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  • 1
    Keywords: Forschungsbericht
    Type of Medium: Online Resource
    Pages: Online-Ressource (29 S., 560 KB) , graph. Darst.
    Language: German , English
    Note: Förderkennzeichen BMBF 07AFC01. - Literaturverz. - Engl. Zsfassung u.d.T.: Investigation of chemical and dynamical processes in the stratosphere and upper troposphrere using isotopes as process tracers (ISOSTRAT) , Unterschiede zwischen der gedruckten und der elektronischen Dokumentversion sind möglich , Auch als gedr. Ausg. vorh , Systemvoraussetzungen: Acrobat reader.
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  • 2
    ISSN: 1573-0662
    Keywords: tropospheric chemistry ; ozone ; Russia ; trans-Siberian railroad ; Siberia ; carbon monoxide ; methane ; nitrogen oxides ; trace gases ; atmospheric composition
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract Using a laboratory wagon traveling along the Trans-Siberian railroad, O3, NO, NO2, CO, CH4, SF6 and black carbon aerosol have been measured during the summer of 1996. The expedition from Niznij Novgorod (500 km east of Moscow) to Vladivostok (and back to Moscow) has shown the great potential of the train method; here the first results are presented and discussed. A wealth of boundary layer air data was obtained during the over 18000 km travel without serious contamination problems from the electric train itself. The diurnal O3 cycle peaked generally below 50 nmole/mole, showed the effects of changes in J(NO2), and often dropped to a few nmole/mole at night time during inversions. Over the vast Siberian lowlands situated between the Ural mountains and the river Yenisey, CH4 levels were consistently elevated at around 1.95 µmole/mole, which we mainly attribute to wetland emissions. Over eastern Siberia, however, CH4 levels were generally lower at 1.85 µmole/mole. In contrast, over the west Siberian lowlands, CO levels were relatively low, often reaching values of only 110 nmole/mole, whereas over eastern Siberia CO levels were higher. Very high CO levels were detected over a 2000 km section east of Chita, along the river Amur, which represented an enormous polluted air mass. 14C analysis performed on several CO samples confirms that the origin was biomass burning. SF6, which was measured as a general conserved tracer, showed an eastward attenuation from 4.0 to 3.9 pmole/mole, with peaks in a number of places due to local Russian emissions.
    Type of Medium: Electronic Resource
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  • 3
    Publication Date: 2019-09-23
    Description: Oceans are a net source of molecular hydrogen (H-2) to the atmosphere, where nitrogen (N-2) fixation is assumed to be the main biological production pathway followed by photochemical production from organic material. The sources can be distinguished using isotope measurements because of clearly differing isotopic signatures of the produced hydrogen. Here we present the first ship-borne measurements of atmospheric molecular H-2 mixing ratio and isotopic composition at the West African coast of Mauritania (16-25 degrees W, 17-24 degrees N). This area is one of the biologically most active regions of the world's oceans with seasonal upwelling events and characterized by strongly differing hydrographical/ biological properties and phytoplankton community structures. The aim of this study was to identify areas of H-2 production and distinguish H-2 sources by isotopic signatures of atmospheric H-2. For this more than 100 air samples were taken during two cruises in February 2007 and 2008. During both cruises a transect from the Cape Verde Islands towards the Mauritanian Coast was sampled to cover differing oceanic regions such as upwelling and oligotrophic regimes. In 2007, additionally, four days were sampled at high resolution of one sample per hour to investigate a possible diurnal cycle of atmospheric H-2. Our results indicate the influence of local sources and suggest the Banc d'Arguin as a pool for precursors for photochemical H-2 production, whereas oceanic N-2 fixation could not be identified as a source for atmospheric H-2 during these two cruises. The variability in diurnal cycles is probably influenced by released precursors for photochemical H-2 production and also affected by a varying origin of air masses. This means for future investigations that only measuring the mixing ratio of H-2 is insufficient to explain the variability of an atmospheric diurnal cycle and support is needed, e.g. by isotopic measurements. Nevertheless, measurements of atmospheric H-2 mixing ratios, which are easy to conduct online during ship cruises, could be a useful indicator of production areas of biological precursors such as volatile organic compounds (VOCs) for further investigations.
    Type: Article , PeerReviewed
    Format: text
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  • 4
    Publication Date: 2021-04-21
    Description: Oceans are a net source of molecular hydrogen (H2) to the atmosphere. The production of marine H2 is assumed to be mainly biological by N2 fixation, but photochemical pathways are also discussed. We present measurements of mole fraction and isotopic composition of dissolved and atmospheric H2 from the southern and northern Atlantic between 2008 and 2010. In total almost 400 samples were taken during five cruises along a transect between Punta Arenas (Chile) and Bremerhaven (Germany), as well as at the coast of Mauretania. The isotopic source signatures of dissolved H2 extracted from surface water are highly deuterium-depleted and correlate negatively with temperature, showing δD values of (−629 ± 54) ‰ for water temperatures at (27 ± 3) °C and (−249 ± 88) ‰ below (19 ± 1) °C. The results for warmer water masses are consistent with biological production of H2. This is the first time that marine H2 excess has been directly attributed to biological production by isotope measurements. However, the isotope values obtained in the colder water masses indicate that beside possible biological production a significant different source should be considered. The atmospheric measurements show distinct differences between both hemispheres as well as between seasons. Results from the global chemistry transport model TM5 reproduce the measured H2 mole fractions and isotopic composition well. The climatological global oceanic emissions from the GEMS database are in line with our data and previously published flux calculations. The good agreement between measurements and model results demonstrates that both the magnitude and the isotopic signature of the main components of the marine H2 cycle are in general adequately represented in current atmospheric models despite a proposed source different from biological production or a substantial underestimation of nitrogen fixation by several authors.
