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Sökning: WFRF:(Aldahan A)

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1.
  • Dahl-Jensen, D., et al. (författare)
  • Eemian interglacial reconstructed from a Greenland folded ice core
  • 2013
  • Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 493:7433, s. 489-494
  • Tidskriftsartikel (refereegranskat)abstract
    • Efforts to extract a Greenland ice core with a complete record of the Eemian interglacial (130,000 to 115,000 years ago) have until now been unsuccessful. The response of the Greenland ice sheet to the warmer-than-present climate of the Eemian has thus remained unclear. Here we present the new North Greenland Eemian Ice Drilling ('NEEM') ice core and show only a modest ice-sheet response to the strong warming in the early Eemian. We reconstructed the Eemian record from folded ice using globally homogeneous parameters known from dated Greenland and Antarctic ice-core records. On the basis of water stable isotopes, NEEM surface temperatures after the onset of the Eemian (126,000 years ago) peaked at 8 +/- 4 degrees Celsius above the mean of the past millennium, followed by a gradual cooling that was probably driven by the decreasing summer insolation. Between 128,000 and 122,000 years ago, the thickness of the northwest Greenland ice sheet decreased by 400 +/- 250 metres, reaching surface elevations 122,000 years ago of 130 +/- 300 metres lower than the present. Extensive surface melt occurred at the NEEM site during the Eemian, a phenomenon witnessed when melt layers formed again at NEEM during the exceptional heat of July 2012. With additional warming, surface melt might become more common in the future.
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  • Leppänen, A. -P, et al. (författare)
  • Cosmogenic Be-7 in air : A complex mixture of production and transport
  • 2010
  • Ingår i: Journal of Atmospheric and Solar-Terrestrial Physics. - : Elsevier BV. - 1364-6826 .- 1879-1824. ; 72:13, s. 1036-1043
  • Tidskriftsartikel (refereegranskat)abstract
    • The long-time series of Be-7 activity in surface air have been studied with the wavelet analysis technique in order to find coherence between Be-7 activity, theoretical production in the troposphere and climatic indices. The Be-7 activity were obtained from five different locations, Angra in the tropics in Brazil, Skane in mid-latitudes in Southern Sweden, Kiruna in Polar region in Northern Sweden, Loviisa in Southern Finland and Rovaniemi in polar region in Northern Finland. The Be-7 data from the Northern hemisphere sites where tested for coherence with theoretical production of the isotope in troposphere and with the North Atlantic Oscillation index. In the Southern hemisphere separate theoretical production was calculated in order to describe local production and Southern Annular Mode was used as the climatic index. Consistent and significant coherence were found with theoretical production at Skane, Kiruna and Loviisa at time-scales of four years or longer. At Angra and Rovaniemi sites, no coherence was detected between Be-7 theoretical tropospheric production and measured activity at ground level. The coherence between Be-7 data from Skane and Angra and climatic indices is insignificant while data from Northern and Eastern Scandinavia show clear coherence with climatic indices at time-scales of four years or longer. Additionally, significant coherence was found between the cosmic ray induced production and NAO at the time band of 8-12 years whereas the coherence between cosmic ray induced production and SAM was insignificant. This feature implies that the ground level Be-7 activity contain mixed information on both production and transport. This conclusion means that further evaluation through models which enable accurate realistic models that will be investigated in future studies.
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  • Kekli, A, Meili M, Aldahan A, Possnert G, Buraglio N, et al. (författare)
  • High levels of 129I in rivers of south
  • 2001
  • Ingår i: Proceedings of the 8th Nordic Seminar on Radioecology., 25-28 Feb. ; , s. 194-
  • Konferensbidrag (refereegranskat)
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  • Kekli, A, et al. (författare)
  • I-129 in Swedish rivers: distribution and sources
  • 2003
  • Ingår i: Science of the Total Environment. - 1879-1026. ; 309:1-3, s. 161-172
  • Tidskriftsartikel (refereegranskat)abstract
    • We analyzed the concentration of I-129 in the water of 26 rivers covering most of the runoff from Sweden, with the aim of assessing current contamination levels, distribution patterns and potential sources in freshwater systems of northern Europe. The results show relatively high values (up to 1.4 x 10(9) atoms 1(-1)), steeply decreasing levels with increasing latitude and a positive correlation with Cl concentration and other chemical parameters. The I-129 concentrations observed in south Sweden are probably the highest ever recorded in rivers without any direct discharge from a nuclear installation. The strong latitudinal dependence suggests a northward dilution and possibly depletion of the isotope and a transport from a source located to the south. The most plausible source of the I-129 in the studied rivers is atmospheric fallout of I-129 emitted either by atmospheric discharges from the nuclear reprocessing facilities at Sellafield (England) and La Hague (France) or by volatilization from seawater contaminated by the same sources. The question is now whether and at what rate the I-129 concentration in Nordic watersheds will increase further if discharges from nuclear reprocessing continue. (C) 2003 Elsevier Science B.V. All rights reserved.
