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21.
Ursula Werner Anna Blazejak Paul Bird Gabriele Eickert Raphaela Schoon Raeid M.M. Abed Andrew Bissett Dirk de Beer 《Estuarine, Coastal and Shelf Science》2008,76(4):876-888
We investigated microphytobenthic photosynthesis at four stations in the coral reef sediments at Heron Reef, Australia. The microphytobenthos was dominated by diatoms, dinoflagellates and cyanobacteria, as indicated by biomarker pigment analysis. Conspicuous algae firmly attached to the sand grains (ca. 100 μm in diameter, surrounded by a hard transparent wall) were rich in peridinin, a marker pigment for dinoflagellates, but also showed a high diversity based on cyanobacterial 16S rDNA gene sequence analysis. Specimens of these algae that were buried below the photic zone exhibited an unexpected stimulation of respiration by light, resulting in an increase of local oxygen concentrations upon darkening. Net photosynthesis of the sediments varied between 1.9 and 8.5 mmol O2 m−2 h−1 and was strongly correlated with Chl a content, which lay between 31 and 84 mg m−2. An estimate based on our spatially limited dataset indicates that the microphytobenthic production for the entire reef is in the order of magnitude of the production estimated for corals. Photosynthesis stimulated calcification at all investigated sites (0.2–1.0 mmol Ca2+ m−2 h−1). The sediments of at least three stations were net calcifying. Sedimentary N2-fixation rates (measured by acetylene reduction assays at two sites) ranged between 0.9 to 3.9 mmol N2 m−2 h−1 and were highest in the light, indicating the importance of heterocystous cyanobacteria. In coral fingers no N2-fixation was measurable, which stresses the importance of the sediment compartment for reef nitrogen cycling. 相似文献
22.
Dr. Ursula Röhl 《International Journal of Earth Sciences》1990,79(1):13-26
The interpretation of microfacial and geochemical sediment features resulted in a detailed sequence analysis of Upper Muschelkalk strata in the northern and middle parts of West-Germany. It is now possible to correlate columnar sections at far distances. The method allows to make a synthesis of basin evolution. In this way it also succeed to reconstruct the dynamic activities in an epicontinental sedimentation area. The Upper Muschelkalk strata shows a hierarchically nested development of stratification cycles. There are minor cycles of probably paleotectonic origin, which are only locally significant. The major cycles are basing probably on sea level changes and allow supraregional parallelizations of sections. Indicators of the sea level maximums are clay horizons. They are called »Tonhorizonte« in Southern Germany and could be proved also in the Upper Muschelkalk strata of Northern Germany. So the stratigraphic correlation of the two sedimentation areas, which were so different in paleotectonic views, is possible. 相似文献
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Heinz Sulser Diego García-Ramos Peter Kürsteiner Ursula Menkveld-Gfeller 《Swiss Journal of Geoscience》2010,103(2):257-272
Terebratuloid and cancellothyridoid brachiopods from the South-Helvetic Lutetian (Eocene) of the Fäneren region (NE Switzerland) are described: Carneithyris subregularis (Quenstedt) and two forms of Terebratulina s.l. under open nomenclature. Several species of Alpine and non-Alpine origin, related to Carneithyris subregularis, like Terebratula kickxi Galeotti, Terebratula aequivalvis Schafhäutl and Terebratula hilarionis Davidson show characters, which compare well with Carneithyris subregularis. Two of them, T. aequivalvis and T. hilarionis, are assigned to the genus Carneithyris. The stratigraphy and lithology of the sediments in the study area are reassessed. Life habits and palaeoecology of the brachiopods are discussed. C. subregularis apparently was a free living brachiopod without attachment to the substrate, as indicated by massive accumulations of callosities in the posterior parts of the shell. The variability of the cardinal process, as seen in the studied Carneithyris group can be interpreted as a morphological element to enlarge the surface of attachment of strong diductor muscles in relation to the internal thickening of the individual. 相似文献
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Ecological classification of macrophytes and phytobenthos for rivers in Germany according to the water framework directive 总被引:9,自引:0,他引:9
Jochen Schaumburg Christine Schranz Julia Foerster Antje Gutowski Gabriele Hofmann Petra Meilinger Susanne Schneider Ursula Schmedtje 《Limnologica》2004,34(4):283-301
A new assessment system for macrophytes and phytobenthos in German rivers meeting the requirements of the Water Framework Directive (WFD) of the European Community is described. Biocoenotic types based on biological, chemical and hydromorphological data from over 200 river sites covering the main ecoregions, hydromorphological stream types and degradation forms have been defined. For developing a classification system the quality element macrophytes and phytobenthos was divided into three components: macrophytes, benthic diatoms and remaining phytobenthos. For macrophytes seven types including one subtype, for benthic diatoms 14 types including three subtypes and for the remaining phytobenthos five river types were identified. The benthic vegetation at reference condition was described for most of the river types. Degradation is characterised as deviation in benthic vegetation species composition and abundance from the reference biocoenosis. For classification in five ecological status classes, several metrics were developed and used in combination with existing indices. For some of the described river types additional investigations are necessary before a classification system can be developed. 相似文献
28.
