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71.
Ulf Högström Hans Bergström Ann-Sofi Smedman Sven Halldin Anders Lindroth 《Boundary-Layer Meteorology》1989,49(1-2):197-217
Measurements of gradients of wind, temperature and humidity and of the corresponding turbulent fluxes have been carried out over a sparse pine forest at Jädra»s in Sweden. In order to ascertain that correct gradient estimates were obtained, two independent measuring systems were employed: one system with sensors at 10 fixed levels on a 51 m tower and another with reversing sensors for temperature and humidity, covering the height interval 23 to 32 m. Turbulent fluxes were measured at three levels simultaneously. Data from three field campaigns: in June 1985, June 1987 and September 1987 have been analyzed. The momentum flux is found on the average to be virtually constant from tree top level, at 20 to 50 m. The average fluxes of sensible and latent heat are not so well behaved. The ratio of the non-dimensional gradients of wind and temperature to their corresponding values under ideal conditions (low vegetation) are both found to be small immediately above the canopy (about 0.3 for temperature and 0.4 for wind). With increasing height, the ratios increase, but the values vary substantially with wind direction. The ratios are not found to vary systematically with stability (unstable stratification only studied). The ratio of the non-dimensional humidity gradient to the corresponding non-dimensional potential temperature gradient (equivalent to k
h
/k
w
) is found to be unity for (z – d)/L
v
less than about –0.1 and about 1.4 for near neutral stratification, but the scatter of the data is very large. 相似文献
72.
73.
Problems associated with luminescence dating of Late Quaternary glacial sediments in the NW Scottish Highlands 总被引:2,自引:0,他引:2
Sven Lukas Joel Q.G. Spencer Ruth A.J. Robinson Douglas I. Benn 《Quaternary Geochronology》2007,2(1-4):243-248
Linking the timing of glacial episodes and behaviour to climatic shifts that are documented in ice and marine sedimentary archives is key to understanding ocean-land interactions. In the NW Scottish Highlands a large number of closely spaced (‘hummocky’) moraines formed at retreating glacier margins. Independent age control on one palaeo-glacier limit is consistent with the timing of Younger Dryas (YD) glaciation in the area, but adjacent glacier lobes have remained undated due to the lack of sites and material for 14C dating. Direct dating of ice-marginal moraines using optically stimulated luminescence (OSL) techniques has never been attempted before in Scotland, but if successful, they may be the most appropriate methods for constraining the age of sediment deposition in the absence of organic material. Coarse-grained quartz and K-feldspar minerals from supraglacial sheet flow deposits and glacilacustrine sediments within ice-marginal moraines were analysed using the single-aliquot regenerative-dose (SAR) protocol. Independent age control and clear geomorphological relationships indicate that all samples should yield YD or post-Last Glacial Maximum (LGM) ages. Quartz OSL shine down curves showed low luminescence sensitivity, significant medium-to-slow components, a weak fast component, and scattered SAR data; Linearly Modulated-OSL (LM-OSL) measurements confirmed that the fast component was weak or absent. In contrast, feldspar infrared stimulated luminescence (IRSL) was highly sensitive with excellent SAR data. However, SAR data from 3 mm diameter aliquots of feldspar (200 grains) give higher than expected equivalent doses (De) by an order of magnitude. SAR measurements of small clusters of feldspar grains (ranging from 1–8) considerably broaden the apparent De distribution, but even the lowest value is about 2–3 times the expected De. Two possibilities arise to explain the quartz and feldspar data: (1) that glacial sequences in the NW Highlands re-work inherited (older) glacial deposits and that some of the pre-Devensian existing glacial landforms have only been modified during Devensian glaciation; or (2) that the sedimentary processes operating in these ice-marginal environments are not conducive to adequate bleaching of quartz and feldspar grains. Our study implies that ice-proximal supraglacial sediments from this region in NW Scotland reflect older ages of deposition, but dating YD sediments has not been possible. 相似文献
74.
75.
