Scour below pipelines and around vertical piles in random waves     

Dag Myrhaug  Hvard Rue 《Coastal Engineering》2003,48(4):227-242

An approach by which the scour depth and scour width below a fixed pipeline and scour depth around a circular vertical pile in random waves can be derived is presented. Here, the scour depth formulas by Sumer and Fredsøe [ASCE J. Waterw., Port, Coastal Ocean Eng. 116 (1990) 307] for pipelines and Sumer et al. [ASCE J. Waterw., Port, Coastal Ocean Eng. 114 (1992) 599] for vertical piles as well as the scour width formula by Sumer and Fredsøe [The Mechanics of Scour in the Marine Environment, World Scientific, Singapore, 2002] for pipelines combined with describing the waves as a stationary Gaussian narrow-band random process are used to derive the cumulative distribution functions of the scour depths and width. Comparisons are made between the present approach and random wave scour data. Tentative approaches to related random wave scour cases are also suggested.  相似文献   

Food webs and carbon flux in the Barents Sea   总被引：6，自引：3，他引：6  

Paul Wassmann  Marit Reigstad  Tore Haug  Bert Rudels  Michael L. Carroll  Haakon Hop  Geir Wing Gabrielsen  Stig Falk-Petersen  Stanislav G. Denisenko  Elena Arashkevich  Dag Slagstad  Olga Pavlova 《Progress in Oceanography》2006,71(2-4):232

Within the framework of the physical forcing, we describe and quantify the key ecosystem components and basic food web structure of the Barents Sea. Emphasis is given to the energy flow through the ecosystem from an end-to-end perspective, i.e. from bacteria, through phytoplankton and zooplankton to fish, mammals and birds. Primary production in the Barents is on average 93 g C m⁻² y⁻¹, but interannually highly variable (±19%), responding to climate variability and change (e.g. variations in Atlantic Water inflow, the position of the ice edge and low-pressure pathways). The traditional focus upon large phytoplankton cells in polar regions seems less adequate in the Barents, as the cell carbon in the pelagic is most often dominated by small cells that are entangled in an efficient microbial loop that appears to be well coupled to the grazing food web. Primary production in the ice-covered waters of the Barents is clearly dominated by planktonic algae and the supply of ice biota by local production or advection is small. The pelagic–benthic coupling is strong, in particular in the marginal ice zone. In total 80% of the harvestable production is channelled through the deep-water communities and benthos. 19% of the harvestable production is grazed by the dominating copepods Calanus finmarchicus and C. glacialis in Atlantic or Arctic Water, respectively. These two species, in addition to capelin (Mallotus villosus) and herring (Clupea harengus), are the keystone organisms in the Barents that create the basis for the rich assemblage of higher trophic level organisms, facilitating one of the worlds largest fisheries (capelin, cod, shrimps, seals and whales). Less than 1% of the harvestable production is channelled through the most dominating higher trophic levels such as cod, harp seals, minke whales and sea birds. Atlantic cod, seals, whales, birds and man compete for harvestable energy with similar shares. Climate variability and change, differences in recruitment, variable resource availability, harvesting restrictions and management schemes will influence the resource exploitation between these competitors, that basically depend upon the efficient energy transfer from primary production to highly successful, lipid-rich zooplankton and pelagic fishes.  相似文献   

Effects of petroleum hydrocarbons on the hepatic cytochrome P450 1A1 system in rainbow trout   总被引：1，自引：0，他引：1  

Malin Celander  Dag Broman  Lars Frlin  Carina Nf 《Marine environmental research》1995,39(1-4)

Effects on the hepatic cytochrome P450 1A1 system were investigated in juvenile rainbow trout i.p. injected with three different aromatic containing fractions: kerosene, light gas oil or heavy gas oil, originated from distilled North Sea crude oil. Kerosene treatment resulted in no effect on the P450 1A1 system, light gas oil injection caused a weak induction of EROD activities and heavy gas oil treatment resulted in a prominent induction of EROD activities as well as accumulation of CYP1A1 mRNA and P450 1A1 protein levels. The effects of heavy gas oil were compared with effects of β-napthoflavone (β-NF) on the P450 1A1 system. It was obvious that important discrepancies seemed to exist between EROD activities and corresponding CYP1A1 mRNA and P450 1A1 levels in rainbow trout treated with either heavy gas oil or β-NF i.e. heavy gas oil treatment resulted in higher specific EROD activities (EROD/P450 1A1) compared to β-NF. GC-MS analyses revealed that liver and bile from heavy gas oil treated rainbow trout in addition to naphthalene also contained polycyclic aromatic hydrocarbons such as phenanthrenes, anthracene, pyrenes, fluoranthene benz(a)anthracene and chrysene, while none of these compounds were detected in control trout.  相似文献   

