德国柏林市Stechlin湖原生动物群落多样性特征的初步研究

本文报道了作者在1994年秋季至1995年冬季利用PFU（Polyurethane Unit Foarm,聚氨酯泡沫塑料块）人工基质和结合传统的采集自然基质方法研究德国柏林市郊Stechlin湖原生动物群落多样性特征的结果,通过连续采样调查,首次记录了该湖128种原生动物,实验结果表明：在相同采样时间内,3个不同生境类型的采样站PFU原生动物的群集速度及个体丰度存在明显差异;在相同采样时间和地点,PFU人工基质能够采集到比自然基质更为多的原生动物种类,从而进一步证实了PFU方法应用在原生动物群落多样性研究上的优势作用。     

Pleistocene stratigraphy in the Devils Hole Area,Central North Sea: Foraminiferal and amino-acid evidence

A detailed study of the foraminiferal assemblages from the 229.1-m-deep core 81/34 in the central North Sea has been combined with a series of measurements of the isoleucine epimerisation of foraminiferal tests. A total of 17 foraminiferal zones have been established and both the faunal compositions and the amino-acid values suggest that a major part of the sequence represents deposits of early and middle Pleistocene age. Only the uppermost zone is referred to the late Pleistocene. The sequence mainly comprises a series of marine zones from cold periods, but with some barren, possibly non-marine intervals in between. Only two of the foraminiferal zones can be referred to interglacial periods. The oldest one of these, defined here as the Devils Hole Interglacial, may belong to the latter part of the Cromerian Complex, while the upper warm interval is correlated with the Holsteinian of northwest Europe on the basis of its amino-acid values. A detailed stratigraphical correlation between core 81/34 and the neighbouring core 81/29 is suggested on the basis of their foraminiferal content, palaeomagnetic evidence and amino-acid measurements from both cores. A characteristic feature of both sequences is that most of the Quaternary record is missing. Similar episodic patterns of deposition and erosion have been reported previously from the North Sea area.     

Petrogenesis and significance of late Caledonian granitoid magmatism in western Norway

Obduction of the late Ordovician Solund-Stavfjord Ophiolite Complex (443±3 Ma), west Norwegian Caledonides, involved generation and high-level emplacement of granitic and granodioritic dikes and plutons. Initial ⁸⁷Sr/⁸⁶Sr ratios in the granites are low (0.7042–0.7059), suggesting either a mantle component or a Rb-poor crustal source. Initial Nd (Nd(t)) ranges from-0.8 to-8.8, indicating that the granites represent recycling of old crustal rocks, which is supported by Precambrian inheritance in zircons from two of the studied granites. I argue that the Rb-Sr and the Sm-Nd isotope systems are decoupled in the sense that the Sr-and the Nd-isotopes derive their dominant signals from two different sources, a mantle source and a crustal source respectively. The granites are metaluminous to peraluminous and typically have high Sr, Ba and Na₂O/K₂O ratios. SiO₂ contents range from 66 to 74 wt%. REE abundances are highly variable; the La contents range from 80 to 200 times chondrite, and are inversely correlated with the contents of SiO₂. The concentration of Nd in the granites decreases asymptotically with decreasing Nd(t) suggesting fractional crystallization of accessory phases and assimilation of continental crust. This argument is supported by the presence of partly dismembered xenoliths in the granites with Nd(t)-values that are significantly lower than Nd(t)-values in the host granite. The following models are suggested for the granites. When the ophiolite complex obducted, an outboard subduction zone approached the continental margin, and subduction-related magmas accumulated beneath the continental margin, and probably intruded the overlying eugeosynclinal deposits. The mantle-derived magmas most likely evolved to granitoid composition by assimilation of these eugeosynclinal sediments and by fractional crystallization of amphibole, feldspar, sphene, and allanite. Alternatively, but less likely, the heat content of the mantle-derived magmas caused extensive melting of immature graywackes and calc-alkaline volcaniclastic rocks in the deepest portions of the eugeosyncline. Either way, during ascent, the compositions of the granitic melts were modified by fractional crystallization of LREE-rich phases and by assimilation of continental metasediments.     

The Trænadjupet Slide: a large slope failure affecting the continental margin of Norway 4,000 years ago

¹⁴C AMS-dated gravity cores reveal that the Trænadjupet Slide offshore Norway occurred about 4,000 ¹⁴C years B.P. (ca. 4,000 cal. years ago). From 4,000 to 3,000 years B.P., minor areas of the newly formed slide scar were probably eroded, the result of smaller episodes of mass wasting caused by delayed collapse of part of the western, upper sidewall or by bottom currents. From about 3,000 years B.P. to the present, sediments were derived from alongslope-flowing, north-eastward-oriented ocean currents carrying sediments in suspension. These results demonstrate that large-scale mass wasting during sea-level highstand is rather common on passive continental margins.     

Environmental estrogens interact with and modulate the properties of plasma sex steroid-binding proteins in juvenile Atlantic salmon (Salmo salar)

Environmental chemicals may modulate the endocrine system through interaction with plasma sex steroid-binding proteins (SBP) and SBP-regulated processes. Some of these chemicals, which are known to interact with the estrogen receptor (ER), were found to bind competitively to the Atlantic salmon (Salmo salar) SBP and potentially disrupt the endocrine function of these proteins. Furthermore, both weakly acting (di-n-butyl phthalate) and potent estrogen mimics (ethynylestradiol), were able to induce a substantial up-regulation of circulating levels of SBP in vivo. Interestingly, modulation of SBP-levels was found to be a more sensitive endpoint than chemically induced interference with classical ER-mediated mechanisms for weakly acting estrogen mimics like di-(n-butyl) phthalate. Interference with the endocrine function of SBPs may thus introduce a novel mechanism for endocrine disruption, and give additional answers to the question why some weakly acting xenoestrogens are causing “estrogen-like” reproductive disturbances in developing males.     

