975 research outputs found
Eskers formed at the beds of modern surge-type tidewater glaciers in Spitsbergen
This is the author accepted manuscript. The final version is available from the Geological Society of London via https://doi.org/doi.org/10.1144/M46.7
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3D seismic imagery of deeply buried iceberg ploughmarks in North Sea sediments
This is the author accepted manuscript. The final version is available from the Geological Society of London via https://doi.org//10.1144/M46.9
Current-modified recessional-moraine ridges on the NW Spitsbergen shelf
Terminal and recessional moraine ridges are built up on high-latitude continental shelves and in fjords during glacial maxima and still-stands punctuating deglaciation. Such ridges are often found in association with relatively shallow banks and are seldom located in major crossshelf troughs where past ice streams tend to have produced subglacial landforms streamlined in the direction of former ice flow (e.g. Dahlgren et al. 2002; Dowdeswell & Elverhøi 2002; Ottesen & Dowdeswell 2009). Many of these ridges are relatively large, at tens of metres in height above the general level of the seafloor, and have been modified little during the Holocene (e.g. Ottesen et al. 2005). The preservation of these prominent submarine glacial landforms is often linked to relatively low interglacial sedimentation rates and to the lowenergy process environment that is typical of many polar shelves after deglaciation. An exception, however, is where moraine ridges are present at relatively shallow water depths, a situation sometimes enhanced by isostatic rebound during the Holocene. In these circumstances, current and wave action can result in significant modification of moraine ridges.This is the author accepted manuscript. The final version is available from the Geological Society of London via https://doi.org/10.1144/M46.6
Avoiding Pandemic Fears in the Subway and Conquering the Platypus.
Metagenomics is increasingly used not just to show patterns of microbial diversity but also as a culture-independent method to detect individual organisms of intense clinical, epidemiological, conservation, forensic, or regulatory interest. A widely reported metagenomic study of the New York subway suggested that the pathogens Yersinia pestis and Bacillus anthracis were part of the "normal subway microbiome." In their article in mSystems, Hsu and collaborators (mSystems 1(3):e00018-16, 2016, http://dx.doi.org/10.1128/mSystems.00018-16) showed that microbial communities on transit surfaces in the Boston subway system are maintained from a metapopulation of human skin commensals and environmental generalists and that reanalysis of the New York subway data with appropriate methods did not detect the pathogens. We note that commonly used software pipelines can produce results that lack prima facie validity (e.g., reporting widespread distribution of notorious endemic species such as the platypus or the presence of pathogens) but that appropriate use of inclusion and exclusion sets can avoid this issue
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Morphology, sedimentary infill and depositional environments of the Early Quaternary North Sea Basin (56°-62°N)
The North Sea Basin has been subsiding during the Quaternary and contains hundreds of metres of fill. Seismic surveys (170 000 km2) provide new evidence on Early Quaternary sedimentation, from about 2.75 Ma to around the Brunhes-Matuyama boundary (0.78 Ma). We present an informal seismic stratigraphy for the Early Quaternary of the North Sea, and calculate sediment volumes for major units. Early Quaternary sediment thickness is > 1000 m in the northern basin and >700 m in the central basin (total about 40 000 km3). Northern North Sea basin-fill comprises several clinoform units, prograding westward over 60 000 km2. Architecture of the central basin also comprises clinoforms, building from the southeast. To the west, an acoustically layered and mounded unit (Unit Z) was deposited. Remaining accommodation space was filled with fine-grained sediments of two Central Basin units. Above these units, an Upper Regional Unconformity-equivalent (URU) records a conformable surface with flat-lying units that indicate stronger direct glacial influence than on the sediments below. On the North Sea Plateau north of 59°N, the Upper Regional Unconformity (URU) is defined by a shift from westward to eastward dipping seismic reflectors, recording a major change in sedimentation, with the Shetland Platform becoming a significant source. A model of Early Quaternary sediment delivery to the North Sea shows sources from the Scandinavian ice sheet and major European rivers. Clinoforms prograding west in the northern North Sea