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71.
Two distinct series of slumps deform the upper part of the sedimentary sequence along the continental margin of the Levant.
One series is found along the base of the continental slope, where it overlies the disrupted eastern edge of the Messinian
evaporites. The second series of slumps transects the continental margin from the shelf break to the Levant Basin. It seemed
that the two series were triggered by two unrelated, though contemporaneous, processes. The shore-parallel slumps were initiated
by basinwards flow of the Messinian salt, that carried along the overlying Plio-Quaternary sediments. Seawater that percolated
along the detachment faults dissolved the underlying salt to form distinctly disrupted structures. The slope-normal slumps
are located on top of large canyons that cut into the pre-Messinian sedimentary rocks. A layer of salt is found in the canyons,
and the Plio-Quaternary sediments were deposited on that layer. The slumps are bounded by large, NW-trending faults where
post-Messinian faulted offset was measured. We presume that the flow of the salt in the canyons also drives the slope-normal
slumps. Thus thin-skinned halokynetic processes generated the composite post-Tortonian structural patterns of the Levant margin.
The Phoenician Structures are a prime example of the collapse of a distal continental margin due to the dissolution of a massive
salt layer. 相似文献
72.
C. Martín-Puertas M. P. Mata M. C. Fernández-Puga V. Díaz del Río J. T. Vázquez L. Somoza 《Geo-Marine Letters》2007,27(2-4):223-235
The Gulf of Cádiz area has been extensively surveyed in recent years and several gas-related fluid escape seafloor structures
have been identified. In this study, gravity cores, collected during the ANASTASYA/00 and ANASTASYA/01 cruises, on mud volcanoes,
hemipelagic sediments and dredged material from diapiric structures, have been studied. A comparative mineralogical analysis
by XRD and SEM of samples from different areas has been performed in order to determine whether there is a characteristic
mineralogy related to these fluid escape structures, and also to determine the origin of the mud matrix and constrain the
depth of the parent units. The mineralogical analysis reflects the different origins of the different units described in the
cores: hemipelagic material of the slope, clays that underlie the mud volcanoes and are discharged at the sea bottom surface,
and authigenic and diagenetic minerals possibly involved in the anaerobic oxidation of methane in the mud volcano sediments. 相似文献
73.
Spatial and Temporal Variations of Sound Speed at the PN Section 总被引:3,自引:0,他引:3
Gridded sound speed data were calculated using Del Grosso's formulation from the temperature and salinity data at the PN section
in the East China Sea covering 92 cruises between February 1978 and October 2000. The vertical gradients of sound speed are
mainly related to the seasonal variations, and the strong horizontal gradients are mainly related to the Kuroshio and the
upwelling. The standard deviations show that great variations of sound speed exist in the upper layer and in the slope zone.
Empirical orthogonal function analysis shows that contributions of surface heating and the Kuroshio to sound speed variance
are almost equivalent.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
74.
Abstract. Rhodoliths provide a stable and three-dimensional habitat to which other seaweeds and invertebrates can attach. Although ecological factors affecting rhodolith beds have been studied, little is known about the effect of rhodolith species and growth-form on associated fauna. Experiments were conducted at three rhodolith beds in the central-west Gulf of California. Faunal abundance differed significantly in relation to rhodolith-forming species, but no significant differences were observed between different growth-forms. Rhodolith structure differs between the species Lithophyllum margaritae and Neogoniolithon trichotomum , and the combination of structure differences and rhodolith abundances may be responsible of the significant differences in faunal abundance and richness. Crustaceans, polychaetes and molluscs were the most important taxa in all three rhodolith beds. The amphipod species Pontogeneia nasa and the cnidarian Aiptasia sp. were dominant in both rhodolith beds, El Requesón and Isla Coyote, in Bahía Concepción. The Isla Coronados rhodolith bed was dominated by an unidentified harpacticoid copepod (Copepoda sp.1). Rhodolith species is more important than growth-form in determining abundance and richness of the associated fauna. Nevertheless, factors such as wave motion, depth, bioturbation and others should be considered when studying organisms associated with rhodolith beds. 相似文献
75.
