Dissolved load of the Loire River: chemical and isotopic characterization   总被引：5，自引：0，他引：5  

C. Grosbois  Ph. Ngrel  C. Fouillac  D. Grimaud 《Chemical Geology》2000,170(1-4):179-201

The Loire River, with one of the largest watersheds in France, has been monitored just outside the city of Orleans since 1994. Physico-chemical parameters and major and trace elements were measured between 2-day and 1-week intervals according to the river flow. The sampling site represents 34% of the total Loire watershed with 76% silicate rocks and 24% carbonate rocks.

Elements are transported mainly in the dissolved phase with the ratio of total dissolved salts (TDS) to suspended matter (SM) ranging between 1.6 and 17.4. Chemical weathering of rocks and soils are thus the dominant mechanisms in the Loire waters composition. The highest TDS/SM ratios are due to dissolved anthropogenic inputs. The database shows no link between NO₃⁻ content and river flow. The Na⁺, K⁺, Mg²⁺, SO₄²⁻, and Cl⁻ concentrations are seen to decrease with increasing discharge, in agreement with a mixing process involving at least two components: the first component (during low flow) is concentrated and may be related with input from the groundwater and sewage station water, the second component (during high flow) is more dilute and is in agreement with bedrock weathering and rainwater inputs. A geochemical behaviour pattern is also observed for HCO₃⁻ and Ca²⁺ species, their concentrations increase with increasing discharge up to 300 m³/s, after which, they decrease with increasing discharge. The Sr isotopic composition of the dissolved load is controlled by at least five components — a series of natural components represented by (a) waters draining the silicate and carbonate bedrock, (b) groundwater, and (c) rainwaters, and two kinds of anthropogenic components.

The aim of this study is to describe the mixing model in order to estimate the contribution of each component. Finally, specific export rates in the upper Loire watershed were evaluated close to 12 t year⁻¹ km⁻² for the silicate rate and 47 t year⁻¹ km⁻² for the carbonate rate.  相似文献   

Mg-Fe partitioning between silicate spinel and magnesiowüstite at high pressure: experimental determination and calculation of phase relations in the system Mg2SiO4-Fe2SiO4     

K. Matsuzaka  M. Akaogi  T. Suzuki  T. Suda 《Physics and Chemistry of Minerals》2000,27(5):310-319

 Mg-Fe partitioning experiments between (Mg,Fe)₂SiO₄ spinel and (Mg,Fe)O magnesiowüstite were carried out at pressures of 17–21.3 GPa at temperatures of 1400 and 1600 °C, using a multi-anvil apparatus, in order to determine interaction parameters of spinel and magnesiowüstite solid solutions and also to constrain the equilibrium boundaries of the postspinel transition in the Fe-rich side in the system Mg₂SiO₄-Fe₂SiO₄. The obtained values of the interaction parameters were 3.4 ± 1.5 and 13.9 ± 1.4 kJ mol⁻¹, respectively, for spinel and magnesiowüstite solid solutions at 19 GPa and 1600 °C. The partitioning data in the system Mg₂SiO₄-Fe₂SiO₄ at 1400 and 1600 °C showed that the transition boundary between spinel and the mixture of magnesiowüstite and stishovite has a negative dP/dT slope. Using the above interaction parameters and available thermodynamic data of the Mg₂SiO₄ and Fe₂SiO₄ end members, the transition boundaries of spinel to the mixture of magnesiowüstite and stishovite were calculated. Within the uncertainties of the data used, the calculated boundaries are in good agreement with the boundaries at 1400 and 1600 °C experimentally determined in this study. The dissociation boundary of Fe₂SiO₄ spinel to wüstite and stishovite, calculated from the thermodynamic data, has a negative slope of −1.5 ± 0.6 MPa K⁻¹. Received: 18 February 1998 / Revised, accepted: 18 October 1999  相似文献   

象山港盐度分布和水体混合 Ⅱ.混合分析   总被引：5，自引：3，他引：2  

董礼先  苏纪兰 《海洋与湖沼》2000,31(3):322-326

利用１９８１－１９９０年象山港的实测水文断面资料和盐度通量分析方法定量检验了各种动力因子对象山港水体混合的贡献,探讨了象山港水体混合的控制机理。象山港牛鼻水道至佛渡水道为平流和潮弥散混合区,水体纵向混合较好。象山港狭湾内段的潮混合强度较弱,垂向环流和潮振荡的垂向切变作用突出,水体纵向混合较狭湾外差。象山港湾外段为内段与田外的过渡区,各种混合因子的地位随季节和潮汛而变,水体混合状况介于狭湾内段和口外  相似文献   

