Now showing items 386-405 of 715

    • Methane at Svalbard and over the European Arctic Ocean 

      Platt, Stephen Matthew; Eckhardt, Sabine; Ferré, Benedicte; Fisher, Rebecca E.; Hermansen, Ove; Jansson, Pär; Lowry, David; Nisbet, Euan G.; Pisso, Ignacio; Schmidbauer, Norbert; Silyakova, Anna; Stohl, Andreas; Svendby, Tove Marit; Vadakkepuliyambatta, Sunil; Mienert, Jurgen; Myhre, Cathrine Lund (Journal article; Tidsskriftartikkel; Peer reviewed, 2018-12-05)
      Methane (CH<sub>4</sub>) is a powerful greenhouse gas. Its atmospheric mixing ratios have been increasing since 2005. Therefore, quantification of CH<sub>4</sub> sources is essential for effective climate change mitigation. Here we report observations of the CH<sub>4</sub> mixing ratios measured at the Zeppelin Observatory (Svalbard) in the Arctic and aboard the research vessel (RV) Helmer Hanssen ...
    • Methane cold seeps as biological oases in the high-Arctic deep sea 

      Åström, Emmelie; Carroll, Michael Leslie; Ambrose, William; Sen, Arunima; Silyakova, Anna; Carroll, JoLynn (Journal article; Tidsskriftartikkel; Peer reviewed, 2017-10-27)
      Cold seeps can support unique faunal communities via chemosynthetic interactions fueled by seabed emissions of hydrocarbons. Additionally, cold seeps can enhance habitat complexity at the deep seafloor through the accretion of methane derived authigenic carbonates (MDAC). We examined infaunal and megafaunal community structure at high-Arctic cold seeps through analyses of benthic samples and ...
    • Methane hydrate formation in Ulleung basin under conditions of variable salinity: reduced model and experiments 

      Peszynska, Malgorzata; Hong, Wei-Li; Torres, Marta E.; Kim, Ji-Hoon (Journal article; Tidsskriftartikkel; Peer reviewed, 2016-06-13)
      In this paper, we present a reduced model of methane hydrate formation in variable salinity conditions, with details on the equilibrium phase behavior adapted to a case study from Ulleung Basin. The model simplifies the comprehensive model considered by Liu and Flemings using common assumptions on hydrostatic pressure, geothermal gradient, and phase incompressibility, as well as a simplified ...
    • Methane release from open leads and new ice following an Arctic winter storm event 

      Silyakova, Anna; Nomura, Daiki; Kotovitch, Marie; Fransson, Agneta; Delille, Bruno; Chierici, Melissa; Granskog, Mats A. (Journal article; Tidsskriftartikkel; Peer reviewed, 2022-08-03)
      We examine an Arctic winter storm event, which led to ice break–up, the formation of open leads, and the subsequent freezing of these leads. The methane (CH<sub>4</sub>) concentration in under–ice surface water before and during the storm event was 8–12 nmol L<sup>−1</sup>, which resulted in a potential sea–to–air CH<sub>4</sub> flux ranging from +0.2 to +2.1 mg CH<sub>4</sub> m<sup>−2</sup> ...
    • Methane release from pingo-like features across the South Kara Sea shelf, an area of thawing offshore permafrost 

      Serov, Pavel; Portnov, Aleksei D; Mienert, Jurgen; Semenov, Peter; Ilatovskaya, Polonia (Journal article; Tidsskriftartikkel; Peer reviewed, 2015-07-16)
      The Holocene marine transgression starting at ~19 ka flooded the Arctic shelves driving extensive thawing of terrestrial permafrost. It thereby promoted methanogenesis within sediments, the dissociation of gas hydrates, and the release of formerly trapped gas, with the accumulation in pressure of released methane eventually triggering blowouts through weakened zones in the overlying and thinned ...
    • Methane seepage at Vestnesa Ridge (NW Svalbard) since the Last Glacial Maximum 

      Schneider, Andrea; Panieri, Giuliana; Lepland, Aivo; Consolaro, Chiara; Crémière, Antoine; Forwick, Matthias; Johnson, J.E.; Plaza-Faverola, Andreia; Sauer, Simone; Knies, Jochen (Journal article; Tidsskriftartikkel; Peer reviewed, 2018-06-21)
      <p>Multiple proxies in the geological record offshore NW Svalbard track shallow subseafloor diagenesis and seafloor methane seepage during the Last Glacial Maximum (LGM) extent and the disintegration of the Svalbard Barents Sea Ice Sheet (SBIS). Vestnesa Ridge, located at 79°N and in 1200 m water depth, is one of the northernmost known active methane seep sites and is characterised by a subseafloor ...
    • Methane transport and sources in an Arctic deep-water cold seep offshore NW Svalbard (Vestnesa Ridge, 79°N) 

