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Valery Shuvalov Henning Dypvik Elin Kalleson Ronny Sets? Fridtjof Riis 《Earth, Moon, and Planets》2012,108(3-4):175-188
The newly discovered Ritland impact structure (2.7?km in diameter) has been modeled by numerical simulation, based on detailed field information input. The numerical model applies the SOVA multi-material hydrocode, which uses the ANEOS equation of state for granite, describing thermodynamical properties of target and projectile material. The model displays crater formation and possible ejecta distribution that strongly supports a 100?m or less water depth at the time of impact. According to the simulations resurge processes and basinal syn- and postimpact sedimentation are highly dependent on water depth; in more than 100?m of water depth, much more powerful resurge processes are generated than at water depths shallower than 100?m (the Ritland case). In Ritland the 100?m high (modeled) crater rim formed a barrier and severely reduced the resurge processes. In the case of deeper water, powerful resurge processes, tsunami wave generations and related currents could have triggered even more violent crater fill sedimentation. The presented model demonstrates the importance of understanding the interactions between water layer and both syn-impact crater fill and ejecta distribution. According to the presented simulations ejecta blocks up to 10?m in diameter could be transported up to about 5?km outside the crater rim. 相似文献
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Fridtjof Mehlum 《Polar Science》2012,6(1):143-153
The breeding performance of high-arctic bird populations shows large inter-annual variation that may be attributed to environmental variability, such as the timing of snow melt and break-up of the landfast sea ice that surrounds breeding colonies on islands and along coasts. In the Kongsfjorden area (79°N) on Svalbard, the number of breeding pairs and the average egg clutch size vary considerably among years. In this study, data on breeding performance are presented from 15 years in the period 1981–2000. The results showed that early break-up of sea ice in Kongsfjorden resulted in larger numbers of nests and larger average clutch sizes than late break-up. Also, individual islands with early break-up of sea ice in a particular year had more nests and larger clutch sizes compared to other islands surrounded by sea ice during a longer period in spring. Thus, the inter-annual variation in the break-up of sea ice in the fjord has considerable implications for the inter-annual variability of recruitment to the population. The results indicate that the effects of global warming on changes in the sea ice melting regime in coastal regions are important for the reproductive output of island-nesting eiders. 相似文献
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Geir Terje Eigestad Helge K. Dahle Bjarte Hellevang Fridtjof Riis Wenche Tjelta Johansen Erlend Øian 《Computational Geosciences》2009,13(4):435-450
The Johansen formation is a candidate site for large-scale CO2 storage offshore of the south-western coast of Norway. An overview of the geology for the Johansen formation and neighboring
geological formations is given, together with a discussion of issues for geological and geophysical modelling and integrated
fluid flow modelling. We further describe corresponding simulation models. Major issues to consider are capacity estimation
and processes that could potentially cause CO2 to leak out of the Johansen formation and into the formations above. Currently, these issues can only be investigated through
numerical simulation. We consider the effect of different boundary conditions, sensitivity with respect to vertical grid refinement
and permeability/transmisibility data, and the effect of residual gas saturations, since these strongly affect the CO2-plume distribution. The geological study of the Johansen formation is performed based on available seismic and well data.
Fluid simulations are performed using a commercial simulator capable of modelling CO2 flow and transport by simple manipulation of input files and data. We provide details for the data and the model, with a
particular focus on geology and geometry for the Johansen formation. The data set is made available for download online. 相似文献
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Ada Pastor Louis J. Skovsholt Kirsten S. Christoffersen Naicheng Wu Tenna Riis 《水文研究》2021,35(10):e14369
Climate change is causing drastic landscape changes in the Arctic, but how these changes modify stream biogeochemistry is not clear yet. We examined how catchment properties influence stream nitrogen (N) and dissolved organic carbon concentrations (DOC) in a high-Arctic environment. We sampled two contrasting headwater streams (10–15 stations over 4.8 and 6.8 km, respectively) in Northeast Greenland (74°N). We characterized the geomorphology (i.e., bedrock, solifluction and alluvial types) and the vegetation (i.e., barren, fell field, grassland and tundra types) cover of each subcatchment area draining into each sampling station and collected water samples for hydrochemistry characterization. The two sampled streams differed in geomorphology and vegetation cover in the catchment. Aucellaelv catchment was mostly covered by a ‘bedrock’ geomorphology (71%) and ‘fellfield’ vegetation (51%), whereas Kæerelv was mostly covered by ‘alluvial’ geomorphology (65%) and ‘grassland’ and ‘tundra’ vegetation (42% and 41% respectively). Hydrochemistry also differed between