The electrical conductivity of the mantle beneath Europe derived from C-responses from 3 to 720 hr   总被引：6，自引：0，他引：6  

Nils Olsen 《Geophysical Journal International》1998,133(2):298-308

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Causes of low-frequency ground motion amplification in the Salt Lake Basin: the case of the vertically incident P wave     

Kim B. Olsen  Gerard T. Schuster 《Geophysical Journal International》1995,122(3):1045-1061

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Rapid and rhythmic ice sheet fluctuations in western Scandinavia 15-40 Kya–a review     

Lars Olsen  Harald Sveian  Klaas van der  Borg  Bjørn Bergstram  Maarten Broekmans 《Polar research》2002,21(2):235-242

The onshore record of Middle to Late Weichselian sediments and glacial history in Norway indicates a succession of four major ice advances alternating with rapid, considerable ice recessions and interstadial conditions. During all the glacial advances the ice sheet expanded from onshore/inland positions to the shelf areas. The basis for visualizing these variations in glaciation curves constructed along nine transects from inland to shelf, and for interpretation of the palaeoclimatic history, is the regional Quaternary stratigraphy, more than 300 datings, fossil content and some palaeomagnetic data. The methods applied in recent years for AMS radiocarbon dating of glacial sediments with low organic carbon content have given promising results with respect to accuracy and precision, and the results of such datings were an important tool for our reconstructions and for timing of the ice oscillations. The rapid and rhythmic ice fluctuations, as reconstructed in our new model, have been fairly synchronous in most parts of Norway. Ice advances commenced and culminated at 40, 30-28, 24-21 and 18-15 (¹⁴C) Kya. We describe three intervening interstadials from inland sites: Hattfjelldal I, Hattfjelldal II and Trofors. Our stratigraphical record also includes many indications of high, pre-Holocene, relative sea levels, suggesting a considerable glacioisostatic depression of western Scandinavia during the interstadials. In our glaciation model we suggest that, in addition to precipitation, the mountainous fjord and valley topography, glacial isostasy and relative sea level changes were probably more important for the size of the glacial fluctuations than were air temperature changes.  相似文献   

Characterizing Non-Industrial Private Forest Landowners' Forest Management Engagement and Advice Sources     

Morgan A. Crowley  Joel Hartter  Russell G. Congalton  Lawrence C. Hamilton  Nils D. Christoffersen 《社会与自然资源》2019,32(2):204-221

Non-industrial private forestland (NIPF) owners have options for engagement by following management strategies that reduce wildfire risk on their forestlands. Forest management engagement is a broad term with underlying categories and management implications. To better understand these categories, we examine interview data on the engagement of forest landowners from a case study of private forestland owner perspectives in northeast Oregon, USA. NIPF landowners outline two types of forest management engagement, one for property and one for community-focused forestland management. NIPF owners describe actions for engagement in public forestland management and how these actions differ from engagement in private management. Additionally, NIPF owners establish barriers to engagement in both public and private forestland management. Our findings can be used to better identify unengaged private forestland owners in the U.S. West, informing the design and implementation of extension and outreach for NIPF owners.  相似文献   

Influence of reversing currents on the erosion stability and bed degradation of widely graded grain material   总被引：1，自引：1，他引：0  

Alexander Schendel  Nils Goseberg  Torsten Schlurmann 《国际泥沙研究》2018,33(1):68-83

Physical model tests were done in a recirculating flume to investigate the overall erosion stability of widely graded bed material in estuarine and coastal conditions by means of simulating tidal flow conditions with reversing currents. As a result of the reversing flow conditions, previously protected sediment eventually became exposed again, leading to bidirectional displacement processes depending on the flow direction. Furthermore, eroded sediment fractions were slightly finer due to flow in the initially applied direction rather than under the subsequently applied flow in the reverse direction. This indicates higher critical shear stresses, and, thus, erosion stability for the initial flow direction. In comparison to the erosional pattern found when subjecting the material to unidirectional currents, this study finds an even higher erosional stability for sediment fractions smaller than the median (d₅₀) diameter of the parent bed material under reversing current conditions. Overall, no significant damage or failure of the bed was observed after subjecting the material to reversing currents, indicating only a small amount of bed degradation, and, thus, high potential for scour and bed protection under the tested flow conditions.  相似文献   

Geomorphic controls on floodplain sediment and soil organic carbon storage in a Scottish mountain river     

Ward Swinnen  Teun Daniëls  Eline Maurer  Nils Broothaerts  Gert Verstraeten 《地球表面变化过程与地形》2020,45(1):207-223

