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  • 601.
    Sternbeck, John
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologi och geokemi.
    Manganese and related elements in aquatic environments: pathways for redox reactions and environmental significance1996Doktoravhandling, med artikler (Annet vitenskapelig)
  • 602.
    Sturkell, Erik
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologi och geokemi.
    The origin of the marine Lockne impact structure, Jämtland1998Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    The Lockne impact structure in Jämtland (63o00'20"N, 14o49'30"E), formed in the Middle Ordovician at approximately 455 Ma. The structure is a concentric crater with a total diameter of 13.5 km. The impact took place in a marine environment. The sea-water played an important role in the cratering process and in crater morphology and the amount of melt remaining in the structure. The sea-water rushed back into the crater in a resurge, eroding and redepositing the ejecta among the resurge deposit. Sea-water furthermore facilitated the hydrothermal system, which was driven by the residual heat in the structure.

    The Lockne structure hosts shocked quartz and an iridium anomaly. The rim wall round the crater collapsed in the modification stage of the crater and was annihilated by the resurge. The fractured basement and the impact breccia were initially rich in open cavities. These became partly filled with dominantly calcite. The filling contributed to a low density contrast, generating a negative gravity anomaly of 22 gu. The gravity model indicates a central uplift and a NW-directed tilt of the structure. This tilt is also seen in the magnetic models. The apparent absence of any impact melt is probably real and related to the environment of impact.

  • 603.
    Sturm, Christophe
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologi och geokemi.
    Noone, David
    University of Colorado.
    Comprehensive dynamical models of global and regional isotope distribution2009Inngår i: Isoscapes: Understanding movement, pattern, and process on Earth through isotope mapping / [ed] West, J.B.; Bowen, G.J.; Dawson, T.E.; Tu, K.P., Springer, 2009, 1, s. Chap 10-Kapittel i bok, del av antologi (Annet vitenskapelig)
  • 604.
    Sturm, Christophe
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologi och geokemi.
    Zhang, Qiong
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    Noone, David
    University of Colorado.
    An introduction to stable water isotopes in climate models: benefits of forward proxy modelling for paleoclimatology2010Inngår i: Climate of the past, ISSN 1814-9332, Vol. 6, s. 115-129Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Stable water isotopes have been measured in a wide range of climate archives, with the purpose of reconstructing regional climate variations. Yet the common assumption that the isotopic signal is a direct indicator of temperature proves to be misleading under certain circumstances, since its relationship with temperature also depends on e.g. atmospheric circulation and precipitation seasonality. The present article introduces the principles, benefits and caveats of using climate models with embedded water isotopes as a support for the interpretation of isotopic climate archives. A short overview of the limitations of empirical calibrations of isotopic proxy records is presented, with emphasis on the physical processes that infirm its underlying hypotheses. The simulation of climate and its associated isotopic signal, despite difficulties related to downscaling and intrinsic atmospheric variability, can provide a "transfer function" between the isotopic signal and the considered climate variable. The multi-proxy data can then be combined with model output to produce a physically consistent climate reconstruction and its confidence interval. A sensitivity study with the isotope-enabled global circulation model CAM3iso under idealised present-day, pre-industrial and mid-Holocene is presented to illustrate the impact of a changing climate on the isotope-temperature relationship.

  • 605.
    Sun, Guangyu
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologi och geokemi.
    The character of magnetic records of deformed soft sediments with emphasis on liquefaction structures2005Doktoravhandling, monografi (Annet vitenskapelig)
    Abstract [en]

    In this thesis the characteristics of magnetic records in deformed soft sediments during postglacial time in Sweden are studied. Magnetic records refer in this study to magnetic remanence (NRM and ChRM) and susceptibility, including its anisotropy (AMS). Four types of soft sediment deformation were investigated in this study: (1) lake sediment of calm depositional conditions, (2) soft sediments of plastic deformation, (3) sediment which experienced earthquake shaking but remained varved and retained horizontal bedding, and (4) sediment with severe liquefaction deformation.

    In the 5 sites, the dominant carriers are magnetite multi-domain grains with minor pseudo single domain and even single domain grains.

    In the calm and undisturbed (or lightly disturbed) sediments (Kroktjärnen), the geomagnetic field is the dominant factor influencing the ChRM. ChRM is consistent with other records from regional sites and recorded the paleosecular variation. AMS is consistent but shows light dispersion in the core.

    In soft sediments of plastic deformation, ChRM is related to the fold correction ( Röbäck group 4). ChRM and AMS are locally consistent.

    In the sediments where varves remained intact, the ChRM declination of the Nykvarn profile possessed a systematic east swing upward whilst the inclination was very shallow.

    AMS was characterized by calm, current-controlled deposition. Both AMS and ChRM in the sand layers have different patterns from those in the silt-clay layers. The study of AMS confirms ChRM unusual pattern cannot be explained by crypt twist deformation but reflects the motion of fine magnetic grains independent of deformation. The ChRM of Mehedeby A reflected the geomagnetic field at the time of deposition. AMS indicates a calm deposition under current-controlled condition. The AMS of Sickla reflects similar deposition condition but with local disturbance in varves 7 and 8.

    In the sediments with liquefaction intrusion deformation (Röbäck groups 7 and 8, and Mehedeby B), the ChRM do not satisfy the fold test and the orientation dispersion is not related to deformation degree. Further study indicates that ChRM is consistent and oriented statistically along the geomagnetic field at the time of liquefaction intrusion. Meanwhile, AMS exhibit nearly random distribution. I interpret this as the re-alignment of fine magnetic particles to the geomagnetic field after the liquefaction intrusion and AMS reflects the disordered orientation of big magnetic grains, induced by the intrusion. These characteristics provide a magnetic method to distinguish between plastic deformation and liquefaction deformation.

    The study supports the assertion that fine magnetic particles play a special role in sedimentary magnetization (DRM/PDRM) and big magnetic grains mainly contribute to AMS.

  • 606.
    Sun, Xiaole
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologi och geokemi.
    Andersson, Per
    Naturhistoriska riksmuseet, Laboratoriet för isotopgeologi .
    Land, Magnus
    WSP Environmental.
    Humborg, Christoph
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för tillämpad miljövetenskap (ITM).
    Mörth, Carl-Magnus
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologi och geokemi.
    Stable silicon isotope analysis on nanomole quantities using MC-ICP-MS with a hexapole gas-collision cell2010Inngår i: Journal of Analytical Atomic Spectrometry, ISSN 0267-9477, E-ISSN 1364-5544, Vol. 25, nr 2, s. 156-162Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We demonstrate in this study that a single focusing multiple collector inductively coupled plasma massspectrometer (MC-ICP-MS) equipped with a hexapole gas-collision cell (GV-instrument Isoprobe) canprecisely determine the d29Si (2S.D., 0.2&) using a total Si consumption of less than 14 nmole (390 ngSi). Testing and evaluation of background, rinse time, and major matrix effects have been performed ina systematic way to establish a procedure to measure d29Si in small quantities. Chemical purificationprior to analysis is required to remove potential interferences. For data collected during a four-yearperiod, the average d29Si value of IRMM-018 relative to NBS-28 was found to be 0.95& (n ¼ 23,2S.D. 0.16&) with a 95% confidence interval (0.95 0.028&). The mean d29Si value of the Big-Batchstandard was found to be 5.50& (n ¼ 6, 2S.D. 0.26&). Although determination of the d30Simeasurements is not possible, with our current instrument we demonstrate that this system providesa fast and long-term reliable method for the analysis of d29Si in purified samples with low Siconcentration (18 mM Si).

