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Prof. Dr. Gregor Rehder - Publications

Published

 

  • H. Niemann, P Linke, K. Knittel, E. MacPherson, A. Boetius A, W. Brückmann, G. Larvik, K. Wallmann, U. Schacht, E. Omoregie, D. Hilton, K. Brown, and G. Rehder. Methane-Carbon Flow into the Benthic Food Web at Cold Seeps – A Case Study from the Costa Rica Subduction Zone. PLoS ONE 8, e74894, doi:10.1371/journal.pone.0074894, (2013).

  • J. Schneider von Deimling, W. Weinrebe, Z. Tóth, H. Fossing, R. Endler, G. Rehder, and V. Spieß. A low frequency multibeam assessment: Spatial mapping of shallow gas by enhanced penetration and angular response anomaly. Marine and Petroleum Geology 44, 217-222, doi.org/10.1016/j.marpetgeo.2013.02.013 (2013).

  • W. Gülzow, G. Rehder, J. Schneider von Deimling, T.Seifert, and Z. Tóth. One year of continuous measurements constraining methane emissions from the Baltic Sea to the atmosphere using a ship of opportunity. Biogeosciences 10, 81-99, doi:10.5194/bg-10-81-2013, (2013).

  • O. Schmale, M. Blumenberg, K. Kießlich, G.Jakobs, C. Berndmeyer, M. Labrenz, V. Thiel, and G. Rehder. Aerobic methanotrophy within the pelagic redox-zone of the Gotland Deep (central Baltic Sea). Biogeosciences 9, 4969-4977, doi:10.5194/bg-9-4969-2012 (2012).

  • K.Yanagawa, Y. Morono, D. de Beer, M. Haeckel, M. Sunamura, T. Futagami, T. Hoshino, T. Terada, K.-i. Nakamura, T. Urabe, G. Rehder, A. Boetius and F. Inagaki. Metabolically active microbial communities in marine sediment under high-CO2 and low-pH extremes. ISME Journal, doi:10.1038/ismej.2012.124 (2012).

  • S. Mau, G. Rehder, H. Sahling, T. Schleicher, and P. Linke. Seepage of methane at Jaco Scar, a slide caused by seamount subduction offshore Costa Rica. Int. J. Earth Sci.8, doi: 10.1007/s00531-012-0822-z (2012).

  • G. Rehder, R. Eckl, M. Elfgen, A. Falenty, R. Hamann, N. Kähler, W.F. Kuhs, H. Osterkamp, and C. Windmeier. Methane hydrate pellet transport unsing the self-preservation effect: a techno-economic analysis. Energies 5: 2499-2523 (2012).

  • O.Schmale, M. Walter, J. Schneider von Deimling, J. Sültenfuß, S. Walker, G. Rehder, and R. Keir. Fluid and gas fluxes from the Logatchev hydorthermal vent area. Geochem. Geophys., Geosys. 13: Q07007, doi: 10.1029/2012GC004158 (2012).
  • A. Löffler, B. Schneider, M. Perttilä, and G. Rehder, Air-sea exchange in the Gulf of Bothnia, Baltic Sea, Continental Shelf Research, 37, 46-56, (2012).

  • P. Holtermann, L. Umlauf, T. Tanhua, O. Schmale, G. Rehder, and J. J. Waniek. The Baltic Sea Tracer Release Experiment. Part I: Mixing rates, J. Geophys. Res., doi:10.1029/2011JC007439, in press (2011).

  • S.B. Joye, I. Leifer, I.R. MacDonald, J.P. Chanton, C.D. Meile, A.P. Teske, J.E. Kostka, L. Chistoserdova, R. Coffin, D. Hollander, M. Kastner, J.P. Montoya, G. Rehder, E.Solomon, T. Treude, and T.A. Villareal. Comment on "A persistent oxygen anomaly reveals the fate of spilled methane in the deep Gulf of Mexico". Science, 332, 10.1126/science.1203307, (2011).

  • J. Schneider von Deimling, G. Rehder, D.F. McGinnnis, J. Greinert, and P. Linke.  Quantification of seep-related methane gas emissions at Tommeliten, North Sea. Continental Shelf  Research, 31, 867-878, (2011).

  • A. Falenty, W.F. Kuhs, M. Glockzin, and G. Rehder: P-T dependent degree of “Self-preservation” of CH4 and NG-Hydrates in the context of offshore gas transport (extended abstract). Proceedings of the 7th International Conference on Gas Hydrates (ICGH 2011), Edinburgh, Scotland, July 17-21, (2011).

  • W. Gülzow, G. Rehder, B. Schneider, J. Schneider v. Deimling, and B. Sadkowiak. A new method for continuous measurement of methane and carbon dioxide in surface waters using off-axis integrated cavity output spectroscopy (ICOS): An example from the Baltic Sea. Limnology Oceanography Methods, 9, 168-174, (2011).

  • A. Falenty, W.F. Kuhs, M. Glockzin, and G. Rehder. “Self-preservation” of CH4 clathrates in the context for offshore gas transport, Proceedings from the 12th International Conference on Physics and Chemistry of Ice, Hokkaido University Press 189-196, (2011).

