Subsurface influence on SST in the tropical Indian Ocean: structure and interannual variability     

Suryachandra A. Rao  Swadhin K. Behera 《Dynamics of Atmospheres and Oceans》2005,39(1-2):103

Interannual variations of subsurface influence on SST in the Indian Ocean show strong seasonality. The subsurface influence on SST confines to the southern Indian Ocean (SIO) in boreal winter and spring; it is observed on both sides of the equator in boreal summer and fall. Interannual long Rossby waves are at the heart of this influence, and contribute significantly to the coupled climate variability in the tropical Indian Ocean (TIO). Principal forcing mechanism for the generation of these interannual waves in the Indian Ocean and the relative influence of two dominant interannual signals in the tropics, namely El Niño and Southern Oscillation (ENSO) and Indian Ocean Dipole (IOD), are also discussed. Two distinct regions dominated by either of the above climate signals are identified. IOD dominates the forcing of the off-equatorial Rossby waves, north of 10°S, and the forcing comes mainly from the anomalous Ekman pumping associated with the IOD. However, after the demise of IOD activity by December, Rossby waves are dominantly forced by ENSO, particularly south of 10°S.It is found that the subsurface feedback in the northern flank of the southern Indian Ocean ridge region (north of 10°S) significantly influences the central east African rainfall in boreal fall. The Indian Ocean coupled process further holds considerable capability of predicting the east African rainfall by one season ahead. Decadal modulation of the subsurface influence is also noticed during the study period. The subsurface influence north of 10°S coherently varies with the IOD, while it varies coherently with the ENSO south of this latitude.  相似文献   

<Superscript>57</Superscript>Fe Mössbauer spectroscopy,X-ray single-crystal diffractometry,and electronic structure calculations on natural alexandrite     

Sven-Ulf Weber  Michael Grodzicki  Werner Lottermoser  Günther J. Redhammer  Gerold Tippelt  Johann Ponahlo  Georg Amthauer 《Physics and Chemistry of Minerals》2007,34(7):507-515

Natural alexandrite Al₂BeO₄:Cr from Malyshevo near Terem Tschanka, Sverdlovsk, Ural, Russia, has been characterized by ⁵⁷Fe Mössbauer spectroscopy, electron microprobe, X-ray single-crystal diffractometry and by electronic structure calculations in order to determine oxidation state and location of iron. The sample contains 0.3 wt% of total iron oxide. The ⁵⁷Fe Mössbauer spectrum can be resolved into three doublets. Two of them with hyperfine parameters typical for octahedrally coordinated high-spin Fe³⁺ and Fe²⁺, respectively, are assigned to iron substituting for Al in the octahedral M2-site. The third doublet is attributed to Fe³⁺ in hematite. Electronic structure calculations in the local spin density approximation are in reasonable agreement with experimental data provided that expansion and/or distortion of the coordination octahedra are presumed upon iron substitution. The calculated hyperfine parameters of Fe³⁺ are almost identical for the M1 and M2 positions, but the calculated ligand-field splitting is by far too large for high-spin Fe³⁺ on M1.  相似文献   

<Superscript>57</Superscript>Fe Mössbauer measurements and electronic structure calculations on natural lawsonites     

S.-U. Weber  M. Grodzicki  C. A. Geiger  W. Lottermoser  G. Tippelt  G. J. Redhammer  M. Bernroider  G. Amthauer 《Physics and Chemistry of Minerals》2007,34(1):1-9

Three natural lawsonites from Syke Rock, Mendocino Co., Reed Ranch, Marin Co., and Blake Gardens, Sonoma Co., all from the Coast Range Region in California, were studied by ⁵⁷Fe Mössbauer spectroscopy, electron microprobe analysis, and X-ray powder diffraction. The samples contain about 0.6, 1.0, and 1.4 wt% of total iron oxide, respectively. ⁵⁷Fe Mössbauer spectra are consistent with the assumption that high-spin Fe³⁺ substitutes for Al in the octahedrally coordinated site. The Mössbauer spectrum of lawsonite from Syke Rock exhibits a second doublet with ⁵⁷Fe hyperfine parameters typical for octahedrally coordinated high-spin Fe²⁺. Electronic structure calculations in the local spin density approximation yield quadrupole splittings for Fe³⁺ in quantitative agreement with experiment indicating, however, that substitution of Al by Fe³⁺ must be accompanied by local distortion around the octahedral site. Model calculations also reproduce the room temperature hyperfine parameters of ferrous high-spin iron assuming the substitution of Ca by Fe²⁺. However, it cannot be excluded that Fe²⁺ may occupy a more asymmetric site within the microstructural cavity occupied by Ca and a H₂O molecule.  相似文献   

沁水煤田霍东地区山西组主要煤层对比     

刘仙平  张学彦 《中国煤田地质》2002,14(3):17-18

运用标志层、层间距、物性特征、煤层本身特征等方法，对霍东地区沁安矿区和沁源矿区山西组1号、2号、3号煤层进行对比，认为沁安矿区未沉积3号煤层，该矿区现有的两个煤与沁源矿区的1号、2号煤层可比，而不是2号、3号煤层，其中既有定性又有定量，较成功的解决了南北两大矿区山本组主要可采煤层间的对比问题。  相似文献   