Abstract— A meteoritic origin was proposed for the New Quebec Crater in 1949 on the basis of an aerial photograph showing its unique circularity and raised rim amid Precambrian gneisses of the Canadian Shield. At that time, only those few craters associated with meteorites were generally accepted as of impact origin. When the earliest field expeditions failed to find meteorites or impact products, two leading meteoriticists, Frederick C. Leonard and Lincoln LaPaz, cited the “Chubb” Crater as a flagrant example for which claims of meteoritic origin were advanced without valid proof. They also listed the Lake Bosumtwi Crater in Ashanti (now Ghana) among crater-like features, clearly of non-meteoritic origin, misidentified as meteorite craters. Controversy over the origin these two craters continued for decades. In Part I of this paper, we trace the investigations that led to the current acceptance of New Quebec as an authentic impact crater. We note that, for reasons that are not entirely clear, a meteoritic origin for the New Quebec Crater achieved wider acceptance at an earlier date than for the Lake Bosumtwi Crater, where petrographic and chemical evidence is more abundant and compelling. In Part II, we describe the petrography of two impact melt samples from the New Quebec Crater and present new evidence on the degrees of shock metamorphism affecting the accessory minerals: apatite, sphene, magnetite and zircon. Zircon, in particular, shows a range from euhedral grains with no signs of alteration to those decomposed to baddeleyite plus silica. 相似文献
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Spatial variability of phytoplankton, nutrients and new production estimates in the waters around Svalbard 总被引:3,自引:0,他引:3
Georgina Owrid Giorgio Socal Giuseppe Civitarese Anna Luchetta Jozef Wiktor Eva-Maria Nöthig Inger Andreassen Ursula Schauer Volker Strass 《Polar research》2000,19(2):155-171
Phytoplankton dynamics and carbon input into Arctic and sub-Arctic ecosystems were investigated around Svalbard, in summer 1991. Phytoplankton biomass, species composition and dissolved nutrient concentrations were analysed from water samples collected along seven transects. Phytoplankton biomass was low especially to the north (Chlorophyll-a mean 0.3 pg 1- '), where flagellates dominated the communities and only ice-diatoms were present. To the west, the phytoplankton composition was representative of a summer Atlantic community, in a post-bloom state. Zooplankton grazing, mainly by copepods, appeared to be the main control on biomass to the west and north of Svalbard.
In the Barents Sea (east of Svalbard), an ice edge bloom was observed (Chlorophyll-a max. 6.8 pgl-') and the ice edge receded at a rate of approximately 1 1 km day-'. The phytoplankton community was represented by marginal ice species, especially Phaeocystis poucherii and Chaeroceros socialis. South of the ice edge, Deep Chlorophyll Maxima (DCM) were observed, as surface waters became progressively nutrient-depleted. In these surface waters, the phytoplankton were predominantly auto- and heterotrophic flagellates.
Carbon production measurements revealed high net production (new and regenerated) to the north of the Barents Sea Polar Front (BSPF); it was especially high at the receding ice edge (reaching 1.44gC m-'day-'). To the south, a low level of production was maintained, mainly through regenerative processes. 相似文献
In the Barents Sea (east of Svalbard), an ice edge bloom was observed (Chlorophyll-a max. 6.8 pgl-') and the ice edge receded at a rate of approximately 1 1 km day-'. The phytoplankton community was represented by marginal ice species, especially Phaeocystis poucherii and Chaeroceros socialis. South of the ice edge, Deep Chlorophyll Maxima (DCM) were observed, as surface waters became progressively nutrient-depleted. In these surface waters, the phytoplankton were predominantly auto- and heterotrophic flagellates.
Carbon production measurements revealed high net production (new and regenerated) to the north of the Barents Sea Polar Front (BSPF); it was especially high at the receding ice edge (reaching 1.44gC m-'day-'). To the south, a low level of production was maintained, mainly through regenerative processes. 相似文献