  • P. Holtermann, L. Umlauf, T. Tanhua, O. Schmale, G. Rehder, and J. J. Waniek. The Baltic Sea Tracer Release Experiment. Part I: Mixing rates, J. Geophys. Res., doi:10.1029/2011JC007439, in press (2011).
  • S.B. Joye, I. Leifer, I.R. MacDonald, J.P. Chanton, C.D. Meile, A.P. Teske, J.E. Kostka, L. Chistoserdova, R. Coffin, D. Hollander, M. Kastner, J.P. Montoya, G. Rehder, E. Solomon, T. Treude, and T.A. Villareal. Comment on "A persistent oxygen anomaly reveals the fate of spilled methane in the deep Gulf of Mexico". Science, 332, 10.1126/science.1203307, (2011).
  • J. Schneider von Deimling, G. Rehder, D.F. McGinnnis, J. Greinert, and P. Linke.  Quantification of seep-related methane gas emissions at Tommeliten, North Sea. Continental Shelf  Research, 31, 867-878, (2011).
  • A. Falenty, W.F. Kuhs, M. Glockzin, and G. Rehder: P-T dependent degree of “Self-preservation” of CH4 and NG-Hydrates in the context of offshore gas transport (extended abstract). Proceedings of the 7th International Conference on Gas Hydrates (ICGH 2011), Edinburgh, Scotland, July 17-21, (2011).
  • W. Gülzow, G. Rehder, B. Schneider, J. Schneider v. Deimling, and B. Sadkowiak. A new method for continuous measurement of methane and carbon dioxide in surface waters using off-axis integrated cavity output spectroscopy (ICOS): An example from the Baltic Sea. Limnology Oceanography Methods, 9, 168-174, (2011).
  • A. Falenty, W.F. Kuhs, M. Glockzin, and G. Rehder. “Self-preservation” of CH4 clathrates in the context for offshore gas transport, Proceedings from the 12th International Conference on Physics and Chemistry of Ice, Hokkaido University Press 189-196, (2011).
  • N. Bigalke, L.I. Enstad, G. Rehder, and G. Alendal, Terminal velocities of pure and hydratecoated
    CO2 droplets and methane bubbles rising in a simulated oceanic environment -
    Deep Sea Research I, doi.: 10.1016/j.dsr.2010.05.008 (2010).
  • O.Schmale, J. Schneider von Deimling, W. Gülzow, G. Nausch, J.J. Waniek, and G. Rehder,
    Distribution of methane in the water column of the Baltic Sea - Geophysical Research
    Letters 37, L12604,doi.:10.1029/2010GL043115 (2010).
  • O. Schmale, S. E. Beaubien, G. Rehder, J. Greinert, and S. Lombardi: Gas seepage in the
    Dnepr-delta area (NW-Black Sea) and its regional impact on the water column
    methane cycle – Journal of Marine Systems, 80, 90-100 (2010).
  • N. Bigalke, G.Rehder, and G. Gust, Methane hydrate dissolution rates in undersaturated
    seawater under controlled hydrodynamic forcing - Marine Chemistry, 115, 226-234
    (2009).
  • G. Rehder, I. Leifer, P.G. Brewer, G. Friederich, and E.T. Peltzer: Physicochemical and hydrodynamic controls on methane bubble dissolution inside and outside the hydrate stability field – Mar. Chem. Submitted
    [Für den Abstract bitte hier klicken]
    The release of methane from the seafloor into the water column within the hydrate stability field (HSF) is a natural and widely observed process. The subsequent bubble dissolution rate determines how far upwards gas is transported and the vertical distribution of this methane source to the water column. Understanding this process is essential to describing natural deep sea seeps, to assess the hazard potential from blowouts in offshore drilling activities for gas and oil, and to refine past and future scenarios of global change involving large-scale destabilization of gas hydrates and free methane gas. We report on in situ experiments on single methane and argon bubbles within and above the HSF for depths from 400 to 1500 m. Single bubbles were injected from the ROV Ventana into an attached, back-illuminated, flow-through imaging box. The ascent of individual bubbles within the imaging box was recorded and analyzed for rise velocity, VB, and radius shrinkage rate, dr/dt. For all bubbles VB=~30 cms−1. Methane bubbles released within the HSF had markedly enhanced lifetimes, attributed to hydrate skin formation. dr/dt varied from −7.5 μm s−1 above the HSF to –1 μm s−1 at 1500 m, well within the HSF. Bubble longevity within the HSF increased with distance into the P/T-space from the hydrate phase boundary. There was a delay prior to the slower dissolution, where dr/dt for methane bubbles was comparable to dr/dt above the HSF, which was interpreted as a time delay before the onset of hydrate skin formation. Although variable, the onset time generally decreased with distance from the hydrate phase boundary. No delay was observed for the deepest releases. We relate these findings to formal calculations of methane solubility and density as a function of pressure. Pressure-dependent deviations from ideal gas law and Henry's law were implemented in a numerical bubble-propagation model which incorporated the effects of decreased solubility and surface mobility after hydrate formation. Inclusion of these effects greatly improved model prediction of observed methane bubble behavior within the HSF. The effect of these individual depth-related effects on bubble dissolution rate and longevity thenwas assessed quantitatively, and assumptions of different gas solubility prior and after hydrate nucleation or an effect of hydrates at the interface on the hydrodynamics at the surface were tested. Here, our approach implements our current knowledge on physicochemical and ydrodynamic control and does not seek the best fit for the given data sets, thus it also reveals current uncertainties in methane bubble processes in the HSF.

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  • L. Umlauf, T. Tanhua, J. Waniek, O.Schmale, P. Holtermann, and G. Rehder, Hunting a New Oceanic Tracer, EOS Trans AGU, 89, 419-420, 2008
    [Für den Abstract bitte hier klicken]
    A useful method to obtain integrated estimates of vertical mixing in the ocean over a long period of time and a large area is the release of a tracer. Recent large-scale tracer release experiments conducted in the Southern Ocean, such as the Diapycnal and Isopycnal Mixing Experiment (DIMES [see Gille et al., 2007]), and in the equatorial Atlantic will rely on a new tracer chemical called trifluoromethyl sulfur pentafluoride (SF5CF3), which is likely to become a standard for future experiments. Here we report results from the first injection of pure SF5CF3 into the ocean, which was carried out in a deep basin of the Baltic Sea. Using the Baltic Sea as a natural laboratory for the investigation of physical mixing processes, this pilot study aims at improving our understanding of one of the most puzzling mixing properties in stratified ocean basins: Almost independent of the basin’s size, the basin- scale vertical mixing rates exceed the rates inferred from local turbulence measurements in the basin center by approximately 1 order of magnitude [see, e.g., Ledwell and Bratkovich, 1995].

