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排序方式: 共有175条查询结果,搜索用时 31 毫秒
41.
Blood metal levels and metal-influenced immune functions of harbour seals in captivity 总被引:2,自引:0,他引:2
Kakuschke A Valentine-Thon E Griesel S Rosenberger T Mundry R Siebert U Prange A 《Marine pollution bulletin》2008,56(4):764-769
Immunological blood parameters and the effects of environmental pollutants on the immune system are important to assess the health status of seals. Animals living permanently in seal centres are useful for development and validation of diagnostic tools for free-ranging animals. In this study, parameters of cellular immunity as well as metal concentrations in blood and metal influence on cell proliferation of seven seals from a seal centre were investigated repeatedly using multi-element analysis and a lymphocyte proliferation assay. The metal concentrations, except for tin and chromium, were in general comparable to those of free-ranging animals of the North Sea. The unstimulated and mitogen-stimulated lymphocyte proliferation showed strong intra- and inter-individual variability, which reflected variability in activation of the immune status. Furthermore, both immunosuppressive and stimulative influences of metals on lymphocytes were found. Summarising, the methods used in this investigation provided useful information on these animals, and their application to free-ranging animals can be recommended. 相似文献
42.
Stefan Jansen Eva Walpersdorf Ursula Werner Markus Billerbeck Michael E Böttcher Dirk de Beer 《Ocean Dynamics》2009,59(2):317-332
In this article, we describe the dynamics of pH, O2 and H2S in the top 5–10 cm of an intertidal flat consisting of permeable sand. These dynamics were measured at the low water line
and higher up the flat and during several seasons. Together with pore water nutrient data, the dynamics confirm that two types
of transport act as driving forces for the cycling of elements (Billerbeck et al. 2006b): Fast surface dynamics of pore water chemistry occur only during inundation. Thus, they must be driven by hydraulics (tidal
and wave action) and are highly dependent on weather conditions. This was demonstrated clearly by quick variation in oxygen
penetration depth: Seeps are active at low tide only, indicating that the pore water flow in them is driven by a pressure
head developing at low tide. The seeps are fed by slow transport of pore water over long distances in the deeper sediment.
In the seeps, high concentrations of degradation products such as nutrients and sulphide were found, showing them to be the
outlets of deep-seated degradation processes. The degradation products appear toxic for bioturbating/bioirrigating organisms,
as a consequence of which, these were absent in the wider seep areas. These two mechanisms driving advection determine oxygen
dynamics in these flats, whereas bioirrigation plays a minor role. The deep circulation causes a characteristic distribution
of strongly reduced pore water near the low water line and rather more oxidised sediments in the centre of the flats. The
two combined transport phenomena determine the fluxes of solutes and gases from the sediment to the surface water and in this
way create specific niches for various types of microorganisms. 相似文献
43.
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
44.
Charles L. Cochran 《Ocean Engineering》1980,7(1):194
45.
46.
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
47.
Jean Manfroid Damien Hutsemékers Anita L. Cochran William M. Jackson Rita Schulz 《Icarus》2007,187(1):144-155
UVES and HIRES high-resolution spectra of Comet 9P/Tempel 1 are used to investigate the impact and rotational light curves of various species with a view toward building a simple model of the distribution and activity of the sources. The emission by OH, NH, CN, C3, CH, C2, NH2, and OI, are analyzed, as well as the light scattered by the dust. It is found that a simple model reproduces fairly well the impact light curves of all species combining the production of the observed molecules and the expansion of the material throughout the slit. The impact light curves are consistent with velocities of 400-600 m/s. Their modeling requires a three-step dissociation sequence “Grand-Parent → Parent → Daughter” to produce the observed molecules. The rotational light curve for each species is explained in terms of a single model with three sources. The dust component can however not easily be explained that way. 相似文献
48.
J.K. Cochran M.P. Bacon S. Krishnaswami K.K. Turekian 《Earth and Planetary Science Letters》1983,65(2):433-452
Disequilibrium between210Po and210Pb and between210Pb and226Ra has been mapped in the eastern and central Indian Ocean based on stations from Legs 3 and 4 of the GEOSECS Indian Ocean expedition.210Po/210Pb activity ratios are less than 1.0 in the surface mixed layer and indicate a residence time for Po of 0.6 years.210Po and210Pb are generally in radioactive equilibrium elsewhere in the water column except at depths of 100–500 m, where Po may be returned to solution after removal from the surface water, and in samples taken near the bottom at a few stations.210Pb excesses relative to226Ra are observed in the surface water but these excesses are not as pronounced as in the North Pacific and North Atlantic. The difference is attributable to a lower flux of210Pb from the atmosphere to the Indian Ocean. Below the main thermocline,210Pb activities increase with depth to a broad maximum before decreasing to lower values near the bottom. Departures from this pattern are especially evident at stations taken in the Bay of Bengal (where210Pb/226Ra activity ratios as low as 0.16 are observed) and near the Mid-Indian Ridge. The data suggest that removal of210Pb at oceanic boundaries, coupled with eddy diffusion along isopycnals, can explain gradients in210Pb near the boundary. Application of a simple model including isopycnal diffusion, chemical removal, production and radioactive decay produces fits the observed210Pb/226Ra gradients for eddy diffusion coeffients of ~ 107 cm2/s. High productivity in surface waters of the Bay of Bengal makes this region a sink for reactive nuclides in the northern Indian Ocean. 相似文献
49.
Tracking particle-associated processes in nearshore environments by use of 234Th/238U disequilibrium
Robert C. Aller Larry K. Benninger J. Kirk Cochran 《Earth and Planetary Science Letters》1980,47(2):161-175
Measurement of excess 234Th (t1/2 = 24.1 days) in surface sediment from 12 stations throughout Long Island Sound, U.S.A., demonstrates: (1) a mean (summer) sediment inventory of 3.6 dpm/cm2 consistent with complete, nearly instantaneous removal of 234Th from the overlying water and capture within the estuary, and (2) preferential association of excess 234Th with small particles and inventory build-ups in muddy bottom areas. There may also be a tendency for higher inventories in areas of high physical or biogenic reworking of surface sediments. A range of particle reworking rates (0–5 cm) from <0.01 × 10?6 to 1.6 × 10?6 cm2/s is found in the Sound with most values ~0.2?0.5 × 10?6 cm2/s. The inventory and reworking patterns demonstrate the high mobility, both horizontal and vertical, of particles in the estuary on 234Th decay time scales and are unequivocal evidence for control of reactive element distribution in the water column by the muddy regions of the basin. 相似文献
50.