Recruitment of Demosponges (Porifera,Demospongiae) in Rocky and Coral Reef Habitats of Santa Marta,Colombian Caribbean*     

Sven Zea 《Marine Ecology》1993,14(1):1-21

Abstract. Recruitment of demosponges (Porifera, Demospongiae) was monitored bimonthly for one year (March 1987 – March 1988) on acrylic plates, and compared to cover of adults, in six rocky and coral reef habitats at Santa Marta, Colombian Caribbean, an area subjected to seasonal, upwelling-outwelling regimes. According to suggestive but not significant trends, recruitment rates are more positively influenced by the total sponge cover near groups of plates than by cover at a larger (habitat) scale; recruit mortality is lower where recruitment is higher. These findings are in agreement with a model of higher settlement (probably due to short-distance dispersal) and lower postsettlement mortality within a few meters of adult sponges. Recruitment varied seasonally, being relatively high from May to November-December during the rainy, outwelling season, when seawater temperature was warmer, water turbidity higher, and benthic algal density lower; it was very low from January to April during the dry, upwelling season.  相似文献   

An improved Kajak-type gravity core sampler for soft bottom sediments     

Sven Blomqvist  Berndt Abrahamsson 《Aquatic Sciences - Research Across Boundaries》1985,47(1):81-84

A new, modified model of the Kajak tube core sampler is presented. The new sampler is intended for use on soft sediments, and hence of light weight (12 kg). The improved sampler offers the following advantages. (1) increased robustness, (2) simplified attachment of the coring tube to the holder and valve assembly, permitting quick exchange of sampling tubes, (3) unimpeded flow of water through the tube during slow descent, (4) a reliable, automatic mechanism closing the top of the core tube after impact, and (5) an easily dismantled supporting frame, which also protects the sampler from damage against the side of the boat in rought weather. The operation of the sampler has been observedin situ and during ordinary shipboard collection of core samples, with satisfactory results.  相似文献   

Geochemical aspects of some accumulation models for primary magmas     

Sven Maaløe  A. Dana Johnston 《Contributions to Mineralogy and Petrology》1986,93(4):449-458

The compositions of primary magmas depend to some degree on the dynamic processes occurring in the partially molten region of the mantle. The compositional dependence is estimated for three models which assume either accumulation from a migmatized source region or accumulation entirely by the interstitial flow of magma. Accumulation from a migmatised region results in magmas with higher concentrations of incompatible elements than does batch melting, whereas accumulation by interstitial flow results in magmas with lower concentrations of these elements. The concentrations of refractory elements are almost independent of both the accumulation process and the degree of partial melting and are therefore usefull for the identification of primary magmas.  相似文献   

Pine forest microclimate simulation using different diffusivities     

Sven Halldin  Anders Lindroth 《Boundary-Layer Meteorology》1986,35(1-2):103-123

Proper understanding of, e.g., evaporation from a forest requires an understanding of its microclimate. A well established, steady-state model was used to simulate microclimate and evaporation of a sparse pine forest in central Sweden. Model input included profiles of turbulent diffusivity, boundary-layer resistance, stomatal resistance, wind speed, net and global radiation and needle area density. Momentum balance, energy balance and exponentially decreasing diffusivities were used to study the sensitivity of the evaporation rates and of the temperature and humidity profiles. Model output proved to be unreliable when measured temperature and humidity at the bottom of the stand were used instead of a measured ground heat flux as the lower boundary condition. Energy balance diffusivity was usually larger than momentum balance diffusivity at the canopy top but decreased rapidly to a minimum at approximately the height where the momentum balance diffusivity had its maximum. Energy balance diffusivity commonly showed a secondary maximum below the height of the maximum needle area density. Profiles of Richardson number showed that thermal effects became important just below the canopy top. Bluff-body effects distinguished the energy balance from the momentum balance diffusivity and both were subject to shelter effects. Total evaporation was not very sensitive to the choice of diffusivity when soil heat flux was given as the lower boundary condition.  相似文献   

A Younger Dryas Ash Bed in western Norway,and its possible correlations with tephra in cores from the Norwegian Sea and the North Atlantic     

Jan Mangerud  Sven Erik Lie  Harald Furnes  Inger Lise Kristiansen  Leif Lømo 《Quaternary Research》1984,21(1):85-104