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  • N. Bigalke, G. Rehder and G. Gust, Experimental Investigation of the Rising Behavior of CO2 Droplets in Seawater under Hydrate-Forming Conditions, Environm. Sci. & Technol., doi: 10.1021/es800228, 2008
    [Für den Abstract bitte hier klicken]
    In a laboratory-based test series, seven experiments along a simulated Pacific hydrotherm at 152°W, 40°N were carried out to measure the rise velocities of liquefied CO2 droplets under (clathrate) hydrate forming conditions. The impact of a hydrate skin on the rising behavior was investigated by comparing the results with those from outside the field of hydrate stability at matching buoyancy. A thermostatted high-pressure tank was used to establish conditions along the natural oceanic hydrotherm. Under P-/T-conditions allowing hydrate formation, the majority of the droplets quickly developed a skin of CO2 hydrate upon contact with seawater. Rise rates of these droplets support the parametrization by Chen et al. (Tellus 2003, 55B, 723-730), which is based on empirical equations developed to match momentum of hydrate covered, deformed droplets. Ourdatadonot support other parametrizations recently suggested in the literature. In the experiments from 5.7 MPa, 4.8 °C to 11.9 MPa, 2.8 °C positive and negative deviations from predicted rise rates occurred, which we propose were caused by lacking hydrate formation and reflect intact droplet surface mobility and droplet shape oscillations, respectively. This interpretation is supported by rise rates measured at P-/Tconditions outside the hydrate stability field at the same liquid CO2- seawater density difference (Δρ) matching the rise rates of the deviating data within the stability field. The results also show that droplets without a hydrate skin ascend up to 50% faster than equally buoyant droplets with a hydrate skin. This feature has a significant impact on the vertical pattern of dissolution of liquid CO2 released into the ocean. The experiments and data presented considerably reduce the uncertainty of the parametrization of CO2 droplet rise velocity, which in the past emerged partly from their scarcity and contradictions in constraints of earlier experiments.

    Möchten Sie das Paper zugeschickt bekommen, klicken sie hier oder schreiben Sie eine Nachricht an gregnullor.rehder@io-warnemuende.de
  • G. Rehder, I. Leifer, and N. Bigalke, Propagation of methane bubbles and carbon dioxide droplets through the water column under hydrate-forming conditions, Proceedings of the 6th International Conference on Gas Hydrates, 2-C6, 8pp, 2008
  • X. Han, E. Suess, Y. Huang, N. Wu, G. Bohrmann, X. Su, A. Eisenhauer, G. Rehder and Y. Fang, Jiulong methane reef: Microbial mediation of seep carbonates in the South China Sea, Marine Geology 249, 243-256, (2008).
    [Für den Abstract bitte hier klicken]
    Chemoherm carbonates, as well as numerous other types of methane seep carbonates, were discovered in 2004 along the passive margin of the northern South China Sea. Lithologically, the carbonates are micritic containing peloids, clasts and clam fragments. Some are highly brecciated with aragonite layers of varying thicknesses lining fractures and voids. Dissolution and replacement is common. Mineralogically, the carbonates are dominated by high magnesium calcites (HMC) and aragonite. Some HMCs with MgCO3 contents of between 30–38 mol%–extreme-HMC, occur in association with minor amounts of dolomite. All of the carbonates are strongly depleted in δ13C, with a range from −35.7 to −57.5‰ PDB and enriched in δ18O (+4.0 to +5.3‰ PDB). Abundant microbial rods and filaments were recognized within the carbonate matrix as well as aragonite cements, likely fossils of chemosynthetic microbes involved in carbonate formation. The microbial structures are intimately associated with mineral grains. Some carbonate mineral grains resemble microbes. The isotope characteristics, the fabrics, the microbial structure, and the mineralogies are diagnostic of carbonates derived from anaerobic oxidation of methane mediated by microbes. From the succession of HMCs, extreme-HMC, and dolomite in layered tubular carbonates, combined with the presence of microbial structure and diagenetic fabric, we suggest that extreme-HMC may eventually transform into dolomites. Our results add to the worldwide record of seep carbonates and establish for the first time the exact locations and seafloor morphology where such carbonates formed in the South China Sea. Characteristics of the complex fabric demonstrate how seep carbonates may be used as archives recording multiple fluid regimes, dissolution, and early transformation events.

    Möchten Sie das Paper zugeschickt bekommen, klicken sie hier oder schreiben Sie eine Nachricht an gregnullor.rehder@io-warnemuende.de
  • S. Mau, G. Rehder, I. G. Arroyo, J. Gossler, and E. Suess: Indications of a link between seismo-tectonics and methane release from seeps off Costa Rica, Geophys. Geochem. Geosys., Q04003, doi:10.1029/2006GC0013262, 2007.
    [Für den Abstract bitte hier klicken]
    Measurements of CH4 concentrations in the bottom water during two discrete sampling periods in subsequent years above different cold seeps at the Pacific margin off Costa Rica indicate large-scale variations of CH4 release. CH4 is emitted from mud extrusions and a slide scar at 1000–2300 m water depth. Maximum CH4 concentrations were found to be lower above all investigated sites in autumn 2003 than in autumn 2002 although seep sites are up to 300 km apart. Tidal and current changes were observed but found to apply only to individual seep sites. Increased seismic activity connected to the moment magnitude (MW) 6.4 earthquake offshore Costa Rica in June 2002 could have had an impact on all seep sites and thereby caused an increase in CH4 emission. This is supported by the largest variations of CH4 concentration found above mud extrusions located above faults likely more strongly affected by tectonic movements. Even though our data indicate a relation between seismicity and CH4 seepage, the relation is not proven, and future work is needed to comprehensively test this hypothesis.

