共查询到20条相似文献，搜索用时 31 毫秒
1.
Maximum species diversity occurs at abyssal depths of greater than 2500 meters. Other diversity peaks occur at depths of 35 to 45 meters and 100 to 200 meters. The peak at 35 to 45 meters is due to species equitability, whereas the other two peaks correspond to an increase in the number of species. 相似文献
2.
Emery KO Wigley RL Bartlett AS Rubin M Barghoorn ES 《Science (New York, N.Y.)》1967,158(3806):1301-1307
Freshwater peats from the continental shelf off northeastern United States contain the same general pollen sequence as peats from ponds that are above sea level and that are of comparable radiocarbon ages. These peats indicate that during glacial times of low sea level terrestrial vegetation covered the region that is now the continental shelf in an unbroken extension from the adjacent land areas to the north and west. 相似文献
3.
Johnson KS Berelson WM Coale KH Coley TL Elrod VA Fairey WR Iams HD Kilgore TE Nowicki JL 《Science (New York, N.Y.)》1992,257(5074):1242-1245
The flux of manganese from continental margin sediments to the ocean was measured with a free-vehicle, benthic flux chamber in a transect across the continental shelf and upper slope of the California margin. The highest fluxes were observed on the shallow continental shelf. Manganese flux decreased linearly with bottom water oxygen concentration, and the lowest fluxes occurred in the oxygen minimum zone (at a depth of 600 to 1000 meters). Although the flux of manganese from continental shelf sediments can account for the elevated concentrations observed in shallow, coastal waters, the flux from sediments that intersect the oxygen minimum cannot produce the subsurface concentration maximum of dissolved manganese that is observed in the Pacific Ocean. 相似文献
4.
The high-velocity core of the Western boundary undercurrent at the base of the u.s. Continental rise
The Western Boundary Undercurrent is a high-velocity, contour-following bottom current that flows southwesterly on the U.S. Atlantic continental margin. A high-velocity core of the Western Boundary Undercurrent is delineated by an analysis of underlying sediments, which are characterized by coarse particle sizes and efficiently aligned magnetic grains in a zone from 4440 meters at the base of the rise to 5200 meters on the adjacent abyssal plain. 相似文献
5.
In distinct contrast to the restricted movements of coastal stocks of lobsters (Homarus americanus), those inhabiting the outer continental shelf undertake extensive seasonal migrations. Of 5710 tagged lobsters released on the outer continental shelf off New England from April 1968 to June 1969, 400 had been recaptured by April 1970. The distribution of the recoveries demonstrated shoalward migration in spring and summer and a return to the edge of the shelf in fall and winter. Deep-sea lobsters have a faster rate of growth than coastal lobsters; growth increments at molting and the frequency of molting are greater. 相似文献
6.
Deep sounding seismic reflection data show undeformed reflectors at depths down to 11 kilometers beneath the continental rise and abyssal plain and 7 kilometers in basins of the lower slope. Weak reflectors are visible beneath the salt of the Sigsbee Scarp and within salt ridges separating the lower slope basins. 相似文献
7.
Teeth of mastodons and mammoths have been recovered by fishermen from at least 40 sites on the continental shelf as deep as 120 meters. Also present are submerged shorelines, peat deposits, lagoonal shells, anz relict sands. Evidently elephants and other large mammals ranged this region during the glacial stage of low sea level of the last 25,000 years. 相似文献
8.
Volcanic glass in marine sediments off Oregon and Washington correlates with continental deposits of Mount Mazama ash by stratigraphic position, refractive index, and radiocarbon dating. Ash deposited in the abyssal regions by turbidity currents is used for tracing of the dispersal routes of postglacial sediments and for evaluation of marine sedimentary processes. 相似文献
9.
Individual heads of two species of reef or herinatypic coral, Solenastrea hyades (Dana) and Siderastrea siderea (Ellis and Solander), occur on rock outcrops on the inner continental shelf off North Carolina in waters where winter bottom temperatures are as low as 10.6 degrees C. These temperatures are significantly lower than previously assumed minimum temperatures for the survival of tropical reef corals in their natural environment. 相似文献
10.
文昌鸡线粒体控制区遗传多态性及系统进化分析 总被引：1，自引：0，他引：1
通过对文昌鸡线粒体基因纽(mitochondrial genome,mtDNA)D-loop区全序列的测序和比对,并结合GenBank已经测出D-loop区全序列的红色原鸡的序列,探讨了文昌鸡的遗传多样性和母系起源。结果发现,文昌鸡mtDNAD-loop区全长1231~1232bp,核苷酸多样性(Pi)为0.09757,单倍型多样性(Hd)为0.874。在30只个体中,共发现20处单核苷酸多态位点,10种单倍型。系统发育分析发现,10种单倍型可以分为B、C和E 3个分支。B分支与红色原鸡滇南亚种(Gallus gallus spadiceus)聚为一类,推测这两个分支可能起源于云南、缅甸附近地区的红色原鸡滇南亚种。E分支与红色原鸡(Gallusgallus murghi)聚为一类,推测可能起源于红色原鸡的印度亚种分支。C分支与4个原鸡亚种聚为一类,可能有多个母系起源。本研究从分子水平上为文昌鸡的遗传资源保护和开发利用提供了参考。 相似文献
11.
On the central portion of the west Florida continental shelf, radionuclide activities show unusually wide variations: radium-226 activities up to 350 disintegrations per minute per 100 liters, radon-222 activities up to 1300 disintegrations per minute per 100 liters, and deficiencies of radon-222 as low as -10 disintegrations per minute per 100 liters. Florida's phosphate-rich strata seerm to be the principal source of the radionuclides, with the transfer occurring directly from sediments or indirectly in streams, ground-water flow, and geothermal springs. Winter storm fronts may enhance radon degassing in the shelf waters. 相似文献
12.
