Fakultet for naturvitenskap og teknologi: Nye registreringer
Viser treff 3541-3560 av 5440
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Variations in gas and water pulses at an Arctic seep: fluid sources and methane transport
(Journal article; Tidsskriftartikkel; Peer reviewed, 2018-04-19)Methane fluxes into the oceans are largely dependent on the methane phase as it migrates upward through the sediments. Here we document decoupled methane transport by gaseous and aqueous phases in Storfjordrenna (offshore Svalbard) and propose a three‐stage evolution model for active seepage in the region where gas hydrates are present in the shallow subsurface. In a preactive seepage stage, solute ... -
Linking the modern distribution of biogenic proxies in High Arctic Greenland shelf sediments to sea ice, primary production and Arctic-Atlantic inflow
(Journal article; Tidsskriftartikkel; Peer reviewed, 2018-01-09)The eastern north coast of Greenland is considered to be highly sensitive to the ongoing Arctic warming, but there is a general lack of data on modern conditions and in particular on the modern distribution of climate and environmental proxies to provide a baseline and context for studies on past variability. Here we present a detailed investigation of 11 biogenic proxies preserved in surface sediments ... -
In Situ Temperature Measurements at the Svalbard Continental Margin: Implications for Gas Hydrate Dynamics
(Journal article; Tidsskriftartikkel; Peer reviewed, 2018-03-30)During expedition MARIA S. MERIAN MSM57/2 to the Svalbard margin offshore Prins Karls Forland, the seafloor drill rig MARUM‐MeBo70 was used to assess the landward termination of the gas hydrate system in water depths between 340 and 446 m. The study region shows abundant seafloor gas vents, clustered at a water depth of ∼400 m. The sedimentary environment within the upper 100 m below seafloor (mbsf) ... -
A Full-Stokes 3-D Calving Model Applied to a Large Greenlandic Glacier
(Journal article; Tidsskriftartikkel; Peer reviewed, 2018-01-30)Iceberg calving accounts for around half of all mass loss from both the Greenland and Antarctic ice sheets. The diverse nature of calving and its complex links to both internal dynamics and climate make it challenging to incorporate into models of glaciers and ice sheets. Here we present results from a new open‐source 3‐D full‐Stokes calving model developed in Elmer/Ice. The calving model implements ... -
Light and photosynthetic microalgae: A review of cellular- and molecular-scale optical processes
(Journal article; Tidsskriftartikkel; Peer reviewed, 2018-09-08)Light and its interaction with microalgae are essential concerns in the context of microalgae studies. The optical properties of microalgae have a great impact on the remote sensing ocean color, underwater light distribution and biomass accumulation, to mention some areas. A deep understanding of these processes requires knowledge on both the physical light interaction mechanisms with algae, and ... -
Comets as a possible source of nanodust in the Solar System cloud and in planetary debris discs
(Journal article; Tidsskriftartikkel; Peer reviewed, 2017-05-29)Comets, comet-like objects and their fragments are the most plausible source for the dust in both the inner heliosphere and planetary debris discs around other stars. The smallest size of dust particles in debris discs is not known and recent observational results suggest that the size distribution of the dust extends down to sizes of a few nanometres or a few tens of nanometres. In the Solar System, ... -
Role of tectonic stress in seepage evolution along the gas hydrate‐charged Vestnesa Ridge, Fram Strait
(Journal article; Tidsskriftartikkel; Peer reviewed, 2015-01-13)Methane expulsion from the world ocean floor is a broadly observed phenomenon known to be episodic. Yet the processes that modulate seepage remain elusive. In the Arctic offshore west Svalbard, for instance, seepage at 200–400 m water depth may be explained by ocean temperature‐controlled gas hydrate instabilities at the shelf break, but additional processes are required to explain seepage in ... -
Challenges and Strategic Research Plans for Earth and Heliosphere: Research Infrastructures, Projects and Initiatives
(Journal article; Tidsskriftartikkel; Peer reviewed, 2018-07-24)We describe existing research infrastructures relevant for space weather and open issues of space weather research including the need for sustainable observation networks and for high-quality data products as basis for model development. The local relevance in Europe for studies of the ionosphere at high latitude is described. We propose as possible a way forward to sustain space weather research ... -
The configuration, sensitivity and rapid retreat of the Late Weichselian Icelandic ice sheet
(Journal article; Tidsskriftartikkel; Peer reviewed, 2017-02-03)The fragmentary glacial-geological record across the Icelandic continental shelf has hampered reconstruction of the volume, extent and chronology of the Late Weichselian ice sheet particularly in key offshore zones. Marine geophysical data collected over the last two decades reveal that the ice sheet likely attained a continental shelf-break position in all sectors during the Last Glacial Maximum, ... -
A Theoretical Model of Drumlin Formation Based on Observations at Múlajökull, Iceland
(Journal article; Tidsskriftartikkel; Peer reviewed, 2017-11-20)The drumlin field at the surge‐type glacier, Múlajökull, provides an unusual opportunity to build a model of drumlin formation based on field observations in a modern drumlin‐forming environment. These observations indicate that surges deposit till layers that drape the glacier forefield, conform to drumlin surfaces, and are deposited in shear. Observations also indicate that erosion helps create ... -