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  • S. Mau, H. Sahling, G. Rehder, E. Soeding, D. Masson, P. Linke, and E. Suess: Estimates of methane output from mud extrusions at the erosive convergent margin off Costa Rica – Marine Geology 225,129-144 (2006)
    [Für den Abstract bitte hier klicken]
    Four mud extrusions were investigated along the erosive subduction zone off Costa Rica. Active fluid seepage from these structures is indicated by chemosynthetic communities, authigenic carbonates and methane plumes in the water column.We estimate the methane output from the individual mud extrusions using two independent approaches. The first is based on the amount of CH4 that becomes anaerobically oxidized in the sediment beneath areas covered by chemosynthetic communities, which ranges from 104 to 105 mol yr-1. The remaining portion of CH4, which is released into the ocean, has been estimated to be 102–104 mol yr-1 per mud extrusion. The second approach estimates the amount of CH4 discharging into the water column based on measurements of the nearbottom methane distribution and current velocities. This approach yields estimates between 104–105 mol yr-1. The discrepancy of the amount of CH4 emitted into the bottom water derived from the two approaches hints to methane seepage that cannot be accounted for by faunal growth, e.g. focused fluid emission through channels in sediments and fractures in carbonates. Extrapolated over the 48 mud extrusions discovered off Costa Rica, we estimate a CH4 output of 20d 106 mol yr-1 from mud extrusions along this 350 km long section of the continental margin. These estimates of methane emissions at an erosional continental margin are considerably lower than those reported from mud extrusion at accretionary and passive margins. Almost half of the continental margins are described as non-accretionary. Assuming that the moderate emission of methane at the mud extrusions off Costa Rica are typical for this kind of setting, then global estimates of methane emissions from submarine mud extrusions, which are based on data of mud extrusions located at accretionary and passive continental margins, appear to be significantly too high.

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  • G. Rehder, H. von Neuhoff, S. von Neuhoff: Expedition Tiefsee, KOSMOS Verlag, Stuttgart, 140pp, ISBN: 978-3-440-10708-9 (2006).
  • G. Alendal, P.M. Haugan, R. Ganst, K. Caldeira, E. Adams, P. Brewer, E. Peltzer, G. Rehder, T. Sato, and B. Chen: Comment on "Fate of Rising CO2 Droplets in Seawater." Environm. Sci. & Technol. 40 (11), 3653-3654 (2006).
  • P. Linke, K. Wallmann, E. Suess, C. Hensen, and G. Rehder: In situ benthic from an intermittently active mud volcano ath the Costa Rica convergent margin. – Earth  Planet. Sci. Letts. 235, 79-95 (2005).
    [Für den Abstract bitte hier klicken]
    Along the erosive convergent margin off Costa Rica a large number of mound-shaped structures exist built by mud diapirism or mud volcanism. One of these, Mound 12, an intermittently active mud volcano, currently emits large amounts of aqueous dissolved species and water. Chemosynthetic vent communities, authigenic carbonates, and methane plumes in the water column are manifestations of that activity. Benthic flux measurements were obtained by a video-guided Benthic Chamber Lander (BCL) deployed at a vent site located in the most active part of Mound 12. The lander was equipped with 4 independent chambers covering adjacent areas of the seafloor. Benthic fluxes were recorded by repeated sampling of the enclosed bottom waters while the underlying surface sediments were recovered with the lander after a deployment time of one day. One of the chambers was placed directly in the centre of an active vent marked by the occurrence of a bacterial mat while the other chambers were located at the fringe of the same vent system at a lateral distance of only 40 cm. A transport-reaction model was developed and applied to describe the concentration profiles in the pore water of the recovered surface sediments and the temporal evolution of the enclosed bottom water. Repeated model runs revealed that the best fit to the pore water and benthic chamber data is obtained with a flow velocity of 10 cm yr-1 at the centre of the vent. The flux rates to the bottom water are strongly modified by the benthic turnover (benthic filter). The methane flux from below at the bacterial mat site is as high as 1032 Amol cm-2 yr-1, out of which 588 Amol cm-2 yr-1 is oxidised in the surface sediments by microbial consortia using sulphate as terminal electron acceptor and 440 Amol cm-2 yr-1 are seeping into the overlaying bottom water. Sulphide is transported to the surface by ascending fluids (238 Amol cm-2 yr-1) and is formed within the surface sediment by the anaerobic oxidation of methane (AOM, 588 Amol cm-2 yr-1). However, sulphide is not released into the bottom water but completely oxidized by oxygen and nitrate at the sediment/water interface. The oxygen and nitrate fluxes into the sediment are high (781 and 700 Amol cm-2 yr-1, respectively) and are mainly driven by the microbial oxidation of sulphide. Benthic fluxes were much lower in the other chambers placed in the fringe of the vent system. Thus, methane and oxygen fluxes of only 28 and 89 Amol cm-2 yr-1, respectively were recorded in one of these chambers. Our study shows that the aerobic oxidation of methane is much less efficient than the anaerobic oxidation of methane so that methane which is not oxidized within the sediment by AOM is almost completely released into the bottom water. Hence, anaerobic rather than aerobic methane oxidation plays the major role in the regulation of benthic methane fluxes. Moreover, we demonstrate that methane and oxygen fluxes at cold vent sites may vary up to 3 orders of magnitude over a lateral distance of only 40 cm indicating an extreme focussing of fluid flow and methane release at the seafloor.

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  • O. Schmale, J. Greinert, and G. Rehder: Methane emission from high-intensity marine gas seeps in the Black Sea into the atmosphere – Geophys Res. Lett. 32, L07609, doi: 10.1029/2004GL021138, (2005).
    [Für den Abstract bitte hier klicken]
    Submarine high-intensity methane seeps have been surveyed in the Sorokin Trough and Paleo Dnepr Area in the Black Sea from May to June, 2003 to estimate the sea-air methane flux. The Sorokin Trough mud volcano area in around 2080 m water depth shows no direct effects on the methane concentration in the surface water and the atmosphere (average methane saturation ratios (SR) of 143%). The average sea-air methane flux can be determined as 0.2–0.57 nmol m-2 s-1, using two different sea-air gas exchange models; mean wind speed were extraordinary low throughout the cruise (1.16 m s-1). The investigations in the Paleo Dnepr Area (60 to 800 m water depth) reflects a more diverse pattern. Spots of high methane concentrations in the surface water have been recorded above a seep location in around 90 m water depth (SR up to 294%). The air-sea methane flux above this seep site (0.96– 2.32 nmol m-2 s-1) is 3 times higher than calculated for the surrounding shelf (0.32–0.77 nmol m-2 s-1) and 5 times higher than assessed for open Black Sea waters (water depth > 200 m, 0.19–0.47 nmol m-2 s-1).

