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Search Results: 1 - 10 of 1208 matches for " continental shelf "
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Placeres marinhos
Silva, Cleverson G.;
Revista Brasileira de Geofísica , 2000, DOI: 10.1590/S0102-261X2000000300010
Abstract: marine placers are located on present beaches or are related to the quaternary sea level oscillatory events, which exposed large areas of the continental shelf or covered portions of the coastal plains. the transgressive sea level events drowned alluvial and colluvial deposits including important heavy minerals concentrations further reworked by current and wave action. this mechanism promoted the re-concentration of the denser minerals such as ilmenite, zircon, tin, gold and diamonds. the main exploration activities of marine placers are located on namibian and south african continental shelves, for diamonds, and on the southeast asia, for tin. important extraction of ilmenite, zircon, rutile and monazite sands occurs in australia, sri lanka and india, as well as on the northern rio de janeiro state, brazil. gold extraction on beaches and on the continental shelf offshore alaska ceased during the nineties. the technology involved on the exploitation of marine minerals can be highly sophisticated, as observed in namibia and south africa, employing massive ships, with specially designed rotation drills, submarine robots and track-mounted vehicles, equipped with powerful suction pumps, remotely controlled. these equipment are used to extract the gravel substrate containing the diamonds in water depths approaching 200 m. the associated environmental impact in dredged areas is substantial and must be constantly monitored and controlled by an efficient legislation and by the local environmental agencies and controlling organisms. this paper presents a review of the current knowledge about the origin of the marine placers, the main world's and brazilian occurrences and exploration techniques and the principal environmental impacts associated with its exploitation.
Bremec,Claudia; Souto,Valeria; Genzano,Gabriel;
Anales del Instituto de la Patagonia , 2010, DOI: 10.4067/S0718-686X2010000200005
Abstract: the aim of this paper is to study the polychaete composition from a wide area in the argentinean shelf, between 36°s and 55°s, by means of samples collected from soft bottoms with picard dredge, during the "shinkai maru" cruises developed in 1978-79. as the study area comprises both the magellanic and argentinean biogeographic provinces, we analyze if these results show differences in polychaete composition between both provinces. a total of 816 individuals was studied; 29 families, represented by 70 taxa, were identified. the most frequent (36-57% sampling stations) and abundant families were onuphidae, nephtyidae and ampharetidae, mainly represented by kinbergonuphis dorsalis, aglaopha-mus sp. and ampharete kerguelensis, respectively. cluster analysis, simper test and anosim showed two different species assemblages in two well defined areas according to a nearly 60m depth boundary, in correspondence with the classical magellanic and argentinean provinces.
Microarthridion corbisierae sp. nov. (Harpacticoida, Tachidiidae), um novo copépode da meiofauna do litoral norte do estado de S?o Paulo, Brasil
Kihara, Terue C.;Rocha, Carlos E. F.;
Revista Brasileira de Zoologia , 2007, DOI: 10.1590/S0101-81752007000400007
Abstract: during studies on the diversity of meiobenthic marine harpacticoid copepods, a new representative of the family tachidiidae was found on the inner continental shelf of s?o paulo state, between s?o sebasti?o channel and ubatumirim bay, ubatuba (23o24's, 44o57,6'w). complementary material was collected near enseada beach, ubatuba (23o30's, 45o05'w). although the new species shares with m. laurenticum (nicholls, 1940) the reduced antennules, it can be easily distinguished from its congeners by leg 4 endopod with only two segments and the reduction of the number of inner setae of legs 1-4 endopod-3 and leg 3 exopod-3. tachidiids, typically inhabiting fine sediments of brackish and marine shallow waters in the northern hemisphere, are good indicators of heavy organic pollution. this is the first record of the family tachidiidae in the southern hemisphere.
Hábitos alimentarios del pez triglido Prionotus ruscarius (Gilbert & Starks, 1904) durante 1996, en las costas de Jalisco y Colima, México
Raymundo-Huizar,Alma Rosa; Saucedo Lozano,Mirella;
Revista de biología marina y oceanografía , 2008, DOI: 10.4067/S0718-19572008000100002
Abstract: the stomach content of the common searobin prionotus ruscarius is described and analysed in this study. a total of 128 specimens, were captured from the continental shelf of jalisco and colima, mexico, between january and december 1996. percentages of numeric, gravimetric, frequency of occurrence and index of relative importance (iir) were calculated for each prey item. thirty food items were observed in the diet. the index of relative importance (iir) showed that p. ruscarius mainly prey on penaeids shrimp (45.5%), brachyuran (37.8%) and stomatopods (9.7%). significant feeding variations were found in different fish body sizes. according to levins index, used to determine the trophic spectrum, p. ruscarius had a medium grade of specialization. penaeid shrimps and brachyurans were observed as secondary food items, based on the feeding index
Determina??o dos elementos-tra?o (Zn, Co e Ni) em sedimentos da Plataforma Continental Amaz?nica sob influência da descarga do rio Amazonas
Siqueira, Gilmar Wanzeller;Pereira, Simone de Fátima Pinheiro;Aprile, Fábio Marques;
Acta Amazonica , 2006, DOI: 10.1590/S0044-59672006000300005
Abstract: determination of trace elements (zn, co and ni) in sediments at the amazon continental shelf on influence of the amazon river discharge this research was developed at amazon continental shelf (acs) between the orange cape (amapá state) and the maguari cape (pará state), to determine the levels of zinc, cobalt and nickel in the superficial sediments identifying its inputs and outputs. the rate of these metallic elements in the sediments decreases following zn> ni> co. the concentrations of total metals in the surface sediments range from zn = 52.8 159.5; ni = 21.7 47.4 and co = 14.3 48.8 (mg.kg-1). the levels of trace elements observed in the sediments at acs are of natural occurrence. pollution sources of metallic elements were not observed.