南海北部1987～1988年颗粒物质和硅藻通量的季节性变化:季风气候与 El Nino的响应   总被引：2，自引：0，他引：2       下载免费PDF全文

郑玉龙  王汝建  郑连福  陈荣华  陈建芳 《第四纪研究》2001,21(4):359-365

南海北部1987年9月～1988年10月沉积物捕获器中颗粒物质和硅藻通量的季节性变化受到季风气候的控制.颗粒物质与硅藻在东北和西南季风盛行期增加,在季风转变期减少.浅层和深层的颗粒总通量、蛋白石通量、碳酸钙通量、蛋白石/颗粒总通量比值、碳酸钙/颗粒总通量比值、有机碳/磷的比值以及浅层硅藻Thalassionema nitzschioides、Coscinodiscus excentricus、Coscinodiscus nodulifer、Nitzschia marina和Rhizosolenia bergonii的通量在东北季风期间明显地增加了,这些变化可能与1987年～1988年发生的EINino事件相关.  相似文献   

古鄱阳湖盆地东北缘白晋纪地层的新材料—兼论陆相地层清理后的问题讨论     

蔡雄飞  章泽军  王少锋 《江西地质》2001,15(1):45-49

古鄱阳湖盆地东北缘白垩系的田坂群历来趋向“二分”，但从对剖在再观察入手，认为田坂群纵向上经历了粗→细→粗的巨旋回，这种巨旋回与盆地演化规律，发展阶段相一致，因而“三分”显著，该剖面地学，9沉积学的一些新发现，不仅便于地层划分与对比，而且对盆内层序地层，岩相分析，构造演化阶段研究都具重要意义。  相似文献   

Sources, distribution and storage of heavy metals in the Río Pilcomayo, Bolivia     

Karen A. Hudson-Edwards  Mark G. Macklin  Jerry R. Miller  Paul J. Lechler 《Journal of Geochemical Exploration》2001,72(3)

The Río Pilcomayo rises on the Cerro Rico de Potosí precious metal-polymetallic tin deposits of Bolivia, and flows in a southeasterly direction for ca. 600 km to Bolivia's southern border with Argentina. Mining of the Potosí deposits has occurred continuously since 1545, generating large quantities of waste materials in the headwater of the basin. In addition, a tailings dam breach at the Porco mine in 1996 released an estimated 235 000 m³ of tailings and fluid into the upper reaches of the Río Pilaya, the largest tributary to the Pilcomayo.Concentrations of As, Sb, Cd, Cu, Pb, Hg, Ag, Tl and Zn in contemporary channel sediments upstream of the Pilaya confluence are significantly elevated above background values. Elevated levels appear to be associated with pyrite- and other sulphide mineral-bearing tailings materials transported more than 200 km downstream of the Potosí mines. Significant downstream declines in elemental concentrations occur within 15 km, and again between 150 and 200 km, from the mines. The initial decrease in concentrations is due to the rapid dilution of nearly pure tailings effluent released to the river from milling facilities near Potosí. The latter decrease results from a combination of geomorphic processes including the storage of sediment-borne metals within the channel bed and the influx of ‘clean’ sediment from several large tributaries. Downstream of the Pilaya confluence, concentrations of Cu, Pb, Hg and Zn are only slightly elevated above background values, and Ag, Cd, Sb and Tl cannot be distinguished from background levels. These data suggest that while the Porco tailings spill may have had a significant short-term impact on sediment and water quality along the lower reaches of the Río Pilcomayo, its longer-term impacts were limited. Metals stored and eroded from alluvial deposits of historical age in upstream reaches appear to be an important source of metals to the river today. An additional, and perhaps more significant source, is the release of tailings effluent to the river from modern milling operations. The transport of these contaminants downstream of Icla (203 km from Potosí) appears to be restricted by aggradational processes occurring in the vicinity of Puente Sucre. In addition, downstream of the confluence of the Río Pilaya, inputs of large amounts of ‘clean’ sediment have caused dilution of the metal contaminants. Data from other studies where similar geomorphic processes have occurred suggest that the metals in the upper Pilcomayo may eventually be moved downvalley as the aggradational processes are reversed and channel stabilisation occurs. Thus, the most significant impacts of metal contamination may not be realised in downstream areas for decades.  相似文献   

Mössbauer investigations and molecular orbital calculations on epidote     

M. Grodzicki  S. Heuss-Assbichler  G. Amthauer 《Physics and Chemistry of Minerals》2001,28(9):675-681

  相似文献   

广西巴里—龙头山100号锡多金属矿床成矿物理化学环境研究——氧逸度(f_(o_2))、CO_2逸度(f_(co_2))、硫逸度(f_(s_2))、mΣs     

邓金灿  李蘅  徐文炘  曾文高  韦少校  韦万川  马文来  苏亚汝  甘文志  左湛松  韦汉蒙 《矿产与地质》2001,(3)

根据已知的 10 0号矿体的成矿温度及成矿压力 ,并结合矿体的矿物组合推算出10 0号矿体是在相对低硫、氧和二氧化碳逸度 ,溶液为酸性至弱碱性的物理化学环境下形成的。  相似文献   

Histological bone structure of Lower Cretaceous dinosaurs from southwest Istria (Croatia)     

Z. Kozari?  M. Šparica  Z. Bajraktarevi? 《Cretaceous Research》1996,17(6):741-749

Recently discovered dinosaur bones in submerged near-shore deposits of southwest Istria include one vertebra, one femur, and two rib fragments. They all show well-developed vascularization. The large amounts of primary bone tissue in the vertebral and femoral compacta as well as in one rib fragment suggest that they belong to sub-adult animals which were growing rapidly. The structure of a second rib fragment differs in that it consists of secondary bone. The absence of lines of arrested growth is evident in all investigated bones. This suggests a sustained manner of bone deposition.  相似文献