Sea ice and wind: Effects on primary productivity in the Barents Sea     

Egil Sakshaug  Dag Slagstad 《大气与海洋》2013,51(4):579-591

Abstract

The Barents Sea is divided into a northern and a southern part by the Polar Front (at about 75–76° N) where Atlantic waters descend under Arctic waters. Near to and north of the Polar Front, the spring bloom of phytoplankton is triggered by the stability induced in the upper 20 m by the melting of ice. The pycnocline is too strong to be eroded by wind. Primary productivity after the bloom is therefore small and largely regenerative. Underneath the pycnocline there is a 3–5 m thick layer characterized by dense, slow‐growing algal populations. New productivity north of the Polar Front is no more than 40 g C m^?2 a^?1.

In permanently open waters south of the Polar Front, the spring bloom starts in early May. Rhythmic wind‐induced mixing related to the atmospheric low‐pressure belt reaches an average 40–60 m depth in the growth season, and secondary phytoplankton maxima may arise. As a result, new annual productivity is more than doubled, i.e. 90 g C m^?2 a^?1, relative to the same system without wind. Although productivity is highest south of the Polar Front, it is more concentrated north of it, in the sense that high new production is mainly related to a 20–50 km wide belt that sweeps the area following the ice edge northwards while the ice melts through the summer.  相似文献   

Transportation planning as an effective tool for sustainable mobility     

Dag Bjrnland 《Marine pollution bulletin》1994,29(6-12):393-397

This paper focuses on goods transportation, but the general reasoning is also relevant for passenger transport. Many factors influence transport development and transport mode distribution. These factors are grouped and listed for clarity and to produce an overview. The interactions between the factor groups and transport and the complexity of the interdependence are discussed. At present, there are no formal models that fully explain goods transport development and transport pattern and that satisfactorily link policy changes and their effects on transport. Results pertaining to goods transport from two Scandinavian long-term planning models are summarized. Additional information is drawn from project work dealing with Western European countries.  相似文献   

Petrology of the Hopen mangerite-charnockite intrusion, Lofoten, north Norway   总被引：1，自引：0，他引：1  

Dag Eigil Ormaasen 《Lithos》1977,10(4):291-310

The Hopen massif, intrusive age 1900 m.y., exposed area 15 km², in the Lofoten-Vesterålen granulite facies province has the mineral assemblages: (1) mesoperthite+plagioclase (An_7–20)+quartz+clinopyroxene (Di_20–25)+orthopyroxene En_15–25+opaques±minor amphibole±minor biotite; (2) mesoperthite+plagioclase (An <2)+quartz+clinopyroxene (Di <10)+olivine Fe lt;5)+opaques. By using mineral and whole rock analyses, the crystallization conditions were estimated to be 1000°C, 12 kb load pressure and an oxygen fugacity approximately corresponding to the WM buffer. Rocks with the assemblage of type (2) contain secondary orthoferrosilite (Fe_0.90–0.95Mn_0.04–0.07Mg_0.01Ca_0.01)₂Si₂O₆, generated by reactions involving fayalite, magnetite and quartz at 800°C, 10kb load pressure and at oxygen fugacities approaching QFM buffer conditions. Subsequent to a crustal thickening, the mangeritic rocks in Lofoten-Vesterålen were emplaced in a tensional environment comparable with modern continental rifts. A ‘gabbro pillow’ magma chamber at the crustal base is proposed as parental magma for the mangeritic rocks, of which the Hopen massif represents a late differentiation.  相似文献   

Chemical stratification and stability of meromictic lakes in the Upper Romerike district     

Dag Hongve 《Aquatic Sciences - Research Across Boundaries》1980,42(2):171-195

A number of lakes in Southeast Norway have developed biogenic meromixis and have typically also considerable concentrations of dissolved iron and manganese in the bottom waters. Eight such lakes are described. Products of biological decomposition like carbon dioxide, methane and some inorganic salts gave a difference in density between mixo- and monimolimnion and hence chemical stability to the lakes. The concentration of iron and manganese gave minor contributions to the density gradients, and these substances are regarded as less important for the stability because of their reduced solubility under oxic conditions. Quantitative expressions of wind influence on lake surfaces were obtained by calculation of the work of the wind during the heating season. These values were low compared with a more exposed lake in the same region. Water movements generated by the wind have eroding effects on the chemical stratification only during short periods of homothermy before icelaying. During the rest of the year the monimolimnion is protected by either thermal stratification or ice cover. During the autumnal partial circulation a substantial reduction in chemical stability took place. For some of the lakes it is assumed that full circulation may take place in years with favourable weather conditions.  相似文献   

