A comparative mineralogical study of gas-related sediments of the Gulf of Cádiz     

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   

Seasonal and inter-annual variation of mesozooplankton in the coastal upwelling zone off central-southern Chile   总被引：1，自引：0，他引：1  

Ruben Escribano  Pamela Hidalgo  Humberto González  Ricardo Giesecke  Ramiro Riquelme-Bugueño  Karen Manríquez 《Progress in Oceanography》2007,75(3):470-485

Zooplankton sampling at Station 18 off Concepción (36°30′S and 73°07′W), on an average frequency of 30 days (August 2002 to December 2005), allowed the assessment of seasonal and inter-annual variation in zooplankton biomass, its C and N content, and the community structure in relation to upwelling variability. Copepods contributed 79% of the total zooplankton community and were mostly represented by Paracalanus parvus, Oithona similis, Oithona nana, Calanus chilensis, and Rhincalanus nasutus. Other copepod species, euphausiids (mainly Euphausia mucronata), gelatinous zooplankton, and crustacean larvae comprised the rest of the community. Changes in the depth of the upper boundary of the oxygen minimum zone indicated the strongly seasonal upwelling pattern. The bulk of zooplankton biomass and total copepod abundance were both strongly and positively associated with a shallow (<20 m) oxygen minimum zone; these values increased in spring/summer, when upwelling prevailed. Gelatinous zooplankton showed positive abundance anomalies in the spring and winter, whereas euphausiids had no seasonal pattern and a positive anomaly in the fall. The C content and the C/N ratio of zooplankton biomass significantly increased during the spring when chlorophyll-a was high (>5 mg m⁻³). No major changes in zooplankton biomass and species were found from one year to the next. We concluded that upwelling is the key process modulating variability in zooplankton biomass and its community structure in this zone. The spring/summer increase in zooplankton may be largely the result of the aggregation of dominant copepods within the upwelling region; these may reproduce throughout the year, increasing their C content and C/N ratios given high diatom concentrations.  相似文献   

On a model to propagate surface waves — A second order approach     

J.Chambel Leito  J.L.M. Fernandes 《Coastal Engineering》1992,18(3-4)

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Processes Causing the Temporal Changes in Si/N Ratios of Nutrient Consumptions and Export Flux during the Spring Diatom Bloom     

Naoki?YoshieEmail author  Yasuhiro?Yamanaka 《Journal of Oceanography》2005,61(6):1059-1073

Two processes are generally explained as causes of temporal changes in the stoichiometric silicon/nitrogen (Si/N) ratios of sinking particles and of nutrient consumption in the surface water during the spring diatom bloom: (1) physiological changes of diatom under the stress of photosynthesis of diatom and (2) differences of regeneration between silicon and nitrogen. We investigated which process plays an important role in these changes using a one-dimensional ecosystem model that explicitly represents diatom and the other non-silicious phytoplankton. The model was applied to station A7 (41°30′ N, 145°30′ E) in the western North Pacific, where diatom regularly blooms in spring. Model simulations show that the Si/N ratios of the flux exported by the sinking particles at 100 m depth and of nutrient consumptions in the upper 100 m surface water have their maxima at the end of the spring diatom bloom, the values and timings of which are significantly different from each other. Analyses of the model results show that the differences of regeneration between silicon and nitrogen mainly cause the temporal changes of the Si/N ratios. On the other hand, the physiological changes of diatoms under stress can hardly cause these temporal changes, because the effect of the change in the diatom's uptake ratio of silicon to nitrogen is cancelled by that in its sinking rate.  相似文献   

A Zonal Pathway for NADW in the South Atlantic     

Nelson?G.?HoggEmail author  Andreas?M.?Thurnherr 《Journal of Oceanography》2005,61(3):493-507

Several large deployments of neutrally buoyant floats took place within the Antarctic Intermediate (AAIW), North Atlantic Deep Water (NADW), and the Antarctic Bottom Water (AABW) of the South Atlantic in the 1990s and a number of hydrographic sections were occupied as well. Here we use the spatially and temporally averaged velocities measured by these floats, combined with the hydrographic section data and various estimates of regional current transports from moored current meter arrays, to determine the circulation of the three major subthermocline water masses in a zonal strip across the South Atlantic between the latitudes of 19°S and 30°S. We concentrate on this region because the historical literature suggests that it is where the Deep Western Boundary Current containing NADW bifurcates. In support of this notion, we find that a net of about 5 Sv. of the 15–20 Sv that crosses 19°S does continue zonally eastward at least as far as the Mid-Atlantic Ridge. Once across the ridge it takes a circuit to the north along the ridge flanks before returning to the south in the eastern half of the Angola Basin. The data suggest that the NADW then continues on into the Indian Ocean. This scheme is discussed in the context of distributions of dissolved oxygen, silicate and salinity. In spite of the many float-years of data that were collected in the region a surprising result is that their impact on the computed solutions is quite modest. Although the focus is on the NADW we also discuss the circulation for the AAIW and AABW layers.  相似文献   

The fate of dumped sediments monitored by a high-resolution multibeam echosounder system,Weser Estuary,German Bight     

Claudia?WienbergEmail author  Jens?Dannenberg  Dierk?Hebbeln 《Geo-Marine Letters》2004,24(1):22-31

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   

Influence of upwelling and river runoff interaction on phytoplankton assemblages in a Middle Galician Ria and Comparison with northern and southern rias (NW Iberian Peninsula)   总被引：2，自引：2，他引：2  

