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1.
Abstract Dahmani is a shocked LL6 fragmental breccia. According to the composition of the silicates (olivine Fa30,32.6, orthopyroxene Fs24.5–26.3) and of the metal (a 60% Ni taenite) it is one of the most oxidised known. 相似文献
2.
Denise Bellan-Santini 《Progress in Oceanography》1990,24(1-4)
The recent revision of the Mediterranean amphipod fauna includes 415 species (i.e. 8% of the worldwide fauna). The number of endemic species is estimated to be about 190 (i.e. 46% of the total fauna).The deep-sea fauna, which includes all those species inhabiting depths >150m, comprises 154 species (37.1% of the total fauna), belonging to 89 genera and 25 families. 84 of these species inhabited depths down to 400m, 47 down to 1000m, and 31 to depths >2000m. Considering the upper limits to their bathymetric ranges, 49 species are restricted to depths >150m, 15 to >400m, 9 to >1000m and just 5 to depths >2000m. 62.9% of the gammaridean fauna is restricted to the continental shelf at depths shallower than 150m. Only 11.3% of this fauna inhabits depths >1000m. and only 2.2% is restricted to these deeper depths.The composition of this deep-living fauna has complex zoogeographical relationships. There are four main categories of species: eurybathic, Atlantico-Mediterranean bathyal, endemic bathyal and endemic abyssal species.The deep-living species include 71 (46%) which are endemic. There are also 71 species which zoogeographically are Atlantico-Mediterranean, 4 which are cosmopolitan, 5 Atlantico-Pacifico-Mediterranean, one Indo-Atlantico-Mediterranean and one Pacifico-Mediterranean. The 71 endemic species belonging to 52 genera. Three of these genera are endemic and five others were previously known only as Indo-Pacific.The presence of bathyal endemic species belonging to bathyal genera, and the affinity of some other species otherwise occurring only in the Indo-Pacific, confirms that a Tethyan component persists in the amphipod fauna, and indicates that during the Messinian Crisis the Mediterranean did not completely dry up. Thus a relict amphipod fauna was able to survive in some of the residual basins. 相似文献
3.
Responses of a Mediterranean soft bottom community to short-term (1993-1996) hydrological changes in the Rhone river 总被引:1,自引:0,他引:1
The polychaete fauna of muddy bottoms off the Rhone delta (NW Mediterranean) was seasonally sampled at two sites at 70 m depth, from 1993 to 1996. During this period, five severe flood events occurred. A clustering analysis (distance coefficient of Whittaker) and three way fixed factor ANOVAs (site x season x year) showed strong year-to-year changes in species density and community structure, changes that masked seasonal variations. Total density increased by a factor of 3 and density of most species significantly increased following the first flooding event. Changes in the community structure were due to the successive dominance of a few species. The opportunistic species, such as Cossura sp., Mediomastus sp. and Polycirrus sp., exhibited peaks in density 1-3 months after the flood. These peaks were followed by a drastic decline. For species with a long life span, such as Sternaspis scutata, a slower but continuous increase in density was observed which was maintained for several months. The density fluctuations of these species exhibited a good correlation with river flow with time lags of 1-2 years. The successional dynamics observed are explained according to the geographical origin of the floods and the biology and feeding ecology of species. 相似文献
4.
The tolerance of the oligochaete Monopylephorus rubroniveus and the polychaete Streblospio benedicti to sediment-associated fluoranthene was characterized under normoxic (>80% dissolved oxygen saturation) and moderately hypoxic ( approximately 50% dissolved oxygen saturation) conditions. Under both conditions, M. rubroniveus was highly tolerant of fluoranthene. Streblospio benedicti was considerably less tolerant of fluoranthene compared with M. rubroniveus. In addition, S. benedicti was less tolerant to fluoranthene under moderately hypoxic conditions, although no differences in sensitivity between the two oxygen conditions were observed based upon median lethal tissue residues. Bioaccumulation factors were higher for S. benedicti exposed to moderate hypoxia, suggesting that behavioral adaptations to compensate for the lower dissolved oxygen increased its bioaccumulation of fluoranthene. The results of the present laboratory study demonstrate that (1). changes in annelid tolerance to fluoranthene under varying oxygen conditions is a species-dependent phenomenon and (2). the differential tolerance of these two annelids to these combined stressors is consistent with their relative abundances in the field. 相似文献
5.
