A numerical approach to boundary layer fractionation: application to differentiation in natural magma systems   总被引：1，自引：1，他引：0  

Roger L. Nielsen  Stephen E. DeLong 《Contributions to Mineralogy and Petrology》1992,110(2-3):355-369

With few exceptions, geochemical models of igneous differentiation have assumed that crystals form homogeneously throughout the cooling magma chamber. This is in spite of field evidence and physical models suggesting for natural systems, that heat loss, and thus most crystallization, occurs primarily along the walls and roof of magma chambers. Such systems would produce aphyric, evolved composition lavas. Existing models of boundary layer crystal fractionation suggest that the products of such a process are significantly different from the products of homogeneous crystallization. To investigate this process further, we have developed a model using a numerical approach to boundary layer crystal fractionation based on new phase equilibria and trace element constraints. In addition to olivine, augite and plagioclase, this new model includes the ability to calculate the effects of oxide (magnetite and ilmenite), apatite and low-Ca pyroxene fractionation. This is critical if we are to effectively evaluate the geochemical signature of boundary layer fractionation. This is because the products of boundary layer fractionation are most different from homogeneous fractionation for high degrees of crystallization in the solidification zone. These are the same conditions where oxides, low-Ca pyroxene and apatite are saturated in most natural, differentiated mafic systems. The results of this model suggest that boundary layer fractionation can help to explain such phenomena as phantom crystallization, variation in incompatible element ratios, and the decoupling of major and trace element systematics. In addition, many of the geochemical patterns that we use to distinguish between the products of low pressure and high pressure differentiation are obscured by the fact that the liquid line of descent can be controlled by the removal of phases not in equilibrium with the entire magma chamber.  相似文献   

Photosynthetic responses to Cu2+ exposure are independent of light acclimation and uncoupled from growth inhibition in Fucus serratus (Phaeophyceae)     

Nielsen HD  Nielsen SL 《Marine pollution bulletin》2005,51(8-12):715-721

We have studied the effect of light acclimation on photosynthetic responses and growth during Cu²⁺ exposure (0–0.84 μM) in the brown seaweed Fucus serratus. Measurements of chlorophyll fluorescence parameters showed that Cu²⁺ exposure amplified ETR, reduced the chlorophyll content at the cellular level and that there was no effect of light adaptation on the Cu²⁺ resistance of the algae. In contrast to the inhibitory effects of Cu²⁺ on chlorophyll fluorescence, O₂ evolution and the total content of chlorophyll and carotenoid of the algae was unaffected by Cu²⁺. We conclude that photoinhibition and perhaps pigment degradation in the meristoderm was compensated for by cells deeper in the thallus with the result that the overall photosynthetic fitness of the algae was maintained. The pronounced inhibitory effects of Cu²⁺ on algae growth was not a consequence of photoinhibition and could be attributed to direct inhibitory effects on the growth process.  相似文献   

Melt inclusion formation mechanisms and compositional effects in high-An feldspar and high-Fo olivine in anhydrous mafic silicate liquids   总被引：1，自引：1，他引：0  

Edward?KohutEmail author  Roger?L.?Nielsen 《Contributions to Mineralogy and Petrology》2004,147(6):684-704

Important aspects of melt inclusion formation and potential compositions effects have been addressed through a series of experiments using anorthite/fosterite saturated anhydrous mafic liquids. Experimental charges were cooled from 1,300 to 1,230 and 1,210°C at rates of 1–10°/min followed by 0–24 h isothermal periods. Hopper and skeletal crystal morphologies with variable degrees of completeness developed during the cooling period. Planar overgrowth of these textures during isothermal periods led to the formation of inclusions, the majority of which formed after 6 h of isothermal run time. We suggest that the change in morphologies is related to a decrease in growth rates and changes in dominant growth mechanisms. In general, inclusion compositions were uniform and similar to the host glass, indicating that with the isothermal times required for most inclusions to form, a boundary layer was not entrapped that could be detected within the limits of our analyses.

