Pattern and timing of the northwestern Barents Sea Ice Sheet deglaciation and indications of episodic Holocene deposition   总被引：1，自引：0，他引：1  

Denise Christina Rüther  Lilja Rún Bjarnadóttir  Juho Junttila  Katrine Husum  Tine Lander Rasmussen  Renata Giulia Lucchi  Karin Andreassen 《Boreas: An International Journal of Quaternary Research》2012,41(3):494-512

The origin of two acoustic sediment units has been studied based on lithological facies, chronology and benthic stable isotope values as well as on foraminifera and clay mineral assemblages in six marine sediment cores from Kveithola, a small trough west of Spitsbergenbanken on the western Barents Sea margin. We have identified four time slices with characteristic sedimentary environments. Before c. 14.2 cal. ka, rhythmically laminated muds indicate extensive sea ice cover in the area. From c. 13.9 to 14.2 cal. ka, muds rich in ice‐rafted debris were deposited during the disintegration of grounded ice on Spitsbergenbanken. From c. 10.3 to 13.1 cal. ka, sediments with heterogeneous lithologies suggest a shifting influence of suspension settling and iceberg rafting, probably derived from a decaying Barents Sea Ice Sheet in the inner‐fjord and land areas to the north of Kveithola. Holocene deposition was episodic and characterized by the deposition of calcareous sands and shell debris, indicative of strong bottom currents. We speculate that a marked erosional boundary at c. 8.2 cal. ka may have been caused by the Storegga tsunami. Whilst deposition was sparse during the Holocene, Kveithola acted as a sediment trap during the preceding deglaciation. Investigation of the deglacial sediments provides unprecedented details on the dynamics and timing of glacial retreat from Spitsbergenbanken.  相似文献   

Chusi Li and Edward M. Ripley (eds) Magmatic Ni–Cu and PGE deposits: geology, geochemistry, and genesis     

Christina Yan Wang 《Mineralium Deposita》2012,47(5):577-578

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Anthropogenic structures and the infiltration of natural benthos by invasive ascidians     

Christina Simkanin  Ian C. Davidson  John F. Dower  Glen Jamieson  Thomas W. Therriault 《Marine Ecology》2012,33(4):499-511

Anthropogenic habitats such as marinas and docks are focal points for marine invasions, but relatively little is known about the infiltration of nearby natural habitats by these invaders. To address infiltration by four geographically widespread ascidian invaders, we used a two‐step approach: (i) a field survey with equitable sampling in adjacent artificial and natural habitats in British Columbia, Canada, and (ii) a literature review, to infer larger scale patterns across species’ introduced global ranges. Our field survey revealed differential distribution patterns among the four ascidians recorded, with infiltration of natural rocky habitats by two species, Botrylloides violaceus and Botryllus schlosseri. We did not record Didemnum vexillum or Styela clava in natural habitats, though they were both recorded on adjacent artificial structures. Globally, these ascidian species are predominantly found associated with anthropogenic habitats including floating docks, pilings and aquaculture installations, but they have infiltrated natural habitats in some areas of their introduced range. The factors contributing to infiltration of nearby natural benthic habitats remains unclear, but determining which mechanisms are important for encouraging or hindering the establishment and spread of nonindigenous species beyond artificial structures requires survey and experimental work beyond anthropogenic habitats. Such work will aid our understanding of marine introduction dynamics, invasiveness, and associated management implications.  相似文献   

Extreme precipitation in Europe: statistical threshold selection based on climatological criteria     

Christina Anagnostopoulou  Konstantia Tolika 《Theoretical and Applied Climatology》2012,107(3-4):479-489

In the present study, both parametric (peak over threshold: mean residual life, dispersion index, threshold choice) and non-parametric (percentiles indices 95% and 99%) statistical techniques are employed, aiming at the identification of rainfall thresholds above which a precipitation event can be characterized as extreme. The analysis is based on 45?years (1960–2004) rain gauge daily records from 65 meteorological stations over the European region. According to two climatologically based criteria that were introduced in the study, it was found that a combined peak over threshold methodology has been shown to yield higher threshold values above which extreme precipitation events occur, in comparison to the 95th percentile indices. Overall, concerning northern Europe, it was found that in the majority of the stations, the threshold values vary from 20 to 30?mm, while the results concerning the Mediterranean region are less coherent and the selection of extreme precipitation thresholds differs from region to region. Stations over eastern Mediterranean appear to have thresholds higher than 30?mm, while stations located over the main cyclone trajectories and the cyclogenesis zone of Mediterranean are those with the higher extreme precipitation thresholds (higher than 45?mm).  相似文献   