Climate change impacts on U.S. Coastal and Marine Ecosystems 总被引:1,自引:0,他引:1
Donald Scavia John C. Field Donald F. Boesch Robert W. Buddemeier Virginia Burkett Daniel R. Cayan Michael Fogarty Mark A. Harwell Robert W. Howarth Curt Mason Denise J. Reed Thomas C. Royer Asbury H. Sallenger James G. Titus 《Estuaries and Coasts》2002,25(2):149-164
Increases in concentrations of greenhouse gases projected for the 21st century are expected to lead to increased mean global air and ocean temperatures. The National Assessment of Potential Consequences of Climate Variability and Change (NAST 2001) was based on a series of regional and sector assessments. This paper is a summary of the coastal and marine resources sector review of potential impacts on shorelines, estuaries, coastal wetlands, coral reefs, and ocean margin ecosystems. The assessment considered the impacts of several key drivers of climate change: sea level change; alterations in precipitation patterns and subsequent delivery of freshwater, nutrients, and sediment; increased ocean temperature; alterations in circulation patterns; changes in frequency and intensity of coastal storms; and increased levels of atmospheric CO2. Increasing rates of sea-level rise and intensity and frequency of coastal storms and hurricanes over the next decades will increase threats to shorelines, wetlands, and coastal development. Estuarine productivity will change in response to alteration in the timing and amount of freshwater, nutrients, and sediment delivery. Higher water temperatures and changes in freshwater delivery will alter estuarine stratification, residence time, and eutrophication. Increased ocean temperatures are expected to increase coral bleaching and higher CO2 levels may reduce coral calcification, making it more difficult for corals to recover from other disturbances, and inhibiting poleward shifts. Ocean warming is expected to cause poleward shifts in the ranges of many other organisms, including commercial species, and these shifts may have secondary effects on their predators and prey. Although these potential impacts of climate change and variability will vary from system to system, it is important to recognize that they will be superimposed upon, and in many cases intensify, other ecosystem stresses (pollution, harvesting, habitat destruction, invasive species, land and resource use, extreme natural events), which may lead to more significant consequences. 相似文献
6.
Andrew E. Laursen Sybil P. Seitzinger Robert Dekorsey James G. Sanders Denise L. Breitburg Richard W. Osman 《Estuaries and Coasts》2002,25(1):57-69
The effects of nutrients, trace elements, and trophic complexity on benthic photosynthesis and respriation were studied in the Paxtuxent River estuary near St. Leonard, Maryland. Experiments were conducted over three years (1995–1997) in mesocosms containing riverine sediment and water. The experimental design was 2×2×3 factorial with two levels of nutrients (ambient and + nutrients), two of trace elements (ambient and + trace elements) and three of trophic complexity (plankton, plankton + fish, and plankton + fish + benthos). Trace elements included arsenic (As), copper (Cu), and cadmium (Cd). The experiment was conducted three times in 1995 and 1997 and four times in 1996. In 1995 and 1996, sediments were muddy, while in the final year sediments were sandy. In mesocoms with sandy sediments, nutrient additions increased benthic photosynthesis overall, while trace element additions increased benthic photosynthesis in two of three experimental runs. Benthic photosynthesis in these mesocosms appeared to be related to nitrogen loading. Benthic respiration increased in nutrient and trace element amended mesocosms with sandy sediments, apparently in response to higher benthic photosynthesis. Increasing trophic complexity, particularly the presence of benthic organisms, also increased benthic respiration in mesocosms with sandy sediments. There were no effects of nutrient or trace element additions on benthic photosynthesis and respiration when the sediments were muddy. The lack of consistent responses to nutrient additions was surprising given that benthic respiration rates (and presumably nutrient regeneration) were similar in all three years, regardless of sediment type. Muddy, sediments did not mask, the effects of nutrient addition by supplying more nutrients to benthic microalgae than sandy sediments. In 1996, the presence of filter feeding bivalves increased the relative heterotrophy of sediments, measured as production: respiration. Consistent with increased heterotrophy, effluxes of ammonium and soluble reactive phosphorus from sediments were greater in mesocosms containing benthic organisms. Anthropogenically-induced changes in estuaries, such as loading of nutrients and trace elements or reduced trophic complexity, can have important effects on benthic processes and potentially pelagic processes through feedback mechanisms. 相似文献
7.