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  • Kulan, A., Aldahan, A., Possnert, G., Vintersved, I (författare)
  • Solar cycle activity recorded in
  • 2002
  • Ingår i: IGBP-PAGES Swedish National Meeting, March 14-16.
  • Konferensbidrag (övrigt vetenskapligt/konstnärligt)
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  • Meili M, Buraglio N, Aldahan A, Possnert G and Kekli, A (författare)
  • Origin and fate of 129I in Swedish
  • 2001
  • Ingår i: Proceedings of the 8th Nordic Seminar on Raioecology., 25-28 Feb. ; , s. p .90-
  • Konferensbidrag (övrigt vetenskapligt/konstnärligt)
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  • Aldahan, Ala Adin, et al. (författare)
  • 10Be in rhodochrosite nodules from Neogene sediments along the Galapagos Ridge, equatorial Pacific
  • 2010
  • Ingår i: Nuclear Instruments and Methods in Physics Research Section B. - : Elsevier BV. - 0168-583X .- 1872-9584. ; 268:7-8, s. 1253-1256
  • Tidskriftsartikel (refereegranskat)abstract
    • Microcrystalline, calcian rhodochrosite occurs as nodules around burrows in late Neogene pelagic sediments from the Galapagos Ridge in the Guatemala Basin, eastern equatorial Pacific (DSDP Leg 68; Site 503). Be-10 isotope revealed that the rhodochrosite nodules have formed under growth conditions much faster than those reported for Fe-Mn nodules. The overall REE patterns of the nodules and host pelagic sediments indicate element derivation mainly from marine pore water. However, variations in the shale normalised Eu values suggest influx of hydrothermal fluids into mounds area at Galapagos, which is also evidenced by the similar minor and major element contents in the nodules and host sediments.
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  • Aldahan, Ala, et al. (författare)
  • Anthropogenic I-129 in the Baltic Sea
  • 2005
  • Ingår i: 10th International conference on accelerator mass spectrometry, Berkeley. ; , s. 33-
  • Konferensbidrag (refereegranskat)
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24.
  • Aldahan, Alan, et al. (författare)
  • Antropogenic I-129 in the Baltic Sea
  • 2007
  • Ingår i: Nuclear Instruments and Methods in Physic research Section B - Beam interactions with materials and atoms. ; B259, s. 491-495
  • Tidskriftsartikel (refereegranskat)
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25.
  • Aldahan, A, et al. (författare)
  • Atmospheric interactions at northern high latitudes from weekly Be-isotopes in surface air
  • 2001
  • Ingår i: APPLIED RADIATION AND ISOTOPES. - : PERGAMON-ELSEVIER SCIENCE LTD. - 0969-8043. ; 54:2, s. 345-353
  • Tidskriftsartikel (refereegranskat)abstract
    • We present weekly Be-7 (from 1972 to 1995), and weekly/seasonal Be-10 (for 1994) data in surface air from ground level stations in Sweden with a coverage of most of the northern high latitudes (56 degrees -68 degrees N). Our Be data are regionally represe
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  • Aldahan, Ala, et al. (författare)
  • Particle-bound Be-10 from a low latitude arid region
  • 2014
  • Ingår i: Journal of Radioanalytical and Nuclear Chemistry. - : Springer Science and Business Media LLC. - 0236-5731 .- 1588-2780. ; 299:3, s. 1709-1713
  • Tidskriftsartikel (refereegranskat)abstract
    • The Be-10 isotope is widely used in geochronology, climate and environmental analyses and astrophysics where atmospheric deposition model estimate plays a vital role for the initial concentration. Data from arid regions have not been well constrained because of sparse measurement and here we present Be-10 concentration in samples of dust, soil, marine sediments and paleosol collected from an arid to semi-arid low latitude region. These results indicate concentrations that are about a factor of three lower than values expected from latitude zonal models, but are comparable with global atmospheric depositional model. The agreement and discrepancy between model and measured data are rather vital for establishing accurate initial Be-10 in the Earth's surface environment for reconstruction of paleoclimatic variability (precipitation rates and temperature).
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41.
  • Aldahan, A, et al. (författare)
  • Sixty year Be-10 record from Greenland and Antarctica
  • 1998
  • Ingår i: PROCEEDINGS OF THE INDIAN ACADEMY OF SCIENCES-EARTH AND PLANETARY SCIENCES. - : INDIAN ACADEMY SCIENCES. - 0253-4126. ; 107:2, s. 139-147
  • Tidskriftsartikel (refereegranskat)abstract
    • We report in this study the distribution of Be-10 in the top 40 m of the Renland ice core (East Greenland) and in a 30 m long core from DML (Dronning Maud Land, Antarctica) for the period 1931-1988. The two sites show differences in Be-10 content, the Ant
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  • Aldahan, A, et al. (författare)
  • The Be-10 marine record of the last 3.5 Ma
  • 2000
  • Ingår i: NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION B-BEAM INTERACTIONS WITH MATERIALS AND ATOMS. - 0168-583X. ; 172, s. 513-517
  • Tidskriftsartikel (refereegranskat)abstract
    • We present in this study a Be-10 profile from a deep-sea sediment section extending to 3.5 Ma. The Be-10 concentration ranges at 2-14 x 10(8) atoms/g and shows a clear decay trend. The flux of Be-10 ranges at 1-5 x 10(6) atoms/cm(2) y and averages at appr
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46.