    Fulltekst (pdf)
    FULLTEXT01
  • 607.
    Sundvall, Rickard
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologi och geokemi.
    Hydrogen diffusion and storage mechanisms in diopside2008Licentiatavhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Hydrogen is a widespread trace element in many nominally anhydrous minerals (minerals without water or hydroxyl ions in their structural formula) from the Earth's crust and mantle. The hydrogen is normally incorporated in the form of hydroxyl ions and can be regarded as structurally bound water. The most important minerals of the upper mantle: olivine, orthopyroxene, clinopyroxene and garnet, all contain small but significant amounts of hydrogen. This means that the upper mantle has the capacity to store the equivalent of several world oceans. To know how much water there is in the Earth's interior is important knowledge, as small differences in mantle water content influences models of mantle dynamics. The mantle plays an important role in the hydrological cycle as water in oceanic crust and sediments is subducted at converging plate boundaries and again released through volcanic eruptions during millions of years. Detailed knowledge of the amount of water that is retained within the mantle for longer periods of time (~109 years) is still lacking.

    Investigating the water content of the mantle is a task shared between the fields of mineralogy, petrology, geophysics, and theoretical physics (i.e. atomistic models).

    My approach as a mineralogist has been to investigate in detail the mechanisms that are responsible for water incorporation in nominally anhydrous upper mantle minerals, with a special emphasis on the pyroxenes as they can carry substantial amounts of water, up to 1300 ppm H2O. The fundamental questions here are how much of the original xenolith water is lost during transport to the surface and if the spectroscopic features measured in the minerals are representative for mantle conditions.

    The redox reaction: Fe2+ + OH- ↔ Fe3+ + O2- + ½H2, which is relatively fast, is thought to be the dominant hydrogen exchange reaction in many minerals (Ingrin & Skogby, 2000). The reaction is fast enough to suggest that water in nominally anhydrous minerals equilibrates with the transporting magma and related fluids during ascent to the surface. Nevertheless, several studies show systematic variations in water content with geological environment (Bell & Rossman, 1992; Peslier et al., 2002), implying a complex relationship between host mineral, mantle source region, magma type and eruption style.

     

    This thesis is focused on the dehydration-hydration mechanisms in diopside, the most common variety of clinopyroxene in the upper mantle. The approach has been to study the kinetics and temperature dependence of the reactions controlling hydrogen diffusion in synthetic Fe-poor diopside.

    Other reactions are likely to be obscured by the iron redox reaction if measured in natural mantle diopside containing several wt% FeO. Therefore, synthetic diopside with very low amounts (0.7 wt% FeO) of iron had to be used in order to measure the influence and co-dependence of the iron redox reaction with other possible reactions.

    The experiments were carried out by stepwise heating of the samples in both air and hydrogen. After each step, OH-absorbance was measured using Fourier Transform Infrared spectroscopy, and the relative amounts of ferric and ferrous iron was monitored by Mössbauer spectroscopy. When comparing the amounts of ferric iron and hydrogen (in atoms per formula unit), there is considerable deviation from the ideal 1:1 relationship expected from the iron redox reaction. The dehydration process is reversible to a great extent and re-hydration continues even after all iron is reduced.

    The results of this study show that other reactions apart from the iron redox reaction are active, and that they are significantly slower. If these slower reactions are active in mantle diopsides, there is a possibility that they may preserve signatures from the mantle source region.

     

  • 608.
    Sundvall, Rickard
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologi och geokemi.
    Water as a trace component in upper mantle pyroxenes2008Inngår i: EURISPET (European Intensive Seminars in Petrology) – Petrology of the lithosphere in extensional settings. Budapest, August 21-31, 2008, 2008Konferansepaper (Annet vitenskapelig)
    Abstract [en]

    Hydrogen is a widespread trace element in many nominally anhydrous minerals (NAMs) from the Earth's crust and mantle. Hydrogen is normally incorporated in the form of hydroxyl ions and can be regarded as structurally bound water. The most important minerals of the upper mantle: olivine, orthopyroxene, clinopyroxene and garnet, all contain small but significant amounts of hydrogen, and the upper mantle has a capacity to store the equivalent of several world oceans. The main objective of this project is to investigate in detail the mechanisms that are responsible for water incorporation in upper mantle pyroxenes (and synthetic analogues) as pyroxenes can carry substantial amounts of water, up to 1300 wt ppm H2O. Fundamental questions are how much of the original xenolith water that is lost during transport to the surface and if the spectroscopic features measured in the minerals are representative for mantle conditions. The redox reaction: Fe2+ + OH- ↔ Fe3+ + O2- + ½H2, which is relatively fast, is thought to be the dominant hydrogen exchange reaction in many minerals (Ingrin & Skogby, 2000). The reaction is fast enough to suggest that water in NAMs equilibrates with the transporting magma and related fluids during ascent to the surface. Nevertheless, several studies show systematic variations in water content with geological environment (Bell & Rossman, 1992; Peslier et al., 2002), implying a complex relationship between host mineral, mantle source region, magma type and eruption style. The current part of the project  is focused on the dehydration-hydration mechanisms in diopside, the most common variety of clinopyroxene in the upper mantle. The approach has been to study the kinetics and temperature dependence of the reactions controlling hydrogen diffusion in synthetic Fe-poor diopside. Other reactions are likely to be obscured by the iron redox reaction if measured in natural mantle diopside containing several wt% FeO. Therefore, synthetic diopside with very low amounts (0.7 wt% FeO) of iron had to be used in order to measure the influence and co-dependence of the iron redox reaction with other possible reactions.

  • 609.
    Sundvall, Rickard
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologi och geokemi.
    Skogby, Henrik
    Sektionen för Mineralogi, Naturhistoriska Riksmuséet, Box 50007, 10405 Stockholm.
    Stalder, Roland
    Geowissenschaftliches Zentrum der Universität Göttingen, Abteilung Mineralogie, Goldschmidtstraβe 1, 37077 Göttingen, Germany.
    Dehydration-hydration mechanisms in synthetic diopside2007Inngår i: Abstract volume of the 6th European Conference on Mineralogy and Spectroscopy, Stockholm 2007, p. 77, 2007Konferansepaper (Annet vitenskapelig)
    Abstract [en]

    DEHYDRATION-HYDRATION MECHANISMS IN SYNTHETIC DIOPSIDE

    Rickard Sundvall(1,2), Henrik Skogby(1), Roland Stalder(3).

    1, Dept. of Mineralogy, Swedish Museum of Natural History, Box 50007, 10405 Stockholm, Sweden. Rickard.sundvall@nrm.se.

    2, Dept. of Geology and Geochemistry, Svante Arrhenius väg 8C, 106 91 Stockholm, Sweden.

    3, Geowissenschaftliches Zentrum der Universität Göttingen, Abteilung Angewandte und Experimentelle Mineralogie, Goldschmidtstraβe 1, 37077 Göttingen, Germany.

    Small amounts (ppm) of OH in nominally anhydrous minerals (NAM:s) can have a dramatic effect on the chemical and physical properties of the upper mantle. The pyroxenes of the upper mantle have been shown to carry substantial amounts of water in the form of hydroxyl ions. Enstatite and diopside are the most important pyroxenes in terms of bulk volume in the upper mantle. To further constrain the behavior of hydroxyl ions in clinopyroxene, the dehydration-hydration mechanisms of synthetic 57Fe-doped diopside were investigated. Dehydration was carried out by stepwise heating in air of three crystals from the same synthesis run. The crystals were synthesized in a piston-cylinder apparatus at 20 kbar by slow cooling from 1330oC to 1100oC under water-saturated conditions with excess silica.

