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norskArtikler, rapporter og annet (geovitenskap): Recent submissions
Now showing items 661-680 of 816
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Temporal constraints on hydrate-controlled methane seepage off Svalbard
(Journal article; Tidsskriftartikkel; Peer reviewed, 2014-01-17)Methane hydrate is an icelike substance that is stable at high pressure and low temperature in continental margin sediments. Since the discovery of a large number of gas flares at the landward termination of the gas hydrate stability zone off Svalbard, there has been concern that warming bottom waters have started to dissociate large amounts of gas hydrate and that the resulting methane release may ... -
Water column methanotrophy controlled by a rapid oceanographic switch
(Journal article; Tidsskriftartikkel; Peer reviewed, 2015-04-20)Large amounts of the greenhouse gas methane are released from the seabed to the water column, where it may be consumed by aerobic methanotrophic bacteria. The size and activity of methanotrophic communities, which determine the amount of methane consumed in the water column, are thought to be mainly controlled by nutrient and redox dynamics. Here, we report repeated measurements of methanotrophic ... -
Deglaciation of the central Barents Sea
(Journal article; Tidsskriftartikkel; Peer reviewed, 2014-05-15)The marine-based Barents Sea Ice Sheet covered the polar continental shelf north of Norway and western Russia during the Last Glacial Maximum. Initial ice sheet retreat along the western margin is well established, while the retreat pattern in the interior parts of the ice sheet remains poorly known. Here we present new geological data from the central Barents Sea. The results are based on analysis ... -
Palaeoceanographic and environmental changes in the eastern Fram Strait during the last 14,000 years based on benthic and planktonic foraminifera
(Journal article; Tidsskriftartikkel; Peer reviewed, 2017-11-14)Benthic and planktonic foraminifera, stable isotopes and other geochemical and sedimentological parameters have been investigated in a sediment core from Vestnesa Ridge (79°N, NW Svalbard margin, 1300 m water depth) in order to reconstruct the palaeoceanographic and palaeoenvironmental evolution of the eastern Fram Strait during the last 14,000 years. Our multiproxy data and, in particular, our ... -
Variations in pockmark composition at the Vestnesa Ridge: Insights from marine controlled source electromagnetic and seismic data
(Journal article; Tidsskriftartikkel; Peer reviewed, 2017-02-10)The Vestnesa Ridge marks the northern boundary of a known submarine gas hydrate province in the west Svalbard margin. Several seafloor pockmarks at the eastern segment of the ridge are sites of active methane venting. Until recently, seismic reflection data were the main tool for imaging beneath the ridge. Coincident controlled source electromagnetic (CSEM), high‐resolution two‐dimensional (2‐D) ... -
The onset of flysch sedimentation in the Kaoko Belt (NW Namibia) – Implications for the pre-collisional evolution of the Kaoko–Dom Feliciano–Gariep orogen
(Journal article; Tidsskriftartikkel; Peer reviewed, 2017-06-17)<p>Detrital zircon provenance study of a metamorphosed sedimentary succession in the eastern part of the Kaoko Belt in Namibia has revealed two distinct sources for the Neoproterozoic sedimentation along the southwestern Congo Craton margin. The lower part of the succession shows detrital zircon ages consistent with erosion of Paleoproterozoic basement of the Congo Craton with an inferred Mesoproterozoic ... -
Bottom-simulating reflector dynamics at Arctic thermogenic gas provinces: An example from Vestnesa Ridge, offshore west Svalbard
(Journal article; Tidsskriftartikkel; Peer reviewed, 2017-06) -
Semi-quantitative reconstruction of early to late Holocene spring and summer sea ice conditions in the northern Barents Sea
(Journal article; Tidsskriftartikkel; Peer reviewed, 2017-06-07)Semi-quantitative estimates of early to late Holocene spring sea ice concentration (SpSIC) andoccurrence of summer sea ice for the northern Barents Sea have been obtained by analysing the biomarkers IP<sub>25</sub>,brassicasterol and a tri-unsaturated highly branched isoprenoid lipid in a Holocene marine sediment core.Sub-surface water mass variations were derived from planktic foraminiferal assemblages ... -
Water redistribution in experimentally deformed natural milky quartz single crystals?Implications for H2O-weakening processes
(Journal article; Tidsskriftartikkel; Peer reviewed, 2017-01-22)Natural quartz single crystals were experimentally deformed in two orientations: (1) ⊥ to one prism plane and (2) in O+ orientation at 900 and 1000°C, 1.0 and 1.5 GPa, and strain rates of ~1 × 10−6 s−1. In addition, hydrostatic and annealing experiments were performed. The starting material was milky quartz, which consisted of dry quartz with a large number of fluid inclusions of variable size up ... -
Microseismicity linked to gas migration and leakage on the western Svalbard shelf
(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 ... -
A flexural isostasy model for the Pleistocene evolution of the Barents Sea bathymetry