the two study streams, with higher concentrations of inorganic N forms in Aucellaelv and lower DOC concentrations, compared to Kærelv. The results from the linear mixed model selection showed that vegetation and geomorphology had contrasting effects on stream hydrochemistry. Subcatchments with higher solifluction sheets and limited vegetation had higher nitrate concentrations but lower DOC concentrations. Interestingly, we also found high variability on the production and removal of nitrate across subcatchments. These results indicate landscape controls to nutrient and organic matter exports via flow paths, soil organic matter stocks and nutrient retention via terrestrial vegetation. Moreover, the results suggest that climate change induced alterations to vegetation cover and soil physical disturbance in high-Arctic catchments will affect stream hydrochemistry, with potential effects in stream productivity, trophic relations as well as change of solute export to downstream coastal areas. 相似文献
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Interferences by Volatile Substances in Measuring the Biological Oxygen Consumption Using the Sapromat Aerobic microbial degradation processes can be well monitored by means of the oxygen consumption. There are special analyzers for these measurements, such as the Sapromat produced by Voith GmbH Heidenheim, Germany. Interference occurs during investigations with (or in the presence of) volatile components of low water solubility, which appear in dissolved state or as an additional phase. Thus, the Sapromat records an apparent oxygen consumption without the participation of microorganisms which is in the order of usual BOD5-values or even above them and is attributable to physico-chemical reasons and the measuring system used. The present paper points out this phenomenon and investigates the reasons. These are demonstrated and discussed. The results emphasize the urgency of blanks in order to detect abiotic effects using the Sapromat. 相似文献
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L. Rise O. Olesen K. Rokoengen D. Ottesen F. Riis 《Quaternary Science Reviews》2004,23(23-24):2323-2335
Several investigations have shown that a huge Late Weichselian ice stream flowed along the Norwegian Channel, and deposited thick debris flow deposits at the North Sea Fan. The development of the channel is probably mainly a result of several cycles of ice stream activity during the Quaternary. A merged 3D seismic image shows a lineated relief pattern interpreted as a uniquely well-preserved footprint of a moving ice sheet. This deep Quaternary horizon corresponds to a slightly irregular reflector on top of a parallel-layered seismic sequence. Seismic tie to the Troll core 8903 south of the study area shows that the sequence comprises Early Middle Pleistocene marine sediments. The pattern of lineations, the seismic stratigraphy, as well as the chronostratigraphic investigations of the Troll core, strongly indicate that the image reflects the initial phase of an extensive Middle Pleistocene glaciation (inferred age ca 0.5 Ma), prior to the development of a massive Norwegian Channel Ice Stream. The northwesterly oriented pattern, seen in the southeastern part of the study area, demonstrates that the ice flowed into the channel mainly from the coastal zone north of Bergen. Farther west various sets of ‘fan-shaped lineations’ partly cross each other, showing that the 3D-image represents a certain short time window. In the northern study area the ice flow was dominantly northwards, and directed towards the area below the present shallow Måløy Plateau. There are no indications that the glaciers north of Sognefjorden affected the marine ice sheet. 相似文献
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Elin Kalleson Henning Dypvik Fridtjof Riis Odd Nilsen 《Meteoritics & planetary science》2013,48(9):1678-1701
A melt‐bearing impactite unit is preserved in the 2.7 km diameter shallow marine Ritland impact structure. The main exposure of the melt‐bearing unit is in an approximately 100 m long cliff about 700 m southwest of the center of the structure. The melt and clast content vary through this maximum 2 m thick unit, so that lithology ranges from impact melt rock to suevite. Stratigraphic variations with respect to the melt content, texture, mineralogy, and geochemistry have been studied in the field, and by laboratory analysis, including thin section microscopy. The base of the melt‐bearing unit marks the transition from the underlying lithic basement breccia, and the unit may have been emplaced by an outward flow during the excavation stage. There is an upward development from a melt matrix‐dominated lower part, that commonly shows flow structures, to an upper part characterized by more particulate matrix with patchy melt matrix domains, commonly as deformed melt slivers intermingled with small lithic clasts. Melt and lithic fragments in the upper part display a variety of shapes and compositions, some of which possibly represent fallback material from the ejecta cloud. The upper boundary of the melt‐bearing impactite unit has been placed where the deposits are mainly clastic, probably representing slump and avalanche deposits from the modification stage. These deposits are therefore considered sedimentary and not impactites, despite the component of small melt fragments and shocked minerals within the lowermost part, which was probably incorporated as the debris moved down the steep crater walls. 相似文献
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