Diatom stratigraphy of the last 250 ka at Lake El’gygytgyn,northeast Siberia     

Marina V. Cherapanova  Jeffrey A. Snyder  Julie Brigham-Grette 《Journal of Paleolimnology》2007,37(1):155-162

Diatom species counts were conducted on 171 sediment samples from the 13-m-long core PG1351 from Lake El’gygytgyn, northeast Siberia. The planktonic Cyclotella ocellata-complex dominates the diatom assemblage through most of the core record, persisting through a variety of climate conditions. Periphytic diatoms, although less abundant, have greater diversity and greater down-core assemblage variation. During warm climate modes, longer summer ice-free conditions may have allowed more complex diatom communities to develop in shallow-water habitats, and enhanced circulation may have increased transport of these diatoms to deeper parts of the lake. Zones of low overall diatom abundance further support inferred intervals of low lake productivity during times of extended lake ice and snow cover. More data on the modern spatial and temporal distribution of diatom species in the Lake El’gygytgyn system will improve inferences from core records. This is the last in a series of eleven papers published in this␣special issue dedicated to initial studies of El'gygytgyn Crater Lake and its catchment in NE Russia. Julie Brigham-Grette, Martin Melles, Pavel Minyuk were guest editors of this special issue.  相似文献   

Diatoms from the genus Achnanthidium in flowing waters of the Appalachian Mountains (North America): Ecology, distribution and taxonomic notes     

Karin C. Ponader  Marina G. Potapova 《Limnologica》2007,37(3):227-241

Diatoms from the genus Achnanthidium are abundant in rivers, streams, and springs of the Appalachian Mountains. They inhabit clean and polluted waters, including those affected by acid mine drainage. The identification of Achnanthidium taxa is difficult due to their small cell size and insufficient information in the diatom floras. We studied the taxonomy and ecology of Achnanthidium in Appalachian rivers by analyzing a data set of benthic diatom samples and corresponding water chemistry data collected during several water-quality surveys from 181 sampling sites. Ten species were identified using scanning electron and light microscopy: A. alpestre (Lowe & Kociolek) Lowe & Kociolek, A. atomus (Hustedt) Monnier, Lange-Bertalot, & Ector, A. deflexum (Reimer) Kingston, A. duthii (Sreenivasa) Edlund, A. eutrophilum (Lange-Bertalot) Lange-Bertalot, A. cf. gracillimum (Meister) Lange-Bertalot, A. cf. latecephalum Kobayasi, A. minutissimum (Kützing) Czarnecki (sensu lato), A. reimeri (Camburn) comb. nov., and A. rivulare Potapova & Ponader. The distribution of common taxa in relation to water chemistry was studied by fitting non-parametric regression models (generalized additive models, GAM, and non-parametric multiplicative regression models, NPMR) to species relative abundances. Studied Achnanthidium species differed considerably in their responses to water chemistry. These results suggest that species-level identifications will lead to more accurate bioassessments.  相似文献   

A rapid x-ray fluorescence procedure applicable to exploration geochemistry     

A.A. Levinson  Liberto De Pablo 《Journal of Geochemical Exploration》1975,4(4):399-408

A rapid X-ray fluorescence method is described for the analysis of all elements heavier than iron. It is based upon the measurement of a peak and background, while primary scattered radiation is used to correct or compensate for matrix effects. About 15 analyses per man hour can be made on individual samples for such elements as Th, Nb, Ta and W, which are normally difficult to determine by other techniques. Lower limits of detection of about 50 ppm are routinely obtained, and even lower limits of detection (e.g., 20 ppm) can be obtained should these be necessary by increasing the counting time (from 20 to 40 seconds).  相似文献   

An electoral geography of Western Europe     

Christian Vandermotten  Pablo Medina Lockhart 《GeoJournal》2000,52(2):93-105

The European Parliament elections give the opportunity to map voting behaviour in Western Europe. The main methodological difficulty is related to the classification of the parties. The cleavage theory is not a sufficient basis for an operational typology. The left-right axis remains an important basis for a classification. We have discriminated three groups of parties (the left, including the ecologists; the moderate centre-right and classical right; a growing populist reactionary right and the extreme-right, with a different geographical pattern). Beyond those families, the regionalist parties can also be isolated. The green voting pattern is more specific to the central regions and not linked to that of the traditional left, which is related to the traditions of the workers' movement or more specific to the peripheral regions. In general, the metropolitan regions vote more to the left than the surrounding regions, today more and more often on the basis of an intellectual voting pattern, including some well to-do urban and periurban districts. The centre-right and classical right voting pattern designate two main spaces: a conservative mid-European area, with a strong Christian-democracy in the Catholic countries with a quite recent State building (however recently collapsed in Italy), and rural peripheral spaces, mainly those dominated for a long time by small familial rural enterprises and/or by strong and conservative religious practices. At the European scale, the new populist reactionary right is stronger in the `central' regions than the traditional extreme right, even if the latter is also present in some central deprived urban and old industrial districts.  相似文献   