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  • K. U. Heeschen, R. W. Collier, M. A. de Angelis, E. Suess, G. Rehder, P. Linke, and G. P. Klinkhammer: Methane sources, distributions, and fluxes from cold vent sites at Hydrate Ridge, Cascadia Margin – Global Biogeochem. Cycl. 19, GB2016, doi: 10.1029/2004GB002266 (2005).
    [Für den Abstract bitte hier klicken]
    To constrain the fluxes of methane (CH4) in the water column above the accretionary wedge along the Cascadia continental margin, we measured methane and its stable carbon isotope signature (δ13C-CH4). The studies focused on Hydrate Ridge (HR), where venting occurs in the presence of gas-hydrate-bearing sediments. The vent CH4 has a light δ13C-CH4 biogenic signature (-63 to -66% PDB) and forms thin zones of elevated methane concentrations several tens of meters above the ocean floor in the overlying water column. These concentrations, ranging up to 4400 nmol L-1, vary by 3 orders of magnitude over periods of only a few hours. The poleward undercurrent of the California Current system rapidly dilutes the vent methane and distributes it widely within the gas hydrate stability zone (GHSZ). Above 480 m water depth, the methane budget is dominated by isotopically heavier CH4 from the shelf and upper slope, where mixtures of various local biogenic and thermogenic methane sources were detected (-56 to -28% PDB). The distribution of dissolved methane in the working area can be represented by mixtures of methane from the two primary source regions with an isotopically heavy background component (-25 to -6%PDB). Methane oxidation rates of 0.09 to 4.1% per day are small in comparison to the timescales of advection. This highly variable physical regime precludes a simple characterization and tracing of ‘‘downcurrent’’ plumes. However, methane inventories and current measurements suggest a methane flux of approximately 3 x 104 mol h-1 for the working area (1230 km2), and this is dominated by the shallower sources. We estimate that the combined vent sites on HR produce 0.6 x 104 mol h-1, and this is primarily released in the gas phase rather than dissolved within fluid seeps. There is no evidence that significant amounts of this methane are released to the atmosphere locally.

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  • G. Rehder, P.G. Brewer, E.T. Peltzer, L. Stern, S. Kirby, B. Durham: Dissolution rates of pure methane and hydrate and carbon-dioxide hydrate in undersaturated seawater at 1000 m depth. – Geochim. Cosmochim. Acta 68 (2), 285-292 (2004).
    [Für den Abstract bitte hier klicken]
    To help constrain models involving the chemical stability and lifetime of gas clathrate hydrates exposed at the seafloor, dissolution rates of pure methane and carbon-dioxide hydrates were measured directly on the seafloor within the nominal pressure-temperature (P/T) range of the gas hydrate stability zone. Other natural boundary conditions included variable flow velocity and undersaturation of seawater with respect to the hydrate-forming species. Four cylindrical test specimens of pure, polycrystalline CH4 and CO2 hydrate were grown and fully compacted in the laboratory, then transferred by pressure vessel to the seafloor (1028 m depth), exposed to the deep ocean environment, and monitored for 27 hours using time-lapse and HDTV cameras. Video analysis showed diameter reductions at rates between 0.94 and 1.20 µm/s and between 9.0 and 10.6 • 10-2 µm/s for the CO2 and CH4 hydrates, respectively, corresponding to dissolution rates of 4.15 ± 0.5 mmol CO2/m2s and 0.37 ± 0.03 mmol CH4/m2s. The ratio of the dissolution rates fits a diffusive boundary layer model that incorporates relative gas solubilities appropriate to the field site, which implies that the kinetics of the dissolution of both hydrates is diffusion-controlled. The observed dissolution of several mm (CH4) or tens of mm (CO2) of hydrate from the sample surfaces per day has major implications for estimating the longevity of natural gas hydrate outcrops as well as for the possible roles of CO2 hydrates in marine carbon sequestration strategies.

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  • K.U. Heeschen, R. S. Keir, G. Rehder, O. Klatt, and E. Suess: Methane dynamics in the Weddell Sea determined via stable isotope ratios and CFC-11, Global Biogeochem. Cycles 18, GB2012, doi:10.1029/2003GB002151 (2004).
    [Für den Abstract bitte hier klicken]
    The physical, chemical/biological processes that control the methane dynamics in the Weddell Sea are revealed by the distributions of methane (CH4), its stable carbon isotope ratio, δ13C-CH4, and the conservative transient tracer, chlorofluorocarbon-11 (CFC-11, CCl3F). In general, a nearly linear correlation between CH4 and CFC-11 concentrations was observed. Air-sea exchange is the major source of methane to this region, and the distribution of methane is controlled mainly by mixing between surface water and methane-poor Warm Deep Water. A significant influence of methane oxidation over the predominant two end-member mixing was only found in the Weddell Sea Bottom Water (WSBW) of the deep central Weddell Basin, where the turnover time of methane appears to be about 20 years. Mixing also controls most of the δ13C-CH4 distribution, but lighter than expected carbon isotopic ratios occur in the deep WSBW of the basin. From box model simulations, it appears that this ‘‘anomaly’’ is due to methane oxidation with a low kinetic isotope fractionation of about 1.004. The surface waters in the Weddell Sea and the Antarctic Circumpolar Current showed a general methane undersaturation of 6 to 25% with respect to the atmospheric mixing ratio. From this undersaturation and model-derived air-sea exchange rates, we estimate a net uptake of CH4 of roughly -0.5 µmol m-2 d-1 during austral autumn.