Taxonomia e distribui??o de Actinocythereis brasiliensis sp. nov. (Podocopida, Trachyleberididae) na plataforma continental brasileira
Machado, Cláudia P.;Drozinski, Núscia G. S.;
Iheringia. Série Zoologia , 2002, DOI: 10.1590/S0073-47212002000300001
Abstract: a new species is described, actinocythereis brasiliensis, from the southern brazilian continental shelf. it is based on the analysis of 766 samples collected by oceanographical projects. the geographical distribution of this species has revealed its preference by the cold waters and terrigenous sediments and, has a bathymetric distribution between 22 and 164 m but, being concentrated in the shallower waters (< 60 m).
The Family Thaerocytheridae Hazel, 1967 (Ostracoda) from the Southern Brazilian Continental Shelf
Feijó Ramos,Maria Inês; Coimbra,Jo?o Carlos; Whatley,Robin;
Ameghiniana , 2009,
Abstract: of a total fauna of 95 species of benthic ostracoda recovered from dry sediments from the southern brazilian continental shelf, 8% belong to the family thaerocytheridae. six species assigned to this family are discussed and figured in this paper; four of these, bradleya pseudonormani, b. kaesleri, muellerina cribrosa and quadracythere nealei are described as new, while brasilicythere reticulispinosa and quadracythere eichlerae were described for the first time from the quaternary of pelotas basin, in southern brazil. most of these species are restricted to the southern part of the southwest atlantic ocean, and their geographical distribution ranges from the southern brazilian continental shelf, in rio de janeiro state (21os), to the argentinian continental shelf (52os). three species are restricted to the southern brazilian continental shelf: b. kaesleri, m. cribrosa. and q. nealei, while three other species have fossil records: b. reticulispinosa (oligocene to recent), q. eichlerae and b. kaesleri (both holocene to recent).
Nutrient and phytoplankton biomass in the Amazon River shelf waters
Santos, Maria L.S.;Muniz, Kátia;Barros-Neto, Benício;Araujo, Moacyr;
Anais da Academia Brasileira de Ciências , 2008, DOI: 10.1590/S0001-37652008000400011
Abstract: the amazon river estuary is notable at the amazon continental shelf, where the presence of the large amount of water originating from the amazon during the river's falling discharge period was made evident by the low salinity values and high nutrient levels. even so, the presence of oceanic waters in the shelf area was significant. dissolved organic nitrogen was the predominant species of the nitrogen cycle phases, followed by total particulate nitrogen, nitrate, ammonium and nitrite. the chlorophyll a data in the eutrophic area indicated that there is sufficient nitrogen in the area to withstand productivity, though dissolved inorganic nitrogen removal processes are faster than regeneration or mineralization. the anomalous amounts of inorganic dissolved nitrogen showed more removal than addition. the simulations with the bidimensional maac-2d model confirmed that high nutrient waters are displaced northwest-ward (two cores at 2.5on-50ow and 4on-51ow) by the stronger nbc during falling river discharge. during high river flow period these nutrient-rich lenses are distributed around 0.5on-48.5ow as well as along the shallow amazonian shelf (20m-50m depth, 1on-3.5on), as a result of the spreading of amazon freshwater outflow.
García-Valencia,Carolina; Díaz,Juan Manuel;
Boletín de Investigaciones Marinas y Costeras - INVEMAR , 2000,
Abstract: during a baseline survey of the shallow bottoms (10-50 m) of the southern continental shelf of the colombian caribbean, a total of 35 molluscan species belonging to 24 families was collected. three main molluscan bottom assemblages were recognized according to species composition and abundance, whose distribution seems likely to be controlled rather by depth than by sediment features. twenty four of the species were not recorded before from this area of the colombian caribbean.
Flórez-Romero,Paola; Montoya-Cadavid,Erika; Reyes-Forero,Javier; Santodomingo,Nadiezhda;
Boletín de Investigaciones Marinas y Costeras - INVEMAR , 2007,
Abstract: the cheilostomes are the most diverse existent bryozoans group. its species are commonly found in all the marine ecosystems around the world. in colombia, however, information about them is scarce and limited to few localities. with the initiative of exploring the soft bottom biodiversity and completing the colombian marine fauna inventories, invemar-macrofauna ii exploration took place in march 2001, during which samples were collected on soft bottoms throughout the colombian caribbean from the continental shelf and the upper slope (20 - 500 m depth) by trawling. 62 species of cheilostomes that belong to 39 families were found, 36 are first records for the colombian caribbean, 4 for the great caribbean and 1 for the tropical west atlantic. bathymetric and geographic ranges are extended for 13 species. taxonomical notes and images of the five species that are first records for the greater caribbean and the tropical west atlantic are included in this survey. it also includes remarks about the distribution, substrata, and growth types of cheilostomata studied.
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