    A series of FTIR-spectra and corresponding Mössbauer-spectra were obtained after each step.

    From the Mössbauer-spectra we see an increase in the Fe3+ doublet with successive dehydration, although the increase in Fe3+ is less than the decrease in OH in terms of atoms per formula unit. This means that the dehydration only partly follows the redox reaction OH- + Fe2+ = O2- + Fe3+ + ½H2, and that additional reactions are also active. Hydration experiments were conducted in the same manner as the dehydrations, with the exception that hydrogen gas was used during heating. Hydration experiments were only conducted on one crystal.

    The calculated diffusion for the dehydration reactions yields a -logD (D in m2/s) of 13.0 (1000oC), 15.1 (900oC), and 15.3 (800oC). Re-hydration of #218 (1000oC) gives a –logD of 13.3. All crystals were oriented parallel to (010). Diffusion rates are in the same order of magnitude as for synthetic enstatite with comparable Fe-contents. Compared to natural diopside, diffusion rates in these synthetic samples are slower, probably because of the low iron content. The Arrhenius equation yields an activation energy (Ea) of -300 kJ mol-1, from the mean of the three reactions at three different temperatures. This Ea is very similar to that of dehydration of pure and low-Fe enstatite.

  • 610.
    Sundvall, Rickard
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologi och geokemi.
    Skogby, Henrik
    Sektionen för Mineralogi, Naturhistoriska Riksmuseet.
    Stalder, Roland
    Institut für Mineralogie und Petrographie, Universität Innsbruck, Österrike.
    Hydrogen diffusion in synthetic Fe-free diopside2009Inngår i: European journal of mineralogy, ISSN 0935-1221, E-ISSN 1617-4011, Vol. 21, nr 5, s. 963-970Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Hydrogen is a widespread trace element in many nominally anhydrous minerals (NAMs) in the Earth's crust and mantle and has profound influence on the physical properties of the host mineral. Of all NAMs from the upper mantle, clinopyroxenes have been shown to contain the highest amount of hydrogen. This study focuses on the dehydration kinetics of pure diopside along [010] and [100]* by thermal annealing under normal atmospheric pressure. The diopside crystals used were synthesized at high pressure under water-saturated conditions. FTIR spectra were obtained after each step, including untreated samples. The Arrhenius equation gives an activation energy (Ea) of -331 ± 50 kJ mol-1 and D0 = 100.9 ± 2.3 m2 s-1 for diffusion along [010]. Diffusion along [100]* gives an Ea-value of -312 ± 55 kJ mol-1 with D0 = 100.5 ± 2.4 m2 s-1. Therefore, our experimental results show no difference between diffusion along [010] and [100]* (within error limits). The diffusion rate in pure synthetic diopside is about one order of magnitude faster than for synthetic diopside with very low Fe contents. A suitable explanation for this behavior is that in the case of low Fe diopside, the rate-limiting process for the protons associated with Fe is probably Fe-diffusion. In contrast, in pure diopside all protons are associated to Mg-defects, which are more mobile than Fe. Nevertheless, compared to natural diopside with appreciable Fe contents, diffusion rates in these synthetic samples are several orders of magnitude slower.

  • 611.
    Svahnberg, Henrik
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologi och geokemi.
    Piazolo, Sandra
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologi och geokemi.
    The initiation of strain localisation in plagioclase-rich rocks: insights from detailed microstructural analyses. 2010Inngår i: Journal of Structural Geology, ISSN 0191-8141, E-ISSN 1873-1201, Vol. 32, nr 10, s. 1404-1416Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In order to shed light on the cause for onset of strain localisation in plagioclase-richrocks we have performed detailedmicrostructuralanalyses on a sheared anorthosite–leucogabbro using optical microscopy, electron backscatter diffraction (EBSD) and chemical analyses. The analysed sample is from an Archaean unit, SW Greenland, deformed at lower to mid crustal conditions (T = 675–700 °C and moderate pressure). The initial deformation occurred dominantly by dislocation creep and the grain size was reduced primarily by subgrain rotation recrystallisation. Recrystallised plagioclase grains (average size 80 μm) are dominantly found in (i) clusters, (ii) lenses and (iii) continuous bands subparallel to shear zone boundaries. Recrystallised grains in clusters and lenses display inherited crystallographic orientations. Their bulk crystallographic preferred orientation (CPO) is random; however, crystallographic characteristics show that parent and daughter grains have the same misorientation axes and possibly the same active slip systems. Recrystallised grains in continuous bands show a CPO with a single dominant active slip system, (001)<110>, aligned with the structural (XYZ) framework. For these parent and daughter grains, misorientation axes are random and the dominant slip system is different. Grain rotations of recrystallised grains are traceable back to the orientation of the adjacent porphyroclast.

    We infer that the cause for strain localisation is recrystallisation and development of a CPO in continuous recrystallised bands. Microstructures in combination with misorientation and slip system analyses indicate a possible change from dislocation creep in clusters and lenses to dislocation-accommodated grain boundary sliding (DisGBS) in continuous bands. This inferred shift in dominant deformation mechanism would lower the strength of the shear zone.

  • 612. Svensson, Teresia
    et al.
    Sandén, Per
    Bastviken, David
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologi och geokemi. Geokemi.
    Öberg, Gunilla
    Chlorine transport in a small catchment in southeast Sweden during two years2007Inngår i: Biogeochemistry, Vol. 82, s. 181-199Artikkel i tidsskrift (Fagfellevurdert)
  • 613.
    Thompson, B.
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologi och geokemi.
    Gnanaseelan, C.
    Parekh, A.
    Salvekar, P. S.
    A model study on oceanic processes during the Indian Ocean Dipole termination2009Inngår i: Meteorology and atmospheric physics (Print), ISSN 0177-7971, E-ISSN 1436-5065, Vol. 105, nr 02-jan, s. 17-27Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this study, the processes affecting the temperature variability over the Southeastern Tropical Indian Ocean (STIO) during 1958-2000, accomplishing the positive and negative Indian Ocean Dipole (IOD) events are analyzed. The upper ocean heat budget analysis of the STIO has been carried out to understand the oceanic process during the termination of the recent strongest IOD events. The three recent strongest positive IOD events (1961, 1994 and 1997) and a strong negative IOD event (1996) are considered for detailed analysis. The heat budget analysis revealed that the positive net-surface heat flux and vertical advection played dominant roles in the termination of 1997 IOD event, whereas horizontal and vertical advections are responsible for the termination of IOD events during 1961 and 1994. The anomalous negative surface heat flux and horizontal advection caused the dipole termination during the negative dipole year 1996. The findings are well supported by the analysis of anomaly correlation between model upper ocean heat content tendency and heat budget components. Significant intra-seasonal oscillations (ISOs) in sea surface temperature (SST) anomaly are seen during the initial phase of termination in the eastern equatorial Indian Ocean during 1961 and 1994 IOD events. The influence of ISOs in SST is not so evident during the IOD termination in 1997. It is found that the termination processes have started more than a month prior to the actual IOD termination.