(Journal article; Tidsskriftartikkel; Peer reviewed, 2017-01-24)The topographic relief of the Barents Sea was subjected to major changes during the past 1.5 million years mostly due to sediment redistribution driven by glacial activity. This paper addresses the problem of Pleistocene bathymetric evolution of the southern Barents Sea using a numerical modelling approach that considers the influence of regional isostasy on relief development. The model presented ... -
U-Th chronology and formation controls of methane-derived authigenic carbonates from the Hola trough seep area, northern Norway
(Journal article; Tidsskriftartikkel; Peer reviewed, 2017-10-20)We investigated methane-derived authigenic carbonate (MDAC) crusts and nodules from a cold seep site on the northern Norwegian continental shelf in ca. 220 m water depth to determine the timing and mode of their formation. Gas bubbling observed during remotely operated vehicle (ROV)-assisted sampling of MDAC crusts revealed ongoing seep activity. Authigenic carbonates were present as crusts on the ... -
Postglacial response of Arctic Ocean gas hydrates to climatic amelioration
(Journal article; Tidsskriftartikkel; Peer reviewed, 2017-06-05)Seafloor methane release due to the thermal dissociation of gas hydrates is pervasive across the continental margins of the Arctic Ocean. Furthermore, there is increasing awareness that shallow hydrate-related methane seeps have appeared due to enhanced warming of Arctic Ocean bottom water during the last century. Although it has been argued that a gas hydrate gun could trigger abrupt climate ... -
Ventilation history of Nordic Seas overflows during the last (de)glacial period revealed by species-specific benthic foraminiferal 14C dates
(Journal article; Tidsskriftartikkel; Peer reviewed, 2017-02-10)Formation of deep water in the high‐latitude North Atlantic is important for the global meridional ocean circulation, and its variability in the past may have played an important role in regional and global climate change. Here we study ocean circulation associated with the last (de)glacial period, using water‐column radiocarbon age reconstructions in the Faroe‐Shetland Channel, southeastern Norwegian ... -
Relationship between mega-scale glacial lineations and iceberg ploughmarks on the Bjørnøyrenna Palaeo-Ice Stream bed, Barents Sea
(Journal article; Tidsskriftartikkel, 2018-02-24)Mega-scale glacial lineations (MSGLs) are ridge-groove corrugations aligned in the direction of the former ice flow, tens of kilometers long and up to a few hundred meters wide. They are the most striking subglacial features on the beds of former ice streams and play an important role in modulating ice flow through their influence on bed roughness and subglacial hydrology. Despite the importance of ... -
Shallow methane hydrate system controls ongoing, downslope sediment transport in a low-velocity active submarine landslide complex, Hikurangi Margin, New Zealand
(Journal article; Tidsskriftartikkel; Peer reviewed, 2014-10-14) -
Thermogenic methane injection via bubble transport into the upper Arctic Ocean from the hydrate-charged Vestnesa Ridge, Svalbard
(Journal article; Tidsskriftartikkel; Peer reviewed, 2014-04-21)We use new gas‐hydrate geochemistry analyses, echosounder data, and three‐dimensional P‐Cable seismic data to study a gas‐hydrate and free‐gas system in 1200 m water depth at the Vestnesa Ridge offshore NW Svalbard. Geochemical measurements of gas from hydrates collected at the ridge revealed a thermogenic source. The presence of thermogenic gas and temperatures of ∼3.3°C result in a shallow top of ... -
Enhanced CO2 uptake at a shallow Arctic Ocean seep field overwhelms the positive warming potential of emitted methane
(Journal article; Tidsskriftartikkel; Peer reviewed, 2017-05-08)Continued warming of the Arctic Ocean in coming decades is projected to trigger the release of teragrams (1 Tg = 106 tons) of methane from thawing subsea permafrost on shallow continental shelves and dissociation of methane hydrate on upper continental slopes. On the shallow shelves (<100 m water depth), methane released from the seafloor may reach the atmosphere and potentially amplify global ... -
Geochemical characterisation of northern Norwegian fjord surface sediments: A baseline for further paleo-environmental investigations
(Journal article; Tidsskriftartikkel; Peer reviewed, 2017-08-26)Norwegian fjord sediments are promising archives for very high resolution records of past environmental changes. Recent investigations of the modern depositional environment within fjords revealed that the accurate quantification of the inputs, sources, and sedimentary preservation of organic and inorganic material is crucial to decipher long term past climate signals in the sedimentary record ... -
Identifying past petroleum exploration related drill cutting releases and influences on the marine environment and benthic foraminiferal communities, Goliat Field, SW Barents Sea, Norway
(Journal article; Tidsskriftartikkel; Peer reviewed, 2017-11-01)The present multiproxy investigation of marine sediment cores aims at: 1) Identifying dispersion of petroleum exploration related drill cutting releases within the Goliat Field, Barents Sea in 2006/07 and 2) Assessing past and present influence of drill cuttings on the marine environment. The cores were recovered 5, 30, 60, 125 and 250 m from the drill site in the eastward downstream direction.<p> ...