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Edward KohutEmail: Phone: +1-541-7373023Fax: +1-541-7371200

Roger L. NielsenEmail: Phone: +1-541-7371235

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A comparison of the NW European glaciated margin with other glaciated margins   总被引：1，自引：4，他引：1  

T. Nielsen  L. De Santis  K.I.T. Dahlgren  A. Kuijpers  J.S. Laberg  A. Nygrd  D. Praeg  M.S. Stoker 《Marine and Petroleum Geology》2005,22(9-10):1149

The present paper provides an overview of glacial related seabed features and sedimentary sequences found along the formerly glaciated NW European margin and compare it with those found on contemporary glaciated margins from both the Southern and Northern Hemispheres. A brief review of the seabed physiography and strata architecture of the margins under consideration is followed by comparison of the most relevant similarities and differences. Comparison of the present-day bathymetric setting of both former and contemporary glaciated margins reveals no clear link to the effect of neither ice sheet or sediment load. Three different types of glacially eroded shelf transverse troughs have been identified, while marginal troughs seem connected to similar geological settings everywhere. Beyond the shelf edge interaction between downslope and alongslope processes has occurred resulting, amongst others, in the formation of large sedimentary mounds on the rise. More frequent large-scale mass wasting occurs on the former glaciated NW European margin than the Greenland and Antarctic margins in the latest Neogene to recent times. A two-stage evolution of the shelf prograding wedges is observed on all margins under consideration, which may reflect a general development of an ice cover from an initial phase of non- to restricted glaciation, evolving to a mature stage of expansive glaciation.  相似文献   

Numerical prediction of green water incidents     

Kristian Bendix Nielsen  Stefan Mayer 《Ocean Engineering》2004,31(3-4):363-399

Green water loads on moored or sailing ships occur when an incoming wave significantly exceeds the freeboard and water runs onto the deck. In this paper, a Navier–Stokes solver with a free surface capturing scheme (i.e. the VOF model; [Hirt and Nichols, 1981]) is used to numerically model green water loads on a moored FPSO exposed to head sea waves. Two cases are investigated: first, green water on a fixed vessel has been analysed, where resulting waterheight on deck, and impact pressure on a deck mounted structure have been computed. These results have been compared to experimental data obtained by [Greco, 2001] and show very favourable agreement. Second, a full green water incident, including vessel motions has been modelled. In these computations, the vertical motion has been modelled by the use of transfer functions for heave and pitch, but the rotational contribution from the pitch motion has been neglected. The computed water height on deck has been compared to the experimental data obtained by [Buchner, 1995a] and it also shows very good agreement. The modelling in the second case was performed in both 2-D and 3-D with very similar results, which indicates that 3-D effects are not dominant.  相似文献   

Explicit formulae for practical wave calculations     

Peter Nielsen 《Coastal Engineering》1982,6(4):389-398

Explicit formulae for linear wave quantities are presented, which are accurate within one percent for (water depth to deep-water wave length) less than 0.20. The formulae are exact in the shallow-water limit ( ) and surprisingly simple. It is shown how they can be applied to obtain direct solutions to refraction and dissipation problems with sufficient accuracy for practical coastal engineering work.  相似文献   

TEMAS: fleet-based bio-economic simulation software to evaluate management strategies accounting for fleet behaviour   总被引：1，自引：0，他引：1  

Ulrich  Clara; Andersen  Bo Solgaard; Sparre  Per J.; Nielsen  J. Rasmus 《ICES Journal of Marine Science》2007,64(4):647-651

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Transformation of South African industrial fisheries     

Jesper Raakjær Nielsen  Mafaniso Hara 《Marine Policy》2006

South African industrial fisheries have been dominated by a few large companies. The Marine Living Resources Act (MLRA) of 1998 emphasised that equity was to be achieved by redistribution through co-operative strategies among stakeholders. Instead, the reallocation of fishing rights has been treated as a resource management issue rather than a socio-economic challenge. Further, the institutional structures for transformation have been inappropriate. This paper investigates the institutional dynamics and discrepancies associated with transformation and concludes that the process became locked in a path dependency, which will eventually undermine the intentions of transformation.  相似文献   

Ecosystem service values of sediment generation and entrapment by marginal coral reefs at Sodwana Bay,South Africa     

SCS Laing  MH Schleyer  JK Turpie 《African Journal of Marine Science》2020,42(2):199-207

Coral reefs provide a multitude of goods and services, some of which are difficult to value due to their intangible nature and the absence of markets to ascribe their relative worth. The coral reefs of Sodwana Bay on the northeast coast of South Africa provide several ecological goods and services, of which only two are considered here: namely, sediment generation and sediment entrapment. Both are deemed essential to the functioning of the Sodwana Bay economy. The replacement-cost method was used to estimate the annual financial cost of sediment provided to the study area if it were replaced by dredging. Sediment generation by the coral reefs was valued at R2.6–R4.8 million, and sediment entrapment valued at R71.8–R84.6 million, totalling between R74.4 million and R89.4 million (≈$5.6–$6.7 million, at R13.38/US$1) per year.  相似文献   

Non-predation natural mortality of Norway pout (Trisopterus esmarkii) in the North Sea     

Sparholt  Henrik; Larsen  Lena I.; Nielsen  J. Rasmus 《ICES Journal of Marine Science》2002,59(6):1276-1284

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