  • 614. Thompson, B.
    et al.
    Nilsson, J.
    Jakobsson, Martin
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologi och geokemi.
    Nycander, J.
    Backman, Jan
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologi och geokemi.
    Döös, K.
    Model Study on the Arctic Ocean Circulation During Early Miocene2008Inngår i: EOS Transactions, American Geophysical Union, v. 89(53): Fall Meet. Suppl., 2008, s. Abstract PP13C-1458Konferansepaper (Annet vitenskapelig)
  • 615.
    Thomsen, Tonny B.
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologi och geokemi.
    Pettke, Thomas
    Bern University.
    Allaz, Julien
    University of Massachusetts, Amherst.
    Engi, Martin
    Bern University.
    LAMBERN - software for U-Pb, Th-Pb and Pb-Pb age dating by LA-ICP-MS analysis2009Inngår i: / [ed] Pierre Dézes, 2009Konferansepaper (Annet vitenskapelig)
  • 616.
    Thomsen, Tonny B.
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologi och geokemi.
    Pettke, Thomas
    Bern University.
    Allaz, Julien
    University of Massachusetts, Amherst.
    Engi, Martin
    Bern University.
    LAMBERN: Software for U-Pb, Th-Pb and Pb-Pb age determination by LA-ICP-MS2009Inngår i: LA-ICP-MS Workshop / [ed] Simon E. Jackson, 2009Konferansepaper (Annet vitenskapelig)
    Fulltekst (pdf)
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    FULLTEXT02
  • 617.
    Torppa, Akseli
    et al.
    Department of Geology, University of Helsinki, P.O. Box 64, Helsinki, FIN-00014, Finland.
    Sundvall, Rickard
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologi och geokemi. Sektionen för Mineralogi, Naturhistoriska Riksmuseet, Box 50 007, 10405 Stockholm.
    The 1.1 Ga ultramafic dikes in Kalix region, northern Sweden – an isotope study2007Inngår i: Geologian 5. Tutkijapäivät 6.-8.5.2007, program with abstracts. p.58, 2007Konferansepaper (Annet vitenskapelig)
    Abstract [en]

    The ultramafic dikes, that are the object of this study, occur as swarms along the western coast of the Bothnian Gulf from the mainland around Kalix in the north to the Luleå archipelago in the south. The dikes were emplaced at ca. 1.1 Ga (Kresten et al. 1997) into Paleoproterozoic igneous and meta-sedimentary rocks. In earlier petrographic and geochemical studies, Kresten et al. (1977, 1981) described the Kalix dikes as picritic (olivine-rich), and alnöitic (micaceous) lamprophyres, and silico-carbonatites. Rare occurrences of carbonatites (beforsites) have also been reported by Kresten et al. (1981), Griffin & Kresten (1987), and Åhman et al (1990).

    For the present study, samples from a total of 6 dikes were collected on the mainland around Kalix, in Storön and in Ryssbält, and in the Kalix archipelago on the islet of Västra Gräddmanhällan. The samples were analyzed for the isotopic composition of strontium and neodymium at the Geological Survey of Finland, and for that of carbon and oxygen at the Department of Geology in the University of Helsinki.

    Based on trace element geochemistry, Kresten et al. (1981) proposed an upper mantle origin for the parental magma to the Kalix dikes. Our Sr and Nd isotopic data, with relatively invariant initial (1.1 Ga) 87Sr/86Sr between 0.7026 and 0.7034 (n=7) and Nd values between +4 and +5 (n=6), support this interpretation by indicating a long-term depleted source for Sr and LREE’s in the studied dikes. However, the isotope ratios of C and O in carbonate samples (n=22) from the dikes are more ambiguous, with 13C and 18O values ranging from -6 to -1‰ (PDB) and from +9 to +17‰ (SMOW), respectively. The observed variations could be explained by mixing of mantle-derived material with that from a crustal source, possibly containing Paleoproterozoic sedimentary carbonate rocks that are abundant in the region.

  • 618.
    Torssander, Peter
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologi och geokemi.
    Mbede, Evelyne
    Maboko, Makenya
    Geochemistry of the Rungwe CO2 springs: Impact into the Rungwe volcanic system, southern rift in Tanzania2007Inngår i: 7th International Symposium on Applied Isotope Geochemistry: Abstract Volume, 2007, s. 149-150Konferansepaper (Annet (populærvitenskap, debatt, mm))
  • 619.
    Torssander, Peter
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologi och geokemi.
    Mbede, Evelyne
    Maboko, Makenya
    Kumpulainen, Risto
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologi och geokemi.
    Geochemisty of the Rungwe CO2 springs - volcanic and environmental impact2008Inngår i: SIDA Conference: Meeting Global Challenges in Research Cooperation, 27-29 May 2008, 2008Konferansepaper (Annet vitenskapelig)
  • 620. Treat, C
    et al.
    Bubier, J
    Varner, R
    Crill, P
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologi och geokemi.
    Timescale dependence of environmental and plant-mediated controls on CH4 flux in a temperate fen.2007Inngår i: Journal of Geophysical Research-Biogeosciences, Vol. 112Artikkel i tidsskrift (Fagfellevurdert)
  • 621.
    Treat, C.
    et al.
    Mount Holyoke College.
    Bubier, J.L.
    Mount Holyoke College.
    Varner, R.K.
    Univ New Hampshire.
    Crill, Patrick
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologi och geokemi.
    Timescale dependence of environmental and plant-mediated controls on CH4 flux in a temperate fen.2007Inngår i: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 112, nr G01014Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This study examined daily, seasonal, and interannual variations in CH4 emissions at a temperate peatland over a 5-year period. We measured net ecosystem CO2 exchange (NEE), CH4 flux, water table depth, peat temperature, and meteorological parameters weekly from the summers (1 May to 31 August) of 2000 through 2004 at Sallie's Fen in southeastern New Hampshire, United States. Significant interannual differences, driven by high variability of large individual CH4 fluxes (ranging from 8.7 to 3833.1 mg CH4 m−2 d−1) occurring in the late summer, corresponded with a decline in water table level and an increase in air and peat temperature. Monthly timescale yielded the strongest correlations between CH4 fluxes and peat and air temperature (r2 = 0.78 and 0.74, respectively) and water table depth (WTD) (r2 = 0.53). Compared to daily and seasonal timescales, the monthly timescale was the best timescale to predict CH4 fluxes using a stepwise multiple regression (r2 = 0.81). Species composition affected relationships between CH4 fluxes and measures of plant productivity, with sedge collars showing the strongest relationships between CH4 flux, water table, and temperature. Air temperature was the only variable that was strongly correlated with CH4 flux at all timescales, while WTD had either a positive or negative correlation depending on timescale and vegetation type. The timescale dependence of controls on CH4 fluxes has important implications for modeling.

