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101.
David Frank Ulf Büntgen Reinhard Bhm Maurizio Maugeri Jan Esper 《Quaternary Science Reviews》2007,26(25-28):3298-3310
Comparison of tree-ring-based warm-season temperature reconstructions and their instrumental target data reveals substantial divergence between (warmer) early instrumental measurements and (colder) proxy estimates. Here we detail this systematic misfit for the Northern Hemisphere before 1900 and the European Alps before 1850. Five hypotheses related to both proxy and target uncertainties are presented towards explaining this phenomenon. These include: (1) tree-ring detrending methods, (2) biological persistence in the proxy time-series, (3) uncertainties and instabilities in the growth response to given climatic parameters, (4) reduced instrumental station availability back in time, and (5) instrumental data homogeneity. We suggest that uncertainties in the choice of instrumental targets at the hemispheric scale, and instrumental data inhomogeneities at the Alpine and possibly also the hemispheric-scale are the most important factors in explaining this offset. Assessment of homogeneity at larger scales remains challenging. Attention is drawn to possible warm biases in early thermometer shelters and the relevance of proxy/target discrepancies for understanding and quantifying the amplitude of both recent anthropogenic and past natural forced climate fluctuations. 相似文献
102.
Ocean Dynamics - Eddies in the global and coastal ocean play a key role in mixing and transport processes. Here, we present an eddy census for the Baltic Sea covering the years 2008–2010. The... 相似文献
103.
104.
Effects of ozone depletion and increased ultraviolet-B radiation on northern vegetation 总被引:2,自引:0,他引:2
Lars Olof Björn Terry V. Callaghan Carola Gehrke Dylan Gwynn-Jones John A. Lee Ulf Johanson Mats Sonesson Nicholas D. Buck 《Polar research》1999,18(2):331-337
The stratospheric ozone layer has been depleted at high and mid-latitudes as a consequence of man's pollution of the atmosphere, and this results in increasing ultraviolet-B radiation at ground level. We investigate the effects of further radiation increases on plants and ecosystems by irradiating natural sub-Arctic and Arctic vegetation with artificial UV-B radiation in field experiments extending over several years. Our experimental sites are located at Abisko, in northern Sweden (68°N), and Adventdalen, on the island of Spitsbergen (78°N). Additional UV-B induced interspecific differences in plant response in terms of reduced (or, in one case, increased) growth, changed morphology and changed pigment content. In some cases effects seem to be accumulated from one year to another. Plant litter decomposition is retarded. We are also studying how UV-B enhancement may affect the interaction between species. In some experiments we combine UV-B enhancement with changes in other factors: carbon dioxide concentration, water availability, and temperature. In some cases the effect of radiation enhancement is modified, or even reversed, by such changes. Over a four year period we did not find any significant radiation induced change in species composition, but based on the effects on individual plant species, such changes can be expected to take place over a longer time. 相似文献
105.
106.
Adrian DeHeer-Amissah Ulf Högström Ann-Sofi Smedman-Högström 《Boundary-Layer Meteorology》1981,20(1):35-49
A set of semi-continuous measurements of temperature, wind and moisture gradients as well as of net radiation and ground heat flux covering a period of about one and a half years has been analysed to give a corresponding set of complete surface energy balance data on an hourly basis. An analysis of the evaporation data so obtained is given.It is shown that surface resistance r
S exhibits a diurnal trend: values are smallest (ca. 150 s m-1) a few hours before noon and increase to as much as 800 s m-1 towards dusk. The minimum values tend to be higher during dry periods when the soil moisture is low. There is also some indication that r
S decreases rapidly soon after rainfall.An exponential relation is found between the fraction of available energy used as evaporative flux, , and r
S for values of r
I/rS <0.70, where r
I is the climatological resistance. On the other hand, the ratio of r
I to r
S is linearly correlated with , implying that an equilibrium state is established between the grass surface and the atmosphere, at least from mid-morning to mid-afternoon when the leaves are dry. Near-noon values calculated by Stewart and Thom for Thetford Forest also follow a linear trend.The above two regression results (In (r
S) versus r
I/rS versus ) are combined to obtain an empirical relation of the form r
I=m exp (a-b) which is used to estimate evaporative flux. The estimates are found to be within 20% of calculated values.Guest Scientist from Department of Physics, University of Cape Coast, Cape Coast, Ghana. 相似文献
107.
