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  • 1
    Book
    Book
    Das Radionuklid Tritium im Ozean : Meßverfahren und Verteilung von Tritium im Südatlantik und im Weddellmeer = The radionuclide Tritium in the ocean (1998)
    Bremerhaven : Alfred-Wegener-Inst. für Polar- und Meeresforschung
    Details Availability
    Keywords: Hochschulschrift ; Forschungsbericht ; Atlantischer Ozean Süd ; Tritium ; Räumliche Verteilung ; Messung ; Methode ; Weddellmeer ; Tritium ; Messung ; Räumliche Verteilung ; Messung ; Methode ; Atlantischer Ozean Süd ; Tritium ; Räumliche Verteilung ; Messung ; Methode ; Weddellmeer ; Tritium ; Messung ; Räumliche Verteilung ; Messung ; Methode
    Type of Medium: Book
    Pages: VII, 200 S. , graph. Darst., Kt.
    Series Statement: Berichte zur Polarforschung 256
    URL: https://www.gbv.de/dms/tib-ub-hannover/241292921.pdf
    RVK:
    RY 20075
    Language: German
    Note: Literaturverz. S. 185 - 199 , Zugl.: Bremen, Univ., Diss., 1997, u.d.T.: Sültenfuß, Jürgen: Tritium-Untersuchungen im Südatlantik
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  • 2
    Online Resource
    Online Resource
    Isotope fractionation and mixing in methane plumes from the Logatchev hydrothermal field (2009)
    Associated volumes
    Details Availability
    In: Geochemistry, geophysics, geosystems, Hoboken, NJ : Wiley, 2000, 10(2009), 5, 1525-2027
    In: volume:10
    In: year:2009
    In: number:5
    In: extent:19
    Type of Medium: Online Resource
    Pages: 19 , graph. Darst
    ISSN: 1525-2027
    URL: http://dx.doi.org/10.1029/2009GC002403^
    DOI: 10.1029/2009GC002403
    Language: English
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  • 3
    Online Resource
    Online Resource
    Flux and dispersion of gases from the Drachenschlundʺ hydrothermal vent at 8ʿ18' S, 13ʿ30' W on the Mid-Atlantic Ridge (2008)
    Associated volumes
    Details Availability
    In: Earth and planetary science letters, Amsterdam [u.a.] : Elsevier, 1966, 270(2008), 3/4, Seite 338-348, 1385-013X
    In: volume:270
    In: year:2008
    In: number:3/4
    In: pages:338-348
    Type of Medium: Online Resource
    Pages: graph. Darst.
    ISSN: 1385-013X
    DOI: 10.1016/j.epsl.2008.03.054
    Language: English
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  • 4
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    Upwelling and associated heat flux in the equatorial Atlantic inferred from helium isotope disequilibrium (2010)
    AGU (American Geophysical Union)
    In:  Journal of Geophysical Research: Oceans, 115 . C08021.
    Details
    Publication Date: 2018-04-25
    Description: Upwelling velocities w in the equatorial band are too small to be directly observed. Here, we apply a recently proposed indirect method, using the observed helium isotope (3He or 4He) disequilibria in the mixed layer. The helium data were sampled from three cruises in the eastern tropical Atlantic in September 2005 and June/July 2006. A one-dimensional two-box model was applied, where the helium air-sea gas exchange is balanced by upwelling from 3He-rich water below the mixed layer and by vertical mixing. The mixing coefficients Kv were estimated from microstructure measurements, and on two of the cruises, Kv exceeded 1 × 10−4 m2/s, making the vertical mixing term of the same order of magnitude as the gas exchange and the upwelling term. In total, helium disequilibrium was observed on 54 stations. Of the calculated upwelling velocities, 48% were smaller than 1.0 × 10−5 m/s, 19% were between 1.0 and 2.0 × 10−5 m/s, 22% were between 2.0 and 4.0 × 10−5 m/s, and on 11% of upwelling velocities exceeded this limit. The highest upwelling velocities were found in late June 2006. Meridional upwelling distribution indicated an equatorial asymmetry with higher vertical velocities between the equator and 1° to 2° south compared to north of the equator, particularly at 10°W. Associated heat flux into the mixed layer could be as high as 138 W/m2, but this depends strongly on the chosen depths where the upwelled water comes from. By combining upwelling velocities with sea surface temperature and productivity distributions, a mean monthly equatorial upwelling rate of 19 Sv was estimated for June 2006 and a biweekly mean of 24 Sv was estimated for September 2005.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1029/2009JC005772
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  • 5
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    Fluid and gas fluxes from the Logatchev hydrothermal vent area (2012)
    AGU (American Geophysical Union)
    In:  Geochemistry, Geophysics, Geosystems, 13 (7). Q07007.