Mercedes García-Muoz Javier Arístegui María F. Montero Eric D. Barton 《Progress in Oceanography》2004,62(2-4):115
The distribution and transport of chlorophyll a (Chla), particulate (POC) and dissolved (DOC) organic carbon, and the respiratory ETS activity of the microplankton community were studied along a filament-eddy system located in the transition zone between the NW Africa upwelling and Canary Islands waters. Two independent filaments (F1 and F2) stemming from the coastal jet, between Cape Juby and Cape Bojador, merged about 100 km offshore, turning southward and onshore forced by the circulation of a recurrent oceanic cyclonic eddy. In general, the coastal upwelling waters presented higher Chla, but lower POC, DOC and ETS activity than filament waters. However, differences in organic carbon distribution and respiratory activity were observed among stations from the two filaments. The bio-chemical fields were strongly influenced by a complex sub-mesoscale hydrography resulting from the interaction of cyclonic and anticyclonic island eddies with the filaments. The combined F1 + F2 filament system transported 97.1 kg s−1 of excess (non-refractory) total organic carbon (e-TOC), a value comparable to other published estimates from upwelling filaments in the NE Atlantic. About 90% of e-TOC was exported as DOC, since eddy re-circulation precluded the offshore transport of POC. Assuming that the calculated transport of e-TOC is representative of the annual average, the yearly offshore transport (3.1 x 109 kg C) would represent about 25% of the upwelling primary production of the region of study. 相似文献
76.
Hydrodynamic and sediment transport measurements from instrumentation deployed during a 54-day winter period at two sites on the Louisiana inner shelf are presented. Strong extratropical storms, with wind speeds of 7.8 to 15.1 m s-1, were the dominant forcing mechanism during the study. These typically caused mean oscillatory flows and shear velocities about 33% higher than fair weather (averaging 12.3 and 3.2 cm s-1 at the landward site, and 11.4 and 2.7 cm s-1 at the seaward site, respectively). These responses were coupled with mean near-bottom currents more than twice as strong as during fair weather (10.3 and 7.5 cm s-1 at the landward and seaward sites, respectively). These flowed in approximately the same direction as the veering wind, causing a net offshore transport of fine sand. Weak storms were responsible for little sediment transport whereas during fair weather, onshore sand transport of approximately 25-75% of the storm values appears to have occurred. This contradicts previous predictions of negligible fair-weather sediment movement on this inner shelf. 相似文献
77.
Remote estimation of surficial seafloor properties through the application Angular Range Analysis to multibeam sonar data 总被引:2,自引:2,他引:2
The variation of the backscatter strength with the angle of incidence is an intrinsic property of the seafloor, which can
be used in methods for acoustic seafloor characterization. Although multibeam sonars acquire backscatter over a wide range
of incidence angles, the angular information is normally neglected during standard backscatter processing and mosaicking.
An approach called Angular Range Analysis has been developed to preserve the backscatter angular information, and use it for
remote estimation of seafloor properties. Angular Range Analysis starts with the beam-by-beam time-series of acoustic backscatter
provided by the multibeam sonar and then corrects the backscatter for seafloor slope, beam pattern, time varying and angle
varying gains, and area of insonification. Subsequently a series of parameters are calculated from the stacking of consecutive
time series over a spatial scale that approximates half of the swath width. Based on these calculated parameters and the inversion
of an acoustic backscatter model, we estimate the acoustic impedance and the roughness of the insonified area on the seafloor.
In the process of this inversion, the behavior of the model parameters is constrained by established inter-property relationships.
The approach has been tested using a 300 kHz Simrad EM3000 multibeam sonar in Little Bay, NH. Impedance estimates are compared
to in situ measurements of sound speed. The comparison shows a very good correlation, indicating the potential of this approach for
robust seafloor characterization. 相似文献
78.