      Sauer, Simone; Hong, Wei-Li; Yao, Haoyi; Lepland, Aivo; Klug, Martin; Eichinger, Florian; Himmler, Tobias; Cremiere, Antoine; Panieri, Giuliana; Schubert, Carsten J.; Knies, Jochen (Journal article; Tidsskriftartikkel; Peer reviewed, 2020-10-29)
      We investigate the uppermost 60 cm of sediment in active pockmarks of a deep-water methane seep site from Vestnesa Ridge offshore NW Svalbard. Using video guided core sampling with a remotely operated vehicle we collected push cores directly from bacterial mats within two active pockmarks, Lunde and Lomvi. Pore water analyses show very shallow sulphate methane transition zones and transport-reaction ...
    • Methane- and dissolved organic carbon-fueled microbial loop supports a tropical subterranean estuary ecosystem 

      Brankovits, D.; Pohlman, J.W.; Niemann, Helge; Leigh, M.B.; Leewis, M.C.; Becker, K.W.; Iliffe, F.A.; Lehmann, M.F.; Phillips, B. (Journal article; Tidsskriftartikkel; Peer reviewed, 2017-11-28)
      Subterranean estuaries extend inland into density-stratified coastal carbonate aquifers containing a surprising diversity of endemic animals (mostly crustaceans) within a highly oligotrophic habitat. How complex ecosystems (termed anchialine) thrive in this globally distributed, cryptic environment is poorly understood. Here, we demonstrate that a microbial loop shuttles methane and dissolved organic ...
    • Methane-fuelled biofilms predominantly composed of methanotrophic ANME-1 in Arctic gas hydrate-related sediments 

      Gründger, Friederike; Carrier, Vincent; Svenning, Mette Marianne; Panieri, Giuliana; Vonnahme, Tobias R.; Klasek, Scott; Niemann, Helge (Journal article; Tidsskriftartikkel; Peer reviewed, 2019-07-05)
      Sedimentary biofilms comprising microbial communities mediating the anaerobic oxidation of methane are rare. Here, we describe two biofilm communities discovered in sediment cores recovered from Arctic cold seep sites (gas hydrate pingos) in the north-western Barents Sea, characterized by steady methane fluxes. We found macroscopically visible biofilms in pockets in the sediment matrix at the depth ...
    • Methods for Predicting the Likelihood of Safe Fieldwork Conditions in Harsh Environments 

      Leidman, Sasha Z.; Rennermalm, Åsa K.; Broccoli, Anthony J.; van As, Dirk; van den Broeke, Michiel R.; Steffen, Konrad; Hubbard, Alun Lloyd (Journal article; Tidsskriftartikkel; Peer reviewed, 2020-07-30)
      Every year, numerous field teams travel to remote field locations on the Greenland ice sheet to carry out polar research, geologic exploration, and other commercial, military, strategic, and recreational activities. In this region, extreme weather can lead to decreased productivity, equipment failure, increased stress, unexpected logistical challenges, and, in the worst cases, a risk of physical ...
    • Microbial activity, methane production, and carbon storage in Early Holocene North Sea peats 

      Lippmann, Tanya J. R.; 't Zandt, Michiel H. in; Van der Putten, Nathalie N. L.; Busschers, Freek S.; Hijma, Marc P.; van der Velden, Pieter; de Groot, Tim; van Aalderen, Zicarlo; Meisel, Ove H.; Slomp, Caroline P.; Niemann, Helge; Jetten, Mike S. M.; Dolman, Han A. J.; Welte, Cornelia U. (Journal article; Tidsskriftartikkel; Peer reviewed, 2021-10-11)
      <p>Northern latitude peatlands act as important carbon sources and sinks, but little is known about the greenhouse gas (GHG) budgets of peatlands that were submerged beneath the North Sea during the last glacial–interglacial transition. <p>We found that whilst peat formation was diachronous, commencing between 13 680 and 8360 calibrated years before the present, stratigraphic layering and local ...
    • Microbial communities from Arctic marine sedimentsrespond slowly to methane addition duringex situenrichments 

      Klasek, Scott; Torres, Martha; Bartlett, Douglas H.; Tyler, Madeline; Hong, Wei-Li; Colwell, Frederick (Journal article; Tidsskriftartikkel; Peer reviewed, 2019-12-15)
      Anaerobic methanotrophic archaea (ANME) consume methane in marine sediments, limiting its release to the water column, but their responses to changes in methane and sulfate supplies remain poorly constrained. To address how methane exposure may affect microbial communities and methane‐ and sulfur‐cycling gene abundances in Arctic marine sediments, we collected sediments from offshore Svalbard that ...
    • Microbial methane formation in deep aquifers of a coal-bearing sedimentary basin, Germany 

      Gründger, Friederike; Jimenez, N.; Thielemann, T.; Straaten, N.; Lüders, T.; Richnow, H. H.; Krüger, M. (Journal article; Tidsskriftartikkel; Peer reviewed, 2015-03-20)
      Coal-bearing sediments are major reservoirs of organic matter potentially available for methanogenic subsurface microbial communities. In this study the specific microbial community inside lignite-bearing sedimentary basin in Germany and its contribution to methanogenic hydrocarbon degradation processes was investigated. The stable isotope signature of methane measured in groundwater and coal-rich ...
    • Microphone recording of flexural waves for estimation of lake ice thickness 