    Details
    Publication Date: 2018-03-01
    Description: The Logatchev hydrothermal field at 14°45′N on the MAR is characterized by gas plumes that are enriched in methane and helium compared to the oceanic background. We investigated CH4 concentration and δ13C together with δ3He in the water column of that region. These data and turbidity measurements indicate that apart from the known vent fields, another vent site exists northeast of the vent field Logatchev 1. The distribution of methane and 3He concentrations along two sections were used in combination with current measurements from lowered acoustic Doppler current profilers (LADCP) to calculate the horizontal plume fluxes of these gases. According to these examinations 0.02 μmol s−1 of 3He and 0.21 mol s−1 of methane are transported in a plume that flows into a southward direction in the central part of the valley. Based on 3He measurements of vent fluid (22 ± 6 pM), we estimate a total vent flux in this region of about 900 L s−1 and a total flux of CH4 of 3.2 mol s−1.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1029/2012GC004158
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  • 6
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    Combined sample collection and gas extraction for the measurement of helium isotopes and neon in natural waters (2013)
    Elsevier
    In:  Deep Sea Research Part I: Oceanographic Research Papers, 76 . pp. 27-34.
    Details
    Publication Date: 2021-05-19
    Description: We present a new method to obtain samples for the measurement of helium isotopes and neon in water, to replace the classical sampling procedure using clamped-off Cu tubing containers that we have been using so far. The new method saves the gas extraction step prior to admission to the mass spectrometer, which the classical method requires. Water is drawn into evacuated glass ampoules with subsequent flame sealing. Approximately 50% headspace is left, from which admission into the mass spectrometer occurs without further treatment. Extensive testing has shown that, with due care and with small corrections applied, the samples represent the gas concentrations in the water within ±0.07% (95% confidence level; ±0.05% with special handling). Fast evacuation is achieved by pumping on a small charge of water placed in the ampoule. The new method was successfully tested at sea in comparison with Cu-tubing sampling. We found that the ampoule samples were superior in data precision and that a lower percentage of samples were lost prior to measurement. Further measurements revealed agreement between the two methods in helium, 3He and neon within ±0.1%. The new method facilitates the dealing with large sample sets and minimizes the delay between sampling and measurement. The method is applicable also for gases other than helium and neon. Highlights ► We describe a novel method to obtain water samples for the measurement of helium isotopes and neon. ► No sample treatment is required between sampling and measurement. ► The method is highly accurate, mechanically simple and well suited for oceanographic work. ► A comparison with Cu-tubing samples has shown full agreement.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1016/j.dsr.2013.02.006
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  • 7
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    Hydrothermal plumes and δ3He anomalies above the Southern Mid-Atlantic Ridge (13°-33°S) indicating previously unknown active vent sites (2018)
    In:  [Poster] In: GeoBonn 2018, 02.09.-06.09.2018, Bonn, Germany .
    Details
    Publication Date: 2019-09-23
    Description: The Mid-Atlantic Ridge south of 13° S was entirely unexplored for hydrothermal activity until recently. In 2013 the expedition MSM-25 of the German research vessel Maria S. Merian set sail to systematically survey the axial region of the Southern Mid-Atlantic Ridge between 13° and 33° S for signs of active hydrothermal venting. Our shipboard sampling gear during the expedition included a typical conductivity-temperature-depth (CTD) probe with an additional turbidity sensor mounted to carousel water sampler and miniaturized plume recorders which were attached to the cable above the CTD system. Turbidity and oxidation-reduction-potential sensors were also mounted to the GEOMAR Abyss, the autonomous underwater vehicle (AUV) operated during the cruise. We intensely surveyed and sampled the water column above 16 separate ridge segments by conducting 65 CTD stations (including single dip casts and tow-yo stations) and 11 successful AUV dives. A total of 973 water samples collected at CTD stations for noble gas analysis were filled in gas-tight glass ampoules or copper tubes and later analysed for their isotopic composition in the Bremen helium isotope lab. About 800 of the samples were successfully analysed and yield meaningful δ3He results. Thus, we achieved a unique dataset of δ3He concentrations above the Southern Mid-Atlantic Ridge which is likely unprecedented in its extent along the spreading axis and density of sampling in particular in the bottom waters filling the axial rift valley. In summary, we identified 10 discrete plumes that are characterized by anomalies either in turbidity, oxidation-reduction-potential, δ3He or most frequently a combination of these parameters. Eight of the plume anomalies were previously unknown. Most of the identified hydrothermal plumes are located above the high-relief segment centres, where the axial morphology indicated robust magmatism. This contribution will give an overview of the hydrothermal plume discoveries made during the MSM-25 expedition which certainly represent promising targets for further exploration of active venting along the Southern Mid-Atlantic Ridge.