  • 622.
    Tröften, Per Einar
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologi och geokemi.
    Neotectonics and paleoseismicity in southern Sweden with emphasis on sedimentological criteria1997Doktoravhandling, monografi (Annet vitenskapelig)
  • 623.
    Tsuchiya, Masashi
    et al.
    Japan Agency for Marine, Earth Science and Technology.
    Grimm, Guido W.
    University of Tubingen.
    Heinz, Petra
    University of Tubingen.
    Stögerer, Karin
    University of Tubingen.
    Ertan, Kemal Topaç
    University of Tubingen.
    Collen, John
    Victoria University of Wellington.
    Brüchert, Volker
    Stockholms universitet. Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologi och geokemi.
    Hemleben, Christoph
    University of Tubingen.
    Hemleben, Vera
    University of Tubingen.
    Kitazato, Hiroshi
    Japan Agency for Marine, Earth Science and Technology.
    Ribosomal DNA shows extremely low genetic divergence in a world-wide 2 distributed, but disjunct and highly adapted marine protozoan (Virgulinella fragilis, Foraminiferida)2009Inngår i: Marine Micropaleontology, ISSN 0377-8398, Vol. 70, s. 8-19Artikkel i tidsskrift (Fagfellevurdert)
  • 624. Tulibonywa, Tulibako
    et al.
    Manya, Shukrani
    Torssander, Peter
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologi och geokemi.
    Maboko, Makenya A. H.
    Geochemistry of the Palaeoproterozoic volcanic and associated potassic granitic rocks of the Ngualla area of the Ubendian Belt, SW Tanzania2017Inngår i: Journal of African Earth Sciences, ISSN 1464-343X, E-ISSN 1879-1956, Vol. 129, s. 291-306Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The Ngualla area of the Lupa terrane in the Ubendian Belt of SW Tanzania is underlain by well-preserved greenschist facies calc-alkaline volcanic rocks which have been intruded by low-Sr, peraluminous K-rich granites. The Ngualla volcanic rocks are subdivided into four groups: the basaltic andesitestrachyandesites, Group I porphyritic dacites-trachytes, Group II porphyritic dacites-trachytes, and rhyolites. The basaltic andesites-trachyandesites were emplaced at similar to 1943 Ma and their most primitive members are characterized by MgO contents of up to 7.43 wt % at a SiO2 content of 54.0 wt %, Ni contents of up to 170 ppm and Mg# of up to 62. They show fractionated REE patterns (La/YbcN = 11.5-36.5), subchondritic Zr/Hf (37.8-43.9) and Nb/Ta (7.14-20.0) ratios, epsilon Nd (1943 Ma) values of 3.33 to 6.24 and TOM ages of 2521-2883 Ma. These geochemical features are consistent with derivation of the basaltic andesites-trachyandesites by at least 0.1% partial melting of garnet peridotite mantle, followed by 50 -80% fractional crystallization involving the removal of 61% clinopyroxene, 20% hornblende, 4% plagioclase and 15% orthopyroxene. The magmas were contaminated by Neoarchaean crustal materials incorporated in the Ubendian Belt during their ascent to the surface. The evolution of these magmas led to the formation of Group I porphyritic dacites-trachytes and rhyolites in a Palaeoproterozoic continental arc setting. The Group II porphyritic dacites-trachytes (1871 5 Ma) were coevally emplaced with the low-Sr, peraluminous K-granites (1878 15 Ma) forming a felsic plutonic-volcanic suite. Despite some differences, these rocks share geochemical features including negative Eu anomalies (mean Eu/Eu* = 0.19 for the dacites and 0.5 for the granites) and eNd (1871 Ma) values of -5.72 for the dacites and eNd (1878 Ma) values of -6.00 to -11.2 for the granites. These geochemical features are consistent with the generation of the similar to 1.87 Ga Ngualla felsic plutonic -volcanic suite by partial melting of heterogeneous Neoarchaean crust at low pressure conditions in the stability field of plagioclase in an intracontinental setting along a sutured margin. The 1.89-1.87 Ga felsic plutonic -volcanic suite also occurs in the Ndembera area of the Usagaran belt to the SW. Our results corroborate previous evidence that the Palaeoproterozoic regional K-granitic magmatism that affected parts of the Ubendian and Usagaran belts was caused by a regional thermal anomaly that was induced by large scale magmatic underplating that precipitated widespread crustal anatexis.

  • 625. Turchyn, Alexandra V.
    et al.
    Brüchert, Volker
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologi och geokemi.
    Lyons, Timothy W.
    Engel, Gregory S.
    Balci, Nurgul
    Schrag, Daniel P.
    Brunner, Benjamin
    Kinetic oxygen isotope effects during dissimilatory sulfate reduction: A combined theoretical and experimental approach2010Inngår i: Geochimica et Cosmochimica Acta, ISSN 0016-7037, E-ISSN 1872-9533, Vol. 74, nr 7, s. 2011-2024Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Kinetic isotope effects related to the breaking of chemical bonds drive Sulfur isotope fraction at ion during dissimilatory sit I fate reduction (DSR), whereas oxygen isotope fractional ion during DSR is dominated by exchange between intercellular sulfur intermediates and water. We use a simplified biochemical model for DSR to explore how a kinetic oxygen isotope effect may be expressed. We then explore these relationships in light of evolving sulfur and Oxygen isotope compositions (delta S-34(SO4) and delta O-18(SO4)) during batch culture growth of twelve strains of surface-reducing bacteria. Cultured under conditions to optimize growth and with identical delta O-18(H2O) and initial delta O-18(SO4), all strains show 34 S enrichment, whereas only six strains show significant O-18 enrichment. The remaining six show no (or minimal) change in delta O-18(SO4) over the growth of the bacteria. We use these experimental and theoretical results to address three questions: (i) which Sulfur intermediates exchange oxygen isotopes with water, (ii) what is the kinetic oxygen isotope effect related to the reduction of adenosine phosphosulfate (APS) to sulfite (SO32-), (iii) does a kinetic oxygen isotope effect impact the apparent oxygen isotope equilibrium values? We conclude that oxygen isotope exchange between water and a sulfur intermediate likely occurs downstream of APS and that our data constrain the kinetic oxygen isotope fractionation for the reduction of APS to sulfite to be smaller than 47 parts per thousand. This small oxygen isotope effect impacts the apparent oxygen isotope equilibrium as controlled by the extent to which APS reduction is rate-limiting.

  • 626. Turley, Carol
    et al.
    Henderiks, Jorijntje
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologi och geokemi.
    Learning from the Distant Past: An IGBP/ SCOR Workshop on “Ocean Acidification – Modern Observations and Past Experiences”2007Inngår i: IMBER Update, Vol. 6, s. 11-13Artikkel i tidsskrift (Annet (populærvitenskap, debatt, mm))
  • 627. Tuuling, Igor
    et al.
    Floden, Tom
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologi och geokemi.
    The Llandovery-lowermost Wenlock sequence in the Baltic Sea between Saaremaa and Gotland: subdivision, thicknesses and correlation, based on marine seismic studies2009Inngår i: Marine Geology, ISSN 0025-3227, E-ISSN 1872-6151, Vol. 267, nr 02-jan, s. 55-70Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The Llandovery-lowermost Wenlock sequence in the Baltic Sea between Saaremaa and Gotland has been studied by means of high resolution seismic reflection profiling. The number and the positions of the seismic reflectors within this sequence change considerably even within short distances, thus showing a high lateral inconsistency both in lithology and thickness. Stratigraphically two unambiguous (S-1 and S-2) and two roughly fixed trans-Baltic seismic reflectors (S-5 and S-7) enabled us to distinguish the pre-Adavere, the Adavere (S-1-S-2 and S-2-S-5) and the Mustjala seismic units (S-5-S-7) and to follow their east-westerly changes across the Baltic. The seismic signatures and thicknesses of these units undergo a sharp transformation midway Baltic, dividing between the Saaremaa type and the Gotland type of Llandovery-lowermost Wenlock sections. This is due to a short and steep northeast-southwest facies transect that was induced by a well differentiated bathymetry in the intracratonic Palaeobaltic basin, thus clearly distinguishing the shallow-shelf (basinal), the slope (transitional) and the deep-shelf (basinal) areas. The slope is furthermore accentuated by the intensive submarine erosion and channelling during the Late Ordovician and Early Silurian times. Thus, the Saaremaa type of section includes the inner to outer shallow-shelf transect, where the pre-Adavere and Adavere units are decreasing in thickness, and the Mustjala unit is increasing in thickness towards Gotland. In the slope area offshore Gotland, all the Llandovery-lowermost Wenlock units thin out rapidly towards the deep-shelf area in south to southeast and the thickness of the pre-Adavere and Adavere units approach zero. Similar features of submarine erosion on Gotland and around the Estonian Latvian border reveal that an unstable basinal slope, from the point of sediment accumulation, extended over large areas along the shallow-shelf edge of the Palaeobaltic basin during the latest Ordovician and earliest Silurian times. Seismic data suggest that the uppermost unidentified subsurface of the Silurian succession in northern Gotland includes a considerable amount of marlstone layers that are coeval with the Mustjala Member in Estonia. 