Deep kernelized autoencoders
(Peer reviewed; Book; Bok; Bokkapittel; Chapter, 2017-05-19)In this paper we introduce the deep kernelized autoencoder, a neural network model that allows an explicit approximation of (i) the mapping from an input space to an arbitrary, user-specified kernel space and (ii) the back-projection from such a kernel space to input space. The proposed method is based on traditional autoencoders and is trained through a new unsupervised loss function. ... -
Range-Doppler Mapping of Space-Based Targets Using the JRO 50 MHz Radar
(Journal article; Tidsskriftartikkel; Peer reviewed, 2017-12-02)The Jicamarca Radio Observatory (JRO) two-dimensional square array radar system operating at ~ 6-m wavelength was used to study the Moon and low Earth orbit satellites using the Range-Doppler inverse synthetic aperture radar technique also known as Delay-Doppler imaging. The radar data was collected on Oct 21, 2015. A circularly polarized coded pulse was transmitted from a quarter-array antenna ... -
Relationship between frequency power spectra and intermittent, large-amplitude bursts in the Alcator C-Mod scrape-off layer
(Journal article; Tidsskriftartikkel; Peer reviewed, 2017-08-21)Fluctuations in the boundary region of the Alcator C-Mod tokamak have been analyzed using gas puff imaging data from a set of Ohmically heated plasma density scan experiments. It is found that the relative fluctuation amplitudes are modest and close to normally distributed at the separatrix but become increasingly larger and skewed towards the main chamber wall. The frequency power spectra are ... -
Modeled deposition of nitrogen and sulfur in Europe estimated by 14 air quality model systems: evaluation, effects of changes in emissions and implications for habitat protection
(Journal article; Tidsskriftartikkel; Peer reviewed, 2018-07-17)<p>The evaluation and intercomparison of air quality models is key to reducing model errors and uncertainty. The projects AQMEII3 and EURODELTA-Trends, in the framework of the Task Force on Hemispheric Transport of Air Pollutants and the Task Force on Measurements and Modelling, respectively (both task forces under the UNECE Convention on the Long Range Transport of Air Pollution, LTRAP), have brought ... -
Advancing relativistic electronic structure methods for solids and in the time domain
(Doctoral thesis; Doktorgradsavhandling, 2018-08-28)Effects arising from the special theory of relativity significantly influence the electronic structure and properties of molecules and solid-state materials containing heavy elements. At the same time, the inclusion of the relativistic effects in theoretical and computational models increases their methodological complexity and the computational cost. In the solid state, additional challenges ... -
Structural glaciology of Isunguata Sermia, West Greenland
(Journal article; Tidsskriftartikkel; Peer reviewed, 2018-08-26)We present a 1:42,000 scale map of Isunguata Sermia, a land-terminating outlet glacier draining the western-sector of the Greenland Ice Sheet. Structure-from-Motion software applied to ∼3,600 aerial images collected by a fixed-wing unmanned aerial vehicle in July 2015 allowed us to produce a high resolution (0.3 m ground sampling distance (GSD)) orthomosaic and digital elevation model (DEM; 1.5 m ... -
BedMachine v3: Complete bed topography and ocean bathymetry mapping of Greenland from multi-beam echo sounding combined with mass conservation
(Journal article; Tidsskriftartikkel; Peer reviewed, 2017-09-18)Greenland's bed topography is a primary control on ice flow, grounding line migration, calving dynamics, and subglacial drainage. Moreover, fjord bathymetry regulates the penetration of warm Atlantic water (AW) that rapidly melts and undercuts Greenland's marine‐terminating glaciers. Here we present a new compilation of Greenland bed topography that assimilates seafloor bathymetry and ice thickness ... -
Robust clustering using a kNN mode seeking ensemble
(Journal article; Tidsskriftartikkel; Peer reviewed, 2017-12-02)In this paper we present a new algorithm for parameter-free clustering by mode seeking. Mode seeking, especially in the form of the mean shift algorithm, is a widely used strategy for clustering data, but at the same time prone to poor performance if the parameters are not chosen correctly. We propose to form a <i>clustering ensemble</i> consisting of repeated and bootstrapped runs of the recent kNN ... -
Enantioselective incorporation of CO2: status and potential
(Journal article; Tidsskriftartikkel; Peer reviewed, 2017-09-09)CO<sub>2</sub> is a promising and sustainable carbon feedstock for organic synthesis. New catalytic protocols for efficient incorporation of CO<sub>2</sub>into organic molecules are continuously being reported. However, little progress has been made in the enantioselective conversion of CO<sub>2</sub>to form enantioenriched molecules. In order to allow CO<sub>2</sub>to become a versatile carbon ... -
Direct measurements of meltwater runoff on the Greenland ice sheet surface
(Journal article; Tidsskriftartikkel; Peer reviewed, 2017-12-05)Meltwater runoff from the Greenland ice sheet surface influences surface mass balance (SMB), ice dynamics, and global sea level rise, but is estimated with climate models and thus difficult to validate. We present a way to measure ice surface runoff directly, from hourly in situ supraglacial river discharge measurements and simultaneous high-resolution satellite/drone remote sensing of upstream ...