We collected surface water along the 142nd E meridian from Tasmania to Antarctica in December 1999. We measured temperature,
salinity and total chlorophyll a; additionally, we collected suspended particle size fractions and used fluorometric analysis to determine the quantity of
chlorophyll a in each of four cell size classes: picoplankton (<3 μm), two nanoplankton fractions (3–10 μm and 10–20 μm) and microplankton
(> 20 μm). Changes in temperature and salinity show that we crossed 6 water masses separated by 5 fronts. We found low abundance
(<0.2 mg m−3) of chlorophyll in all size classes, with the exception of higher values near the continent (0.2 to 0.4 mg m−3). Lowest chlorophyll values (<0.1 mg m−3) were found in the Polar Frontal Zone (51° to 54°S). Microplankton made up the largest portion of total chlorophyll throughout
most of the region. We conclude that biomass of all phytoplankton fractions, especially pico-and nanoplankton, was constrained
by limiting factors, most probably iron, throughout the region and that ecosystem dynamics within a zone are not circumpolar
but are regionalized within sectors. 相似文献
79.
Young-Ok Kim Eun Jin Yang Jung-Hoon Kang Kyoungsoon Shin Man Chang Cheol Soo Myung 《Ocean Science Journal》2007,42(1):9-17
The summer distributions of planktonic microbial communities (heterotrophic and phtosynthetic bacteria, phtosynthetic and
heterotrophic nanoflagellates, ciliate plankton, and microphytoplankton) were compared between inner and outer areas of Lake
Sihwa, divided by an artificial breakwater, located on the western coast of Korea, in September 2003. The semienclosed, inner
area was characterized by hyposaline surface water (<17 psu), and by low concentrations of dissolved oxygen (avg. 0.4 mg L1) and high concentrations of inorganic nutrients (nitrogenous nutrients >36 μM, phosphate <4 μM) in the bottom layer. Higher
densities of heterotrophic bacteria and nanoflagellates also occurred in the inner area than did in the outer area, while
microphytoplankton (mainly diatoms) occurred abundantly in the outer area. A tiny tintinnid ciliate, Tintinnopsis nana, bloomed
into more than 106 cells L1 at the surface layer of the inner area, while its abundance was much lower (103-104 cells L1) in the outer area of the breakwater. Ciliate abundance was highly correlated with heterotrophic bacteria (r = 0.886, p <
0.001) and heterotrophic flagellates (r = 0.962, p < 0.001), indicating that rich food availability may have led to theT. nana bloom. These results suggest that the breakwater causes the eutrophic environment in artificial lakes with limited flushing
of enriched water and develops into abundant bacteria, nanoflagellates, and ciliates. 相似文献
80.
Jue Lin-Ye Begoña Pérez-Gómez Enrique Álvarez-Fanjul Javier García-Valdecasas 《Marine Geodesy》2020,43(5):509-539
AbstractThe sea level station operating since 1996 at Mazagón (Huelva, Spain) has been progressively upgraded to fit tsunami warning requirements, due to its location in one of the main regions at risk. Its radar water level sensor was complemented in 2017, with the addition of a pressure sensor. The performance of both sea level sensors and their response to sea level oscillations, at different frequencies, is assessed. Particular emphasis is put on the effect of extreme events, such as Storm Emma, when alternative methods to obtain 1-min data are tested, in contrast to the one based on arithmetic means. The overall differences are small, for the whole period of study (centered-root-mean-square-error below 1?cm, for 5-min, and hourly data; similar tidal parameters and sea level oscillations with periods between 30?s and 5?min). However, during Storm Emma, the pressure sensor presents sensibly lower readings than the radar, with the centered-root-mean-square-error rising to 80?mm on the March 2nd 2018. A new method to compute 1-min data, based on medians, reduced this value to 10?mm for the same day. 相似文献