  • 628.
    Tuuling, Igor
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologi och geokemi.
    Flodén, Tom
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologi och geokemi.
    The Ordovician-Silurian boundary beds between Saaremaa and Gotland, Baltic Sea, based on high resolution seismic data.2007Inngår i: Geological Quaternarly, Vol. 51, nr 3, s. 217-229Artikkel i tidsskrift (Fagfellevurdert)
  • 629. Unkel, I.
    et al.
    Björck, Svante
    Lund University.
    Wohlfarth, Barbara
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologi och geokemi.
    Deglacial environmental changes on Isla de los Estados (54.4 degrees S), southeastern Tierra del Fuego2008Inngår i: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 27, nr 15-16, s. 1541-1554Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The island of Isla de los Estados is situated at 54.5°S, 64°W, east of Argentinian Tierra del Fuego, and is located in a sensitive geographic position in relation to the zonal circulation between Antarctica and South America. Its terrestrial records of the last deglaciation, recording atmospheric conditions but within an oceanic setting, can help to clarify changes of regional circulation patterns, both atmospheric and marine. Here, we present geochemical analyses from 16–10 ka cal BP of a peat core from Lago Galvarne Bog at the northern coast of the island, and a lake sediment core from Laguna Cascada 3 km further south. The data comprise TC, TN, loss on ignition analyses and continuous XRF scanning on both cores as well as age–depth modeling based on AMS-14C dating. Deglaciation and onset of peat formation in the coastal areas began before 16 ka cal BP followed by a rapid glacial retreat and the start of lacustrine sedimentation further inland. Data suggest initially windy conditions with permafrost succeeded by gradually warmer and wetter conditions until ca 14.5 ka cal BP. The warming trend slows down until ca 13.5 ka cal BP, followed by arid conditions culminating around 12.8 ka cal BP. Our data suggest fairly warm conditions and the establishment of denser peat and forest vegetation ca 10.6 ka cal BP, contemporaneous with the onset of the Antarctic thermal optimum. This indicates large-scale shifts in the placement of zonal flow and the Westerlies at the beginning of the Holocene.

  • 630.
    van Mourik, Caroline A.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologi och geokemi.
    The Greenhouse - Icehouse Transition: a dinoflagellate perspective2006Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Through the analysis of the stratigraphic and spatial distribution of organic walled dinoflagellate cysts (dinocysts) from climatologically and oceanographically key sites, this project aims to contribute to a better understanding of the Eocene-Oligocene (E/O) environmental changes and their timing. A central issue is to identify the global environmental changes which are responsible for the Eocene cooling and its underlying mechanisms with the focus on the Oligocene isotope-1 (Oi-1) event, thought to mark the onset of major Antarctic glaciation.

    Two low-latitude sites were selected, Blake Nose (western North Atlantic) and Massignano (central Italy). For the first time a coherent taxonomy and biostratigraphy of dinocysts was established for the late Eocene at these latitudes. A high resolution correlation was established between the Massignano E/O Stratotype Section and the stratigraphically more extended ‘Massicore’. The composite section was used to analyse sea surface temperature (SST) change across the greenhouse-icehouse transition by means of dinocyst distribution.

    At Massignano, the Oi-1 event was recognised both qualitatively and quantitatively. In the power spectrum of the SSTdino the ~100 and ~400 kyr eccentricity cycles may be distinguished and correlated with La04. When orbitally tuned, the E/O GSSP dates ~100 kyr older than the Oi-1 event. The boundary’s age could either be ~33.75 or ~34.1 Ma, both differ significantly from the ~33.9 Ma age in the GTS 2004.

    Furthermore, when the data from the low-latitude sites were combined with extensive datasets from the Proto North Atlantic and adjacent regions, a suite of species sensitive to changes in SST was recognised. Their first and last occurrences reflect seven distinct phases of decreasing SSTs during the Middle Eocene to earliest Oligocene.

    These results clearly indicate that atmospheric cooling together with higher frequency orbital forcing played a key role in the transition from the Greenhouse to the Icehouse world.

    Fulltekst (pdf)
    FULLTEXT01
  • 631.
    van Mourik, Caroline A.
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologi och geokemi.
    Brinkhuis, Henk
    The Massignano Eocene-Oligocene golden spike section2005Inngår i: Stratigraphy, ISSN 1547-139X, E-ISSN 2331-656X, Vol. 2, nr 1, s. 13-30Artikkel i tidsskrift (Fagfellevurdert)
  • 632.
    van Mourik, Caroline A.
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologi och geokemi.
    Brinkhuis, Henk
    Williams, Graham L.
    Mid- to Late Eocene organic-walled dinoflagellate cysts from ODP Leg 171B, offshore Florida.2001Inngår i: Western North Atlantic Paleogene and Cretaceous Paleoceanography., 2001, s. 225-252Kapittel i bok, del av antologi (Annet vitenskapelig)
  • 633.
    van Mourik, Caroline A.
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologi och geokemi.
    Lourens, Lucas. J.
    Brinkhuis, Henk
    Pälike, Heiko
    Hilgen, Frits J.
    Montanari, Allessandro
    Coccioni, Rodolfo
    From Greenhouse to Icehouse at the Massignano Eocene - Oligocene GSSP;: implications for the cause, timing and effects of the Oi-1 glaciation.Manuskript (Annet vitenskapelig)
  • 634.
    Veres, Daniel
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi och kvartärgeologi. Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi och kvartärgeologi.
    Davies, Siwan M
    Wohlfarth, Barbara
    Institutionen för geologi och geokemi. Institutionen för geologi och geokemi.
    Preusser, Frank
    Wastegård, Stefan
    Ampel, Linda
    Hormes, Anne
    Possnert, Göran
    Raynal, Jean-Paul
    Vernet, Gérard
    Age, origin and significance of a new middle MIS 3 tephra horizon identified within a long-core sequence from Les Echets, France2008Inngår i: Boreas, Vol. 37, nr 434-443Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A new tephra has been identified within a long core (EC 3) sequence recovered from Les Echets, near Lyon, France. This visible tephra was discovered as part of a high resolution multiproxy re-investigation of the Les Echets sequence. Independent chronological information suggests that the tephra is c. 2 000-45 000 years old, and geochemical analysis indicates that it is of basanitic composition. The latter suggests a possible origin in the Eifel; however, as yet, no other volcanic events or deposits can be correlated to the Les Echets tephra. New sedimentological and chronological data are presented indicating that the tephra falls within an interval that most likely correlates with Dansgaard-Oeschger events 12-9. Thus, this tephra could potentially be an important middle MIS 3 marker horizon in central Europe if it can be traced in other palaeorecords.

