Effects of trawl sampling variability on precision of acoustic abundance estimates of gadoids from the Barents Sea and the Gulf of Alaska   总被引：3，自引：2，他引：1  

Godo  Olav Rune; Karp  William A.; Totland  Atle 《ICES Journal of Marine Science》1998,55(1):86-94

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A flow-foliated ignimbrite related to the Åland rapakivi granite in SW Finland     

Olav Eklund  Alexey Shebanov  Soren Fröjdö  Kari Yli-kyyny  Ulf B. Andersson 《地学学报》1996,8(6):548-557

A flow-foliated felsic ignimbrite constitutes the uppermost lithological unit of the 1.58 Gyr anorogenic magmatic rocks in SW Finland. The ignimbrite is derived from an explosive eruption of hot (≅ 950 °C) phenocryst-bearing A-type (rapakivi-type granite magma.
The ignimbrite is close in composition to subvolcanic rapakivi granites that occur in the margins of the kand rapakivi batholith. The subvolcanic granites crystallized under a pressure of ≅ 1 kbar and at temperatures of about 650–700 °C. However, both major and rare earth elements show that the ignimbrite- forming magma was more fractionated than the magma forming the subvolcanic varieties.
Supported by evidence of mafic-felsic magma mingling, it is suggested that injection of hot mafic magma into a shallow magma chamber produced the high temperature of the ignimbrite-forming magma. This injection increased the magmatic and the volatile pressure that caused the eruption of the dry felsic magma.  相似文献   

An explication of the radiometric method for size and albedo determination     

Olav L. Hansen 《Icarus》1977,31(4):456-482

A new radiometric model for disk-integrated photometry of asteroids is presented. With empirical support from photometry of Mercury and the Moon, the model assumes that observed sunward beaming of the infrared emission is due to craters. In contrast to earlier theoretical studies of the lunar emission, the observable flux ratio between a cratered sphere and a smooth sphere is calculated for large ranges in wavelength, temperature, and phase angle. Revised diameters and albedos based on the crater model are given for 84 asteroids. The revised values are in good agreement with Morrison's (1977) radiometric results. It is shown that the systematic discrepancy between radiometric and polarimetric albedos (Zellner and Gradie, 1976) is probably a double-valued function of albedo. Some typical geometric albedos from this paper, Morrison (1977), and Zellner and Gradie (1976), respectively, are: Ceres (0.050 ± 0.005, 0.053 ± 0.004, 0.068), Vesta (0.235 ± 0.032, 0235 ± 0.11, 0.271), mean C type (0.031 ± 0.009, 0.035 ± 0.009, 0.061 ± 0.005), mean S type (0.117 ± 0.030, 0.136 ± 0.032, 0.181 ± 0.23), and mean M type (0.105 ± 0.037, 0.115 ± 0.033, 0.157 ± 0.079). Areas of disagreement between radiometry and polarimetry are underscored, and research to resolve them is suggested.  相似文献   

Comparisons between macro‐ and microfabrics in a pebble‐rich,sandy till deposited by the Cordilleran Ice Sheet          下载免费PDF全文

Christina M. Neudorf  Tracy A. Brennand  Olav B. Lian 《Boreas: An International Journal of Quaternary Research》2015,44(3):483-501

It is standard practice to measure particle fabrics in glacial studies to infer palaeo‐ice flow directions and processes of till formation but few studies examine the relationships between particle fabrics at different (i.e. the macro‐ and micro‐) scales. This knowledge is critical to inform the utility of the methods and limitations of the associated interpretations. Micro‐ (sand grain) and macro‐ (pebble) fabrics of pebble‐rich, sandy subglacial till (Kamloops Lake till) deposited by the Cordilleran Ice Sheet, south‐central British Columbia, were compared to assess their similarities and differences, and therefore their utility for understanding subglacial processes. Before comparisons were made, the data were tested for robustness by assessing various controls (e.g. sampling face orientation, number of particles measured, statistical variation resulting from sampling effects, particle shape, size and concentration) on particle fabrics. A new method of microfabric analysis was applied that involves the identification and delineation of distinct clusters of similarly orientated sand grains in order to compare them with macrofabrics and inferred ice‐flow directions. The results show that microfabrics, on their own, are an unreliable indicator of ice‐flow direction in Kamloops Lake till in the study area and should not be used as a substitute for macrofabric data, as they probably record late‐stage microscale strain patterns and pore‐water flow in addition to till deposition and deformation by overriding ice. We suspect that this would also be the case for coarse‐grained till elsewhere. Our findings suggest that till microfabric interpretations should always be made after assessing corresponding macrofabric data alongside sedimentological and structural observations.  相似文献   