Consumers’ knowledge about climate change   总被引：2，自引：2，他引：0  

Christina Tobler  Vivianne H. M. Visschers  Michael Siegrist 《Climatic change》2012,114(2):189-209

Several studies have unveiled various misconceptions about climate change that the public holds, for instance, confusion about climate change and ozone depletion. However, so far, there has been no uniform and standardized way to measure climate-related knowledge, which complicates comparisons between different countries or samples. To develop an extensive knowledge scale, we therefore examined the Swiss public??s understanding of climate change in a mail survey and related this scale to attitudes toward climate change. We thereby aimed to consider a broad range of climate-related knowledge, namely physical knowledge about CO₂ and the greenhouse effect, knowledge about climate change and its causes, knowledge about the expected consequences of climate change, and action-related knowledge. The questionnaire included items of different degrees of difficulty, ranging from knowledge that is covered by newspapers to experts?? knowledge. Our findings indicate that people still hold several misconceptions, although people??s knowledge related to CO₂ seems to have increased compared to previous studies. Of all knowledge subscales, knowledge about climate change and causes was most strongly related to attitudes toward climate change.  相似文献   

Water security: Debating an emerging paradigm   总被引：2，自引：0，他引：2  

Christina Cook  Karen Bakker 《Global Environmental Change》2012,22(1):94-102

This paper presents a comprehensive review of the concept of water security, including both academic and policy literatures. The analysis indicates that the use of the term water security has increased significantly in the past decade, across multiple disciplines. The paper presents a comparison of definitions of, and analytical approaches to, water security across the natural and social sciences, which indicates that distinct, and at times incommensurable, methods and scales of analysis are being used. We consider the advantages and disadvantages of narrow versus broad and integrative framings of water security, and explore their utility with reference to integrated water resources management. In conclusion, we argue that an integrative approach to water security brings issues of good governance to the fore, and thus holds promise as a new approach to water management.  相似文献   

Simulating the effects of geologic heterogeneity and transient boundary conditions on streambed temperatures — Implications for temperature-based water flux calculations     

Christina Schornberg  Christian Schmidt  Edda Kalbus  Jan H. Fleckenstein 《Advances in water resources》2010

Analytical solutions to the one-dimensional heat transport equation for steady-state conditions can provide simple means to quantify groundwater surface water exchange. The errors in exchange flux calculations that are introduced when the underlying assumptions of homogeneous sediments and constant temperature boundary conditions are violated were systematically evaluated in a simulation study. Temperatures in heterogeneous sediments were simulated using a numerical model. Heterogeneity in the sediments was represented by discrete, binary geologic units. High contrasts between the hydraulic conductivities (K) of the geologic units were found to lead to large errors, while the influence of the structural arrangement of the units was smaller. The effects of transient temperature boundary conditions were investigated using an analytical equation. Errors introduced by transient boundary conditions were small for Darcy-velocities > 0.1 m d^− 1 in the period near maximum and minimum annual surface water temperatures. For smaller fluxes, however, errors can be large. Assuming steady-state conditions and vertical flow in homogeneous sediments is acceptable at certain times of the year and for medium to high exchange fluxes, but pronounced geologic heterogeneity can lead to large errors.  相似文献   

Arsenic Management Through Well Modification and Simulation     

Keith J. Halford  Christina L. Stamos  Tracy Nishikawa  Peter Martin 《Ground water》2010,48(4):526-537