黑龙江五大连池火山群大地电磁探测和研究初步结果   总被引：2，自引：0，他引：2  

詹艳  赵国泽  白登海  晋光文  王继军  宣飞  江钊  任锦章  曲家志  郭德明 《地质论评》1999,45(7):400-408

对黑龙江五大连池火山群新近观测的7条大地电磁测深剖面资料进行了处理、解释和分析。研究表明,在地下约几百米深度至15～20 km左右,存在一个上宽下窄似铆钉状的高阻异常体,推测为固结过程中的火山岩浆体。该高阻体一直穿过地壳与上地幔连接,有向深处延伸的通道,并随着深度的加大,其电阻率逐渐减小。该火山群属于岩浆直接来自上地幔的火山类型,在地壳内没有明显的低阻岩浆囊存在。火山区的构造走向为近南北方向。  相似文献   

Disturbance of meromixis in saline Lake Shira (Siberia,Russia): Possible reasons and ecosystem response     

《Limnologica》2017

Saline Lake Shira (Southern Siberia, Russia) was meromictic through the observation period 2002–2015. During the under-ice periods of 2015 and 2016, complete mixing of the water column was recorded for the first time, and hydrogen sulphide temporarily disappeared from the water column of the lake; i.e. in those years the lake turned to holomixis. In the summer of 2015, a sharp increase in chlorophyll a, organic carbon, zooplankton, and phytoflagellates was observed in the lake, which was probably due to the release of nutrients from the monimolimnion. Purple sulfur bacteria completely disappeared from the lake after the first mixing in 2015, and did not reappear despite the restoration of meromixis in 2017. Thus, it was demonstrated that purple sulfur bacteria are sensitive to the weakening of the stratification of Lake Shira. Based on the data of the seasonal monitoring of temperature and salinity profiles over the period 2002–2017, it was presumed that the main cause of deep mixing in 2015 was the weakening of the salinity gradient due to strong wind impact and early ice retreat in the spring of 2014. In addition, it was shown that in previous years a significant contribution to the maintenance of meromixis was made by an additional influx of fresh water, which caused a rise in the lake level in the period 2002–2007. Thus, we identified a relationship between the stratification regime of the lake and the change in its level, which provides valuable information both for the forecast of water quality and for reconstruction of the Holocene climate humidity in this region of Southern Siberia from the sediment cores of Lake Shira.  相似文献   

地震氡观测计量溯源初步探究     

黄仁桂  赵影  李雨泽  汪世先  罗齐彬  肖健 《地震》2019,39(2):183-190

根据氡观测仪的氡室校准和氡气固体源校准两种校准方式的实验结果, 讨论了使用标准仪器校准氡观测仪器的可靠性问题。 用国际公认的计量传递仪器AlphaGUARD P2000Pro或AlphaGUARD P2000F测氡仪作为氡气溯源仪器, 对九江地震台FD-125氡钍分析器的三个闪烁室进行了氡室校准、 氡气固体源校准和仪器校准三种方法实验, 得到标准仪器校准、 氡气固体源校准得出K值相对氡室校准结果偏差均小于6%, 结果表明, 三种方法的校准结果均符合目前氡观测计量溯源技术要求, 能达到与国家氡计量刻度相统一目的。  相似文献   

Coexistence of natural gas hydrate,free gas and water in the gas hydrate system in the Shenhu Area,South China Sea     

《China Geology》2020,3(2):210-220

Shenhu Area is located in the Baiyun Sag of Pearl River Mouth Basin, which is on the northern continental slope of the South China Sea. Gas hydrates in this area have been intensively investigated, achieving a wide coverage of the three-dimensional seismic survey, a large number of boreholes, and detailed data of the seismic survey, logging, and core analysis. In the beginning of 2020, China has successfully conducted the second offshore production test of gas hydrates in this area. In this paper, studies were made on the structure of the hydrate system for the production test, based on detailed logging data and core analysis of this area. As to the results of nuclear magnetic resonance (NMR) logging and sonic logging of Well GMGS6-SH02 drilled during the GMGS6 Expedition, the hydrate system on which the production well located can be divided into three layers: (1) 207.8–253.4 mbsf, 45.6 m thick, gas hydrate layer, with gas hydrate saturation of 0–54.5% (31% av.); (2) 253.4–278 mbsf, 24.6 m thick, mixing layer consisting of gas hydrates, free gas, and water, with gas hydrate saturation of 0–22% (10% av.) and free gas saturation of 0–32% (13% av.); (3) 278–297 mbsf, 19 m thick, with free gas saturation of less than 7%. Moreover, the pore water freshening identified in the sediment cores, taken from the depth below the theoretically calculated base of methane hydrate stability zone, indicates the occurrence of gas hydrate. All these data reveal that gas hydrates, free gas, and water coexist in the mixing layer from different aspects.  相似文献   

