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61.
Lars Eklundh Ulrik Mårtensson 《International journal of geographical information science》2013,27(3):329-340
Abstract In this article we demonstrate that substantial gains in time can be made when using point sampling rather than contour line digitising for generation of Digital Elevation Models (DEMs). A simple sampling scheme, based on regularly distributed points, was used supplemented with points near break-lines in the terrain. An evaluation of surfaces created with three different interpolation methods at three different resolutions shows that the statistical distribution was better when using points as opposed to contours, and that the accuracy was comparable despite the much smaller amount of input data. 相似文献
62.
The legacy of crystal-plastic deformation in olivine: high-diffusivity pathways during serpentinization 总被引:1,自引:1,他引:0
Oliver Plümper Helen E. King Christian Vollmer Quentin Ramasse Haemyeong Jung Håkon Austrheim 《Contributions to Mineralogy and Petrology》2012,163(4):701-724
Crystal-plastic olivine deformation to produce subgrain boundaries composed of edge dislocations is an inevitable consequence
of asthenospheric mantle flow. Although crystal-plastic deformation and serpentinization are spatio-temporally decoupled,
we identified compositional readjustments expressed on the micrometric level as a striped Fe-enriched (
[`(X)]\textFe \bar{X}_{\text{Fe}} = 0.24 ± 0.02 (zones); 0.12 ± 0.02 (bulk)) or Fe-depleted (
[`(X)]\textFe \bar{X}_{\text{Fe}} = 0.10 ± 0.01 (zones); 0.13 ± 0.01 (bulk)) zoning in partly serpentinized olivine grains from two upper mantle sections in
Norway. Focused ion beam sample preparation combined with transmission electron microscopy (TEM) and aberration-corrected
scanning TEM, enabling atomic-level resolved electron energy-loss spectroscopic line profiling, reveals that every zone is
immediately associated with a subgrain boundary. We infer that the zonings are a result of the environmental Fe2+Mg−1 exchange potential during antigorite serpentinization of olivine and the drive toward element exchange equilibrium. This
is facilitated by enhanced solid-state diffusion along subgrain boundaries in a system, which otherwise re-equilibrates via
dissolution-reprecipitation. Fe enrichment or depletion is controlled by the silica activity imposed on the system by the
local olivine/orthopyroxene mass ratio, temperature and the effect of magnetite stability. The Fe-Mg exchange coefficients
K\textD\textAtg/\textOl K_{\text{D}}^{{{\text{Atg}}/{\text{Ol}}}} between both types of zoning and antigorite display coalescence toward exchange equilibrium. With both types of zoning, Mn
is enriched and Ni depleted compared with the unaffected bulk composition. Nanometer-sized, heterogeneously distributed antigorite
precipitates along olivine subgrain boundaries suggest that water was able to ingress along them. Crystallographic orientation
relationships gained via electron backscatter diffraction between olivine grain domains and different serpentine vein generations
support the hypothesis that serpentinization was initiated along olivine subgrain boundaries. 相似文献
63.
The heavily eutrophicated Limfjorden (Denmark) provides a good illustration of the value of long-term monitoring, especially
if this is combined with an experimental, interdisciplinary research approach. Here, we first give a short overview of the
environmental status of Limfjorden, including the historical development of nutrient overloading and subsequent oxygen depletion
in near-bottom water, and how the annual landings of edible bottom-dwelling fish species (plaice, flounder, eel and others)
caught in Limfjorden have decreased from about 2,500 t in the early 1920s to only about 20 t in recent years where the fish
have been replaced by an increasing number of especially the moon jellyfish, Aurelia aurita, which mainly preys on zooplankton. Next, we evaluate the ecological consequences of the present high number of jellyfish,
based on data from recent years’ research on the abundance of jellyfish, their population dynamics and predation impact. In
Limfjorden, the benthic polyp stage of A. aurita ensures a large number of small ephyrae in the early spring and subsequently a large population of adult medusae that control
the zooplankton during summer and autumn. The holopelagic invasive ctenophore Mnemiopsis leidyi, which was observed in Limfjorden for the first time in 2007, is a second carnivore adding additional predation pressure
of the indigenous A. aurita so that copepods and other mesozooplankton organisms may be virtually absent, as observed in 2008 and 2009 where ciliates
made up a substantial part of the zooplankton biomass. Marine environmental management programmes should be aware of the increasing
importance of both indigenous and new invasive jellyfish species that may show mass occurrence in especially eutrophicated
and over-fished areas. 相似文献
64.
P.G. Langdon C.J. Caseldine I.W. Croudace S. Jarvis S. Wastegrd T.C. Crowford 《Quaternary Research》2011,75(3):451-460
Few studies currently exist that aim to validate a proxy chironomid-temperature reconstruction with instrumental temperature measurements. We used a reconstruction from a chironomid percentage abundance data set to produce quantitative summer temperature estimates since AD 1650 for NW Iceland through a transfer function approach, and validated the record against instrumental temperature measurements from Stykkishólmur in western Iceland. The core was dated through Pb-210, Cs-137 and tephra analyses (Hekla 1693) which produced a well-constrained dating model across the whole study period. Little catchment disturbance, as shown through geochemical (Itrax) and loss-on-ignition data, throughout the period further reinforce the premise that the chironomids were responding to temperature and not other catchment or within-lake variables. Particularly cold phases were identified between AD 1683–1710, AD 1765–1780 and AD 1890–1917, with relative drops in summer temperatures in the order of 1.5–2°C. The timing of these cold phases agree well with other evidence of cooler temperatures, notably increased extent of Little Ice Age (LIA) glaciers. Our evidence suggests that the magnitude of summer temperature cooling (1.5–2°C) was enough to force LIA Icelandic glaciers into their maximum Holocene extent, which is in accordance with previous modelling experiments for an Icelandic ice cap (Langjökull). 相似文献
65.