Jochen Kolb Sven Sindern Alexander F. M. Kisters F. Michael Meyer Stephan Hoernes Jens Schneider 《Mineralium Deposita》2005,40(5):473-491
Gold mineralization at Kochkar (Urals, Russia) is hosted mainly by quartz lodes, which developed at lithological contacts
between mafic dikes and granitoids of the Plast massif during late Carboniferous to early Permian, regional E–W compression
in the East Uralian Zone (EUZ). The alteration mineralogy in mafic dikes comprises biotite, actinolite, albite, K-feldspar,
quartz, epidote, tourmaline, sericite, pyrite, arsenopyrite, chalcopyrite, sphalerite, fahlores, galena, bismuthinite, and
gold, and in Plast granitoids quartz, sericite, calcite, epidote, and ore minerals. Geochemically, an enrichment of Si, K,
Rb, Ba, S, base metals, W, and Au can be observed. The ore fluid had δ18O values between 8.2‰ and 9.5‰ typical for metamorphic or deep magmatic fluids. The tectonometamorphic evolution of the EUZ
is marked by peak metamorphic conditions at 635±40°C and 5–6 kbar through 500±20°C during gold mineralization, and 300–350°C
and 2–3 kbar. The last event was dated on a late, barren quartz vein formed during greenschist facies metamorphism at 265±3 Ma
by the Rb–Sr method. Fluids related to this overprint had a δ18O value of 5.2‰ and an initial 87Sr/86Sr ratio of 0.70685 indicating that they are largely equilibrated with metamorphic lithologies of the EUZ. The Plast granitoids
and the adjacent Borisov granite, which was dated at 358±23 Ma (U–Pb zircon age), have an adakitic character. This, together
with the arc-signature of the mafic dikes, supports the setting of the EUZ within the Valerianovsky continental arc. Eastward
subduction of the Uralian Ocean below this arc began during the late Devonian to early Carboniferous. Between 320 and 265 Ma,
the oblique closure of the ocean resulted in doming of granitoid massifs in a sinistral transpressional regime, subsequent
retrograde gold mineralization during E–W compression and a later greenschist facies overprint. This long-lasting retrograde
evolution of the EUZ was caused by the lack of postcollisional collapse. Heat for a “deep-later" type of metamorphism and
triggering the auriferous fluid system was supplied by radiogenic heating of an overthickened crust. The greenschist facies
overprint at Kochkar and coeval crustal melting in the EUZ was additionally initiated by local external heating of the terrane.
This could have been caused by syn- to postcollisional slab rollback or delamination resulting in magmatic underplating of
the EUZ, which postdates orogenic gold mineralization at Kochkar. The tectonic interpretation of the EUZ indicates that gold
mineralization at Kochkar formed in a mid-crustal environment of a continental magmatic arc at the cessation of active subduction
predating post orogenic plutonism. 相似文献
76.
Waldo Sven Lavado Casimiro David Labat Jean Loup Guyot Sandra Ardoin‐Bardin 《水文研究》2011,25(24):3721-3734
In this article, we propose an investigation of the modifications of the hydrological response of two Peruvian Amazonas–Andes basins in relationship with the modifications of the precipitation and evapotranspiration rates inferred by the IPCC. These two basins integrate around 10% of the total area of the Amazonian basin. These estimations are based on the application of two monthly hydrological models, GR2M and MWB3, and the climatic projections come from BCM2, CSMK3 and MIHR models for A1B and B1 emission scenarios (SCE A1B and SCE B1). Projections are approximated by two simple scenarios (anomalies and horizon) and annual rainfall rates, evapotranspiration rates and discharge were estimated for the 2020s (2008–2040), 2050s (2041–2070) and 2080s (2071–2099). Annual discharge shows increasing trend over Requena basin (Ucayali river), Puerto Inca basin (Pachitea river), Tambo basin (Tambo river) and Mejorada basin (Mantaro river) while discharge shows decreasing trend over the Chazuta basin (Huallaga river), the Maldonadillo basin (Urubamba river) and the Pisac basin (Vilcanota river). Monthly discharge at the outlet of Puerto Inca, Tambo and Mejorada basins shows increasing trends for all seasons. Trends to decrease are estimated in autumn discharge over the Requena basin and spring discharge over Pisac basin as well as summer and autumn discharges over both the Chazuta and the Maldonadillo basins. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
77.
Haosheng Huang Silvia Klettner Manuela Schmidt Georg Gartner Sven Leitinger Andreas Wagner 《International journal of geographical information science》2014,28(12):2456-2473
Humans perceive and evaluate environments affectively. Some places are experienced as unsafe, while some others as attractive and interesting. These affective responses to environments influence people’s daily behavior and decision-making in space, e.g., choosing which route to take, or which place to visit. In this article, we report on a methodology of using people’s affective responses to environments for enhancing computer-based route planning. More specifically, we explore a crowdsourcing approach to model and collect people’s affective responses to environments; an Affect-Space-Model and a mobile application are developed to facilitate this crowdsourcing approach; a routing algorithm (named AffectRoute) is then proposed to aggregate and integrate the collected data for automatic route planning. Evaluation with human participants shows that the routes generated by considering people’s affective responses to environments are significantly preferred over the conventional shortest ones, which are employed in car navigation systems and many online route planners. In conclusion, considering people’s affective responses to environments contributes to the improvement of automatic route planning. The proposed method can be integrated into existing route-planning services (e.g., location-based services) to provide users with more satisfying routing results. 相似文献
78.
