type granodiorites, and from 180 to 158 Ma for the counterpart Huangshaping and Tuling A-type granites. Petrologically, the I-type granodiorites consist of mafic minerals such as hornblende whereas the A-type granites are dominated by felsic minerals (e.g., quartz, K-feldspar and plagioclase). Major and trace element analyses indicate that the I-type granodiorites have relatively low SiO₂ (64.5–71.0%) and relatively high TiO₂ (0.28–0.51%), Al₂O₃ (13.8–15.5%), total FeO (2.3–4.7%), MgO (1.3–2.6%) and P₂O₅ (0.10–0.23%) contents, and the A-type granites are characterized by high concentrations of Rb (212–1499?ppm), Th (18.3–52.6?ppm), U (11.8–33.6?ppm), Ga (20.0–36.6?ppm), Y (27.1–134.0?ppm) and HREE (20.3–70.0?ppm), with pronounced negative Eu anomalies (Eu/Eu*?=?0.01–0.15). Moreover, the I-type granodiorites are classified as collision-related granites emplaced under a compressional environment, whereas the A-type granites are within-plate granites generated in an extensional setting. Zircon Hf isotopic compositions vary substantially for these granitic rocks. The I-type granodiorites are characterized by relatively young Hf model ages (T_DM1?=?1065–1302 Ma, T_DM^C =1589–2061 Ma) and moderately negative εHf(t) values (–5.9 to –11.5), whereas the A-type granites have very old model ages (T_DM1?=?1454–2215 Ma, T_DM^C?=?2211–2974 Ma) and pronounced negative εHf(t) values (–15.8 to –28.3). These petrochemical and isotopic characteristics indicate that the I-type granodiorites may have been derived from a deep source involving mantle-derived juvenile (basaltic) and crustal (pelitic) components, whereas the A-type granites may have been sourced from melting of meta-greywacke in the crust. This study proposes that the pressure and temperature differences in the source regions caused by combined effects of intra-plate mantle upwelling and plate subduction are the major controlling factors of the co-development of the two different types of magmas. Crustal anatexis related to lithospheric delamination and upwelling of hot asthenosphere under a high pressure and temperature environment led to the formation of the I-type magmas. On the other hand, the A-type magmas were formed from melting of the shallower part of the crust, where extensional stress was dominant and mantle-crust interaction was relatively weak. Rifts and faults caused by mantle upwelling developed from surface to depth and successively became channels for the ascending I- and A-type magmas, resulting in the emplacement of magmas in adjacent areas from sources at different depths.  相似文献   

中国东部中、新生代软流圈上涌与构造-岩浆-矿集区   总被引：1，自引：0，他引：1       下载免费PDF全文

邢集善  杨巍然  邢作云  刘建华 《地球科学》2019,44(5):1570-1583

以深部地球物理资料为基础,结合大地构造环境、岩浆岩同位素示踪及矿产资源分布规律,加以综合分析.通过热力学计算可知,中国东部近2亿年来的上地幔岩石圈/软流圈构造可以存留至今,且能区分出中、新生代.软流圈上涌与矿集区:(1)中生代金属矿:(a)克拉通区,软流圈沿柱身上涌,其柱头上方形成幔壳混熔花岗质岩及相应Au、Cu、Mo、Pb-Zn等矿集区,并于柱身与岩石圈块体陡接触带,形成中基性杂岩及相应富Fe矿集区;(b)褶皱带区,在软流圈上涌柱上方形成近幔源型花岗质岩,相应为Cu、Au、Pb-Zn、Mo、Ag矿集区;(c)南岭带,软流圈层在适当深度、热量充足、较大范围内"平卧",因热传导而致使地壳内物质部分重熔,形成壳源型花岗质岩及相应的W、Sn、稀有元素矿集区;(2)新生代油气田:(a)与太平洋板块俯冲有关的软流圈上涌,其上方出露玄武岩,形成较大型油田;(b)与裂陷盆地有关的软流圈上涌,其上方形成大型油田,也有中小型油田.软流圈上涌与大地构造:中生代J-K时期,通过构造力特征等的综合分析,阐明燕山运动的根源及其影响;新生代侧重剖析大陆裂谷相关特征.总之,软流圈上涌是岩石圈减薄,以及中、新生代构造-岩浆-矿集区形成的根源.  相似文献   

Upper ocean responses to category 5 typhoon Megi in the western north Pacific     

CHEN Xiaoyan  PAN Delu  HE Xianqiang  BAI Yan  WANG Difeng 《海洋学报(英文版)》2012,31(1):51-58

Category 5 typhoon Megi was the most intense typhoon in 2010 of the world. It lingered in the South China Sea (SCS) for 5 d and caused a significant phytoplankton bloom detected by the satellite image. In this study, the authors investigated the ocean biological and physical responses to typhoon Megi by using chlorophylla (chla) concentration, sea surface temperature (SST), sea surface height anomaly (SSHA), sea surface wind measurements derived from different satellites and in situ data. The chla concentration (>3 mg/m³) increased thirty times in the SCS after the typhoon passage in comparison with the mean level of October averaged from 2002 to 2009. With the relationship of wind stress curl and upwelling, the authors found that the speed of upwelling was over ten times during typhoon than pretyphoon period. Moreover, the mixed layer deepened about 20 m. These reveal that the enhancement of chla concentration was triggered by strong vertical mixing and upwelling. Along the track of typhoon, the maximum sea surface cooling (6-8℃) took place in the SCS where the moving speed of typhoon was only 1.4-2.8 m/s and the mixed layer depth was about 20 m in pretyphoon period. However, the SST drop at the east of the Philippines is only 1-2℃ where the translation speed of typhoon was 5.5-6.9 m/s and the mixed layer depth was about 40 m in pretyphoon period. So the extent of the SST drop was probably due to the moving speed of typhoon and the depth of the mixed layer. In addition, the region with the largest decline of the sea surface height anomaly can indicate the location where the maximum cooling occurs.  相似文献   

A review on the South China Sea western boundary current   总被引：7，自引：2，他引：5  

FANG Guohong  WANG Gang  FANG Yue  FANG Wendong 《海洋学报(英文版)》2012,31(5):1-10

The advances in understanding the South China Sea (SCS) western boundary current (SCSwbc) have been reviewed since the works of Dale (1956) and Wyrtki (1961) in the middle of the 20th century. The features of the pattern of SCSwbc and the oceanic phenomena associated with it are focused on. The current is driven mainly by monsoon over the SCS and partially by winds over the tropical Pacific governed by the island rule. The SCSwbc exhibits strong seasonal variation in its direction and patterns. In winter, the current is strong and flows southwestward along the South China shelf and slope from the east of Dongsha Islands to the northern central Vietnamese coast, then turns to the south along the central and southern Vietnamese coast, and finally partially exits the SCS through the Karimata Strait. In summer and early fall, the SCSwbc can be divided into three segments based on their characteristics. The southern segment is stable, flowing northward from the Karimata Strait up to about 11 N, where it separates from the coast forming an eastward offshore current. The separation of the current from Vietnamese coast induces some striking features, such as upwelling and cold sea-surface temperature. The middle segment off the central Vietnamese coast may have a bimodal behavior: northward coastal current and meandering current in early summer (June-July), and cyclonic gyre in later summer and early fall (August-September). The northern segment is featured by the summer SCS Warm Current on the South China shelf and a southwestward subsurface current along the continental slope.  相似文献