IMO legislation and its implementation: Accident risk,vessel deficiencies and national administrative practices     

Olav F. Knudsen  Björn Hassler 《Marine Policy》2011

The article takes as its point of departure the apparently contradictory findings in recent research about accident rates in shipping and IMO implementation records. It is argued here that although IMO conventions have probably greatly improved shipping safety, they cannot credibly be held to be the chief cause of reduced accident rates as claimed in a recent Marine Policy article, when the documented failures of flag state and port state implementation continue to leave vessels sailing with grave deficiencies. The present analysis posits and corroborates a cluster of linked tendencies that jointly undermine IMO implementation. The core problem is IMO’s weak connection to the national maritime administrations, leading to broadly discretionary practices, exacerbated by language difficulties. Adding new rules is no panacea, as new rules in some cases negatively affect the functioning of existing regulations, and sometimes seem motivated mainly to show political alertness. The structural weakness of the IMO/member state link is the core implementation problem that urgently needs to be dealt with if marine safety is to be improved. The concluding section proposes a reform to bring the IMO out of this conundrum and ensure effective implementation.  相似文献   

Cenozoic uplift of Fennoscandia inferred from a study of the mid-Norwegian margin     

Liv M. Stuevold  Olav Eldholm 《Global and Planetary Change》1996,12(1-4)

Studies of the mid-Norwegian margin reveal that the Fennoscandian continental uplift represents a flexural intraplate deformation event separated in time and space from the regional syn-rift uplift associated with crustal breakup at the Plaeocene-Eocene transition. In the area 64–68°N, the uplift occurred from late Oligocene through Pliocene. During Late Pliocene and Pleistocene times the tectonic uplift was amplified by isostatic rebound in response to the Northern Hemisphere glaciation. The tectonic uplift component reaches 1 km in the northern part of the study area decreasing to the south. The shelf stratigraphy and sediment composition record the combined effects of tectonic uplift, eustatic sea level changes and Neogene climatic deterioration. The coeval uplift and climatic change may suggest causal relations. The resulting depositional model has three stages: (1) late Miocene ( 10.5-5.5 m.y.) increased continental erosion and deposition of prograding wedges most of which were later removed; (2) early-middle Pliocene (5.5-2.6 m.y.) development of extensive local ice-sheets reaching the coastline and deposition of the prominent, oldest Pliocene wedges; (3) Northern Hemisphere glaciation (2.6-0.01 m.y.) resulting in the younger wedges farther west covered by Quaternary deposits. The model is consistent with the development of landforms on the adjacent mainland. Both the tectonic and isostatic components of the Fennoscandian uplift appear to vary in magnitude along the uplift axis, however separation of the syn-rift plate boundary related uplift and the intraplate event support the Neogene age of the main Fennoscandian uplift. We document a correspondence between structural and physiographic margin segmentation and uplift magnitude and suggest that the intraplate deformation has a thermal origin. A hot-cold asthenosphere boundary beneath the Caledonide-Baltic Shield transition combined with pre-Tertiary relief at the base of the lithosphere might induce small-scale convection and preferential volume expansion beneath the observed elongate uplift.  相似文献   

A comparison of spicules in the Hα and HeII (304 Å) lines     

Olav Kjeldseth Moe  Oddbjorn Engvold  Jacques Maurice Beckers 《Solar physics》1975,40(1):65-68