Coastal lateral spreading in the world heritage site of the Tramuntana Range (Majorca,Spain). The use of PSInSAR monitoring to identify vulnerability     

Rosa María Mateos  Pablo Ezquerro  Jose Miguel Azañón  Bernadí Gelabert  Gerardo Herrera  Jose Antonio Fernández-Merodo  Daniele Spizzichino  Roberto Sarro  Inmaculada García-Moreno  Marta Béjar-Pizarro 《Landslides》2018,15(4):797-809

The Bàlitx area is located on the steep coastal side of the Tramuntana Range (Majorca), a mountainous region which was declared a World Heritage Site by UNESCO in 2011 in the cultural landscape category. The Bàlitx site was occupied by farming areas with dry stone constructions and water storing systems of both Roman and Islamic origin. The coastal landscape is characterised by a large fault escarpment of up to 260 m in height. Lateral spreading processes are favoured by local stratigraphy and tectonics in an energetic coastal dynamics scenario. Block spreading morphologies are identified along the escarpment, with large, rocky blocks of volumes up to 60?×?10³ m³ moving very slowly until their collapse. Consequently, a thick and highly karstified breccia deposit is accumulated at the base of the scarp. The lowest, oldest breccia outcrop has been dated (Th/U), and an age of 82.5?±?5.6 kyr was obtained, reflecting the time span this process has been active. Additionally, numerous geomorphological slope features are identified in the area: landslides, rockfalls, and, more specifically, long and deep cracks in the hanging wall block of the fault, which also reveal active lateral spreading processes. Coastal dynamics have been investigated by interpreting offshore geophysical studies, bathymetry data and borehole information to determine the role of wave energy in the stability of the slope. Additionally, 14 SAR images from the ALOS PALSAR satellite have been exploited for the present work, covering a period spanning from 2007 to 2010, an anomalous rainy period in the region. Images were processed using the Persistent Scattered Interferometry (PSI) technique. PSInSAR results reveal that the rate of movement for the Bàlitx lateral spreading is extremely low (??5.2 mm/year on average), but major activity has been detected in the NE sector, where velocity rates can reach values of up to ??16 mm/year Coastal dynamics in the area can explain this, as a small island generates wave refraction and reflection determining more intense erosive processes in the NE part, which lead to a greater destabilising effect on the slopes. A simple vulnerability approach has been developed to take the elements of cultural heritage into account. Vulnerability increases from SW to NE, in accordance with landslide activity. The Bàlitx case study could provide a testimony to the effects of mass movements and coastal dynamics in an exceptional example of Mediterranean agricultural landscape.  相似文献   

Enhanced pumping test using physicochemical tracers to determine surface-water/groundwater interactions in an alluvial island aquifer,river Rhône,France     

Poulain  Angélique  Marc  Vincent  Gillon  Marina  Mayer  Adriano  Cognard-Plancq  Anne-Laure  Simler  Roland  Babic  Milanka  Leblanc  Marc 《Hydrogeology Journal》2021,29(4):1569-1585

Groundwater extracted from the Barthelasse Island aquifer, surrounded by the river Rhône (southeastern France), contributes to the drinking water supplies of 180,000 inhabitants. Owing to its location close to the river and the presence of two backwaters (oxbow lakes), the pumped groundwater is highly vulnerable to river pollution. A pumping test was conducted over 24 h to analyse and quantify the water exchange processes between the river, backwaters and groundwater. During the pumping test, isotopic (δ¹⁸O, δ²H and ²²²Rn), hydrochemical and hydrophysical monitoring of the groundwater was undertaken. Hydraulic heads were measured in pumping wells and at a piezometer located between the wells. Discrete water samples were collected at several observation points in the field, including the backwater and river. The results show mixing between three end-members, as defined by the deuterium excess and silica concentration, led by river Rhône water which had been affected by water–rock interactions over time and mixing with surface evaporated waters. The pumped water resulted from mixing between three end-members, all of which depended on the river Rhône but differed in terms of residence time in the system. Although the groundwater pumping wells are close to each other (<70 m) and have similar depths, the changes in the contributions from end-member waters at each well were different during the pumping test. Comparing isotopic tracers and geochemistry made it possible to quantify the different hydrological compartments that contribute to the groundwater pumped from the boreholes, which is critical in constructing a conceptual flow model.

