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71.
72.
73.
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
74.
We review the spatial and temporal patterns of zooplankton in the eastern tropical Pacific Ocean and relationships with oceanographic factors that affect zooplankton distribution, abundance and trophic relationships. Large-scale spatial patterns of some zooplankton groups show broad coincidence with surface water masses, circulation, and upwelling regions, in agreement with an ecological and dynamic partitioning of the pelagic ecosystem. The papers reviewed and a new compilation of zooplankton volume data at large-scale show that abundance patterns of zooplankton biomass have their highest values in the upwelling regions, including the Gulf of Tehuantepec, the Costa Rica Dome, the equatorial cold tongue, and the coast of Peru.Some of the first studies of zooplankton vertical distribution were done in this region, and a general review of the topic is presented. The possible physiological implications of vertical migration in zooplankton and the main hypotheses are described, with remarks on the importance of the oxygen minimum zone (OMZ) as a barrier to both the vertical distribution and migration of zooplankton in the region. Recent results, using multiple-net gear, show that vertical distribution is more complex than previously thought. There are some well-adapted species that do live and migrate within the OMZ.Temporal patterns are reviewed and summarized with historical data. Seasonal variations in zooplankton biomass follow productivity cycles in upwelling areas. No zooplankton time series exist to resolve ENSO effects in oceanic regions, but some El Niño events have had effects in the Peru Current ecosystem. Multidecadal periods of up to 50 years show a shift from a warm sardine regime with a low zooplankton biomass to a cool anchovy regime in the eastern Pacific with higher zooplankton biomasses. However, zooplankton volume off Peru has remained at low values since the 1972 El Niño, a trend opposite to that of anchoveta biomass since 1984.Studies of trophic relations emphasize the difference in the productivity cycle in the eastern tropical Pacific compared to temperate or polar ecosystems, with no particular peaks in the stocks of either zooplankton or phytoplankton. Productivity is more dependent on local events like coastal upwelling or water circulation, especially in the equatorial countercurrent and around the equatorial cool-tongue. Micrograzers are very important in the tropics as are predatory mesozooplankton. Up to 70% of the daily primary productivity is consumed by microzooplankton, which thus regulates the phytoplankton stocks. Micrograzers are an important link between primary producers, including bacteria, and mesozooplankton, constituting up to 80% of mesozooplankton food. Oceanography affects zooplankton trophic relationships through spatial–temporal effects on primary productivity and on the distributions of metabolic factors, food organisms, and predators. This paper is part of a comprehensive review of the oceanography of the eastern tropical Pacific. 相似文献
75.
The Neogene is the period in which the Betic Cordillera, the Rif, and the Alboran Sea acquired their present configuration. The Neogene sediments of the Betic Internal Zones (located directly to the North of the Alboran Sea) show the effects of important periods of deformation. Deposition was clearly controlled by tectonics. Therefore the generation, evolution, and total or partial destruction of basins and the formation of new, often superimposed, basins are common phenomena, according to the locations of the basins in the Betic Cordillera and to the different geodynamic situations. 相似文献
76.
Ana Luisa Rosa Yutaka Isoda Kazuyuki Uehara Tomokazu Aiki 《Journal of Oceanography》2007,63(4):573-588
Hydrographic data and composite current velocity data (ADCP and GEK) were used to examine the seasonal variations of upper-ocean
flow in the southern sea area of Hokkaido, which includes the “off-Doto” and “Hidaka Bay” areas separated by Cape Erimo. During
the heating season (April–September), the outflow of the Tsugaru Warm Current (TWC) from the Tsugaru Strait first extends
north-eastward, and then one branch of TWC turns to the west along the shelf slope after it approaches the Hidaka Shelf. The
main flow of TWC evolves continuously, extending eastward as far as the area off Cape Erimo. In the late cooling season (January–March),
part of the Oyashio enters Hidaka Bay along the shallower part of the shelf slope through the area off Cape Erimo, replacing
almost all of the TWC water, and hence the TWC devolves. It is suggested that the bottom-controlled barotropic flow of the
Oyashio, which may be caused by the small density difference between the Oyashio and the TWC waters and the southward migration
of main front of TWC, permits the Oyashio water to intrude along the Hidaka shelf slope. 相似文献
77.
