Multi-bioindicator study of a small estuary in Vendée (France)     

J. P. Debenay  P. Carbonel  M. -T. Morzadec-Kerfourn  A. Cazaubon  M. Denfle  A. -M. Lzine 《Estuarine, Coastal and Shelf Science》2003,58(4):843-860

Surficial sediment (about 5 mm) was scraped off in 15 stations selected in the Vie Estuary, a small estuary on the French Atlantic coast. The samples, prepared using the suitable methods, were used for comparing the behaviour of periphytic algae, sporopollinic and other palynologic material, ostracoda and foraminifera for proposing a synthetic evaluation of the information provided by each of them. Dinoflagellate cysts, which are found in an almost monospecific assemblage in low-salinity water, are dispersed by tidal currents, but the location of tintinnids in only the lower reaches shows a limited inward transport. Sporopollinic material is clearly related to the adjacent vegetation, indicating a local origin, and then little influence of transport on the microbenthos, even if fragments of freshwater crustaceans and of Pediastrum alga are found down to the mouth in the sporopollinic deposits. This limited transport of microbenthos allows the use of periphytic algae, benthic ostracoda and benthic foraminifera as indicators of local environmental conditions. It was then possible to determine the extent of marine influence in the estuary, to discriminate between the main channel and adjacent basins, and between different stages of evolution of the basins, from a recently dug basin to a eutrophicated one.  相似文献   

Modeling bed-load transport of coarse sediments in the Great Bay Estuary, New Hampshire   总被引：1，自引：0，他引：1  

A. Bilgili  M. R. Swift  D. R. Lynch  J. T. C. Ip 《Estuarine, Coastal and Shelf Science》2003,58(4):937-950

Current, sea level and bed-load transport are investigated in the Lower Piscataqua River section of the Great Bay Estuary, New Hampshire, USA—a well-mixed and geometrically complex system with low freshwater input, having main channel tidal currents ranging between 0.5 and 2 m s⁻¹. Current and sea level forced by the M₂M₄M₆ tides at the estuarine mouth are simulated by a vertically averaged, non-linear, time-stepping finite element model. The hydrodynamic model uses a fixed boundary computational domain and accounts for flooding–drying of tidal flats by making use of a groundwater component. Inertia terms are neglected in comparison with pressure gradient and bottom friction terms, which is consistent with the observed principal dynamic balance for this section of the system. The accuracy of hydrodynamic predictions in the study area is demonstrated by comparison with four tidal elevation stations and two cross-section averaged current measurements. Simulated current is then used to model bed-load transport in the vicinity of a rapidly growing shoal located in the main channel of the lower system. Consisting of coarse sand and gravel, the shoal must be dredged every five to eight years. Two approaches are taken—an Eulerian parametric method in which nodal bed-load flux vectors are averaged over the tidal cycle and a Lagrangian particle tracking approach in which a finite number of sediment particles are released and tracked. Both methods yield pathways and accumulations in agreement with the observed shoal formation and the long-term rate of sediment accumulation in the shoal area.  相似文献   

Thermal structures in the Kuroshio extension measured with a towed thermistor chain     

Yoshihiko Sekine  Fukuji Yamada  Yoshiaki Toba  Eugene C. Lafond 《Journal of Oceanography》1994,50(4):391-401

Two-dimensional temperature data observed by use of a 275 meter towed thermistor chain deployed from an oceanographic research vessel USS MARYSVILLE, which cruised with a speed of 6.2 knots in July 1966 across the Kuroshio Extension in the North Pacific, are investigated. Two-dimensional variations of the distribution of the isotherms along the ship's track are analyzed with special reference to their slope, wavelength and wave height. The results show that the slope and wave height of isotherms have a tendency to increase as the temperature decreases. Even if the contribution of wave heights smaller than 1.5 m is neglected, i.e., contribution of large scale slope with a horizontal scale of 5–30 km is subtracted, this tendency is still detected. In contrast to this, the wavelength evaluated by the crest to crest method has no dependency on the temperature. Power spectrum of the isotherm depth is proportional tok ^–1.87 for 13°C andk ^–2.13 for 27°C, wherek is the wave number. It is shown that the spectra of warmer isotherms are relatively well approximated by –2 power law (Garrett and Munk spectrum) for internal waves rather than the –5/3 power law (Kolmogorov spectrum) for three dimensional isotropic turbulence.  相似文献   