Marc Peters Harald Strauss Sven Petersen Nicolai-Alexeji Kummer Christophe Thomazo 《Chemical Geology》2011,280(1-2):217-231
The Palinuro volcanic complex and the Panarea hydrothermal field, both located in the Tyrrhenian Sea (Italy), are associated with island arc magmatism and characterized by polymetallic sulfide mineralization. Dissolved sulfide concentrations, pH, and Eh measured in porewaters at both sites reveal a variable hydrothermal influence on porewater chemistry.Multiple sulfur isotopic measurements for disseminated sulfides (CRS: chromium reducible sulfur) extracted from sediments at Palinuro yielded a broad range in δ34S range between ?29.8 and + 10.2‰ and Δ33S values between + 0.015 and + 0.134‰. In contrast, sediments at Panarea exhibit a much smaller range in δ34SCRS with less negative values between ?11.3 and ?1.8‰. The sulfur isotope signatures are interpreted to reflect a mixture between hydrothermal and biogenic sulfide, with a more substantial biogenic contribution at Panarea.Multiple sulfur isotope measurements were performed on sulfides and elemental sulfur from drill core material from the Palinuro massive sulfide complex. δ34S and Δ33S values for pyrite between ?32.8 and ?1.1‰ and between ?0.012 to + 0.042‰, respectively, as well as for elemental sulfur with δ34S and Δ33S values between ?26.7 and ?2.1‰ and between + 0.035 and + 0.109‰, respectively, point to a microbial origin for much of the sulfide and elemental sulfur studied. Moreover, data suggest a coupling of bacterial sulfate reduction, sulfide oxidation and sulfur disproportionation. In addition, δ34S values for barite between + 25.0 and + 63.6‰ are also in agreement with high microbial turnover of sulfate at Palinuro.Although a magmatic SO2 contribution towards the formation of the Palinuro massive sulfide complex is very likely, the activity of different sulfur utilizing microorganisms played a fundamental role during its formation. Thus, porewater and multiple sulfur isotope data reveal differences in the hydrothermal activity at Palinuro and Panarea drill sites and underline the importance of microbial communities for the origin of massive sulfide mineralizations in the hydrothermal subsurface. 相似文献
79.
Thomas Leipe Franz Tauber Henry Vallius Joonas Virtasalo Szymon U?cinowicz Nicole Kowalski Sven Hille Susanna Lindgren Tero Myllyvirta 《Geo-Marine Letters》2011,31(3):175-188
In this study, particulate organic carbon (POC) contents and their distribution pattern in surficial sediments of the Baltic
Sea are presented for 1,471 sampling stations. POC contents range from approx. 0.1% in shallow sandy areas up to 16% in deep
muddy basins (e.g. Gotland Basin). Some novel relationships were identified between sediment mass physical properties (dry
bulk density (DBD), grain size) and POC levels. Notably, the highest POC concentrations (about 10–17 mg cm–3) occur in sandy mud to mud (60–100% mud content) with intermediate POC contents of about 3–7% and DBDs of 0.1–0.4 g cm–3. Areas with this range in values seem to represent the optimum conditions for POC accumulation in the Baltic Sea. The maximum
POC contents (8–16%) are found in fluid mud of the central Baltic Sea characterized by extremely low DBDs (<0.1 g cm–3) and moderate POC concentrations (4–7 mg cm–3). Furthermore, sediment mass accumulation rates (MAR), based on 210Pb and 137Cs measurements and available for 303 sites of the Baltic Sea, were used for assessing the spatial distribution of POC burial
rates. Overall, these vary between 14 and 35 g m–2 year–1 in the mud depositional areas and, in total, at least 3.5 (±2.9) Mt POC are buried annually. Distribution patterns of POC
contents and burial rates are not identical for the central Baltic Sea because of the low MAR in this area. The presented
data characterize Baltic Sea sediments as an important sink for organic carbon. Regional differences in organic carbon deposition
can be explained by the origin and transport pathways of POC, as well as the environmental conditions prevailing at the seafloor
(morphology, currents, redox conditions). These findings can serve to improve budget calculations and modelling of the carbon
cycle in this large brackish-water marginal sea. 相似文献
80.
A five-member ensemble of regional climate model (RCM) simulations for Europe, with a high resolution nest over Germany, is analysed in a two-part paper: Part I (the current paper) presents the performance of the models for the control period, and Part II presents results for near future climate changes. Two different RCMs, CLM and WRF, were used to dynamically downscale simulations with the ECHAM5 and CCCma3 global climate models (GCMs), as well as the ERA40-reanalysis for validation purposes. Three realisations of ECHAM5 and one with CCCma3 were downscaled with CLM, and additionally one realisation of ECHAM5 with WRF. An approach of double nesting was used, first to an approximately 50 km resolution for entire Europe and then to a domain of approximately 7 km covering Germany and its near surroundings. Comparisons of the fine nest simulations are made to earlier high resolution simulations for the region with the RCM REMO for two ECHAM5 realisations. Biases from the GCMs are generally carried over to the RCMs, which can then reduce or worsen the biases. The bias of the coarse nest is carried over to the fine nest but does not change in amplitude, i.e. the fine nest does not add additional mean bias to the simulations. The spatial pattern of the wet bias over central Europe is similar for all CLM simulations, and leads to a stronger bias in the fine nest simulations compared to that of WRF and REMO. The wet bias in the CLM model is found to be due to a too frequent drizzle, but for higher intensities the distributions are well simulated with both CLM and WRF at the 50 and 7 km resolutions. Also the spatial distributions are close to high resolution gridded observations. The REMO model has low biases in the domain averages over Germany and no drizzle problem, but has a shift in the mean precipitation patterns and a strong overestimation of higher intensities. The GCMs perform well in simulating the intensity distribution of precipitation at their own resolution, but the RCMs add value to the distributions when compared to observations at the fine nest resolution. 相似文献