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941.
942.
The nonlinear energy transfer through the wave spectrum is studied on the basis of the previously obtained explicit equation for matrix elements of a four-wave kinetic integral. The equation describes the evolution of a system of gravity waves at the surface of a sea of finite depth with a uniform distribution of broken ice over the sea surface. Particular attention is paid to the analytical part of the algorithm of the calculation of the kinetic integral. This part differs from the standard algorithm by a set of prominent features of the dispersion relation for wave oscillations in the ice-covered water. The kinetic integral for the system under consideration is calculated, and the results are compared with the results obtained for the ice-free water. 相似文献
943.
Until recently, the ideas about the age of the Black Sea deep-water basin have been based on land geological observations in the coastal areas at the interaction periphery, underwater observations from manned submersibles, and on the data of seismic reflection and refraction studies and drilling. Formerly, the scarcity of the information led to a wide scattering of the age determinations: from the Jurassic to the Eocene. Recently, with the appearance of reliable geological and geophysical data, the range of the age estimates has been considerably reduced during the last few years, although there is no commonly accepted opinion on this issue. Therefore, the first attempt to determine the age of the Western Black Sea basin using an analysis of the anomalous magnetic field is of certain interest. The following results were obtained: the basin probably opened between 71.338 and 71.587 My B.P. (subchron C32n.1r). During the interval 68.737–71.071 My B.P. (subchron C31r), extinction of the spreading axes took place. Thus, the total duration of the Campanian-Maestrichtian phase of the opening was about 3 My (interval from 71.587 to 68.737 My B.P.). This result does not agree with the geological and geophysical data available to date. To solve this problem, collection of new geological data and further studies of the structure of the anomalous magnetic field are required. 相似文献
944.
C. Svensen D. Vili
i P. Wassmann E. Arashkevich T. Ratkova 《Estuarine, Coastal and Shelf Science》2007,71(3-4):381-390
The aim of this study was to investigate phytoplankton abundance, composition and vertical export in the highly stratified Krka estuary, Croatia. The estuary is stratified throughout the year, and an interface between fresh- and brackish water plays an important role in production and degradation of biogenic matter. Vertical export of particulate organic carbon (POC), phytoplankton carbon (PPC) and faecal pellet carbon (FPC) was studied by deploying sediment traps in the middle and lower reach of the estuary and in the adjacent coastal zone. Zooplankton faecal pellet (FP) production experiments were conducted to provide additional information on the potential contribution of FP to the total carbon flux. High suspended concentrations of POC, chlorophyll a and phytoplankton was found in the lower reaches of the Krka estuary, adjacent to a source of anthropogenic eutrophication. The fraction of organic detritus to the total POC flux was 61–69% inside the estuary but only 7% at the marine station. This indicates that the primary producers in the surface layer of the Krka estuary are decomposed in and below the interface and then settle as detritus to the bottom. Low sedimentation rates in the coastal zone outside the estuary revealed that the eutrophication does not spread out of the estuary. Mesozooplankton played a modest role in vertical flux regulation, due to their low abundance and dominance of smaller forms as well as low faecal pellet production rates. It is concluded that processes taking place at the freshwater-seawater interface are of major importance for the vertical carbon flux in the investigated area. 相似文献
945.
Seismic analyses of Cenozoic contourite drift development in the Northern Norwegian Sea 总被引:1,自引:0,他引:1
Laberg Jan Sverre Dahlgren Torbjørn Vorren Tore O. Haflidason Haflidi Bryn Petter 《Marine Geophysical Researches》2001,22(5-6):401-416
Four drift accumulations have been identified on the continental margin of northern Norway; the Lofoten Drift, the Vesterålen Drift, the Nyk Drift and the Sklinnadjupet Drift. Based on seismic character these drifts were found to belong to two main groups; (1) mounded, elongated, upslope accretion drifts (Lofoten Drift, Vesterålen Drift and Nyk Drift), and (2) infilling drifts (Sklinnadjupet Drift). The drifts are located on the continental slope. Mainly surface and intermediate water circulation, contrary to many North Atlantic and Antarctic drifts that are related to bottom water circulation, and sediment availability have controlled their growth. Sediments were derived both from winnowing of the shelf and upper slope and from ice sheets when present on the shelf. The main source area was the Vøring margin. This explains the high maximum average sedimentation rate of the nearby Nyk (1.2 m/ka) and Sklinnadjupet (0.5 m/ka) Drifts compared with the distal Lofoten (0.036 m/ka) and Vesterålen (0.060 m/ka) Drifts. The high sedimentation rate of the Nyk Drift, deposited during the period between the late Saalian and the late Weichselian is of the same order of magnitude as previously reported for glacigenic slope sediments deposited during glacial maximum periods only. The Sklinnadjupet Drift is infilling a paleo-slide scar. The development of the infilling drift was possible due to the available accommodation space, a slide scar acting as a sediment trap. Based on the formation of diapirs originating from the Sklinnadjupet Drift sediments we infer these sediments to have a muddy composition with relatively high water content and low density, more easily liquefied and mobilised compared with the glacigenic diamictons. 相似文献
946.