A bed of volcanic ash up to 23 cm thick is found in lacustrine and marine sediments in western Norway. It is formally mamed the Vedde Ash Bed, and its age is approximately 10,600 yr B.P., i.e., mid-Younger Dryas. The bed consits of pure glass having a bimodal basaltic and rhyolitic somposition. The geochemistry of the glass shards suggests an Icelandic source. By means of stratigraphic position and geochemistry, the ash is correlated with ash zones found in cores from the continental shelf, the Norwegian Sea, and the North Atlatic.  相似文献   

Population density and zoning of olivine phenocrysts in tholeiites from Kauai,Hawaii     

Sven Maaløe  Ole Tumyr  Dodie James 《Contributions to Mineralogy and Petrology》1989,101(2):176-186

The population density of olivine phenocrysts of the tholeiites display an exponential variation, which is typical of igneous as well as contact metamorphic rocks. The exponential variation is explained by a new growth probability model, which is consistent with experimental work. The forsterite content of the olivine phenocrysts decreases with decreasing size. Various phenocryst features suggest that the tholeiites first crystallized slowly in a magma chamber, after which they underwent crystallization for a short period of time in a feeder dyke before eruption took place.  相似文献   

Implication for mantle flow from the Hawaiian-Emperor chain     

Sven Maale  Ole Tjugen 《Earth and Planetary Science Letters》1988,91(1-2)

Assuming that Rayleigh-Benard flow occurs within the upper mantle, ascending plumes must undergo horizontal displacement during ascent that can be traced at the surface. It is shown that the Hawaiian-Emperor bend cannot be formed if the convection rate is of the same order of magnitude as the ascent rate of the plumes. The plume patterns obtained by push-pull or lithospheric sliding are similar to that of the Hawaiian-Emperor chain. Hence the present results support the sliding model.  相似文献   

Automated Multi-class Classification of Remotely Sensed Hyperspectral Imagery Via Gaussian Processes with a Non-stationary Covariance Function     

Anna Chlingaryan  Arman Melkumyan  Richard J. Murphy  Sven Schneider 《Mathematical Geosciences》2016,48(5):537-558

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Electrical properties of seafloor massive sulfides     

Giovanni Spagnoli  Mark Hannington  Katharina Bairlein  Andreas Hördt  Marion Jegen  Sven Petersen  Tea Laurila 《Geo-Marine Letters》2016,36(3):235-245

Seafloor massive sulfide (SMS) deposits are increasingly seen as important marine metal resources for the future. A growing number of industrialized nations are involved in the surveying and sampling of such deposits by drilling. Drill ships are expensive and their availability can be limited; seabed drill rigs are a cost-effective alternative and more suitable for obtaining cores for resource evaluation. In order to achieve the objectives of resource evaluations, details are required of the geological, mineralogical, and physical properties of the polymetallic deposits and their host rocks. Electrical properties of the deposits and their ore minerals are distinct from their unmineralized host rocks. Therefore, the use of electrical methods to detect SMS while drilling and recovering drill cores could decrease the costs and accelerate offshore operations by limiting the amount of drilling in unmineralized material. This paper presents new data regarding the electrical properties of SMS cores that can be used in that assessment. Frequency-dependent complex electrical resistivity in the frequency range between 0.002 and 100 Hz was examined in order to potentially discriminate between different types of fresh rocks, alteration and mineralization. Forty mini-cores of SMS and unmineralized host rocks were tested in the laboratory, originating from different tectonic settings such as the intermediate-spreading ridges of the Galapagos and Axial Seamount, and the Pacmanus back-arc basin. The results indicate that there is a clear potential to distinguish between mineralized and non-mineralized samples, with some evidence that even different types of mineralization can be discriminated. This could be achieved using resistivity magnitude alone with appropriate rig-mounted electrical sensors. Exploiting the frequency-dependent behavior of resistivity might amplify the differences and further improve the rock characterization.  相似文献   

Micro-sized enterprises: vulnerability to flash floods     

Konstantinos Karagiorgos  Micha Heiser  Thomas Thaler  Johannes Hübl  Sven Fuchs 《Natural Hazards》2016,81(2):1091-1106

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