    Type: Conference or Workshop Item , NonPeerReviewed
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  • 8
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    Rapid dispersal of a hydrothermal plume by turbulent mixing (2010)
    Elsevier
    In:  Deep Sea Research Part I: Oceanographic Research Papers, 57 (8). pp. 931-945.
    Details
    Publication Date: 2016-11-01
    Description: The water column imprint of the hydrothermal plume observed at the Nibelungen field (8 18'S 13 degrees 30'W) is highly variable in space and time. The off-axis location of the site, along the southern boundary of a non-transform ridge offset at the joint between two segments of the southern Mid-Atlantic Ridge, is characterized by complex, rugged topography, and thus favorable for the generation of internal tides, subsequent internal wave breaking, and associated vertical mixing in the water column. We have used towed transects and vertical profiles of stratification, turbidity, and direct current measurements to investigate the strength of turbulent mixing in the vicinity of the vent site and the adjacent rift valley, and its temporal and spatial variability in relation to the plume dispersal. Turbulent diffusivities K(rho) were calculated from temperature inversions via Thorpe scales. Heightened mixing (compared to open ocean values) was observed in the whole rift valley within an order of K(rho) around 10(-3) m(2) s(-1). The mixing close to the vent site was even more elevated, with an average of K(rho) = 4 x 10(-2) m(2) s(-1). The mixing, as well as the flow field, exhibited a strong tidal cycle, with strong currents and mixing at the non-buoyant plume level during ebb flow. Periods of strong mixing were associated with increased internal wave activity and frequent occurrence of turbulent overturns. Additional effects of mixing on plume dispersal include bifurcation of the particle plume, likely as a result of the interplay between the modulated mixing strength and current speed, as well as high frequency internal waves in the effluent plume layer, possibly triggered by the buoyant plume via nonlinear interaction with the elevated background turbulence or penetrative convection. (C) 2010 Elsevier Ltd. All rights reserved.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1016/j.dsr.2010.04.010
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  • 9
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    Flux and dispersion of gases from the "Drachenschlund" hydrothermal vent at 8°18' S, 13°30'W on the Mid-Atlantic Ridge (2008)
    Elsevier
    In:  Earth and Planetary Science Letters, 270 . pp. 338-348.
    Details
    Publication Date: 2017-02-09
    Description: Hydrothermal emission of mantle helium appears to be directly related to magma production rate, but other processes can generate methane and hydrogen on mid-ocean ridges. In an on-going effort to characterize these processes in the South Atlantic, the flux and distribution of these gases were investigated in the vicinity of a powerful black smoker recently discovered at 8°17.9' S, 13°30.4' W. The vent lies on the shoulder of an oblique offset in the Mid-Atlantic Ridge and discharges high concentrations of methane and hydrogen. Measurements during expeditions in 2004 and 2006 show that the ratio of CH4 to 3He in the neutrally buoyant plume is quite high, 4 × 108. The CTD stations were accompanied by velocity measurements with lowered acoustic Doppler current profilers (LADCP), and from these data we estimate the methane transport to have been 0.5 mol s− 1 in a WSW-trending plume that seems to develop during the ebb tidal phase. This transport is an order of magnitude greater than the source of CH4 calculated from its concentration in the vent fluid and the rise height of the plume. From this range of methane fluxes, the source of 3He is estimated to be between 0.14 and 1.2 nmol s− 1. In either case, the 3He source is significantly lower than expected from the spreading rate of the Mid-Atlantic Ridge. From the inventory of methane in the rift valley adjacent to the vent, it appears that the average specific rate of oxidation is 2.6 to 23 yr− 1, corresponding to a turnover time between 140 and 16 days. Vertical profiles of methane in the surrounding region often exhibited Gaussian-like distributions, and the variances appear to increase with distance from the vent. Using a Gaussian plume model, we obtained a range of vertical eddy diffusivities between 0.009 and 0.08 m2m2 s− 1. These high values may be due to tidally driven internal waves across the promontory on which the vent is located.
    Type: Article , PeerReviewed
    Format: text
    Format: video
    Format: text
    Format: text
    Format: text
    DOI: 10.1016/j.epsl.2008.03.054
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  • 10
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    Methane and methane carbon isotopes in the Northeast Atlantic including the Mid-Atlantic Ridge (50°N) (2005)
    Elsevier
    In:  Deep Sea Research Part I: Oceanographic Research Papers, 52 (6). pp. 1043-1070.
    Details
    Publication Date: 2019-09-23
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1016/j.dsr.2004.12.006
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