Remembering Tore Gjelsvik (1916–2006)     

Olav Orheim 《Polar research》2006,25(2):145-153

Tore Gjelsvik, former director of the Norwegian Polar Institute, died at the beginning of this year. He is fondly remembered by a great many people. In this piece, Olav Orheim recalls the man and his key role in Norwegian polar activities. Orheim was head of Antarctic Research at the Norwegian Polar Institute in 1972–1993 and was the institute's director from 1993 to 2005.  相似文献   

Progress in optical dating of guano-rich sediments associated with the Deep Skull, West Mouth of the Great Cave of Niah, Sarawak, Borneo     

Mark Stephens  Richard G. Roberts  Olav B. Lian  Hiroyuki Yoshida 《Quaternary Geochronology》2007,2(1-4):330-336

The West Mouth of the Great Cave of Niah is one of the major archaeological sites in Southeast Asia; the radiocarbon chronology of this site currently places the earliest presence of Homo sapiens (a Deep Skull find) in Southeast Asia at about 45 ka BP. An optical dating programme using sand-sized quartz was initiated in the West Mouth to complement the radiocarbon chronology. This paper reports on the progress in dating a key sample (sample 376r) that was taken from deposits containing the Deep Skull. A somewhat novel procedure was developed to separate and clean quartz grains from the unusual guano-rich deposits. From this, only a small quantity of quartz grains could be recovered and 36 aliquots (1 mm in diameter) were prepared, each consisting of 80 grains. This sample was dated by means of the single-aliquot regenerative-dose (SAR) method using the protocols of Murray and Wintle [2000. Luminescence dating of quartz using an improved single-aliquot regenerative-dose protocol. Radiation Measurements 32, 57–73], and of Choi et al. [2003. Luminescence dating of well-sorted marine terrace sediments on the southeastern coast of Korea. Quaternary Science Reviews 22, 407–421]. The results showed a wide distribution of equivalent doses; this distribution is inferred to be due to bioturbation, variable bleaching at deposition, and to local variations in the dose rate within the sample site. Dose rates were measured using both field (in-situ γ-ray spectrometry, IGRS) and laboratory (inductively coupled plasma mass spectrometry/atomic emission spectrometry, ICP-MS/AES; and isotope dilution, ID) methods. There was significant disagreement between the concentrations of radioisotopes found using laboratory and field measurements, indicating sediment heterogeneity and also possible disequilibrium in the ²³⁸U decay chain. Future work in the West Mouth should therefore concentrate on taking sediment samples of at least 500–600 cm³, improving the dose rate estimates (e.g. by high-resolution γ-ray spectrometry) and investigating other luminescence signals (e.g. red thermoluminescence) as potential geochronometers.  相似文献   

Notiz überDidymium nigripes (Myxomycetes) aus einer Abwasserbiozönose     

Olav M. Skulberg 《Aquatic Sciences - Research Across Boundaries》1958,20(2):210-217

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Cellular plagioclase intergrowths as a result of crystal-magma mixing in the Proterozoic Åland rapakivi batholith,SW Finland     

Ulf B. Andersson  Olav Eklund 《Contributions to Mineralogy and Petrology》1994,117(2):124-136

Finely cellular plagioclase intergrowths have been studied in xenocrystic andesine (An₃₂) and andesine mantled K-feldspars within mafic magmatic enclaves in a quartz-feldspar porphyry from the Proterozoic subvolcanic Hammarudda complex, Åland rapakivi batholith, SW Finland. The cellular intergrowths usually occur as 0.2–2.0 mm mantles around xenocrysts but also as entirely cellular grains, and are built up of a network of two distinct phases: one relatively Na-rich (An₃₁) and one relatively Ca-rich (An₅₀). The grains are also covered by a thin (0.08–0.12 mm), continuous, normally zoned rim outside the cellular mantle. Small inclusions (0.01–0.05 mm) of Fe–Mg minerals are concentrated in the Ca-rich part of the network. Compositionally, the Na-rich phase of the network is close to the inner non-cellular andesine of the xenocrysts. However, it has a lower Or- and a slightly lower An-content. The Ca-rich phase has the same composition as the inner part of the normally zoned rim, which outwards grades into lower An-contents that overlap the An-content of the matrix plagioclases. The cellular network was developed after the andesine xenocrysts (or andesine mantled K-feldspars) were engulfed in mafic magmatic enclaves during a mixing event. The xenocrysts became heated to a temperature just below the liquidus of the mafic magma. Dissolution of the xenocrysts developed a spongy cellular texture which was penetrated by enclave magma. Ca-rich plagioclase crystallized in the cells in equilibrium with the enclave magma, trapping Fe–Mg-rich melt. As the enclaves cooled the outermost thin rim and matrix plagioclases crystallized from the mafic melt. These processes operated in fairly large enclaves, as the one studied here, which has a diameter of 70cm. Smaller enclaves, on the other hand, were cooled more rapidly to temperatures close to the solidus of the enclave magma, and consequently had no time to dissolve the xenoxrysts.  相似文献   

The morphometric and stratigraphic framework for estimates of debris flow incidence in the North Cascades foothills, Washington State, USA   总被引：1，自引：0，他引：1  

