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71.
Abstract. Microplankton (silicoflagellates, dinoflagellates, tintinnids, pteropods, crustaceans, and fecal pellets) was analysed in 71 0–95 m samples from the Greenland Sea collected from May to June 1989. Abundances were clearly associated with the ice edge, highest concentrations occurring in ice-free waters. The 15 to 30 m stratum was generally richer in microplankton than deeper waters, with the exception of microcrustaceans, which often peaked below 30 m. Six tintinnid species were identified. The mean size of the tintinnid Parafavella denticulata from the Greenland Sea was consistently greater than that of Barents Sea specimens. It is suggested that colder waters and scarcer food are responsible for these morphometric differences. 相似文献
72.
Seismic reflection profiles from the northern end of Juan de Fuca Ridge reveal three axial valleys having a basement relief of as much as 2 sec (two-way travel time). A thick sequence, presumably of turbidites, mainly less than 0.7 m.y. old, covers much of the area. The oldest turbidites form the upper part of the fill of a possible Tertiary trench between the ridge and North America. The second turbidite unit extends beyond the trench and once formed an abyssal plain over most of northern Juan de Fuca Ridge and the area west to Explorer Ridge. Following formation of the plain, vertical movements began that broadly uplifted the crest of Juan de Fuca Ridge, block-faulted its northern end, produced faulting along Sovanco Fracture Zone, and upwarped the basement north of the ridge. Younger turbidites have filled the lowlands created by the vertical movements. The present sea floor topography and seismic activity show evidence of continued movements. 相似文献
73.
74.
The Ter Vell (NE Iberian Peninsula) is a eutrophic coastal lagoon which has been flooded by the excess irrigation water and the agricultural runoff during the last decades. Between 1999 and 2003, restoration measures were applied to improve its water quality. At the same time, but independently, agricultural water management drastically reduced the freshwater inflow. The short-term effects of these management actions on the limnological characteristics of the lagoon were analysed by comparing two hydrological cycles, one before (1999/2000) and the other one after (2002/2003) the actions. The two cycles are illustrative of opposite situations in the hydrological functioning of coastal wetlands. In the first, the lagoon was exorheic, with prolonged flooding periods and a low residence time; in the second, it had a more endorheic character, with scarce water inputs and prolonged periods of confinement. Consequently, nitrogen inputs diminished and organic load and salinity increased as the internal loading and the accumulation effects became more relevant. These effects were actually caused by the drastic reduction in the freshwater inflow which prevented, in turn, the success of the restoration measures. The zooplankton community of the Ter Vell lagoon was not significantly altered by the hydrological change, at least in the short-term, and rotifers and cladocerans, mainly those species indicative of eutrophy, dominated the community. 相似文献
75.
Sandy Wyllie-Echeverria Sandra Looman Talbot Jolene Rae Rearick 《Estuaries and Coasts》2010,33(4):811-827
Using data from eight autosomal microsatellite loci, we investigated levels of within- and between-site variation in the seagrass
Zostera marina L. (eelgrass) from eight locations in the San Juan Archipelago, located in the northwest corner of Washington, USA. Only
117 of the 365 samples collected were unique individuals, and there were large differences in the estimates of clonality among
sites. Site-specific genotypic richness ranged from 0.082 to 0.688, and the distribution of ramets and genets varied widely
within sites. No multilocus genotypes were shared between sites. We found significant differences in distribution of alleles
and variance in allele frequencies among sites, suggesting substantial genetic population substructuring. We detected low
levels of genetic diversity in two sites known to have undergone recent declines and a genetic signature of population expansion
in a site known to be increasing. Thus, like elsewhere, we find that genetic studies add an important component to monitoring
programs in this region. 相似文献
76.
Eric Armynot du Châtelet François GuillotPhilippe Recourt Sandra VentalonNicolas Tribovillard 《Comptes Rendus Geoscience》2010,342(9):710-717
Testate amoebae are increasingly used for environmental monitoring as well as paleoenvironmental reconstructions. Paleoecological interpretations of testate amoebae assemblages depend on the understanding of the ecological processes operating today. We then ask the question of the link between testate structure and its environment. This study analyses both the grain size and mineralogical assemblage of tests of common species belonging to the genus Centropyxis and Difflugia. It is concluded that grain size is a limiting factor for test construction, whereas mineral composition is not. Hence, when analyzing agglutinated testate amoebae for paleoenvironmental reconstructions, it should be taken into account the mean grain size of the sediment. A non-appropriate grain-size probably inhibits the development of a testate amoebae specific assemblage. 相似文献
77.
Lago Roca-Lapataia valley (54°50′S, 68°34′W) is a paleofjord that was occupied by a valley-glacier system during the glacial maximum of the late Pleistocene (estimated ca. 18–20 ka BP). Deglaciation began before 10,080 ± 270 BP. The marine fauna in several marine terraces found in the area shows that early-middle Holocene climatic conditions were basically the same as at present. Species found are characteristic of cold and shallow waters, although minor temperature fluctuations cannot be ruled out for this period. A recent radiocarbon date of 7518 ± 58 BP on Chlamys patagonica (NZ # 7730) confirms that Lago Roca was transformed into a fjord ca. 7500–8000 BP. The sea reached its maximum level of 8–10 m a.s.l. around 6000 BP and at 4000–4500 BP was at least above 6 ± 1 m a.s.l. Later, when sea level fell, Lago Roca was occupied by fresh water and was no longer tidal. The relative land-sea positions during this period are a consequence of combined eustatic and neotectonic processes. 相似文献
78.
A simple inexpensive photometer designed for Winkler titration end-point detection is described. The precision of replicate dissolved oxygen measurements using this instrument was 0.06–0.22%. This high precision is needed to measure the small changes in dissolved oxygen concentration for determining the respiration rate of small aquatic organisms. Other recommendations for improving precision are also presented. 相似文献
79.
The stable isotopic composition of coral skeletons: control by environmental variables 总被引:1,自引:0,他引:1
Sandra M. Weil Robert W. Buddemeier Stephen V. Smith Peter M. Kroopnick 《Geochimica et cosmochimica acta》1981,45(7):1147-1153
The reef corals Pocillopora damicornis and Montipora verrucosa were cultured under various controlled temperature and light conditions. The corals were analyzed for growth rate, tissue pigment content and skeletal 13C and 18O. Coral skeletal δ13C values varied with light dose and correlated with changes in zooxanthellar pigment. The δ13C values of skeletal aragonite seem to be modified by oxidation of photosynthetically produced organic matter.Functionally significant relationships between coral skeletal δ18O values and temperature have been determined. The temperature coefficients of the δ18O values [?4.4°C (%.)?1] are similar to the first order coefficient in the equilibrium paleotemperature equation, but the δ18O values have taxonomically consistent offsets from equilibrium. The offsets may be attributed to the coral metabolism with slight but statistically significant differences between the two genera. Environmental and metabolic variables other than temperature have little or no effect on skeletal δ18O. 相似文献
80.
Diffusion of ions in sea water and in deep-sea sediments 总被引:3,自引:0,他引:3
Sandra Gregory 《Geochimica et cosmochimica acta》1974,38(5):703-714
The tracer-diffusion coefficient of ions in water, Dj0, and in sea water, , differ by no more than zero to 8 per cent. When sea water diffuses into a dilute solution of water, in order to maintain the electro-neutrality, the average diffusion coefficients of major cations become greater but of major anions smaller than their respective or Dj0 values. The tracer diffusion coefficients of ions in deep-sea sediments, Dj,sed., can be related to by , where θ is the tortuosity of the bulk sediment and a a constant close to one. 相似文献