Distribution and transport of organic matter along a filament-eddy system in the Canaries – NW Africa coastal transition zone region     

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   

Onshore Neogene stratigraphy in the North of the Alboran Sea (Betic Internal Zones): Paleogeographic implications     

J. Rodríguez Fernández  C. Sanz de Galdeano 《Geo-Marine Letters》1992,12(2-3):123-128

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   

Palynological characterization of gassy sediments in the inner part of Ría de Vigo (NW Spain). New chronological and environmental data     

C. Muñoz Sobrino  S. García-Gil  J. B. Diez  J. Iglesias 《Geo-Marine Letters》2007,27(2-4):289-302

Palynological characterization of the pollen assemblages from core ZV-01 offers a reliable age record of shallow ‘gas seal’ and ‘gas reservoir’ sediments from the Ría de Vigo (NW Spain). Gassy sediments show a direct correspondence with the palynological assemblage zones (LPAZ) 2, 3 and 4, which range in age from 950 to 1510 a.d. for the interval 81–176 cm where gas is found. The facies acting as a seal would correspond to the sedimentation in the ria starting from 1510 a.d. These assemblages also provide significant data which make it possible to reconstruct the palaeoenvironmental changes recorded in the sedimentary infill of the Ría de Vigo. The gassy horizon corresponds to the phase when riparian and mesophilous forest were better represented. This coincides with a relative high abundance of Lingulodinium machaerophorum, which indicates that the waters of the ria had been less renewed by oceanic waters and had a plentiful supply of continental nutrients. At that time, anoxic conditions resulted from restricted vertical circulation of seawater and/or high biological productivity. The dinocyst assemblages overlying and underlying the gassy horizon in core ZV-01 are clearly different from those concomitant with the accumulation of the gassy sediments. This suggests that oceanographic conditions in the Ría de Vigo may have changed several times during the time interval covered by our record. The weaker relationship between L. machaerophorum/Spiniferites spp., and simultaneous significant increases in Impagidinium spp. and Bitectatodinium tepikiense may indicate a greater intrusion of colder, more oceanic waters into the Ría de Vigo, which may have provoked intensification in upwelling during two periods, ca. 700–850 a.d. and ca. 1500–1750 a.d.  相似文献   

The Huelva (Spain) Tsunami-Ready Station and Its Interaction with Storm Emma (March 2018)     

Jue Lin-Ye  Begoña Pérez-Gómez  Enrique Álvarez-Fanjul  Javier García-Valdecasas 《Marine Geodesy》2020,43(5):509-539

Abstract

The 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 2^nd 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   

Parabolic Wave Propagation Modelling in Orthogonal Coordinate Systems     

袁德奎  林斌良肖鸿 《中国海洋工程》2004,18(3):445-456

This paper presents a numerical model study of the propagation of water waves using the parabolic approximation of the mild-slope equation in the orthogonal coordinate system. Two types of coordinate systems are studied: (a) a general form of orthogonal coordinate system and (b) the conformal system, a special form of orthogonal coordinate system. Two typical examples, namely, expanded breakwaters and a circular channel, are studied to validate the model. First, the examples are studied by use of the general orthogonal coordinates. Then the same examples are computed by use of the confonnal system. The computational results show that the confonnal coordinate system generally gives better predictions than the general orthogonal system. A numerical technique for generating the conformal grid is combined with the numerical model to improve the practicability of the model. The comparison between the result from the numerical grid system and that from the analytical grid system shows that reliable computational results can be obtained by use of the numerical confonnal grid system.  相似文献   

Numerical Investigation on the Generation and Propagation of Irregular Waves in A Two-Dimensional Wave Tank     

Ruey-syanSHIH Chung-renCHOU JohnZ.YIM 《中国海洋工程》2004,18(4):551-566

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Short-Term Benthic Recolonization after Dredging in the Harbour of Ceuta, North Africa   总被引：2，自引：0，他引：2  

José M. Guerra-García  Juan Corzo  & J. Carlos García-Gómez 《Marine Ecology》2003,24(3):217-229

Abstract. The benthic recovery after dredging (area: 2625 m²) was studied in a polluted and enclosed area of the harbour of Ceuta, in which the recolonization through the water column (larvae and adult bedload transport) could be limited by the lack of renewal. The benthos was sampled at two sites (control and dredged) using a van Veen grab and adopting a BACI (Before, After, Control, Impacted) approach. Five samplings were conducted after dredging (3, 15, 30, 90, 180 days). The proportion of gravel in the sediment of the dredged site increased after dredging, while the organic matter decreased. The impact on the community was estimated at species level, using both univariate and multivariate analyses. The maximum negative effect on benthic macrofauna was a reduction by 65% for species richness (15 days after dredging) and by 75% for abundance (3 days after dredging). Between 15 and 30 days after dredging, the abundance of some species such as the molluscs Parvicardium exiguum and Retusa obtusa and the polychaete Pseudomalacoceros tridentata increased considerably in the dredged site, while typical ‘opportunistic’ species such as Capitella capitata were disfavoured by the disturbance. For this small‐scale dredging, about 6 months are required for the disturbed area to re‐establish a sediment structure and a macrobenthic community similar to the undisturbed area. Small‐patch dredging operations are proposed in harbour management whenever possible, since they allow a quick re‐adjustment of the initial sediment structure and benthic communities.  相似文献   