Several intrusions of ultrabasic to basic composition occur in the Roslagen area of east‐central Sweden in close spatial and temporal association with the surrounding 1.90–1.87 Ga old early orogenic Svecofennian granitoids. An imprecise Sm‐Nd WR errorchron yields an age of 1895 ± 71 Ma. In spite of the penetrative deformation in the granitoids, the basic–ultrabasic rocks mostly appear undeformed and largely preserve magmatic textures with plagioclase, olivine (in some rock types), orthopyroxene and clinopyroxene, and amphibole as major constituents. The plagioclase is typically very anorthitic (ca. An90). The Roslagen intrusions range in composition from primitive to evolved (Mg# 80 to 49) but contain only 40–50 wt% SiO2. Many samples are highly elevated in Al2O3 (up to 30 wt%), CaO (up to 16 wt%) and Sr (up to 800 ppm), with strongly positive Eu and Sr anomalies, in line with being plagioclase cumulates. Although masked by cumulus effects, the relative trace element contents indicate a volcanic arc signature. The initial Nd isotope composition is homogeneously ‘mildly depleted’, with εNd of +0.3 to +1.1, and the initial Sr isotope composition ‘mildly enriched’, with εSr of +8 to +15. Non‐cumulus rocks with small Eu and Sr anomalies can be used to deduce the composition of the parental magma. This LILE‐ and LREE‐enriched and HFSE‐depleted high‐alumina basalt magma, with Mg# of ca. 50–60 and Ca# of ca. 80, most likely formed by partial melting of mantle material, enriched by fluids in a subduction environment, at 1.9 Ga. The cumulate rocks apparently crystallized from a somewhat more evolved water‐rich magma with Mg# of ca. 40. Crystallization was followed by the development of late‐magmatic to post‐magmatic coronas between olivine and plagioclase in the presence of H2O‐rich fluids. The subduction‐related setting would make these intrusions Palaeoproterozoic counterparts of Alaskan‐type ultramafic intrusions, but they differ from those in being plagioclase enriched, possibly reflecting different levels of exposure. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
108.
Jens Götze Hans-Peter Schertl Rolf D. Neuser Ulf Kempe John M. Hanchar 《Mineralogy and Petrology》2013,107(3):373-392
Optical microscope-cathodoluminescence (OM-CL) microscopy is a modern luminescence technique with widespread applications in geosciences. Many rock-forming and accessory minerals show specific CL properties that can be successfully used in geoscience and materials science research. One of the most spectacular applications is the visualization of growth textures, alteration, and other internal textures in minerals that are not discernible with other analytical techniques. These results provide information about the real structure of minerals and materials and can be used for the reconstruction of geological processes of mineral formation and subsequent alteration. The information obtained from CL imaging in combination with spectral measurements of the CL emission allows for a more thorough understanding of structural states of solids and/or trace-element incorporation. Additional information can be obtained when luminescence studies are combined with other analytical techniques with high sensitivity and high spatial resolution. 相似文献
109.
Ole Humlum Birger Ulf Hansen Niels Nielsen Hanne H. Christiansen 《Geografisk tidskrift / udgivet af Bestyrelsen for Det Kongelige danske geografiske selskab》2013,113(1):113-121
An automatic meteorological station has been operating at the Arctic Station (69°15'N, 53°31'W) in West Greenland since 1990. This paper summarises meteorological parameters during 1998, including snow cover, ground temperatures and active layer development, and presents comments on the local permafrost thickness. Abstract Active layer monitoring in Greenland was started in 1996 and 1997, and forms part of the Circumpolar Active Layer Monitoring (CALM) Network of the International Permafrost Association (IPA). The results of the first years of this monitoring of thaw progression and maximum active layer thickness in two Greenlandic permafrost areas are presented. Two sites are in the continuous permafrost zone at Zackenberg in NE Greenland (74 °N), and one at Disko Island in W Greenland (69 °N), at the border between discontinuous and continuous permafrost. The data collected at Zackenberg demonstrate interannual variation in the timing of thaw progression in the monitoring grid holding a seasonal snowpatch, while there is less variation in the horizontal grid without a snowpatch. The maximum active layer thickness for the two Zackenberg grids is more or less consistent for the first three years with averages from 58 to 66 cm in mid and late August. At Disko the active layer reached 71 cm in mid August 1998. Spatially the distribution of the maximum, annual active layer thickness within the grids is concordant. 相似文献
110.
Sebastian H. Mernild Bent Hasholt Birger Ulf Hansen 《Geografisk tidskrift / udgivet af Bestyrelsen for Det Kongelige danske geografiske selskab》2013,113(2):49-56
Geografisk Tidsskrift, Danish Journal of Geography 105(2):49–56, 2005 Meteorological stations have been in operation since 1993 at Sermilik (65°40'N, 38°10'W), located in southeast Greenland. This note presents meteorological observations for the year 2003, including ground temperature, orographic effect (liquid precipitation) and air temperature lapse rates between two meteorological stations, Station Nunatak (515 m a.s.l.) and Station Coast (25 m a.s.l.). 相似文献