Dowty RA Shaffer GP Hester MW Childers GW Campo FM Greene MC 《Marine environmental research》2001,52(3):195-211
Research was conducted to assess the impact of oiling on fresh-marsh plant communities and to test the efficacy of techniques that may be used to enhance the bioremediation of crude oil spills in these environments while minimizing secondary anthropogenic impacts. To emulate field conditions, a mesocosm facility was used that houses 120 mesocosm vessels, each of 200-1 capacity. A five-way factorial treatment arrangement was used that included two substrates (inorganic, organic), two nutrient regimes (fertilized, not fertilized), two aeration levels (substrate aeration, no aeration), three oiling concentrations (0-, 5-, 10-1 m(-2) of South Louisiana Sweet Crude oil), and four vascular plant species (Alternanthera philoxeroides, Panicum hemitomon, Phragmites australis, Sagittaria lancifolia, and an unplanted control). Under the 5- and 10-1 m(-2) oiling concentrations, S. lancifolia displayed a short-term response of increased productivity, whereas P. hemitomon had the highest biomass production and photosynthetic rates at the end of the 18-month experiment. Overall plant growth and productivity, as well as oil degradation, were significantly higher in the inorganic substrate, indicating that biodegradation of oil spills in organic substrates may require a longer time period. Time-released fertilizer also stimulated plant productivity and resulted in higher soil respiratory quotients, suggestive of greater microbial activity, particularly in aerated mesocosms. The amount of oil remaining after 18 months was lowest in aerated and fertilized mesocosms containing either P. hemitomon or S. lancifolia and a substrate of low organic matter content. 相似文献
947.
948.
G.P. Glasby 《Marine Chemistry》1973,1(2):105-125
The rare-earth distribution has been determined in five manganese nodules from a range of marine environments. Manganese nodules from Loch Fyne, Scotland, and the Gulf of Aden are characterized by a low absolute abundance of the rare-earth elements and a low Ce/La ratio compared with deep-sea nodules. This difference is interpreted in terms of the diagenetic remobilization of manganese in the high sedimentation regimes leading to the effective fractionation of manganese from the rare-earth elements and the resultant depletion of the rare earths in nodules from these environments. The mechanism of incorporation of the rare-earth elements into manganese nodules is thought to be either the direct adsorption of these elements from seawater or the scavenging of the elements by colloidal iron oxide prior to their incorporation into the authigenic phase of nodules. There appears to be no evidence for the surface transfer of these elements from inorganic detritus into the authigenic phase of nodules as suggested by previous authors. The distribution of U and Th in the nodules is controlled by factors similar to those controlling the rare-earth abundance in nodules. The higher U/Th ratios in nodules from Loch Fyne and the Gulf of Aden is considered to be due to the preferential reduction of UO2(CO3)34? to some lower-valency uranium species such as U3O8 in nodules from less oxidizing environments. 相似文献
949.
A detailed survey of a 1°×1°-square of seafloor 100 miles south-east of the Azores shows a strong correlation between directions of regional topographic and magnetic lineations. The area is dissected by the East Azores Fracture Zone at 36°55N, identified as the active Eurasian-African plate boundary, and by another large, non-active fracture zone at 36°10N. Both fracture zones strike 265° and are accompanied by large amplitude magnetic anomalies. The general strike in the area in between is 000°–015°. The skewing effect at this magnetic latitude is very sensitive to variations in strike of the magnetic contrasts. This effect was eliminated by a non-linear transformation which also gives the positions of magnetic contrasts. Some N-S contrasts were identified as sea floor spreading polarity contrasts (anomalies 31 and 32). Weak contrasts could be identified as topographic effects and gave a magnetization intensity of 5 A m-1. The identified sea floor spreading anomalies to both sides of the fracture zone at 36°10N agree very well, also quantatively, with a three-dimensional model for the fracture zone anomalies. This model describes the non-linear anomalies as end effects of the magnetic layer which is divided in blocks of alternating polarity. 相似文献
950.
Sand ridges on the inner Atlantic shelf of North America: Morphometric comparisons with Huthnance stability model 总被引:1,自引:0,他引:1
A. G. Figueiredo Jr. D. J. P. Swift Stubblefield T. L. Clarke 《Geo-Marine Letters》1981,1(3-4):187-191
Sand ridge fields on the inner shelf of the Middle Atlantic Bight are generally thought to have formed in response to northeasterly
storm flows as the shoreface underwent erosional retreat with postglacial sea-level rise. However, the hydrodynamic mechanism
is poorly unerstood. Coastal boundary models see the ridges as responses of the seafloor to distortions in the flow induced
by the coastal boundary. Stability models propose that an irregular initial topography will evolve toward an ordered array
of bedforms in response to repeated flow events. The two classes of models are not mutually exclusive, nor are members within
each class mutually exclusive. Results of measurements of ridge spacing on the inner Atlantic shelf of North America agree
with the predictions of stability models. 相似文献