Warmer early instrumental measurements versus colder reconstructed temperatures: shooting at a moving target     

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   

Comparing Eulerian and Lagrangian eddy census for a tide-less,semi-enclosed basin,the Baltic Sea     

Vortmeyer-Kley  Rahel  Holtermann  Peter  Feudel  Ulrike  Gräwe  Ulf 《Ocean Dynamics》2019,69(6):701-717

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   

Measures to restore and protect the Baltic Sea environment     

Ulf Ehlin   《Limnologica》1999,29(3):212

  相似文献   

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   

Characterisation of juvenile flatfish habitats in the Baltic Sea     

Ann-Britt Florin  Göran Sundblad  Ulf Bergström 《Estuarine, Coastal and Shelf Science》2009

  相似文献   

Petrogenesis and geotectonic setting of early Svecofennian arc cumulates in the Roslagen area,east‐central Sweden     

ke Johansson  ULF B. Andersson  Ulf Hlenius 《Geological Journal》2012,47(6):557-593

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 ε_Nd of +0.3 to +1.1, and the initial Sr isotope composition ‘mildly enriched’, with ε_Sr 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   

Optical microscope-cathodoluminescence (OM–CL) imaging as a powerful tool to reveal internal textures of minerals     

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   

Meteorological observations 1998 at the arctic station,Qeqertarsuaq (69°15'N), Central West Greenland/Active layer monitoring in two Greenlandic permafrost areas: Zackenberg and Disko Island     

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   

Meteorological observations 2003 at the Sermilik Station,Ammassalik Island,Southeast Greenland     

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   

Response of the coccolithophores Emiliania huxleyi and Coccolithus braarudii to changing seawater Mg and Ca concentrations: Mg/Ca, Sr/Ca ratios and δCa, δMg of coccolith calcite     

Marius N. Müller  Ba?ak K?sakürek  Ruth Gutperlet  Ulf Riebesell  Anton Eisenhauer 《Geochimica et cosmochimica acta》2011,75(8):2088-5818

Calcium and magnesium concentrations in seawater have varied over geological time scales. On short time scales, variations in the major ion composition of seawater influences coccolithophorid physiology and the chemistry of biogenically produced coccoliths. Validation of those changes via controlled laboratory experiments is a crucial step in applying coccolithophorid based paleoproxies for the reconstruction of past environmental conditions. Therefore, we examined the response of two species of coccolithophores, Emiliania huxleyi and Coccolithus braarudii, to changes in the seawater Mg/Ca ratio (≈0.5 to 10 mol/mol) by either manipulating the magnesium or calcium concentration under controlled laboratory conditions. Concurrently, seawater Sr/Ca ratios were also modified (≈2 to 40 mmol/mol), while keeping salinity constant at 35. The physiological response was monitored by measurements of the cell growth rate as well as the production rates of particulate inorganic and organic carbon, and chlorophyll a. Additionally, coccolithophorid calcite was analyzed for its elemental composition (Sr/Ca and Mg/Ca) as well as isotope fractionation of calcium and magnesium (Δ^44/40Ca and Δ^26/24Mg). Our results reveal that physiological rates were substantially influenced by changes in seawater calcium rather than magnesium concentration within the range estimated to have occurred over the past 250 million years when coccolithophores appear in the fossil record. All physiological rates of E. huxleyi decreased at a calcium concentration above 25 mmol L⁻¹, whereas C. braarudii displayed a higher tolerance to increased seawater calcium concentrations. Partition coefficient of Sr was calculated as 0.36 ± 0.04 (±2σ) independent of species. Partition coefficient of Mg²⁺ increased with increasing seawater Ca²⁺ concentrations in both coccolithophore species. Calcium isotope fractionation was constant at 1.1 ± 0.1‰ (±2σ) and not altered by changes in seawater Mg/Ca ratio. There is a well-defined inverse linear relationship between calcium isotope fractionation and partition coefficient of Sr²⁺ in all experiments, suggesting similar controls on both proxies in the investigated species. Magnesium isotope ratios were relatively stable for seawater Mg/Ca ratios ranging from 1 to 5, with a higher degree of fractionation in Emiliania huxleyi (by ≈0.2‰ in Δ^26/24Mg). Although Mg/Ca ratios in the calcite of coccolithophores and foraminifera are similar, the former have considerably higher Δ^26/24Mg (by >+3‰), presumably due to differences in calcification mechanisms between the two taxa. These observations suggest, a physiological control over magnesium elemental and isotopic fractionation during the process of calcification in coccolithophores.  相似文献