Arsenic concentrations can be managed with a relatively simple strategy of grouting instead of completely destroying a selected interval of well. The strategy of selective grouting was investigated in Antelope Valley, California, where groundwater supplies most of the water demand. Naturally occurring arsenic typically exceeds concentrations of 10 µg/L in the water produced from these long-screened wells. The vertical distributions of arsenic concentrations in intervals of the aquifer contributing water to selected supply wells were characterized with depth-dependent water-quality sampling and flow logs. Arsenic primarily entered the lower half of the wells where lacustrine clay deposits and a deeper aquifer occurred. Five wells were modified by grouting from below the top of the lacustrine clay deposits to the bottom of the well, which reduced produced arsenic concentrations to less than 2 µg/L in four of the five wells. Long-term viability of well modification and reduction of specific capacity was assessed for well 4-54 with AnalyzeHOLE, which creates and uses axisymmetric, radial MODFLOW models. Two radial models were calibrated to observed borehole flows, drawdowns, and transmissivity by estimating hydraulic-conductivity values in the aquifer system and gravel packs of the original and modified wells. Lithology also constrained hydraulic-conductivity estimates as regularization observations. Well encrustations caused as much as 2 µg/L increase in simulated arsenic concentration by reducing the contribution of flow from the aquifer system above the lacustrine clay deposits. Simulated arsenic concentrations in the modified well remained less than 3 µg/L over a 20-year period.  相似文献   

Quantification of groundwater discharge into lakes using radon-222 as naturally occurring tracer     

Axel Schmidt  Christina E. Stringer  Ulrike Haferkorn  Michael Schubert 《Environmental Geology》2009,56(5):855-863

A case study was carried out with the aim to practically test whether estimates of groundwater discharge rates into dredging lakes can be made via an uncomplicated and straightforward technique using radon-222 as naturally-occurring groundwater tracer. Lake Ammelshainer See, a dredging, seepage lake, approximately 25 km east of Leipzig, Germany, was chosen as the investigation site. In order to evaluate changes in the spatial and temporal radon-222 patterns in the lake during different stages of stratification, sampling campaigns were conducted in April 2007 (well mixed stage) and in May 2007 (thermal stratification stage). Groundwater flow estimates were made using a radon mass balance approach accounting for all radon fluxes into and out of the lake and assuming steady-state conditions with respect to these radon fluxes. Once all positive and negative radon fluxes related to the lake water volume were determined, groundwater discharge was estimated by using the advective radon input and the radon activity concentration of the pore water as key parameters. The results showed that in case of a lake with a size and shape of Lake Ammelshainer See (530,000 m²) reasonable groundwater discharge estimates can be made by collection and analyzing just a few water samples and a few samples from the sediment layer.  相似文献   

Phytoplankton,protozooplankton and nutrient dynamics in the Bornholm Basin (Baltic Sea) in 2002–2003 during the German GLOBEC Project     

Justus E. E. van Beusekom  Dirk Mengedoht  Christina B. Augustin  Mario Schilling  Maarten Boersma 《International Journal of Earth Sciences》2009,98(2):251-260

From March 2002 to until April 2003 we investigated the seasonal nutrient and phytoplankton dynamics in the central Bornholm Basin (Baltic Sea) within the framework of the German GLOBEC Project. We choose a nested approach consisting of vertical fluorescence profiles, phytoplankton counts and nutrient analyses. The Fluoroprobe (MultiProbe, BBE Moldaenke) is capable of distinguishing four algal groups (Cryptophyceae, Cyanophyceae, Chlorophyceae, Bacillariophyceae + Dinophyceae). Winter nutrient concentrations were about 5 μM NO₃ and 0.5 μM PO₄ in the central Basin. The spring phytoplankton bloom was dominated by the diatom Skeletonema sp. and reached a maximum of about 270 μg C/l before the onset of the seasonal stratification. Protozooplankton was dominated by the Mesodinium rubrum (a phototrophic ciliate = Myrionecta rubra) and reached a maximum biomass of about 200–300 μg C/l about 2 weeks after the demise of the diatom spring bloom. During summer, the water column was stratified and a subsurface maximum developed near the thermocline consisting of Bacillariophyceae, Cryptophycea and other phototrophic flagellates. Phytoplankton and protozooplankton biomass was generally low. Nutrient concentrations point towards a nitrogen limitation during this period. The stratification period ended during September and surface nutrient concentrations increased again. Protozooplankton reached a second maximum during September. With the Fluoroprobe small scale structures in the plankton community could be detected like a subsurface Cryptophyceae maximum near the thermocline that however, could not be confirmed by cell counts. The chlorophyll a estimate of the Fluoroprobe was in good agreement with the phytoplankton biomass estimated from counts. We conclude that only by combining modern sensing technology with microscopy, the small-scale dynamics and taxonomic spectrum of the plankton can be fully captured.  相似文献