Fakultet for naturvitenskap og teknologi: Recent submissions
Now showing items 3681-3700 of 5442
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An integrated view of the methane system in the pockmarks at Vestnesa Ridge, 79°N
(Journal article; Tidsskriftartikkel; Peer reviewed, 2017-07-08)The Vestnesa Ridge is a NW-SE trending, ~ 100 km-long, 1–2 km-thick contourite sediment section located in the Arctic Ocean, west of Svalbard, at 79°N. Pockmarks align along the ridge summit at water depths of ~ 1200 m; they are ~ 700 m in diameter and ~ 10 m deep relative to the surrounding seafloor. Observations of methane seepage in this area have been reported since 2008. Here we summarize and ... -
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 ... -
Peer Observations of Observation Units
(Master thesis; Mastergradsoppgave, 2018-06-01)The Arctic Tundra in the far northern hemisphere is one of ecosystems that are most affected by the climate changes in the world today. Five Fram Center institutions developed a long-term research project called Climate-ecological Observatory for Arctic Tundra (COAT). Their goal is to create robust observation systems which enable documentation and understanding of climate change impacts on the ... -
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 ... -
On a class of integrable systems of Monge-Ampère type
(Journal article; Tidsskriftartikkel; Peer reviewed, 2017-06-08)We investigate a class of multi-dimensional two-component systems of Monge-Ampère type that can be viewed as generalisations of heavenly type equations appearing in a self-dual Ricci-flat geometry. Based on the Jordan-Kronecker theory of the skew-symmetric matrix pencils, a classification of normal forms of such systems is obtained. All two-component systems of Monge-Ampère type turn out to be ... -
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 ... -
On the theory of the incoherent scatter gyrolines
(Journal article; Tidsskriftartikkel; Peer reviewed, 2017-07-20)The incoherent scatter spectrum feature referred to as the “gyroline” is investigated theoretically and experimentally. The gyroline is associated with the dispersion relation for electrostatic whistler waves. Earlier treatments by Trulsen and Bj⊘rna (1978, and references therein) derive the frequency and growth rate for these waves, but their derivation is only accurate for very small magnetic ... -
Penalising Model Component Complexity: A Principled, Practical Approach to Constructing Priors
(Journal article; Tidsskriftartikkel; Peer reviewed, 2017-04-06)In this paper, we introduce a new concept for constructing prior distributions. We exploit the natural nested structure inherent to many model components, which defines the model component to be a flexible extension of a base model. Proper priors are defined to penalise the complexity induced by deviating from the simpler base model and are formulated after the input of a user-defined scaling parameter ... -
GNSS Observations of Ionospheric Variations During the 21 August 2017 Solar Eclipse
(Journal article; Tidsskriftartikkel; Peer reviewed, 2017-11-20)On 21 August 2017, during daytime hours, a total solar eclipse with a narrow ∼160 km wide umbral shadow occurred across the continental United States. Totality was observed from the Oregon coast at ∼9:15 local standard time (LST) (17:20 UT) to the South Carolina coast at ∼13:27 LST (18:47 UT). A dense network of Global Navigation Satellite Systems (GNSS) receivers was utilized to produce total ... -
The metagenomic data life-cycle: standards and best practices
(Journal article; Tidsskriftartikkel; Peer reviewed, 2017-08-01)Metagenomics data analyses from independent studies can only be compared if the analysis workflows are described in a harmonized way. In this overview, we have mapped the landscape of data standards available for the description of essential steps in metagenomics: (i) material sampling, (ii) material sequencing, (iii) data analysis, and (iv) data archiving and publishing. Taking examples from marine ... -
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) -
Determination of the Edge of Criticality in Echo State Networks Through Fisher Information Maximization
(Journal article; Tidsskriftartikkel; Peer reviewed, 2017-03)It is a widely accepted fact that the computational capability of recurrent neural networks (RNNs) is maximized on the so-called “edge of criticality.” Once the network operates in this configuration, it performs efficiently on a specific application both in terms of: 1) low prediction error and 2) high shortterm memory capacity. Since the behavior of recurrent networks is strongly influenced by the ...