Washburn L Swenson MS Largier JL Kosro PM Ramp SR 《Science (New York, N.Y.)》1993,261(5128):1560-1564
A combination of satellite imagery, shipboard profiles, drifter tracks, and moored current observations reveals that an anticyclonic eddy off the coast of northern California transported plumes of suspended sediments from the continental shelf into the deep ocean. The horizontal scale of the eddy was about 90 kilometers, and the eddy remained over the continental shelf and slope for about 2 months during the summer of 1988. The total mass of sediments transported by the eddy was of order 105 metric tons. Mesoscale eddies are recurrent features in this region and occur frequently in eastern boundary currents. These results provide direct evidence that eddies export sediments from continental shelves. 相似文献
13.
Feely RA Sabine CL Hernandez-Ayon JM Ianson D Hales B 《Science (New York, N.Y.)》2008,320(5882):1490-1492
The absorption of atmospheric carbon dioxide (CO2) into the ocean lowers the pH of the waters. This so-called ocean acidification could have important consequences for marine ecosystems. To better understand the extent of this ocean acidification in coastal waters, we conducted hydrographic surveys along the continental shelf of western North America from central Canada to northern Mexico. We observed seawater that is undersaturated with respect to aragonite upwelling onto large portions of the continental shelf, reaching depths of approximately 40 to 120 meters along most transect lines and all the way to the surface on one transect off northern California. Although seasonal upwelling of the undersaturated waters onto the shelf is a natural phenomenon in this region, the ocean uptake of anthropogenic CO2 has increased the areal extent of the affected area. 相似文献
14.
Beal RC 《Science (New York, N.Y.)》1980,208(4450):1373-1375
A well-organized, very low energy ocean swell system off the East Coast of the United States was tracked with the Seasat synthetic aperture radar from deep water, across the continental shelf, and into shallow, water. The results indicate that spaceborne imaging radar may be used to accurately measure ocean wavelength and direction, even in coastal areas and in the presence of a mixed ocean. 相似文献
15.
Paull CK Hecker B Commeau R Freeman-Lynde RP Neumann C Corso WP Golubic S Hook JE Sikes E Curray J 《Science (New York, N.Y.)》1984,226(4677):965-967
Dense biological communities of large epifaunal taxa similar to those found along ridge crest vents at the East Pacific Rise were discovered in the abyssal Gulf of Mexico. These assemblages occur on a passive continental margin at the base of the Florida Escarpment, the interface between the relatively impermeable hemipelagic clays of the distal Mississippi Fan and the jointed Cretaceous limestone of the Florida Platform. The fauna apparently is nourished by sulfide rich hypersaline waters seeping out at near ambient temperatures onto the sea floor. 相似文献
16.
On the southeastern U.S. continental shelf, phytoplankton primary production and the densities of zooplankton, fish eggs, and fish larvae peak simultaneously in late summer and early fall. Some community response to irregular storm events is observed. However, the gross plankton community dynamics on this shelf are dominated by couplings with the local estuaries and shallow nearshore zone. 相似文献
17.
Makris NC Ratilal P Symonds DT Jagannathan S Lee S Nero RW 《Science (New York, N.Y.)》2006,311(5761):660-663
Until now, continental shelf environments have been monitored with highly localized line-transect methods from slow-moving research vessels. These methods significantly undersample fish populations in time and space, leaving an incomplete and ambiguous record of abundance and behavior. We show that fish populations in continental shelf environments can be instantaneously imaged over thousands of square kilometers and continuously monitored by a remote sensing technique in which the ocean acts as an acoustic waveguide. The technique has revealed the instantaneous horizontal structural characteristics and volatile short-term behavior of very large fish shoals, containing tens of millions of fish and stretching for many kilometers. 相似文献
18.
Hathaway JC Poag CW Valentine PC Manheim FT Kohout FA Bothner MH Miller RE Schultz DM Sangrey DA 《Science (New York, N.Y.)》1979,206(4418):515-527
The first broad program of scientific shallow drilling on the U.S. Atlantic continental shelf has delineated rocks of Pleistocene to Late Cretaceous age, including phosphoritic Miocene strata, widespread Eocene carbonate deposits that serve as reflective seismic markers, and several regional unconformities. Two sites, off Maryland and New Jersey, showed light hydrocarbon gases having affinity to mature petroleum. Pore fluid studies showed that relatively fresh to brackish water occurs beneath much of the Atlantic continental shelf, whereas increases in salinity off Georgla and beneath the Florida-Hatteras slope suggest buried evaporitic strata. The sediment cores showed engineering properties that range from good foundation strength to a potential for severe loss of strength through interaction between sediments and man-made structures. 相似文献
19.
Lower Miocene microfossils occur in basaltic glass in two dredge hauls from the crestal area of the Mid-Atlantic Ridge near 30 degrees N. From the ridge and adjoining abyssal hills 43 pre-Pleistocene cores were identified, including one Cretaceous and four Eocene. Dredgings and cores now available suggest that the upper layer of the crust of the ridge is constructed of layers of interbedded sediments and basalt flows. The data rule out the possibility of large-scale continental drifting or spreading of the ocean floor since the Lower Miocene. 相似文献
20.
Relative sea levels for early post-Pleistocene time are best known from radiocarbon dates of sediments on the continental shelves off Texas and off northeastern United States. Differences in indicated rates of the rise of relative sea level and in depths of the shelf-breaks reveal differential vertical movement of the two shelves during this time, with the result that the Atlantic shelf has sunk with respect to the Texas shelf. 相似文献