浙东晚白垩世酸性岩浆的自混合作用及其意义   总被引：1，自引：1，他引：0  

高丽  杨祝良  余明刚 《岩石学报》2020,36(4):1015-1029

岩浆混合作用是造成火成岩多样性的主要原因之一,也是诱发火山喷发的重要机制。以往的研究多集中于基性和酸性岩浆之间的混合作用,但近年来酸性岩浆之间的混合作用受到越来越多的关注和研究。本文报道了浙东小雄破火山一个次级火山口内粗面质和流纹质两种酸性岩浆之间的混合现象。野外调查及岩相学研究显示,粗面质岩浆多呈大小不一的条带状以及透镜体状分布于流纹质岩浆内,局部发生扩散,粗面岩中斑晶大多为粗大的正长石斑晶,强烈熔蚀且聚斑结构普遍;在副矿物聚晶(由钛磁铁矿+磷灰石+锆石组成)的周围常可见反应边结构。流纹岩的斑晶主要由正长石、透长石及石英组成,晶体粒径较小,且熔蚀现象不发育。全岩主、微量元素特征及其他地质证据均显示,两种酸性岩浆之间以机械混合为主,其地球化学成分变化趋势主要受结晶分异过程控制。粗面质及流纹质岩浆在矿物组成、结构等方面的差异表明两者来源于同一层状岩浆房内的不同部位,其中粗面质岩浆应代表岩浆房底部及边部富晶体、贫熔体的粥状层部分(正长石+磁钛铁矿+锆石+磷灰石);而分异程度较高的流纹质岩浆则聚集于岩浆房上部形成富熔体、贫晶体的部分。两种酸性岩浆的混合现象是它们在地壳浅部层状岩浆房内自混合的结果,这一过程可能受岩浆房底部基性岩浆的聚集作用所控制,当更热、更基性的岩浆聚集时,岩浆房下部晶粥区内的粗面质岩浆迅速升温、活化,从而向上运移并与上部富熔体贫晶体的流纹质岩浆发生自混合作用。这一发现为我们理解中国东南沿海地区晚中生代大规模酸性火山喷发及岩浆演化机制、岩浆房结构提供了重要的参考,同时也为认识地壳浅部岩浆房内岩浆之间的自混合作用提供了可靠的例证。  相似文献   

Study About Ocean Eddy Effect on Strong Convection in Local Atmosphere over the Kuroshio Extension Region     

Qinyu Liu  Suping Zhang  Yinglai Jia 《地球科学进展》2020,35(5):441-451

The Kuroshio Extension （KE） is the key area where the water heats the atmosphere in the northwestern Pacific Ocean in winter. Previous studies show that the active eddies in the KE area can affect sea surface temperature and thus sea surface winds. The present study reviewed the progress about the influences of the eddies on local atmosphere in recent years. Analysis and comparison were made especially for the achievements from shipboard sounding data, satellite observations and numerical experiments. Based on the geostrophic adaptation theory involved in atmospheric anomalies induced by the eddies, the following new scientific deductions were suggested: Air pressure adjustment mechanism dominated in the atmospheric response to eddies under the conditions of weaker wind speed over the eddies. The influence of eddies was often limited in the atmospheric boundary layer. On the other hand, vertical mixing mechanism played a major role in the response of the atmosphere to warm (cold) eddies when air moved faster over the eddies. Surface wind speed increased (decreased) over the warm (cold) water. Significant wind convergence took place downwind the warm water, and large amount of water vapor was transported also downwind from the warm water surface. The positive feedback between water vapor condensation and rising air forced by the surface convergence provided necessary conditions for the development of strong convection in atmosphere. These deductions will be conducive to further depicting the impact of oceanic eddies on the atmosphere quantitatively.  相似文献   

小振幅海洋内波的演变、破碎和所致混合   总被引：1，自引：1，他引：0       下载免费PDF全文

李丙瑞  范海梅  田纪伟  孙波  张占海 《海洋与湖沼》2010,41(6):807-815

利用基于谱方法和MPI并行运算的数值模式SpectralModel,直接数值模拟了三维小振幅海洋内波的演变、破碎和所致湍流混合,指出导致其不稳定而破碎的为PSI(parametric subharmonic instability)机制;对于内波破碎所致的湍流混合过程,分析了跨等密度面扩散系数kρ、混合效率γ、浮力通量谱、动能谱以及势能谱等统计性质:内波破碎前,kρ和γ保持低值水平,浮力通量谱值为负,且集中在低波数段;内波破碎后,kρ和γ迅速增大,最大值分别约为0.9×103m2/s和0.18,浮力通量谱值在低波数段为负值,在高波数段为正值,这是因为层化湍流中势能向小尺度运动传递和动能向小尺度运动传递相比更为有效。在内波破碎、强湍流混合阶段,势能谱存在一谱段满足kz3律,P(kz)=0.2N2kz3。此外,与二维模拟结果相比较,导致内波不稳定而破碎的均为PSI机制,kρ、浮力通量谱、势能谱变化趋势大体一致;但三维数值实验中,内波破碎时间提前,湍流衰减加快;KE谱在高波数部分下降速度相对减小,更接近于kz3。  相似文献