  • Alshamsi, Dalal M., et al. (författare)
  • Uranium isotopes in carbonate aquifers of arid region setting
  • 2013
  • Ingår i: Journal of Radioanalytical and Nuclear Chemistry. - : Springer Science and Business Media LLC. - 0236-5731 .- 1588-2780. ; 298:3, s. 1899-1905
  • Tidskriftsartikel (refereegranskat)abstract
    • Groundwater in arid and semiarid regions is vital resource for many uses and therefore information about concentrations of uranium isotopes among other chemical parameters are necessary. In the study presented here, distribution of U-238 and U-235 in groundwater of four selected locations in the southern Arabian peninsula, namely at two locations within the United Arab Emirates (UAE) and two locations in Oman are discussed. The analyses of the uranium isotopes were performed using ICP-MS and the results indicated a range of concentrations for U-235 and (238) U at 3-39 ng L-1 (average: 18 ng L-1) and 429-5,293 ng L-1 (average: 2,508 ng L-1) respectively. These uranium concentrations are below the higher permissible WHO limit for drinking water and also comparable to averages found in groundwater from similar aquifers in Florida and Tunisia. Negative correlation between rainfall and uranium concentrations suggests that in lithologically comparable aquifers, climate may influence the concentration of uranium in subtropical to arid regions.
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47.
  • Berggren, Ann-Marie, et al. (författare)
  • Variability of 10Be and δ18O in snow pits from Greenland and a surface traverse from Antarctica
  • 2013
  • Ingår i: Proceedings of the Twelfth International Conference on Accelerator Mass Spectrometry. - : Elsevier BV. ; , s. 568-572
  • Konferensbidrag (refereegranskat)abstract
    • To examine temporal variability of 10Be in glacial ice, we sampled snow to a depth of 160 cm at the NEEM (North Greenland Eemian Ice Drilling) drilling site in Greenland. The samples span three years between the summers of 2006 and 2009. At the same time, spatial variability of 10Be in glacial ice was explored through collection of the upper ∼5 cm of surface snow in Antarctica during part of the Swedish-Japanese traverse from Svea to Syowa station during the austral summer in 2007-2008. The results of the Greenlandic 10Be snow suggested variable concentrations that apparently do not clearly reflect the seasonal change as indicated by the δ18O data. The 10Be concentration variability most likely reflects also effects of aerosol loading and deposition pathways, possibly in combination with post-depositional processes. The Antarctic traverse data expose a negative correlation between 10Be and δ18O, while there are weaker but still significant correlations to altitude and distance to the coast (approximated by the distance to the 70th latitude). These relationships indicate that geographical factors, mainly the proximity to the coast, may strongly affect 10Be concentrations in snow in Queen Maud Land, Antarctica.
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  • Berggren, Ann-Marie, et al. (författare)
  • Variability of Be-10 and delta O-18 in snow pits from Greenland and a surface traverse from Antarctica
  • 2013
  • Ingår i: Nuclear Instruments and Methods in Physics Research Section B. - : Elsevier BV. - 0168-583X .- 1872-9584. ; 294, s. 568-572
  • Tidskriftsartikel (refereegranskat)abstract
    • To examine temporal variability of Be-10 in glacial ice, we sampled snow to a depth of 160 cm at the NEEM (North Greenland Eemian Ice Drilling) drilling site in Greenland. The samples span three years between the summers of 2006 and 2009. At the same time, spatial variability of Be-10 in glacial ice was explored through collection of the upper similar to 5 cm of surface snow in Antarctica during part of the Swedish-Japanese traverse from Svea to Syowa station during the austral summer in 2007-2008. The results of the Greenlandic 1 Be snow suggested variable concentrations that apparently do not clearly reflect the seasonal change as indicated by the delta O-18 data. The Be-10 concentration variability most likely reflects also effects of aerosol loading and deposition pathways, possibly in combination with post-depositional processes. The Antarctic traverse data expose a negative correlation between Be-10 and delta O-18, while there are weaker but still significant correlations to altitude and distance to the coast (approximated by the distance to the 70th latitude). These relationships indicate that geographical factors, mainly the proximity to the coast, may strongly affect 1 Be concentrations in snow in Queen Maud Land, Antarctica.
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  • Buraglio, N, et al. (författare)
  • I-129 from the nuclear reprocessing facilities traced in precipitation and runoff in northern Europe
  • 2001
  • Ingår i: ENVIRONMENTAL SCIENCE & TECHNOLOGY. - : AMER CHEMICAL SOC. - 0013-936X. ; 35:8, s. 1579-1586
  • Tidskriftsartikel (refereegranskat)abstract
    • A huge amount of radioactive I-129 has been released into the environment from the nuclear energy industry, atomic weapon tests, and nuclear accidents. In this study, we present weekly and seasonal data on I-129 measured in precipitation and runoff of nor
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  • Resultat 1-50 av 83

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