The concentrations of copper, zinc, cadmium, selenium and mercury were determined in eggs, muscle, liver, kidney and stomach content of nestilings and adults of the Antarctic petrel, Thalassoica antarctica, and its predator, the south polar skua, Chataracta maccormicki, from Svarthamaren, Dronning Maud Land, Antarctica. The dominant food of the petrels is krill, Euphausia superba. The results show relatively high levels of cadmium in krill, which is assumed to be the main reason for the high levels of cadmium in petrels and skuas. Cadmium is almost absent in eggs, but accumulates very rapidly with age in nestlings. The copper concentrations in livers of nestling petrels reach very high levels during growth. This may be seen in connection with physiological development processes. Mercury seems to be accumulated with age and between trophic levels. Among the nestlings, the mercury levels decrease with increasing age, which may be accomplished by the excretion of mercury through the growth of feathers and as a dilution effect during growth. Selenium and mercury are inversely correlated in nestlings. The levels of zinc were similar for different nestling stages and between nestlings and adults in skuas and petrels. 相似文献
66.
Nuclear reaction analyses on boron in flux-grown Me3+- and Na+-doped diopside crystals utilising the 11B(p,2α)4He reaction in conjunction with EMP analyses for major elements and optical absorption spectroscopy for determination of Me-valence
state distributions show that appreciable amounts of B may enter the diopside lattice in crystals produced in Na2B4O7 fluxes. The results indicate that the substitution [6]Me3+[4]B3+[6]Mg2+
−1
[4]Si4+
−1 operates in the present diopside samples in addition to the coupled substitution [6]Me3+[8]Na+[6]Mg2+
−1
[8]Ca2+
−1. The specific NRA technique applied allows for quantitative, high resolution (ca. 5 μm) B analyses at ppm level as well as
high-resolution and high-contrast imaging of B-concentration patterns in minerals. The estimated detection limit and relative
error of the B analyses are 10 ppm and 5–10%, respectively.
Received: 20 September 1999 / Accepted: 6 June 2000 相似文献
67.
The present contribution gives an overview of current knowledge of a comprehensive and steadily growing research field. The first section deals with water pumping and particle retention mechanisms in ciliary and muscular filter feeders. The second section examines the biological filter pumps in order to assess adaptation to the environment. Filter-feeding benthic invertebrates have evolved filter pumps to solve common basic problems. This has led to a large degree of similarity between otherwise distant standing species, which makes comparative studies interesting and important. The present review of zoobenthic filter feeding aims at accentuating such recognition. 相似文献
68.
Sören Håkansson 《Quaternary Science Reviews》1985,4(2):135-146
A survey is made of various factors influencing the ratio of the organic component in lake sediments, focusing on the behaviour at the change from glacial to post-glacial environmental conditions.Increase in the 13C content of the organic sediment is caused by increase in temperature and the corresponding decrease of the supply of molecular CO2 in the water of the lakes. An increase in the rate of organic production in the lakes may also, perhaps, cause a corresponding 13C increase. An increase of the fermentation of organic mud in the lakes may also have an effect in the same direction.Decrease in the 13C content of the organic sediment is caused by the change of the relative amounts of production of plankton and submersed macrophytes in the lakes from mainly submersed macrophytes to mainly plankton. A decrease towards almost complete absence of bicarbonate and CO2 originating from carbonate rocks will also lead to a 13C decrease in the organic sediments. The same effect has the change of the terrestrial vegetation cover from almost complete absence to complete cover. A possible decrease of the 13C content in the atmospheric CO2 has an effect in the same direction. 相似文献
69.
70.
Szilárd Oszlaczky 《Pure and Applied Geophysics》1947,10(1-2):174-180
Summary The gravimetric effect of a two dimensional parallelepipedon measurable by Torsion Balance in the vertical plane is examined. It is found that the places of the equal gradients and curvatures of a rectangle stretching into the infinity are orthogonal circles. The gradients and curvatures of a parallelogramm (stretching into the infinity) which has the finite side in common with the rectangle are expressed by those of the latter, their extreme values lie along isosceles hyperbolas.
Riassunto Si esamina l'azione gravimetrica di un parallelepipedo bidimensionale in base agli elementi misurabili con la bilancia di torsione nel piano verticale. Risulta che il luogo dei punti di eguali gradienti e curvature di un parallelogrammo pure estendentesi all'infinito con il lato finito in comune col rettangolo sono esprimibili a mezzo degli analoghi elementi di quest'ultimo ed 1 loro valori estremi risultano distribuiti lungo iperboli isosceli.相似文献