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  • K.U. Heeschen, A.M. Tréhu, R.W. Collier, E. Suess, and G. Rehder: Distribution and height of methane bubble plumes on the Cascadia Margin characterized by acoustic imaging – Geophys. Res. Lett. 30 (12), 10.1029/2003GL016974 (2003).
  • P.G. Brewer, E.T. Peltzer, G. Rehder, and R. Dunk: Advances in deep-ocean CO2 sequestration experiments. In: J. Gale and Y. Kaya (eds.) Greenhouse Gas Control Technologies, Vol. II, Pergamon Press,pp. 1667 – 1670, (2003).
  • C. K. Paull, P. G. Brewer, W. Ussler III, E. T. Peltzer, G. Rehder and D. Clague: An experiment demonstrating that marine slumping is a mechanism to transfer methane from seafloor gas-hydrate deposits into the upper ocean and atmosphere: Geo-Marine Letters 22, 198-203 (2003)(DOI 10.1007/s00367-002-0113-y.
    [Für den Abstract bitte hier klicken]
    The scientific community is engaged in a lively debate over whether and how venting from the gas-hydrate reservoir and the Earth’s climate is connected. The various scenarios which have been proposed are based on the following assumptions: the inventory of methane gas-hydrate deposits is locally enormous, the stability of marine gas-hydrate deposits can easily be perturbed by temperature and pressure changes, enough methane can be released from these deposits to contribute adequate volumes of this isotopically distinct greenhouse gas to alter the composition of oceanic or atmospheric methane reservoirs, and the mechanisms exist for the transfer of methane from deeper geologic reservoirs to the ocean and/or atmosphere. However, some potential transfer mechanisms have been difficult to evaluate. Here, we consider the possibility of marine slumping as a mechanism to transfer methane carbon from gas hydrates within the seafloor into the ocean and atmosphere. Our analyses and field experiments indicate that large slumps could release volumetrically significant quantities of solid gas hydrates which would float upwards in the water column. Large pieces of gas hydrate would reach the upper layers of the ocean before decomposing, and some of the methane would be directly injected into the atmosphere.

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  • J. Greinert, G. Rehder, Y. Artemov, and P. Gimpel: Visual and hydroacoustic investigations of gas bubbles: Detection and quantification of natural and man-made methane expulsions. – Energy, Exploration & Exploitation, 21 (4),293 – 297, (2003).
  • G. Rehder, P. Brewer, E. Peltzer, and G. Friederich: Enhanced lifetime of methane bubble streams within the deep ocean. – Geophys. Res. Lett.29 (15), 10.1029/2001GL13966 (2002).
    [Für den Abstract bitte hier klicken]
    We have made direct comparisons of the dissolution and rise rates of methane and argon bubbles experimentally released in the ocean at depths from 440 to 830 m. The bubbles were injected from the ROV Ventana into a box open at the top and the bottom, and imaged by HDTV while in free motion. The vehicle was piloted upwards at the rise rate of the bubbles. Methane and argon show closely similar behavior at depths above the methane hydrate stability field. Below that boundary (~520 m) markedly enhanced methane bubble lifetimes are observed. This effect greatly increases the ease with which methane gas released at depth, either by natural or industrial events, can penetrate the shallow ocean layers.

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  • P. G. Brewer, C. Paull, E.T. Peltzer, W. Ussler, G. Rehder, and G. Friederich: Measurements of the fate of gas hydrates during transit through the ocean water column. – Geophys. Res. Lett. 29 (22), 10.1029/2002GL014727 (2002).
    [Für den Abstract bitte hier klicken]
    We report on controlled experiments to document the fate of naturally occurring methane hydrate released from the sea floor (780 m, 4.3°C) by remotely operated vehicle (ROV) disturbance. Images of buoyant sediment-coated solids rising (~0.24 m/s) from the debris cloud, soon revealed clear crystals of methane hydrate as surficial material sloughed off. Decomposition and visible degassing began close to the predicted phase boundary, yet pieces initially of ~0.10m size easily survived transit to the surface ocean. Smaller pieces dissolved or dissociated before reaching the surface ocean, yet effectively transferred gas to depths where atmospheric ventilation times are short relative to methane oxidation rates.

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  • G. Rehder, R.W. Collier, K. Heeschen, P.M. Kosro, J. Barth, and E. Suess: Enhanced marine CH4 emissions to the atmosphere off Oregon caused by coastal upwelling. – Global Biogeochem. Cycl.16 (3), 10.1029/2000GB001391 (2002).
    [Für den Abstract bitte hier klicken]
    Methane in surface waters and marine air off Oregon (44°24’N to 44°54’N; 124° 36’W to 125° 24’W) was continuously surveyed in July 1999. During a high-resolution survey after a period of steady winds from the north, CH4 concentrations were high in the northeastern region, near the shelf edge. The highest CH4 concentrations were 2.5 times higher than equilibrium with the atmospheric partial pressure. In contrast, concentrations were near equilibrium in the western part of the survey area, the Hydrate Ridge. The increase in CH4 from SW to NE correlates with a drop in sea surface temperature (SST), from 16.5°C to less than 13.5°C, towards the shelf edge. The observed SST pattern was caused by summer upwelling off Oregon. The results suggest that CH4 derived from bottom sources near the shelf/slope break and methane found in connection with shallow (100-300 m) turbidity layers is transported to the surface by coastal upwelling, which causes an enhanced net flux of CH4 to the atmosphere. Vertical profiles of the methane distribution on the shelf in October demonstrate the accumulation of methane introduced by shelf sources. Surface concentrations at these stations in October (during non-upwelling conditions) were lower than in July (during upwelling) and only slightly oversaturated with respect to the atmosphere. An ADCP survey indicates that the observed trend can not be attributed to a surface flow reversal in the area. The low salinity waters in the core of the Columbia River plume (S < 31 PSU) showed no enhanced CH4 concentrations. The trend of higher CH4 concentrations at lower temperatures existed over the whole 17-day survey, but large spatial and temporal variations existed. The presence of methane sources in regions of coastal upwelling worldwide, such as shallow seeps, gas hydrates, and intermediate nepheloid layers, suggests that the enhancement of CH4 fluxes to the atmosphere by coastal upwelling occurs on a global scale.

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  • P.G. Brewer, E.T. Peltzer, G. Friederich, and G. Rehder: Experimental determination of the fate of rising CO2 droplets in seawater. – Environ. Sci. Technol. 26, 5441-5446 (2002).
    [Für den Abstract bitte hier klicken]
    Direct oceanic disposal of fossil fuel CO2 is being considered as a possible means to moderate the growth rate of CO2 in the atmosphere. We have measured the rise rate and dissolution rate of freely released CO2 droplets in the open ocean to provide fundamental data for carbon sequestration options. A small amount of liquid CO2 was released at 800 m, at 4.4 °C, and the rising droplet stream was imaged with a HDTV camera carried on a remotely operated vehicle. The initial rise rate for 0.9-cm diameter droplets was 10 cm/s at 800 m, and the dissolution rate was 3.0 µmol cm-2 s-1. While visual contact was maintained for 1 h and over a 400 m ascent, 90% of the mass loss occurred within 30 min over a 200 m ascent above the release point. Images of droplets crossing the liquid-gasphase boundary showed formation of a gas head, pinching off of a liquid tail, and rapid gas bubble separation and dissolution.