  • 635. Veres, Daniel
    et al.
    Lallier-Vergès, Elisabeth
    Wohlfarth, Barbara
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologi och geokemi.
    Lacourse, Terri
    Keravis, Didier
    Björck, Svante
    Preusser, Frank
    Andrieu-Ponel, Valerie
    Ampel, Linda
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologi och geokemi.
    Climate-driven changes in lake conditions during late MIS 3 and MIS 2: a high-resolution geochemical record from les Echets, France2009Inngår i: Boreas, ISSN 0300-9483, E-ISSN 1502-3885, Vol. 38, nr 2, s. 230-243Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A new set of geochemical data obtained from a long sediment sequence from the Les Echets basin provides a new record of palaeoenvironmental change for western Europe. The sequence covers the late part of Marine Isotope Stage (MIS) 3 and MIS 2 ( c. 46.1–15.0 cal. kyr BP) and extends over 30 m of sediment, allowing for high sampling resolution. Distinct cyclic fluctuations in aquatic productivity proxies suggest a tempo of environmental change at Les Echets that resembles the one established for Dansgaard-Oeschger cycles and Heinrich events. Increases in organic carbon are paralleled by high hydrogenous contents and enriched δ<sup>13</sup>C<sub>org</sub> and C<sub>org</sub>/N<sub>tot</sub> ratios, implying a mixture of aquatic and land-derived constituents. The stable isotope values are directly linked to primary aquatic productivity and the input of terrestrial organic matter, enriched during warm, productive, periods, and drastically depleted during cold periods, particularly Heinrich events. Phases of relatively high productivity correlate with Dansgaard-Oeschger interstadials 8–2, while Heinrich events 3 and 2 are also clearly delineated by distinct lithological horizons with very low organic contents, high dry densities and enhanced organic matter oxidation. A large hiatus occurring about the time of Heinrich event 4 suggests that the cold and dry climate reconstructed for this event in the North Atlantic region also greatly affected Les Echets and its catchment.

  • 636.
    Veres, Daniel
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi och kvartärgeologi (INK).
    Lallier-Vergès, Elisabeth
    Wolfarth, Barbara
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologi och geokemi.
    Lacourse, Terri
    Kéravis, Didier
    Björck, Svante
    Preusser, Frank
    Andrieu-Ponel, Valérie
    Ampel, Linda
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi och kvartärgeologi (INK).
    Climate-driven changes in lake conditions during late MIS 3 and MIS 2: a high-resolution geochemical record from Les Echets, France2009Inngår i: Boreas, ISSN 0300-9483 , Vol. 38, nr 2, s. 230-243Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A new set of geochemical data obtained from a long sediment sequence from the Les Echets basin provides a new record of palaeoenvironmental change for western Europe. The sequence covers the late part of Marine Isotope Stage (MIS) 3 and MIS 2 (c. 46.1–15.0 cal. kyr BP) and extends over 30 m of sediment, allowing for high sampling resolution. Distinct cyclic fluctuations in aquatic productivity proxies suggest a tempo of environmental change at Les Echets that resembles the one established for Dansgaard-Oeschger cycles and Heinrich events. Increases in organic carbon are paralleled by high hydrogenous contents and enriched δ13Corg and Corg/Ntot ratios, implying a mixture of aquatic and land-derived constituents. The stable isotope values are directly linked to primary aquatic productivity and the input of terrestrial organic matter, enriched during warm, productive, periods, and drastically depleted during cold periods, particularly Heinrich events. Phases of relatively high productivity correlate with Dansgaard-Oeschger interstadials 8–2, while Heinrich events 3 and 2 are also clearly delineated by distinct lithological horizons with very low organic contents, high dry densities and enhanced organic matter oxidation. A large hiatus occurring about the time of Heinrich event 4 suggests that the cold and dry climate reconstructed for this event in the North Atlantic region also greatly affected Les Echets and its catchment.

  • 637. Vogt, P.R.
    et al.
    Jung, W.-Y
    Jakobsson, Martin
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologi och geokemi.
    Mayer, L.A.
    Williamson, M-C
    The Alpha-Mendeleev Magmatic Province:: A new synthesis2006Inngår i: Atlantic Geoscience Society Colloquium and Annual Meeting, 2006, s. Abstracts, p. 72-73Konferansepaper (Annet vitenskapelig)
  • 638. von Wachenfeldt, Eddie
    et al.
    Bastviken, David
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologi och geokemi.
    Tranvik, Lars J.
    Microbially induced flocculation of allochthonous dissolved organic carbon in lakes2009Inngår i: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 54, nr 5, s. 1811-1818Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The flocculation of allochthonous dissolved organic carbon (DOC) in lakes was investigated in a series of laboratory experiments. Flocculation was enhanced by increased temperatures, and addition of glucose increased the flocculation further. A change in pH within the range of 3.3 to 7.3 resulted in decreased flocculation with increasing deviation from the original pH. Flocculation was similar under oxic and anoxic conditions. For all treatments (i.e., temperature and glucose, pH, and O2 regime), occulation was positively correlated to bacterial respiration. However, bacterial biomass made up a negligible fraction of the formed flocs, suggesting that the formation of detrital particles was a result of bacterial activity, but there was no significant contribution of bacteria to the mass of the particles formed. In all experiments, both the concentration of DOC and concentration of colored dissolved organic matter (CDOM) decreased concomitantly with flocculation, suggesting that CDOM is the precursor of the flocs. Bacteria mediate a translocation of DOC in the water column into particles prone to gravitational settling.

  • 639. von Wachenfeldt, Eddie
    et al.
    Sobek, Sebastian
    Bastviken, David
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologi och geokemi.
    Tranvik, Lars J.
    Linking allochthonous dissolved organic matter and boreal lake sediment carbon sequestration: The role of light-mediated flocculation2008Inngår i: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 53, nr 6, s. 2416-2426Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We measured flocculation of dissolved organic carbon (DOC) in the water from a humic lake (DOC = 14.9 mg C L-1) and from an adjacent mire (DOC = 25.7 mg C L-1), in in situ enclosure experiments with different light regimes. Light stimulated the formation of organic particles in both waters, and organic particle formation was observed at all incubation depths, even in the dark controls. Production of phytoplankton biomass was negligible, and allochthonous DOC was the most important precursor of the sinking particles. 8-22% and 25-60% of the loss of DOC in lake and mire water, respectively, could be accounted for by flocculation. Depth-integrated flocculation based on the enclosure experiments was 14.7 mg C m(-2) d(-1). Lake-water DOC concentration and water color has been increasing during the last decade, and sediment trap studies show that gross sedimentation of organic carbon also increased. Thus flocculation of allochthonous DOC, stimulated by light, constitutes a pathway for the sequestration of carbon in lake sediments.

  • 640. Weiss, Dominik J.
    et al.
    Kylander, Malin E.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologi och geokemi.
    Reuer, Matt
    The environmental geochemistry of lead2007Inngår i: Advances in Earth Science: From Earthquakes to Global Warming, Imperial College Press , 2007, s. 344-Kapittel i bok, del av antologi (Fagfellevurdert)
    Abstract [en]

    The global biogeochemical cycles of several trace metals are presently dominated by human activities, a result of the nature and magnitude of historical resource consumption. Lead has been mined since ancient times, often as a by-product of silver extraction, and has one of the longest associations with man of all heavy metals [Nriagu, 1983]. As of 1983, human activities accounted for an estimated 97% of the global mass balance of lead [Nriagu and Pacyna, 1988]. At that time as well as today, most of the lead was derived from leaded gasoline [Nriagu, 1990], where it was used as an anti-knock agent.