Manuel Varela  Ricardo Prego  Yolanda Pazos  ngeles Moroo 《Estuarine, Coastal and Shelf Science》2005,64(4):721-737

The first oceanographic research (hydrography, nutrient salts, chlorophyll, primary production and phytoplankton assemblages) in a Middle Galician Ria was carried out in Corme-Laxe during 2001, just a year before the Prestige oil spill, being the only reference to evaluate eventual changes in the phytoplankton community. Due to the small size of this ria (6.5 km²), oceanographic processes were driven by the continental water supplied by Anllons River during the wet season (20–30 m³ s⁻¹ in winter), and the strong oceanic influence from the nearby shelf during the dry season. The annual cycle showed a spring bloom with high levels of chlorophyll (up to 14 μg Chl-a L⁻¹) and primary production (3 g C m⁻² d⁻¹) and a summer upwelling bloom (up to 8 μg Chl-a L⁻¹ and 10 g C m⁻² d⁻¹) where the proximity of the Galician upwelling core (<13.5 °C at sea surface) favors the input of upwelled seawater (up to 9 μM of nitrate and silicate) to the bottom ria layer, even during summer stratification events (primary production around 2 g C m⁻² d⁻¹). Thus, phytoplankton assemblages form a “continuum” from spring to autumn with a predominance of diatoms and overlapping species between consecutive periods; only in autumn dinoflagellates and flagellates characterized the phytoplankton community. In the Middle Rias as Corme-Laxe, the nutrient values, Chl-a, primary production and phytoplankton abundance for productive periods were higher than those reported for the Northern (Ria of A Coruña) and Southern Rias (Ria of Arousa) for year 2001; this suggests the importance of the hydrographic events occurring in the zone of maximum upwelling intensity of the Western Iberian Shelf, where a lack of annual cycles studies exists.  相似文献   

The DNA de-methylating agent 5-azacytidine does not restore CYP1A induction in PCB resistant Newark Bay killifish (Fundulus heteroclitus)     

Xabier Arzuaga  Wanda Calcao  Adria Elskus 《Marine environmental research》2004,58(2-5):517

Newark Bay (NB) killifish (Fundulus heteroclitus) have been chronically exposed to environmental contaminants that activate the aryl hydrocarbon receptor (AHR) and are tolerant to toxic effects and CYP1A induction provoked by AHR ligands. Resistance to CYP1A induction could be due to an epigenetic mechanism such as DNA methylation. We measured in-ovo CYP1A catalytic activity (ethoxyresorufin-O-deethylase, EROD) in NB and reference site killifish embryos aqueously exposed to various concentrations of the de-methylating agent 5-azacytidine, 5-AC (5, 50 and 500 μ(micro)M) with or without 0.2 μ(micro)g/l of the CYP1A inducer 3,3^′,4,4^′,5 pentachlorobiphenyl (IUPAC PCB126). Neither PCB126 alone, nor PCB126 plus 5-AC, induced EROD above levels in vehicle treated Newark Bay fish. In reference site fish, the same PCB126 dose provoked a 7.4-fold EROD induction relative to controls. We conclude that Newark Bay killifish are resistant to CYP1A induction by co-planar PCBs during early embryological development and our data suggests that DNA methylation does not play a critical role in resistance to CYP1A induction in this model.  相似文献   

Size-Fractionated Primary Production Estimated by a Two-Phytoplankton Community Model Applicable to Ocean Color Remote Sensing   总被引：3，自引：0，他引：3  

Takahiko?KamedaEmail author  Joji?Ishizaka 《Journal of Oceanography》2005,61(4):663-672

In order to estimate primary production from ocean color satellite data using the Vertical Generalized Production Model (VGPM; Behrenfeld and Falkowski, 1997), we propose a two-phytoplankton community model. This model is based on the two assumptions that changes in chlorophyll concentration result from changes of large-sized phytoplankton abundance, and chlorophyll specific productivity of phytoplankton tends to be inversely proportional to phytoplankton size. Based on the analysis of primary production data, P _opt ^B , which was one parameter in the VGPM, was modeled as a function of sea surface temperature and sea surface chlorophyll concentration. The two-phytoplankton community model incorporated into the VGPM gave good estimates in a relatively high productive area. Size-fractionated primary production was estimated by the two-phytoplankton community model, and P _opt ^B of small-sized phytoplankton was 4.5 times that of large-sized phytoplankton. This result fell into the ranges observed during field studies.  相似文献   

Long-term Sensor Drift Found in Recovered Argo Profiling Floats   总被引：5，自引：0，他引：5  

Eitarou?OkaEmail author 《Journal of Oceanography》2005,61(4):775-781

We recovered three Argo profiling floats after 2 to 2.5 years of operation, and recalibrated their temperature, conductivity, and pressure sensors. The results demonstrate that these floats exhibited a significant drift in salinity of −0.0074 to −0.0125, primarily due to the conductivity sensor drift. Combined with the recalibration result for another previously recovered float, the indication is that the negative salinity drift increases nearly in proportion to the operating period of floats. The increasing rate is −0.0041 (±0.0015) year⁻¹, which yields a salinity drift of −0.016 (±0.006) for the expected float lifetime of four years. The present result suggests that reducing the float surfacing time would improve the accuracy of the salinity measurements.  相似文献