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  • G. Winckler, W. Aeschback-Hertig, J. Holocher, R. Kipfer, I. Levin, C. Poss, G. Rehder, E. Suess, and P. Schlosser: Noble gases and radiocarbon in natural gas hydrates. - Geophys. Res. Lett.29 (10), 10.1029/2001GL014013 (2002) – (Correction printed in 29 (15, 10.1029/2002GL015735 (2002)).
    [Für den Abstract bitte hier klicken]
    In samples of pure natural gas hydrates from Hydrate Ridge, Cascadia Margin, virtually no helium and neon components are present providing evidence that the light noble gases are not incorporated into the structure of natural methane hydrates. In contrast, the hydrates contain significant amounts of argon, krypton and xenon. These gases show a distinct fractionation pattern, with the heavier ones preferentially incorporated into the gas hydrate structure. The hydrate methane is devoid of 14C indicating that there is no contribution of a recent (14C-active) organic carbon reservoir to the hydrate carbon pool. On the basis of the δ13C and δ2H signature, it appears that microbial CO2-reduction is the dominant CH4 production pathway.

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  • C. Paull, W. Ussler III, N. Maher, H.G. Greene, G. Rehder, T. Lorenson, and H. Lee: Pockmarks off Big Sur, California. – Marine Geology 181, 323-335 (2002).
  • R.S. Keir, G. Rehder, and M. Frankignoulle: Partial pressure and air-sea flux of CO2 in the Northeast Atlantic during September 1995. – Deep-Sea Res. II 48, 3179-3189 (2001).
    [Für den Abstract bitte hier klicken]
    Previous work has shown that during early summer, the partial pressure of CO2 (pCO2) in surface waters north of about 45°N in the Atlantic exhibits widespread undersaturation. In many areas this follows after a “Spring bloom” of phytoplankton, at which time nutrient concentrations and pCO2 decrease sharply from their winter surface values. As part of OMEX1, the late summer distribution of surface water pCO2 was surveyed in the northeastern Atlantic on cruises of R/V Poseidon and R/V Belgica in 1995. The pattern of the surface distribution of the sea-air pCO2 difference (ΔpCO2) measured on these ship surveys was generally in accord with that observed in this area in early to mid summer of 1981. The greatest CO2 undersaturation (-95 µatm) during our surveys was observed near the west coast of Iceland, with ΔpCO2 increasing to about -60 µatm away from the coast. In shelf waters south of Ireland, the pCO2 was relatively higher than in surface waters off of the Celtic Shelf, but these shelf waters were still undersaturated relative to the atmospheric CO2 concentration. Because of the variation of wind speed, the synoptic distribution of air-sea CO2 flux, derived from the transfer velocity and ΔpCO2, does not resemble the distribution of ΔpCO2 itself. The sharp increase in wind speed at about 53°N, 20°W during the Poseidon survey produces an order of magnitude rise in the estimated air-sea flux of CO2, to a level of about 10 to 14 mol m-2 y-1. The overall synoptic picture appears to be one of moving centers of higher air-sea fluxes that occur where storms pass over regions of surface water pCO2 undersaturation.

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  • G. Rehder and E. Suess: Methane and pCO2 in the Kuroshio and the South China during maximum summer surface temperatures. - Marine Chemistry 75, 89-108 (2001).
    [Für den Abstract bitte hier klicken]
    The methane concentration and pCO2 in surface waters and the overlying atmosphere were continuously surveyed along the pathway of the Kuroshio, from the eastern coast of Honshu to Taiwan, and in the eastern part of the East China and South China Seas in September of 1994. Off Honshu, the CH4 content was controlled by the confluence of the relatively CH4-poor waters of the Kuroshio and the Oyashio and the CH4-rich Tsugaru Warm Current, the latter carrying water into the Pacific ocean with a methane content more than twice equilibrium with the atmospheric CH4 partial pressure. Along the Kuroshio, the surface water was supersaturated with respect to the atmosphere by 10-15% and appears considerably enriched in methane relative to open Pacific surface waters at same latitudes. The northeastern part of the South China Sea, part of the deep basin of this marginal sea, showed CH4 concentrations similar to those found in open ocean waters. In contrast, highly variable oversaturations up to 700% were observed along the northwestern coast of Borneo. Off Brunei, these high CH4 contents are related to known seepage from oil-gas deposits. The pCO2 of surface water was higher than the atmospheric pCO2 throughout the area surveyed. However, the ∆pCO2 of the surface waters varied from close to 0 to more than 60 µatm. The observed oversaturation in areas influenced by the Kuroshio confirm that, during a short period in late summer, the surface waters of this current between Taiwan and Japan act as a moderate source for atmospheric CO2.

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  • G. Rehder, R.S. Keir, M. Rhein, and E. Suess: Methane in the northern Atlantic controlled by microbial oxidation and atmospheric history. - Geophys. Res. Lett. 26, 587-590 (1999).
    [Für den Abstract bitte hier klicken]
    During May - August, 1997, the distributions of dissolved methane and CCl3F (CFC11) were measured in the Atlantic between 50° and 60°N. In surface waters throughout the region, methane was observed to be close to equilibrium with the atmospheric mixing ratio, implying that surface ocean methane is tracking its atmospheric history in regions of North Atlantic Deep Water formation. Despite the different atmospheric history and ocean chemistry of CH4 and CFC11, their spatial distribution patterns in the water column are remarkably similar. One-dimensional distributions have been simulated with an advection-diffusion model forced by the atmospheric histories. The results suggest that the similar patterns result from the increasing input of CH4 and CFC11 to newly formed deep waters over time, combined with the effect of horizontal mixing and the oxidation of methane on a 50 year time scale.