River floodplains constitute an important element in the terrestrial sediment and organic carbon cycle and store variable amounts of carbon and sediment depending on a complex interplay of internal and external driving forces. Quantifying the storage in floodplains is crucial to understand their role in the sediment and carbon cascades. Unfortunately, quantitative data on floodplain storage are limited, especially at larger spatial scales. Rivers in the Scottish Highlands can provide a special case to study alluvial sediment and carbon dynamics because of the dominance of peatlands throughout the landscape, but the alluvial history of the region remains poorly understood. In this study, the floodplain sediment and soil organic carbon storage is quantified for the mountainous headwaters of the River Dee in eastern Scotland (663 km²), based on a coring dataset of 78 floodplain cross-sections. Whereas the mineral sediment storage is dominated by wandering gravel-bed river sections, most of the soil organic carbon storage can be found in anastomosing and meandering sections. The total storage for the Upper Dee catchment can be estimated at 5.2 Mt or 2306.5 Mg ha^-1 of mineral sediment and 0.7 Mt or 323.3 Mg C ha^-1 of soil organic carbon, which is in line with other studies on temperate river systems. Statistical analysis indicates that the storage is mostly related to the floodplain slope and the geomorphic floodplain type, which incorporates the characteristic stream power, channel morphology and the deposit type. Mapping of the geomorphic floodplain type using a simple classification scheme shows to be a powerful tool in studying the total storage and local variability of mineral sediment and soil organic carbon in floodplains. © 2019 John Wiley & Sons, Ltd.  相似文献   

Holocene sedimentary and environmental development of Aarhus Bay,Denmark – a multi-proxy study     

Peter Rasmussen  George Pantopoulos  Jørn B. Jensen  Jesper Olsen  Hans Røy  Ole Bennike 《Boreas: An International Journal of Quaternary Research》2020,49(1):108-128

Holocene sedimentation patterns and environmental development in Aarhus Bay, Denmark, were reconstructed based on proxy analyses of two sediment cores (M1 and M5). Together, the two cores offer an opportunity to examine the history of the area during the past c. 10 000 years. The investigation consisted of acoustic mapping and multi-proxy analyses of the sediment cores including macrofossils, sediment physical properties, sediment accumulation rates, grain size, and X-ray fluorescence elemental counts. Radiocarbon dating of the two sediment successions revealed that they cover the periods c. 10 000–3700 cal. a BP (M1) and c. 4400 cal. a BP to the present (M5). The data from the M1 site indicate the presence of a near-shore lake environment between c. 10 000 and 9000 cal. a BP. The first intrusion of marine water into the area is dated to c. 9000 cal. a BP. In the following c. 1300 years, brackish-water conditions prevailed in the area characterized by a mixture of taxa from marine, limnic and terrestrial habitats, reflecting a shallow estuarine environment. Around 7700 cal. a BP full marine conditions were established, accompanied by a marked increase in sedimentation rates. The changes to full marine conditions and higher sedimentation rates are probably due to a significant sea-level rise leading to flooding of former land areas and intensified erosion. A subsequent distinct decrease in sedimentation rates around 6350 cal. a BP is presumably linked to a previously documented sea-level drop about this time. Continuous sedimentation ceased around 3700 cal. a BP in the central part of the bay, most probably due to a major sea-level lowering involving widespread erosion. In the eastern and deeper part of the bay, sedimentation continued until today. Fully marine conditions prevailed there for at least the last 4400 years.  相似文献   

CFD modeling of plume and free surface behavior resulting from a sub-sea gas release     

Schalk Cloete  Jan Erik Olsen  Paal Skjetne 《Applied Ocean Research》2009,31(3):220-225

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Cellular energy allocation in the Arctic sea ice amphipod Gammarus wilkitzkii exposed to the water soluble fractions of oil     

Olsen GH  Carroll J  Sva E  Camus L 《Marine environmental research》2008,66(1):213-214

Increasing offshore oil and gas activities in the European Arctic has raised concerns of the potential anthropogenic impact of oil-related compounds on the polar marine ecosystem. We measured cellular energy allocation (CEA) in the sea ice amphipod Gammarus wilkitzkii after exposure for one month to the water soluble fraction (WSF) of oil. The CEA biomarker measures the energy budget of organisms by biochemically assessing changes in carbohydrates, protein and lipid content as well as the electron transport system activity. A significantly higher protein content was observed in the medium dose compared to controls, while the total energy budget was not affected in G. wilkitzkii. This indicates that parts of the energy budget of G. wilkitzkii, which is a key species in the Arctic ecosystem, is affected by a WSF of oil.  相似文献   

VUGS IN ORDINARY CHONDRITES     

Edward Olsen 《Meteoritics & planetary science》1981,16(1):45-59

Large vugs occur in the ordinary chondrite, Farmington. They contain the same phases present in the body of the meteorite, either as vug wall lining or as crystals attached to linings. The morphologies of these phases indicate a history of melting and vapor deposition. These vugs are compared with vugs in the ordinary chondrites, Orvinio and Tadjera, and with published reports of vugs in Rose City and Shaw. It is concluded that although shock events may not cause heating above the liquidus for the body of the meteorite, local pockets of melting and vapor formation do occur due to inhomogenieties in the shock wave pattern. Vugs represent such pockets. Vug formation, as a consequence of shock processing, is widespread among ordinary chondrites and shows no correlation with the average temperature of shock heating, subsequent average cooling rate (as indicated by metallurgical criteria), or blackening of body color.  相似文献