J. van de Kreeke 《Coastal Engineering》1990,14(6)
The stability analysis for a double-inlet bay system is applied to an inlet system resembling Big Marco Pass and Capri Pass on the lower west coast of Florida. Since the opening of Capri Pass in 1967, the length of Big Marco Pass has increased from 2000 m in 1967 to 3000 m in 1988 and the cross-sectional area has decreased from 1200 m2 in 1967 to 1000 m2 in 1988. Since 1967, the cross-sectional area of Capri Pass has steadily increased and in 1988 was 700 m2. Tides off the inlets are of the mixed type with a diurnal range of 1 m. The gross littoral transport rate in the vicinity of the inlets is estimated at 150,000 m3 yr−1.For each inlet the maximum tidal velocities are calculated as a function of the gorge cross-sectional areas using a lumped-parameter model to describe the hydrodynamics of the flow. In the model it is assumed that the bay level fluctuates uniformly and the bay surface area remains constant. The velocities are used to calculate the tidal maximum of the bottom shear stress in each inlet as a function of the cross-sectional areas of the two inlets (=closure surface). Values of the equilibrium shear stress are derived from an empirical relationship between cross-sectional area and tidal prism for stable inlets along the west coast of Florida. Closure surfaces and equilibrium stress values are calculated for values of friction factors ranging from F=4×10−3 to F=6×10−3. Using the closure surfaces and equilibrium stress values, the equilibrium flow curve for each inlet is determined. The equilibrium flow curve represents the locus of the combination of cross-sectional areas for which the actual bottom shear stress in the inlet equals the equilibrium shear stress.Based on the equilibrium flow curves and the known values of the cross-sectional areas of the two inlets in 1988, it is expected that, ultimately, Big Marco Pass will close and Capri Pass will remain as the sole inlet with a cross-sectional area of 1250 m2 and a maximum tidal velocity pertaining to a diurnal tide of 0.85 m s−1. 相似文献
78.
79.
The influence of salinity on the solubility of Zn and Cd sulphides in the Scheldt estuary 总被引:2,自引:0,他引:2
In the estuary of the river Scheldt, where an oxygen gradient exists in addition to the salinity gradient, redox processes will be of major importance for trace metal mobilisation. In this study, the influence of salinity and pH on the redox processes of dissolved Zn and Cd sulphides is investigated together with the effects on the ratio of the dissolved Zn and Cd concentrations. The speciation of these metals is calculated with the chemical equilibrium programme
+. Zn sulphides are oxidised at lower oxygen concentrations than Cd sulphides, due to lower stability constants, causing a sudden increase or peak in the dissolved Zn/Cd ratio. The formation of dissolved Cd chloride complexes when oxidation occurs at high salinities (S=15) increases the mobility of Cd, causing a decrease in the Zn/Cd peak of the total dissolved concentrations. The peak is three to four times smaller at S=15 than when oxidation occurs at S=2. The simple model calculations compare very well with field data. The Scheldt estuary is suitable to illustrate these calculations. In the 1970s, the anoxic part of the estuary reached S=15–20, but since the early 1980s it has dropped to S=2–10. Historic data on metals in the estuary from 1978, 1987 and the 1990s were used to compare with the equilibrium calculations. The increase of the dissolved Zn/Cd peak at low salinity as a consequence, of the decreasing anoxic region is confirmed well by the data. The good agreement between model calculations and field data is a proof of the extreme importance of redox processes for the solubility of Zn and Cd sulphides in the estuary. 相似文献
80.
With the development of high-resolution multibeam echosounder systems (MBES) for surveying shallow-water areas a new tool is available to monitor rapid changes in seabed morphology as, e.g., caused by the dumping of dredge spoil in coastal waters. In this study, four data sets of repeated bathymetric surveys with a MBES were processed and analyzed. The data were collected in a 1.94-km2 dumping site in the outer Weser Estuary (German Bight). Between June and December 1998, 2.6 million m3 of dredged sediment were deposited there. The bathymetric maps generated in the course of this study reveal features such as subaqueous dunes, scour holes, and mounds of dumped dredge spoil. The mean water depth decreased by about 1 m during the dumping period. Furthermore, difference grids showing changes in sediment volume allowed a calculation of the sediment budget for the monitored area. After a time period of only 5 months, 0.5 million m3 of the originally dumped 2.6 million m3 of dredge spoil had already been removed from the dumping site. 相似文献