      Romeyn, Rowan Peter; Hanssen, Alfred (Journal article; Tidsskriftartikkel; Peer reviewed, 2023-04-20)
      In this study we took an intentionally low-tech approach, aiming to estimate key physical parameters of lake ice using a single, inexpensive microphone. We consider this approach highly relevant to the issue of transport safety and the relatively high number of accidents involving breakthrough failure of thin ice underlines the importance of this topic. We conducted a range of experiments on three ...
    • Microseismicity linked to gas migration and leakage on the western Svalbard shelf 

      Franek, Peter; Plaza-Faverola, Andreia; Mienert, Jurgen; Bünz, Stefan; Ferré, Benedicte; Hubbard, Alun Lloyd (Journal article; Tidsskriftartikkel; Peer reviewed, 2017-12-26)
      The continental margin off Prins Karls Forland, western Svalbard, is characterized by widespread natural gas seepage into the water column at and upslope of the gas hydrate stability zone. We deployed an ocean bottom seismometer integrated into the MASOX (Monitoring Arctic Seafloor-Ocean Exchange) automated seabed observatory at the pinch-out of this zone at 389 m water depth to investigate passive ...
    • Microstructure and fluid flow in the vicinity of basin bounding faults in rifts – The Dombjerg Fault, NE Greenland rift system 

      Salomon, Eric; Rotevatn, Atle; Kristensen, Thomas Berg; Grundvåg, Sten-Andreas; Henstra, Gijs Allard (Journal article; Tidsskriftartikkel; Peer reviewed, 2021-10-14)
      Faults commonly form loci for high fluid flux in sedimentary basins, where fluids, rocks and deformation processes frequently interact. Here, we elucidate the interaction of fluid flow, diagenesis and deformation near basin-bounding faults in sedimentary basins through a study in the vicinity (0–3.5 km) of the Dombjerg Fault in the NE Greenland rift system. Due to fault-controlled fluid circulation, ...
    • Middle to Late Devonian–Carboniferous collapse basins on the Finnmark Platform and in the southwesternmost Nordkapp basin, SW Barents Sea 

      Koehl, Jean-Baptiste; Bergh, Steffen G; Henningsen, Tormod; Faleide, Jan Inge (Journal article; Tidsskriftartikkel; Peer reviewed, 2018-03-28)
      The SW Barents Sea margin experienced a pulse of extensional deformation in the Middle–Late Devonian through the Carboniferous, after the Caledonian Orogeny terminated. These events marked the initial stages of formation of major offshore basins such as the Hammerfest and Nordkapp basins. We mapped and analyzed three major fault complexes, (i) the Måsøy Fault Complex, (ii) the Rolvsøya fault, and ...
    • Middle to late Holocene paleoproductivity reconstructions for the western Barents Sea: a model-data comparison 

      Pathirana, Irene Dorothea; Knies, Jochen; Felix, Maarten; Mann, U.; Ellingsen, Ingrid H. (Journal article; Tidsskriftartikkel; Peer reviewed, 2015-11-30)
      In this study we focus on late Holocene primary productivity (PP) variability in the western Barents Sea and its response to variable sea ice coverage by combining PP reconstructed from several sediment cores with regional PP trends simulated with a well-constrained organic facies model, OF-Mod 3D. We find that modern production rates reconstructed from buried marine organic matter ...
    • Millennial-scale oscillations and an environmental regime shift around the Middle to Late Holocene transition in the North Atlantic region based on a multiproxy record from Isfjorden, West Spitsbergen 

      Brice, Camile; de Vernal, Anne; Francus, Pierre; Forwick, Matthias; Nam, Seung-II (Journal article; Tidsskriftartikkel; Peer reviewed, 2022-10-04)
      Palynological and sedimentological analyses were performed on the sediment core HH16-1205-GC retrieved from the central Isfjorden, West Spitsbergen. The sequence, which spans the last 7000 years, revealed an overall cooling trend with an important climate shift between 4.4 and 3.8 cal. ka BP, in addition to millennial-scale oscillations. Sea-surface reconstruction from dinocyst assemblages indicates ...
    • Millennial‐scale changes in bottom water temperature and water mass exchange through the Fram Strait 79ºN, 63–13 ka 

      El Bani Altuna, Naima; Ezat, Mohamed; Greaves, M.; Rasmussen, Tine Lander (Journal article; Tidsskriftartikkel; Peer reviewed, 2020-12-31)
      The Svalbard margin, in the eastern Fram Strait with its high sediment accumulation, form a key area for the reconstruction of water mass and heat exchange between the North Atlantic and Arctic Ocean in relation to abrupt climate changes as seen in glacial Greenland Interstadial and Greenland Stadial (GI‐GS) events. Here, we present a bottom water temperature (BWT) record from the northern Nordic ...