Gas hydrate disturbance fabrics of southern Hydrate Ridge sediments (ODP Leg 204): Relationship with texture and physical properties   总被引：1，自引：0，他引：1  

Elena Piñero  Eulàlia Gràcia  Francisca Martínez-Ruiz  Juan Cruz Larrasoaña  Alexis Vizcaino  Gemma Ercilla 《Geo-Marine Letters》2007,27(2-4):279-288

Soupy and mousse-like fabrics are disturbance sedimentary features that result from the dissociation of gas hydrate, a process that releases water. During the core retrieval process, soupy and mousse-like fabrics are produced in the gas hydrate-bearing sediments due to changes in pressure and temperature conditions. Therefore, the identification of soupy and mousse-like fabrics can be used as a proxy for the presence of gas hydrate in addition to other evidence, such as pore water freshening or anomalously cool temperature. We present here grain-size results, mineralogical composition and magnetic susceptibility data of soupy and mousse-like samples from the southern Hydrate Ridge (Cascadia accretionary complex) acquired during Leg 204 of the Ocean Drilling Program. In order to study the relationship between sedimentary texture and the presence of gas hydrates, we have compared these results with the main textural and compositional data available from the same area. Most of the disturbed analyzed samples from the summit and the western flank of southern Hydrate Ridge show a mean grain size coarser than the average mean grain size of the hemipelagic samples from the same area. The depositional features of the sediments are not recognised due to disturbance. However, their granulometric statistical parameters and distribution curves, and magnetic susceptibility logs indicate that they correspond to a turbidite facies. These results suggest that gas hydrates in the southern Hydrate Ridge could form preferentially in coarser grain-size layers that could act as conduits feeding gas from below the BSR. Two samples from the uppermost metres near the seafloor at the summit of the southern Hydrate Ridge show a finer mean grain-size value than the average of hemipelagic samples. They were located where the highest amount of gas hydrates was detected, suggesting that in this area the availability of methane gas was high enough to generate gas hydrates, even within low-permeability layers. The mineralogical composition of the soupy and mousse-like sediments does not show any specific characteristic with respect to the other samples from the southern Hydrate Ridge.  相似文献   

In Situ Measurement of Pinna nobilis Shells for Age and Growth Studies:
A New Device     

Jos Rafael García‐March  Antonio Manuel García‐Carrascosa  lvaro Luís Pea 《Marine Ecology》2002,23(3):207-217

Abstract. Pinna nobilis Linnaeus 1758 is an endemic bivalve mollusc in the Mediterranean Sea, where it inhabits seagrass meadows, especially Posidonia oceanica (L.) Delile. It is the largest bivalve in the Mediterranean, reaching lengths up to 120 cm. In its natural habitat, P. nobilis lives with the anterior part of the valve buried in the seabed, attached to Posidonia rhizomes by byssus threads.
This habit makes it impossible to measure its total length directly in situ. As the only way to determine the individual age is the relationship between age and total length, several equations have been proposed to estimate total length by relating it to the unburied parts of the shell. Such measurements are essential to ecological studies that consider age, growth, and population dynamics, and that evaluate the environmental factors that affect this species.
Accurately estimating total length depends on the accuracy and precision of the method employed to measure the unburied shell parts. In this paper, we point out the lack of precision of the instruments and methods used until now; we also demonstrate the reason for this imprecision. A new device to measure unburied parts of Pinna nobilis with a precision comparable to that obtained when measuring extracted valves is described. This device is unaffected by substratum type and reduces measurement time. The latter is a very important feature, because these procedures are usually performed whilst SCUBA diving. Finally, a growth equation has been fitted to the measurements obtained with the new device from a population located in Moraira (Alicante, western Mediterranean).  相似文献   

Prediction of Load Carrying Capacity of Corroded Reinforced Concrete Beam     

范颖芳  周晶冯新 《中国海洋工程》2004,18(1):107-118

A novel method for prediction of the load carrying capacity of a corroded reinforced concrete beam (CRCB) is presented in the paper. Nine reinforced concrete beams, which had been working in an aggressive environment for more than 10 years, were tested in the laboratory. Comprehensive tests, including flexural test, strength test for corroded concrete and rusty rebar, and pullout test for bond strength between concrete and rebar, were condueted. The flexural test results of CRCBs reveal that the distribution of surface cracks on the beams shows a fractal behavior. The relationship between the fractal dimensions and mechanical properties of CRCBs is then studied. A prediction model based on artificial neural network (ANN) is established by the use of the fractal dimension as the corrosion index, together with the basic intbrmation of the beam. The validity of the prediction model is demonstrated through the experimental data, and satisfactory resuits are achieved.  相似文献