Basin, representing glacigenic debris flows, indicate an ice sheet on the western Scandinavian margin. In the central basin, sediments are generally fine-grained, suggesting a distal fluvial or glacifluvial origin from European rivers. Ploughmarks also demonstrate that icebergs, derived from an ice sheet to the north, drifted into the central North Sea Basin. By contrast, sediments and glacial landforms above the URU provide evidence for the later presence of a grounded ice sheet.We thank Det norske oljeselskap for financial support and permission to publish this work. We also thank Petroleum Geoservices and TGS for permission to publish seismic lines and seismic amplitude maps and Exploro AS for their support of the project.This is the final published version. It first appeared at http://www.sciencedirect.com/science/article/pii/S0264817214001342
Submarine slides from the walls of Smeerenburgfjorden, NW Svalbard
The steep slopes of glacially eroded fjord walls are potential sites for slope failure and mass wasting (Syvitski et al. 1987). Slides of
sedimentary material are relatively common, but require that sediment is present on fjord sides, often deposited from glaciers before and
during their retreat through fjord systems. This debris then fails to produce slides that run out onto fjord floors and leave scars on fjord sidewalls.This is the author accepted manuscript. The final version is available from the Geological Society of London via https://doi.org//10.1144/M46.2
Skjoldryggen terminal moraine on the mid-Norwegian shelf
Terminal moraines are relatively large ridges of diamictic glacial debris produced at the outermost margins of past glaciers and ice sheets. Their identification on land is important in mapping the maximum extent of Quaternary ice sheets (Svendsen et al. 2004). In marine environments where fast-flowing ice streams reach the shelf edge during full-glacial intervals, moraine ridges are not usually present and the seafloor is characterised by parallel-to-flow streamlined sediments (Ottesen & Dowdeswell 2009). Submarine terminal moraine ridges, by contrast, appear more typical of slower-flowing ice margins (Dahlgren et al. 2002; Dowdeswell & Elverhøi 2002).This is the author accepted manuscript. The final version is available from the Geological Society of London via https://doi.org/10.1144/M46.6
Rhombohedral crevasse-fill ridges at the marine margin of a surging Svalbard ice cap
The ice cap of Ausftonna in eastern Svalbard is the largest in the Eurasian Arctic at 8,000 km2 and has about 200 km of marine-terminating ice cliffs (Dowdeswell et al. 2008). Several of its drainage basins are of surge-type (Meier & Post 1969) and between 1936 and 1938 one of these basins, Bråsvellbreen (1,100 km2), increased its velocity rapidly and underwent an advance of about 20 km along a 30 km-wide front (Schytt 1969). Since that time the ice-cap terminus has stagnated and retreated, losing mass by a combination of surface melting, thinning and iceberg production. Retreat has revealed several distinctive and well-preserved submarine landforms (Fig. 1) linked to this recent surge activity (Solheim & Pfirman 1985; Solheim 1991).This is the author accepted manuscript. The final version is available from the Geological Society of London via https://doi.org/10.1144/M46.6
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3D seismic imagery of mega-scale glacial lineations and flow-switching by ice streams on the Norwegian continental shelf
This is the author accepted manuscript. The final version is available from the Geological Society of London via https://doi.org/doi.org/10.1144/M46.96Streamlined glacial landforms, produced by deformation of soft sediments at glacier beds (Dowdeswell et al. 2004; Ó Cofaigh et al. 2005; King et al. 2009), provide clear evidence of the direction of ice-flow at the time of their formation (e.g. Ottesen et al., 2005; Livingstone et al. 2012). Where sets of streamlined landforms are present at or close to the seafloor, swath-bathymetric imagery enables the reconstruction of multiple phases of ice-flow (e.g. Greenwood et al. 2012). In many cases, however, key morphological evidence is buried on palaeo-shelves within the Quaternary glacial sedimentary record (Fig. 1c-d), and can only be analysed by tracing these buried horizons in 3D-seismic datasets (Dowdeswell et al. 2007)
Boundedness properties of fermionic operators
The fermionic second quantization operator is shown to be
bounded by a power of the number operator given that the operator
belongs to the -th von Neumann-Schatten class, . Conversely,
number operator estimates for imply von Neumann-Schatten
conditions on . Quadratic creation and annihilation operators are treated as
well.Comment: 15 page
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