Institutt for geovitenskap: Recent submissions
Now showing items 681-700 of 1035
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Character of seismic motion at a location of a gas hydrate-bearing mud volcano on the SW Barents Sea margin
(Journal article; Tidsskriftartikkel; Peer reviewed, 2014-07-09)The Håkon Mosby mud volcano (HMMV) at 1270 m water depth on the SW Barents Sea slope has been intensively studied since its discovery in 1989. A variety of sensors monitored morphological, hydrological, geochemical, and biological parameters in the HMMV area. An ocean bottom seismometer deployment allowed us to register seismic motion for 2 years, from October 2008 to October 2010. The analysis of ... -
Sediment transport on the Palos Verdes shelf, California
(Journal article; Tidsskriftartikkel; Peer reviewed, 2010-02-01)Sediment transport and the potential for erosion or deposition have been investigated on the Palos Verdes (PV) and San Pedro shelves in southern California to help assess the fate of an effluent-affected deposit contaminated with DDT and PCBs. Bottom boundary layer measurements at two 60-m sites in spring 2004 were used to set model parameters and evaluate a one-dimensional (vertical) model of local, ... -
Experimental investigation of the brittle-viscous transition in mafic rocks – Interplay between fracturing, reaction, and viscous deformation
(Journal article; Tidsskriftartikkel; Peer reviewed, 2017-11-03)Rock deformation experiments are performed on fault gouge fabricated from ‘Maryland Diabase’ rock powder to investigate the transition from dominant brittle to dominant viscous behaviour. At the imposed strain rates of γ = 3 • 10⁻⁵ − 3 • 10⁻⁶ s-1 the transition is observed in the temperature range of (600 °C < T < 800 °C) at confining pressures of (0.5 GPa ≤ Pc ≤ 1.5 GPa). The transition thereby ... -
The influence of Coriolis force driven water circulation on the palaeoenvironment of Hornsund (S Spitsbergen) over the last century
(Journal article; Tidsskriftartikkel; Peer reviewed, 2017-04-22)The influence of the Coriolis force on the Hornsund fjord environment (southern Spitsbergen) was investigated in the marine sedimentary record from the last century. Due to the influence of the rotational effects, Atlantic and Arctic Water enter the fjord along the southern shore and exit along the northern shore. Thus, the sedimentary record from the southern part reflects the large‐scale hydrological ... -
Abiotic methane from ultraslow-spreading ridges can charge Arctic gas hydrates
(Journal article; Tidsskriftartikkel; Peer reviewed, 2015-05)Biotic gas generation from the degradation of organic carbon in marine sediments supplies and maintains gas hydrates throughout the world’s oceans. In nascent, ultraslow-spreading ocean basins, methane generation can also be abiotic, occurring during the high-temperature (>200 °C) serpentinization of ultramafic rocks. Here, we report on the evolution of a growing Arctic gas- and gas hydrate–charged ... -
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 ...