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Benthonic foraminifera as indicators of the paleoposition of the Subarctic Convergence in the Norwegian-Greenland Sea     

Hans-Petter Sejrup  Hans Holtedahl  Olav Norvik  Ivar Miljeteig 《Boreas: An International Journal of Quaternary Research》1980,9(3):203-207

A method is presented for correlating benthonic foraminiferal communities in Late Quaternary marine sediments on continental shelves and in coastal areas with the planktonic foraminiferal stratigraphy of the North Atlantic and Norwegian Sea deep-sea sediments.  相似文献   

Landslide inventory in a rugged forested watershed: a comparison between air-photo and field survey data   总被引：2，自引：0，他引：2  

Francesco Brardinoni  Olav Slaymaker  Marwan A. Hassan   《Geomorphology》2003,54(3-4):179-196

Landslide inventories are routinely compiled by means of aerial photo interpretation (API). When examining photo pairs, the forest canopy (notably in old-growth forest) hides a population of “not visible” landslides. In the present study, we attempt to estimate how important is the contribution of landslides not detectable from aerial photographs to the global mass of sediment production from mass failures on forested terrain of the Capilano basin, coastal British Columbia. API was coupled with intensive fieldwork for identification and measurement of all landslides. A 30-year framework was adopted. We show that “not visible” landslides can represent up to 85% of the total number of failures and account for 30% of the volume of debris mobilised. Such percentages display high sub-basin variability with rates of sediment production varying by one order of magnitude between two sub-basins of the study area. This is explained qualitatively by GIS-based analysis of slope frequency distributions, drainage density, and spatial distribution of surficial materials. Such observations find further support in the definitions of transport-limited and supply-limited basins. As a practical consideration to land managers, we envisage that supplementary fieldwork for landslide identification is mandatory in transport-limited systems only. Fieldwork has demonstrated that gully-related failures have a greater importance than one could expect from API.  相似文献   

Advances in Holocene mountain geomorphology inspired by sediment budget methodology     

Olav Slaymaker  Catherine Souch  Brian Menounos  Gabriel Filippelli 《Geomorphology》2003,55(1-4):305

The sediment budget, which links sediment sources to sediment sinks with hydroclimatic and weathering processes mediating the response, is applied to the analysis of sediments in three alpine lakes in British Columbia. We provide two ways of using the sediment budget as an integrating device in the interpretation of mountain geomorphology. These approaches differ in their resolution and ability to budget the major components of the fine-sediment cascade in glaciated environments. Taken together, they provide an integrated index of landscape change over the Holocene. The first example compares the hydroclimatic controls of lake sedimentation for the last 600 years (A.D. 1370–1998) preserved in varved sediments from two of the lake basins. This hydroclimatological approach incorporates contemporary monitoring, air photo analysis, and detailed stratigraphy of sedimentation events within a single varve to infer the timing, sources, and preferred pathways of fine-grained sediments reaching the lake basins. The results indicate that glaciers, hillslope, and channel instability within the major subbasins are the principal sediment sources to the lake basins. Transitory sediment storage of glacially derived sediments within the channels is believed to modulate the episodic and more frequent delivery of sediments from adjacent hillslope and fluvial storage sites and direct routing of glacial rock flour during years of prolonged glacial melt. The second example, relying on the phosphorus geochemistry of sediments in an alpine lake basin, considers the evolution of phosphorus forms (from mineral to occluded and organic fractions) as a function of the soil development, inherent slope instability, and repeated cycles of glaciation and neoglaciation over the Holocene. This geochemical approach demonstrates that both neoglaciation and full glaciation have essentially zeroed the system in such a way that a high proportion of mineral phosphorus remains in the present lake sediments and the bioavailability of phosphorus (a key to ecosystem development) is low. Both examples illustrate the importance of variable sediment sources; the seasonality, frequency, and magnitude of sediment transfers; and the profound influence of ice cover over contemporary, neoglacial and Pleistocene time scales. They also signal the value of including both clastic and dissolved components in the sediment budget.  相似文献