    Type: Article , PeerReviewed , info:eu-repo/semantics/article
    Format: text
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  • 5
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    In:  [Poster] In: SOLAS Open Science Conference, 16.-19.11.2009, Barcelona, Spain .
    Publication Date: 2014-06-23
    Type: Conference or Workshop Item , NonPeerReviewed
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  • 6
    Publication Date: 2019-08-28
    Description: Methane is a powerful greenhouse gas and its biological conversion in marine sediments, largely controlled by anaerobic oxidation of methane (AOM), is a crucial part of the global carbon cycle. However, little is known about the role of iron oxides as an oxidant for AOM. Here we provide the first field evidence for iron-dependent AOM in brackish coastal surface sediments and show that methane produced in Bothnian Sea sediments is oxidized in distinct zones of iron- and sulfate-dependent AOM. At our study site, anthropogenic eutrophication over recent decades has led to an upward migration of the sulfate/methane transition zone in the sediment. Abundant iron oxides and high dissolved ferrous iron indicate iron reduction in the methanogenic sediments below the newly established sulfate/methane transition. Laboratory incubation studies of these sediments strongly suggest that the in situ microbial community is capable of linking methane oxidation to iron oxide reduction. Eutrophication of coastal environments may therefore create geochemical conditions favorable for iron-mediated AOM and thus increase the relevance of iron-dependent methane oxidation in the future. Besides its role in mitigating methane emissions, iron-dependent AOM strongly impacts sedimentary iron cycling and related biogeochemical processes through the reduction of large quantities of iron oxides.
    Type: Article , PeerReviewed
    Format: text
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  • 7
    Publication Date: 2019-07-17
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , notRev
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  • 8
    Publication Date: 2019-07-17
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
    Format: application/pdf
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  • 9
    Publication Date: 2019-07-17
    Description: Methane and nitrous oxide are important greenhouse gases which show a strong increase in atmospheric mixing ratios since pre-industrial time as well as large variations during past climate changes. The understanding of their biogeochemical cycles can be improved using stable isotope analysis. However, high-precision isotope measurements on air trapped in ice cores are challenging because of the high susceptibility to contamination and fractionation. Here, we present a dry extraction system for combined CH4 and N2O stable isotope analysis from ice core air, using an ice grating device. The system allows simultaneous analysis of δD(CH4) or δ13C(CH4), together with δ15N(N2O), δ18O(N2O) and δ15N(NO+fragment) on a single ice core sample, using two isotope mass spectrometry systems. The optimum quantity of ice for analysis is about 600g with typical "Holocene" mixing ratios for CH4 and N2O. In this case, the reproducibility (1σ) is 2.1 ‰ for δD(CH4), 0.18 ‰ for δ13C(CH4), 0.51 ‰ for δ15N(N2O), 0.69 ‰ for δ18O(N2O) and 1.12 ‰ for δ15N(NO+fragment). For smaller amounts of ice the standard deviation increases, particularly for N2O isotopologues. For both gases, small-scale intercalibrations using air and/or ice samples have been carried out with other institutes that are currently involved in isotope measurements of ice core air. Significant differences are shown between the calibration scales, but those offsets are consistent and can be corrected for.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , notRev
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  • 10
    Publication Date: 2019-07-17
    Description: Stable carbon isotope analysis of methane (δ13C of CH4) on atmospheric samples is one key method to constrain the current and past atmospheric CH4 budget. A frequently applied measurement technique is gas chromatography (GC) isotope ratio mass spectrometry (IRMS) coupled to a combustion-preconcentration unit. This report shows that the atmospheric trace gas krypton (Kr) can severely interfere during the mass spectrometric measurement, leading to significant biases in δ13C of CH4, if krypton is not sufficiently separated during the analysis. According to our experiments, the krypton interference is likely composed of two individual effects, with the lateral tailing of the doubly charged 86Kr peak affecting the neighbouring m/z 44 and partially the m/z 45 Faraday cups. Additionally, a broad signal affecting m/z 45 and especially m/z 46 is assumed to result from scattered ions of singly charged krypton. The introduced bias in the measured isotope ratios is dependent on the chromatographic separation, the krypton-to-CH4 mixing ratio in the sample, the focusing of the mass spectrometer as well as the detector configuration and can amount to up to several per mil in δ13C. Apart from technical solutions to avoid this interference, we present correction routines to a posteriori remove the bias.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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