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  • E. Suess, M.E. Torres, G. Bohrmann, R.W. Collier, J. Greinert, P. Linke, G. Rehder, A. Trehu, K. Wallmann, G. Winckler, and E. Zuleger: Gas hydrate destabilization: Enhanced dewatering, benthic material turnover and large methane plumes at the Cascadia convergent margin. - Earth Planet. Sci. Lett. 170, 1-15 (1999).
    [Für den Abstract bitte hier klicken]
    Mixed methane-sulfide hydrates and carbonates are exposed as a pavement at the seafloor along the crest of one of the accretionary ridges of the Cascadia convergent margin. Vent fields from which methane-charged, low-salinity fluids containing sulfide, ammonia, 4He, and isotopically light CO2 escape are associated with these exposures. They characterize a newly recognized mechanism of dewatering at convergent margins, where freshening of pore waters from hydrate destabilization at depth and free gas drive fluids upward. This process augments the convergence-generated overpressure and leads to local dewatering rates that are much higher than at other margins in the absence of hydrate. Discharge of fluids stimulates benthic oxygen consumption which is orders of magnitude higher than is normally found at comparable ocean depths. The enhanced turnover results from the oxidation of methane, hydrogen sulfide, and ammonia by vent biota. The injection of hydrate methane from the ridge generates a plume hundreds of meters high and several kilometers wide. A large fraction of the methane is oxidized within the water column and generates δ13C anomalies of the dissolved inorganic carbon pool.

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  • G. Bohrmann, C. Chin, S. Petersen, H. Sahling, U. Schwarz-Schampera, J. Greinert, S. Lammers, G. Rehder, A. Dählmann, K. Wallmann, S. Diijkstra, and H.-W. Schenke: Hydrothermal activity in the central Bransfield Basin, Antarctica: First evidence from near-bottom observation and sampling. - Geo-Marine Lett. 18, 277-284 (1999).
    [Für den Abstract bitte hier klicken]
    Hydrothermal activity in the Central Brans"eld Basin revealed an active low-temperature vent "eld on top of a submarine volcanic structure. A temperature anomaly was detected and the sea floor showed various patches of white silica (opal-A) precipitate exposures and some yellow-brown Fe-oxyhydroxide crusts. Enriched dissolved methane concentrations were encountered. Sediment was near 24°C just after the grab came on deck. No dense population of chemosynthetically based macrofauna known from other hydrothermal venting areas was present, except for pogonophora. The observations suggest that the sedimented hydrothermal "eld at Hook Ridge is a low-temperature end-member branch from a deeper hydrothermal source.

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  • G. Rehder: Sources and Sinks of Marine Methane between Shelf and Open Ocean: Regional Variability and Controlling Processes of the Methane Distribution and Air-Sea Exchange (German with abstract in English), GEOMAR REPORT 83 (1999).
  • M.E. Torres, K. Brown, R.W. Collier, M. deAngelis, D. Hammond, J. McManus, G. Rehder, A. Trehu: Tecflux-98: Geochemical observations on Hydrate Ridge, Cascadia Margin during R/V Brown - Ropos cruise, August 1998. College of Oceanic and Atmospheric Sciences, Oregon State University, Data Report 171.
  • G. Rehder, R.S.Keir, E. Suess, and T. Pohlmann: The multiple sources and patterns of methane in North Sea waters. Aquatic Geochem., 4, 403-429, (1998).
    [Für den Abstract bitte hier klicken]
    The methane concentration in the atmosphere and surface water was surveyed along 58°N across the North Sea. In addition, the vertical methane distribution in the water column was determined at six stations along the transect. The methane contents of the surface water as well as in the water column were extremely inhomogeneous. Input by freshwater from river discharge and injection of methane from the sediment were both observed. The survey continued from the western side of the North Sea to the Elbe River estuary. The Elbe River appears to have low methane concentrations compared to other European rivers, its average input into the North Sea is estimated to be 70 nmol s-1 of methane. Near 58 °N, 1° 40 ´E, an abandoned drill site releases about 25% of the North Sea´s emission of methane to the atmosphere. The advective methane transport induced by water circulation was assessed for May 16, 1994, using a 3-D North Sea circulation model. For the period of this survey, the North Sea ´s source strength for atmospheric methane is estimated using in situ wind velocities. In comparison to the advective transport by the water circulation, the gas flux to the atmosphere appears to be the dominant sink of North Sea methane. This flux is estimated to be between 1500 • 106 mol a-1 and 3100 • 106 mol a-1, depending on the relation between wind speed and gas transfer velocity.

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  • R.S. Keir, G. Rehder, E. Suess, and H. Erlenkeuser: The 13C anomaly in the northeastern Atlantic. - Global Biogeochem. Cycl., 12, 467-477 (1998).
    [Für den Abstract bitte hier klicken]
    The δ13C of dissolved inorganic carbon was measured on samples collected at 49°N in the northeast Atlantic in January 1994. Deeper than 2000 m, δ13C exhibits the same negative correlation versus dissolved phosphate that is observed elsewhere in the deep Atlantic. Upward from 2000 m to about 600 m, δ13C shifts to values more negative than expected from the correlation with nutrients at depth, which is likely due to penetration of anthropogenic CO2. From these data, the profile of the anthropogenic δ13C decrease is calculated by using either dissolved phosphate or apparent oxygen utilization as a proxy for the preanthropogenic δ13C distribution. The shape of the anthropogenic anomaly profile derived from phosphate is similar to that of the increase in dissolved inorganic carbon derived by others in the same area. The reconstruction from oxygen utilization results in a lower estimate of the anthropogenic δ13C decrease in the upper water column, and the vertical anomaly profile is less similar to that of the dissolved inorganic carbon increase. A 13C budget for the atmosphere, ocean, and terrestrial biosphere indicates that within the range of probable ocean CO2 uptake the ratio of δ13C to inorganic carbon change should be mostly influenced by the 13C inventory change of the biosphere. However, the uncertainty in the ratio we derive prevents a strong contraint on the size of the exchangeable biosphere.

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