    New estimates of anthropogenic sources of lead suggest that the overall burden of anthropogenic lead emissions has decreased but new pollution sources (e.g., China, Mexico) have become important [Pacyna and Pacyna, 2001; Pacyna et al., 1995] leaving anthropogenic Pb emission to remain a global problem and leaded gasoline as the main source. In addition, as metals are not biodegradable, the Pb in the environment has accumulated over the decades and its fate and pathways within the ecosystem need to be investigated.

    In a manner similar to chlorofluorocarbons and radionuclides derived from atomic testing, the release of lead into the environment represents an inadvertent geochemical tracer experiment, providing new insights into its fate and transport within marine and terrestrial systems. There have been several review papers and books discussing lead, its historical place in society and its impact on human and environmental health [Boutron, 1995; Needleman, 1997; Nriagu, 1983; Nriagu, 1989b; Nriagu, 1990; Reuer and Weiss, 2002; Shotyk and Le Roux, 2005; Weiss et al., 1999] and the reader is encouraged to refer to these works as well.

  • 641. Westman, Per
    et al.
    Borgendahl, Johanna
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologi och geokemi.
    Bianchi, Thomas S.
    Chen, Nianhong
    Probable causes for cyanobacterial expansion in the Baltic Sea: role of anoxia and phosphorus retention2003Inngår i: Estuaries, ISSN 0160-8347, Vol. 26, nr 3, s. 680-689Artikkel i tidsskrift (Fagfellevurdert)
  • 642. Wheeler, John
    et al.
    Mariani, Elisabetta
    drury, martyn
    piazolo, sandra
    Stockholms universitet. Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologi och geokemi.
    trimby, patrick
    The Weighted Burgers Vector: a new quantity for constraining dislocation densities and types using Electron Backscatter Diffraction on 2D sections through crystalline materials2009Inngår i: Journal of Microscopy, Vol. 233, s. 482-494Artikkel i tidsskrift (Fagfellevurdert)
  • 643.
    White, M.L.
    et al.
    Univ New Hampshire.
    Varner, R.K.
    Univ New Hampshire.
    Crill, Patrick
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologi och geokemi.
    Mosedale, C.H.
    Univ New Hampshire.
    Controls on the Seasonal Exchange of CH3Br in Temperate Peatlands.2005Inngår i: Global Biogeochemical Cycles, ISSN 0886-6236, E-ISSN 1944-9224, Vol. 19, nr GB4009Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Measurements of CH3Br exchange at two New Hampshire peatlands (Sallie's Fen and Angie's Bog) indicate that net flux from these ecosystems is the sum of competing production and consumption processes. Net CH3Br fluxes were highly variable and ranged from net emission to net uptake between locations within a single peatland. At Sallie's Fen, net CH3Br flux exhibited positive correlations with peat temperature and air temperature during all seasons sampled, but these relationships were not observed at Angie's Bog where flux varied according to microtopography. The major CH3Br production process at Sallie's Fen appeared dependent on aerobic conditions within the peat, while CH3Br production at Angie's Bog was favored by anaerobic conditions. There was evidence of aerobic microbial consumption of CH3Br within the peat at both sites. In a vegetation removal experiment conducted at Sallie's Fen with dynamic chambers, all collars exhibited net consumption of CH3Br. Net CH3Br flux had a negative correlation with surface temperature and a positive correlation with water level in collars with all vegetation clipped consistent with aerobic microbial consumption. Vegetated collars showed positive correlations between net CH3Br flux and air temperature. A positive correlation between net CH3Br flux and surface temperature was also observed in collars in which all vegetation except Sphagnum spp. were clipped. These correlations are consistent with seasonal relationships observed in 1998, 1999, and 2000 and suggest that plants and/or fungi are possible sources of CH3Br in peatlands. Estimates of production and consumption made on two occasions at Sallie's Fen suggest that peatlands have lower rates of CH3Br consumption compared to upland ecosystems, but a close balance between production and consumption rates may allow these wetlands to act as either a net source or sink for this gas.

  • 644. Wilhelm, Thorsten
    et al.
    Brüchert, Volker
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologi och geokemi.
    Schubotz, Florence
    Zabel, Matthias
    Kasten, Sabine
    Asphalt/oil seepage and its impact on the formation of stable sulfur isotope signatures in sediments of Chapopote Knoll/Gulf of Mexico2007Konferansepaper (Annet vitenskapelig)
  • 645. Winter, Amos
    et al.
    Henderiks, Jorijntje
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologi och geokemi.
    Beaufort, Luc
    Implications of coccolithophores expanding to polar waters2008Konferansepaper (Annet (populærvitenskap, debatt, mm))
  • 646.
    Wohlafrth, Barbara
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi och kvartärgeologi. Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi och kvartärgeologi.
    Tarasov, Pavel
    Bennike, Ole
    Lacourse, Terri
    Subetto, Dmitry
    Torssander, Peter
    Institutionen för geologi och geokemi. Institutionen för geologi och geokemi.
    Romanenko, Feodor
    Late Glacial and Holocene palaeoenvironmental changes in the Rostov-Yaroslavl’ area, central-west Russia.2006Inngår i: Journal of Paleolimnology, Vol. 35, s. 543-569Artikkel i tidsskrift (Annet (populærvitenskap, debatt, mm))
  • 647.
    Wohlfarth, Barbara
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologi och geokemi.
    Björck, Svante
    Människan påverkade klimatet redan före industriella revolutionen: bokrecension2007Inngår i: Geologiskt Forum, nr 53, s. 38-39Artikkel i tidsskrift (Annet (populærvitenskap, debatt, mm))
  • 648.
    Wohlfarth, Barbara
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologi och geokemi.
    Björck, Svante
    Vart är klimatet på väg?2007Inngår i: Framtider, nr 1, s. 4-11Artikkel i tidsskrift (Annet (populærvitenskap, debatt, mm))
  • 649.
    Wohlfarth, Barbara
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologi och geokemi. Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologi och geokemi.
    Björck, Svante
    Funder, Sven
    Houmark-Nielsen, Michael
    Ingolfsson, Olafur
    Lunkka, J. P.
    Mangerud, Jan
    Saarnisto, Matti
    Vorren, Tore
    Quaternary of Norden2008Inngår i: Episodes, Vol. 31, nr 1, s. 73-81Artikkel i tidsskrift (Fagfellevurdert)
  • 650.
    Wohlfarth, Barbara
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologi och geokemi.
    Blaauw, Maarten
    Davies, Siwan
    Andersson, Mamite
    Institutionen för naturgeografi och kvartärgeologi.
    Wastegård, Stefan
    Institutionen för naturgeografi och kvartärgeologi.
    Hormes, Anne
    Possnert, Göran
    Constraining the age of Lateglacial and early Holocene pollen zones and tephra horizons in southern Sweden with Bayesian probability methods2006Inngår i: Journal of Quaternary Science, Vol. 21, nr 4, s. 321-334Artikkel i tidsskrift (Fagfellevurdert)
1011121314 601 - 650 of 658
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