Effects of hypoxia, and the balance between hypoxia and enrichment, on coastal fishes and fisheries 总被引:2,自引:0,他引:2
Denise Breitburg 《Estuaries and Coasts》2002,25(4):767-781
A reduction in dissolved oxygen concentration is one of the most important direct effects of nutrient over-enrichment of coastal waters on fishes. Because hypoxia can cause mortality, reduced growth rates, and altered distributions and behaviors of fishes, as well as changes in the relative importance of organisms and pathways of carbon flow within food webs, hypoxia and anoxia can lead to large reductions in the abundance, diversity, and harvest of fishes within affected waters. Nutrient enrichment, however, typically increases prey abundance in more highly oxygenated surface waters and beyond the boundaries of the hypoxic zone. Because of this mosaic of high and low oxygen areas within a system, not only the actual oxygen concentration of bottom waters, but the spatial arrangement, predictability, and persistence of highly oxygenated, high productivity habitats, and the ability of fishes to locate and use those favorable habitats, will determine the ultimate effect of low oxygen on fish populations. Negative effects of hypoxia on fish, habitat, and food webs potentially make both fish populations and entire systems more susceptible to additional anthropogenic and natural stressors. 相似文献
8.
Patricia Fortes Sofia Simões Júlia Seixas Denise Van Regemorter Francisco Ferreira 《Climate Policy》2013,13(3):285-304
Bottom-up and top-down models are used to support climate policies, to identify the options required to meet GHG abatement targets and to evaluate their economic impact. Some studies have shown that the GHG mitigation options provided by economic top-down and technological bottom-up models tend to vary. One reason for this is that these models tend to use different baseline scenarios. The bottom-up TIMES_PT and the top-down computable general equilibrium GEM-E3_PT models are examined using a common baseline scenario to calibrate them, and the extend of their different mitigation options and its relevant to domestic policy making are assessed. Three low-carbon scenarios for Portugal until 2050 are generated, each with different GHG reduction targets. Both models suggest close mitigation options and locate the largest mitigation potential to energy supply. However, the models suggest different mitigation options for the end-use sectors: GEM-E3_PT focuses more on energy efficiency, while TIMES_PT relies on decrease carbon intensity due to a shift to electricity. Although a common baseline scenario cannot be ignored, the models’ inherent characteristics are the main factor for the different outcomes, thereby highlighting different mitigation options. Policy relevance The relevance of modelling tools used to support the design of domestic climate policies is assessed by evaluating the mitigation options suggested by a bottom-up and a top-down model. The different outcomes of each model are significant for climate policy design since each suggest different mitigation options like end-use energy efficiency and the promotion of low-carbon technologies. Policy makers should carefully select the modelling tool used to support their policies. The specific modelling structures of each model make them more appropriate to address certain policy questions than others. Using both modelling approaches for policy support can therefore bring added value and result in more robust climate policy design. Although the results are specific for Portugal, the insights provided by the analysis of both models can be extended to, and used in the climate policy decisions of, other countries. 相似文献
9.
Jaume Llopart Roger Urgeles Carl Fredrik Forsberg Angelo Camerlenghi Maarten Vanneste Michele Rebesco Renata Giulia Lucchi Denise Christina Rüther Hendrik Lantzsch 《Basin Research》2019,31(3):487-513
Using a combination of geophysical and geotechnical data from Storfjorden Trough Mouth Fan off southern Svalbard, we investigate the hydrogeology of the continental margin and how this is affected by Quaternary glacial advances and retreats over the continental shelf. The geotechnical results show that plumites, deposited during the deglaciation, have high porosities, permeabilities and compressibilities with respect to glacigenic debris flows and tills. These results together with margin stratigraphic models obtained from seismic reflection data were used as input for numerical finite element models to understand focusing of interstitial fluids on glaciated continental margins. The modelled evolution of the Storfjorden TMF shows that tills formed on the shelf following the onset of glacial sedimentation (ca. 1.5 Ma) acted as aquitards and therefore played a significant role in decreasing the vertical fluid flow towards the sea floor and diverting it towards the slope. The model shows that high overpressure ratios (up to λ ca. 0.6) developed below the shelf edge and on the middle slope. A more detailed model for the last 220 kyrs accounting for ice loading during glacial maxima shows that the formation of these aquitards on the shelf focused fluid flow towards the most permeable plumite sediments on the slope. The less permeable glacigenic debris flows that were deposited during glacial maxima on the slope hinder fluid evacuation from plumites allowing high overpressure ratios (up to λ ca. 0.7) to develop in the shallowest plumite layers. These high overpressures likely persist to the Present and are a critical precondition for submarine slope failure. 相似文献
10.