Centrifuge tests on installation of suction anchors in soft clay

Three centrifuge model tests were performed in normally consolidated Speswhite Kaolin to study the penetration of suction anchors in soft clay. The suction anchors could be penetrated by means of underpressure to a depth of about 12.4 to a little more than 14.5 times the diameter. When the anchors were penetrated by underpressure, all clay displaced by the skirt moved into the anchor. At a penetration depth of about half the maximum penetration depth, the volume of the soil heave inside the anchor actually increased more than the volume of the displaced clay. When a material coefficient of 1.5 against plug failure was mobilized, more than the clay displaced by the skirts had accumulated inside the anchor. The penetration resistance increased by 42 and 26% during rest periods of 4.5 and 0.8 days prototype time, respectively. Some uncertainty in the shear strength of the clay beds gave some uncertainty with respect to the interpretation, but the observed behaviour generally confirmed the theoretical analyses.     

Increasing concentrations of arsenic and vanadium in (southern) Swedish streams

The aim of this study was to investigate temporal trends and controlling factors of As and V in running waters throughout Sweden. For this purpose, data on stream water chemistry from 62 streams of varying catchment size and characteristics, included in the Swedish environmental monitoring programmes were evaluated. The geochemical software Visual MINTEQ was used to model the speciation and trend analyses were performed on total concentrations of As and V as well as modelled fractions (dissolved species as well as arsenate and vanadate adsorbed to ferrihydrite). The trend analyses showed increasing total concentrations of As and V in southern Sweden. Concentrations of As and V correlated significantly to Fe concentrations in 59 and 60 of the 62 streams respectively, indicating that Fe is an important determining factor for As and V concentrations in Swedish streams. This was confirmed by the geochemical modelling that indicated that the adsorbed fraction is the dominant form of As and V and that the concentrations of As and V in Swedish streams are thus highly determined by concentrations of colloidal or particulate Fe. It is therefore suggested that the increasing trends of As and V are to a large extent due to increasing concentrations of colloidal Fe, which is stabilised by increasing concentrations of DOC. Further the geochemical modelling indicates that the dissolved fraction of As and V generally is small, with the exception of a few streams with high pH and/or phosphate concentrations.     

Tropical sugar beet land evaluation scheme: development, validation and application under Kenyan conditions

In Kenya the government is promoting diversification of crops to embrace high value crops and drought resistant crop varieties in efforts to reduce poverty in rural areas. Sugar beet is one of the crops considered as an option in this context and it is therefore important to increase knowledge about the potentials in the country for cultivating this crop. Sugar beet trials conducted in Nyandarua and Butere Mumias Districts of Kenya have shown that the crop yields are comparable to those obtained in traditional sugar-beet cultivation regions of Europe. Since sugar beet yield is affected by climate and soils, the results of Nyandarua and Butere Mumias sugar beet trials are not adequate to propose that comparable yields can be obtained elsewhere in the country and other tropical regions. Physical land evaluations assessing the potentials and constraints for sugar beet production are therefore essential. The objectives of this study was to develop a Tropical Sugar Beet Land Evaluation Scheme (TSBLES) that can aid assessment of the suitability of different areas in the tropics for sugar beet cultivation; and to test this scheme for an assessment of suitable sugar beet zones and land areas in Kenya. The development of the scheme was based on various literature sources and expert judgment on sugar beet requirements, and a Tropical Sugar Beet yield prediction Model. The TSBLES accounts for physical conditions of land i.e. climatic, edaphic and topographic conditions. According to the assessment results 27% of the land area in Kenya is suitable for sugar beet cultivation. Of this area, 5% is highly suitable, another 5% is moderately suitable and 17% is marginally suitable. Most of the highly suitable land area is concentrated in Rift Valley, Central and Nyanza provinces. The Rift Valley has the highest share of the suitable land area.     

The 2.40 Ga Ringvassøy mafic dykes, West Troms Basement Complex, Norway: The concluding act of early Palaeoproterozoic continental breakup

A north to northwest trending mafic dyke swarm of gabbronoritic and gabbroic composition makes up a significant part of the Archean basement on the island of Ringvassøy in northern Norway. U–Pb geochronology of zircon and baddeleyite in a gabbronorite provides an age of emplacement of 2403 ± 3 Ma. Metamict zircon in a plagioclase phyric dyke yield data that are discordant but consistent with the age of the gabbronoritic dyke. Titanite indicates a metamorphic overprint at 1768 ± 4 Ma. The two types of dyke show some distinct chemical characteristics. They are both tholeiitic, enriched in LREEs and LILE elements but depleted in HFS elements including Nb. Their Nd isotopic composition yields _Nd values of −1.5 to −1.8 for gabbronorites and −0.4 to +1.3 for the plagioclase phyric dykes. The chemical and isotopic constraints are typical of continental basalts.The Ringvassøy mafic dykes correlate broadly with a global Palaeoproterozoic magmatic event that formed extensive bimodal intrusive and extrusive suites in most Archaean cratons, including the northeastern Fennoscandian Shield. In detail, the 2403 ± 3 Ma Ringvassøy dykes postdated most episodes of magmatism at this time. On the regional scale there is a distinct trend from a 2505–2490 Ma suite present in the Kola Peninsula, over a second 2460–2440 Ma suite present both in Kola and further south in Karelia, to the 2403 Ma dykes on Ringvassøy. This variation suggests that the locus of maximum extension and magmatic activity may have been shifting with time.