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Constraining magma sources using primitive olivine-hosted melt inclusions from Puñalica and Sangay volcanoes (Ecuador)     

Diego?F.?NarvaezEmail authorView author&#;s OrcID profile  Estelle?F.?Rose-Koga  Pablo?Samaniego  Kenneth?T.?Koga  Silvana?Hidalgo 《Contributions to Mineralogy and Petrology》2018,173(10):80

Constraining arc magma sources at continental arc settings is a delicate task, because chemical signatures from crustal processes obscure the slab and mantle signatures. Here, we present major, trace, and volatile element compositions of olivine-hosted melt inclusions (Fo_82–89) selected from the most primitive lavas (Mg# >?60) from two Ecuadorian volcanoes (Puñalica and Sangay) situated at the southern termination of the Andean Northern Volcanic Zone. Melt inclusions (MI) from Puñalica are nepheline normative and have basaltic-to-basaltic-andesite compositions (45–56 wt% SiO₂) similar to peridotite-derived melts. Sangay MI is also nepheline normative, with high CaO (up to 16 wt% and CaO/Al₂O₃?<?1) and low silica contents (41.9–44.5 wt%) pointing out an amphibole-bearing clinopyroxenite source. Both volcanoes display volatile-rich compositions (up to 6100 ppm Cl, 2200 ppm F, and 6700 ppm S). These MI cannot be related to their host lavas by fractional crystallization, implying that they represent true primitive liquids. The source of Puñalica MI was metasomatized by slab-derived melts that imprints its low Ba/Th, Sr/Th, and high Th/La (average values of 66, 129, and 0.22, respectively). On the contrary, the slab component added to the source of Sangay MI has a higher Ba/Th, Sr/Th, and low Th/La (average values of 261, 517, and 0.11, respectively) which could suggest a relative contribution of aqueous fluids. This dichotomy is related to the presence of the Grijalva Fracture Zone that separates a younger and hotter oceanic crust to the north (below Puñalica) from a colder and older oceanic crust to the south (below Sangay).  相似文献   

Short-term changes in the aerosol characteristics at Kharagpur (22°19′N, 87°19′E) during winter     

Prabha R. Nair  K. Susan George  K. Parameswaran  Marina Aloysius  Denny P. Alappattu  Mannil Mohan  P.K. Kunhikrishnan 《Journal of Atmospheric and Solar》2009,71(17-18):1771-1783

In-situ measurements of number density, size distribution, and mass loading of near-surface aerosols were carried out at Kharagpur, a site on the eastern part of Indo-Gangetic Plains during the winter month of December 2004. The data have been used to investigate wintertime characteristics of aerosols and their effects on the occurrence of haze. The aerosol number density is found to be of the order of 10⁹ m^?3 and mass loading is ~265±70 μg m^?3 (5–8 times that reported from south Indian sites). The diurnal patterns and day-to-day variations in aerosol number density and mass loading are closely associated with atmospheric boundary layer height. During haze events, the number density of submicron particles is found to be 2–5 times higher than that during non-hazy period. This could be attributed to the enhanced concentration of anthropogenic aerosols, low atmospheric boundary layer height/ventilation coefficient and airflow convergence.  相似文献   

ENAA Studies of pollution in anoxic Black Sea sediments     

Octavian G. Duliu  Carmen Cristache  Otilia A. Culicov  Marina V. Frontasyeva 《Marine pollution bulletin》2009,58(6):827-831

The vertical distributions of five potential pollutants - Zn, As, Br, Sn, and Sb - were determined via epithermal neutron activation in the upper 50 cm of unconsolidated sediments from the Black Sea, which were collected 600 m below sea surface. This analysis demonstrated increasing concentrations towards the upper limits of sediments, which were greater than alert concentrations in the case of As and Br, and in accordance with Romanian Environment Regulations. The utilization of Chernobyl ¹³⁷Cs as a time marker allowed for dating of this region to the last 100 years.  相似文献   

An elasto-visco-plastic model using the finite element method for crustal and lithospheric deformation     

Javier Quinteros  Víctor A. Ramos  Pablo M. Jacovkis   《Journal of Geodynamics》2009,48(2):83-94

A novel numerical model based on solid deformation is presented in this paper. This thermo-mechanical model can simulate the tectonic evolution of crust and (lithospheric and asthenospheric) mantle under different conditions. Our implementation uses the finite element method (FEM) in order to solve the equations. As a Lagrangian approach is employed, remeshing techniques are implemented to avoid distortion problems when a certain deformation threshold is reached. The translation of the state between the old and new mesh is achieved by means of the information stored on Lagrangian particles, which minimizes the diffusion. The model is able to represent elastic, viscous and plastic behaviour inside the studied domain. Three types of creep mechanism (diffusion, dislocation and Peierls) are included. Two different quadrilateral isoparametric elements were implemented and can be employed to perform the calculations. The first one is an element with 4 nodes, selective reduced integration and a stabilization operator to diminish hourglass modes, which reduces the computational time needed. The second one has 8 nodes located in standard positions, uses full integration scheme and has no hourglass modes as it satisfies the Inf-Sup condition. Several test cases with known solutions were run to validate the different aspects of the implementation.  相似文献