Dori J. Kovanen  Olav Slaymaker 《Geomorphology》2008,99(1-4):224-245

Active debris flow fans in the North Cascade Foothills of Washington State constitute a natural hazard of importance to land managers, private property owners and personal security. In the absence of measurements of the sediment fluxes involved in debris flow events, a morphological-evolutionary systems approach, emphasizing stratigraphy, dating, fan morphology and debris flow basin morphometry, was used. Using the stratigraphic framework and 47 radiocarbon dates, frequency of occurrence and relative magnitudes of debris flow events have been estimated for three spatial scales of debris flow systems: the within-fan site scale (84 observations); the fan meso-scale (six observations) and the lumped fan, regional or macro-scale (one fan average and adjacent lake sediments). In order to characterize the morphometric framework, plots of basin area v. fan area, basin area v. fan gradient and the Melton ruggedness number v. fan gradient for the 12 debris flow basins were compared with those documented for semi-arid and paraglacial fans. Basin area to fan area ratios were generally consistent with the estimated level of debris flow activity during the Holocene as reported below. Terrain analysis of three of the most active debris flow basins revealed the variety of modes of slope failure and sediment production in the region.Micro-scale debris flow event systems indicated a range of recurrence intervals for large debris flows from 106−3645 years. The spatial variation of these rates across the fans was generally consistent with previously mapped hazard zones. At the fan meso-scale, the range of recurrence intervals for large debris flows was 273−1566 years and at the regional scale, the estimated recurrence interval of large debris flows was 874 years (with undetermined error bands) during the past 7290 years. Dated lake sediments from the adjacent Lake Whatcom gave recurrence intervals for large sediment producing events ranging from 481−557 years over the past 3900 years and clearly discernible sedimentation events in the lacustrine sediments had a recurrence interval of 67−78 years over that same period.  相似文献   

Canadian geomorphology 2000: Introduction     

John J. Clague  Olav Slaymaker   《Geomorphology》2000,32(3-4)

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Assessing socio-economic impacts of wave overtopping: An institutional perspective     

Jan Jaap Bouma  Delphine François  Albert Schram  Tom Verbeke 《Coastal Engineering》2009

One way to address the assessment of strategies to control wave overtopping at seawalls and related coastal defence structures is to make use of Cost-Benefit Analysis. The institutional context in which Cost-Benefit Analysis takes place influences decisions on the types of values that are taken into consideration and the subsequent selection of valuation methods. We suggest to consider Cost-Benefit Analysis in a broad institutional framework when decisions are to be made on coastal defence strategies. It is argued that the institutional context provides the rules of the game on how a balance can be found between social, economic and ecologic functions of projects that protect societies against overtopping.  相似文献   

Suspended sediment balance for the mainstem of Changjiang (Yangtze River) in the period 1964–1985     

Marwan A. Hassan  Michael Church  Yunxia Yan  Olav Slaymaker  Jiongxin Xu 《水文研究》2011,25(15):2339-2353

Suspended sediment dynamics during the period 1964–1985 are examined along the mainstem of Changjiang (Yangtze River). The period represents a basin condition prior to major changes in land management policy and dam building on the river's mainstem. The downstream sediment dynamics reflect basin geology and topography and channel morphology. Sediment exchange within the mainstem was calculated by the development of reach sediment balances that reveal complex temporal and spatial patterns. There is relatively little sediment exchange in the upper, bedrock‐controlled reaches, with systematic increases in the downstream alluvial reaches. Degrading, transfer, and aggrading reaches were identified. Relations between input and output in all reaches were significant but no relation was found between sediment exchange and input/output. Comparison between ‘short‐term’ (22 years) and ‘long‐term’ (52 years) records demonstrates the importance of the record length in studying the suspended sediment dynamics in a large fluvial system. The longer record yielded better correlation and different trends than the shorter record. Sediment transfer (output/input ratio) changes downstream: the dominance of the upstream contributing area in sustaining the appearance of net degradation through most of the river system highlights the importance of reach length on characterisation of suspended sediment dynamics in large fluvial systems. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

Projective ordination by SIMCA: A dynamic strategy for cost-efficient environmental monitoring around offshore installations     

Bernard G. J. Massart  Olav M. Kvalheim  Fred Olav Libnau  Karl I. Ugland  Kjell Tjessem  Karl Bryne 《Aquatic Sciences - Research Across Boundaries》1996,58(2):120-138

A method for environmental monitoring using benthic species profiles as input is developed in this work. The method, referred to as projective ordination, utilises local principal component modelling (SIMCA) to obtain a cross-validated model which spans the natural variation in a region around offshore oil-producing installations. The borderline between regions with disturbed and non-disturbed species communities is subsequently decided from the residual distribution. This distribution is used to design an approximate F-test for assessing whether a community at a particular sampling location is disturbed or not. If so, the nature of the disturbance is determined by projecting the data on the PC model.Projective ordination utilises information from previous surveys to define the permissible variation in species communities, i.e. the limit of the natural variation. In addition, the method is dynamic, in a sense that the sampling locations may vary from survey to survey.Furthermore, our analysis shows that the customary number of replicate samples per station can be reduced. Modelling with only four randomly chosen replicates out of the complete set of five for each sampling location, does not affect the model significantly. On the other hand, taking only 3 replicates into account leads to significant divergences.A model based on the 1990 and 1993 surveys at the Statfjord field is presented as an example of the technique.  相似文献   

Pre-23 magnetic anomalies between Jan Mayen and Greenland-Senja fracture zones in the Norwegian sea     

Terje Hagevang  Olav Eldholm  Inge Aalstad 《Marine Geophysical Researches》1983,5(4):345-363

Analysis of magnetic data between the Jan Mayen and Senja fracture zones indicates that the anomaly 24A-B sequence extends from the Lofoten Basin onto the outer Vøring Plateau. Anomaly patterns, including those on the conjugate margin, suggest that the pre-23 sea floor spreading was characterized by an unstable plate boundary between fracture zones. The pre-23 spreading rate was at least 2.5 cm yr^-1 which is remarkably high compared with the post-23 rates. An evolutionary model which assumes Cenozoic oceanic crust as far landward as the Vöring Plateau and Greenland escarpments is suggested.  相似文献