Improved seismic discrimination using pattern recognition     

Dag Tjøstheim 《Physics of the Earth and Planetary Interiors》1978,16(2):85-108

The problem of discriminating between earthquakes and underground nuclear explosions is formulated as a problem in pattern recognition. As such it may be separated into two stages, feature extraction and classification. The short-period (SP) features consist of m_b and autoregressive parameters characterising the preceding noise, signal and coda. The long-period (LP) features consist of LP power spectral estimates taken within various group velocity windows. Contrary to common usage we have extracted features from horizontal Rayleigh waves and Love waves as well as vertical Rayleigh waves. The classification is performed by approximating the statistical distribution of earthquake and explosion feature vectors by multivariate normal distributions.The method has been tested on a data base containing 52 explosions and 73 earthquakes from Eurasia recorded at NORSAR between 1971 and 1975. Several of these events are difficult on the m_b : M_s diagram [m_b(PDE) and M_s (NORSAR) have been used]. The data set was divided into a learning and an independent data set. All of the events both from the learning data set and the independent data set were correctly classified using the new procedures. Furthermore, the increase in separation as compared to the m_b : M_s discriminant is significant.  相似文献   

First reports of a mass mortality event across multiple life stages in a mesopelagic jellyfish in high latitude coastal waters          下载免费PDF全文

Andrea Bozman  Dag L. Aksnes  Ketil Eiane 《Marine Ecology》2018,39(2)

Mass mortality events can occur naturally and may have important ecological impacts on local populations. The abundance and stage structure of the coronate scyphozoan Periphylla periphylla in a Northern Norwegian fjord were studied between October 2010 and August 2011. Developmental stage composition varied for the duration of the study, with early developmental stages only present in the autumn and winter. Records of large number of dead P. periphylla across multiple life stages revealed that a mass mortality event occurred towards the end of the study period. The abundance of live medusa increased from 27 to 39 individuals (ind.)·1,000 m^–3 from October 2010 to February 2011, then fell to <10 ind.·1,000 m^–3 in August 2011. The estimated abundance of dead jellyfish increased from slightly >1 ind.·1,000 m^–3 in October 2010 to >34 ind.·1,000 m^–3 in August 2011, corresponding to an estimated population mortality of >80% on the last sampling date. Mortality increased as the length of high solar irradiance periods increased. Based on previous published evidence that strong light is harmful to P. periphylla, we speculate whether the light climate of this high latitude location may have contributed to the mass mortality of P. periphylla.  相似文献   

Pockmark-like depressions near the Goliat hydrocarbon field,Barents Sea: Morphology and genesis     

S. Chand  L. RiseD. Ottesen  M.F.J. DolanV. Bellec  R. Bøe 《Marine and Petroleum Geology》2009

Pockmarks are observed worldwide along the continental margins and are inferred to be indicators of fluid expulsion. In the present study, we have analysed multibeam bathymetry and 2D/3D seismic data from the south-western Barents Sea, in relation to gas hydrate stability field and sediment type, to examine pockmark genesis. Seismic attributes of the sediments at and beneath the seafloor have been analysed to study the factors related to pockmark formation. The seabed depths in the study area are just outside the methane hydrate stability field, but the presence of higher order hydrocarbon gases such as ethane and/or propane in the expelled fluids may cause localised gas hydrate formation. The selective occurrence of pockmarks in regions of specific seabed sediment types indicates that their formation is more closely related to the type of seabed sediment than the source path of fluid venting such as faults. The presence of high acoustic backscatter amplitudes at the centre of the pockmarks indicates harder/coarser sediments, likely linked to removal of soft material. The pockmarks show high seismic reflection amplitudes along their fringes indicating deposition of carbonates precipitated from upwelling fluids. High seismic amplitude gas anomalies underlying the region away from the pockmarks indicate active fluid flow from hydrocarbon source rocks beneath, which is blocked by overlying less permeable formations. In areas of consolidated sediments, the upward flow is limited to open fault locations, while soft sediment areas allow diffused flow of fluids and hence formation of pockmarks over a wider region, through removal of fine-grained material.  相似文献