Morphology and tectonics of the Romanche Transform and its environs     

R. C. Searle  M. V. Thomas  E. J. W. Jones 《Marine Geophysical Researches》1994,16(6):427-453

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CO₂ cycling in the coastal ocean. I – A numerical analysis of the southeastern Bering Sea with applications to the Chukchi Sea and the northern Gulf of Mexico     

John J. Walsh  Dwight A. Dieterle 《Progress in Oceanography》1994,34(4)

A quasi-two dimensional model of the carbon and nitrogen cycling above the 70m isobath of the southeastern Bering Sea at 57°N replicates the observed seasonal cycles of nitrate, ammonium, ΣCO₂, pCO₂, light penetration, chlorophyll, phytoplankton growth rate, and primary production, as constrained by changes in wind, incident radiation, temperature, ice cover, vertical and lateral mixing, grazing stress, benthic processing of phytodetritus and zooplankton fecal pellets, and the pelagic microbial loop of DOC, bacteria, and their predators. About half of the seasonal resupply of nitrate stocks to their initial winter conditions is derived from in situ nitrification, with the rest obtained from deep-sea influxes. Under the present conditions of atmospheric forcing, shelf-break exchange, and food web structure, this shelf ecosystem serves as a sink for atmospheric CO₂, with storage in the forms of exported DOC, DIC, and unutilized POC (phytoplankton, bacteria, and fecal pellets).As a consequence of just the rising levels of atmospheric pCO₂ since the the Industrial Revolution, however, the biophysical CO₂ status of the Southeastern Bering Sea shelf may have switched over the last 250 years, from a prior source to the present sink, since this relatively pristine ecosystem has unergone little eutrophication. Such fluctuations of CO₂ status may thus be reversed by the physical processes of : (1) reduction of atmospheric pCO₂, (2) increased on welling of deep-sea ΣCO₂, and (3) warming of shelf waters. Based on our application of this model to the Chukchi Sea and the Gulf of Mexico, about 1.0–1.2 gigatons C y^-1 of atmospheric CO₂ may now be sequestered by temperate and polar shelf ecosystems. When tropical systems are included, however, a positive net sink of only 0.6–0.8. × 10¹⁵g C y⁻¹ may prevail over all shelves.  相似文献   

Trends in biomass, density and diversity of North Sea macrofauna   总被引：6，自引：2，他引：6  

Heip  C.; Basford  D.; Craeymeersch  J. A.; Dewarumez  J. M.; Dorjes  J.; de Wilde  P.; Duineveld  G.; Eleftheriou  A.; Herman  P. M. J.; Niermann  U.; Kingston  P.; Kunitzer  A.; Rachor  E.; Rumohr  H.; Soetaert  K.; Soltwedel  T. 《ICES Journal of Marine Science》1992,49(1):13-22

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Fishing mortality and the variation of catches: a time series approach     

MacLennan  D. N.; Shepherd  J. G.; Pope  J. G.; Gislason  H. 《ICES Journal of Marine Science》1992,49(4):425-430

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Wave direction measurements using pitch-roll buoys   总被引：2，自引：0，他引：2  

K. E. Steele  Chung-Chu Teng  D. W. C. Wang 《Ocean Engineering》1992,19(4)

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Particulate flux in the water column overlying Santa Monica Basin     

Michael R. Landry  Willis K. Peterson  Christine C. Andrews 《Progress in Oceanography》1992,30(1-4)

Fluxes of particulate carbon, nitrogen, phytoplankton pigments, biogenic silica and dry mass were measured using free-floating and moored sediment trap arrays in the Santa Monica Basin during the period from October 1985 to August 1990 as part of the California Basin Study (CaBS) Program. In field testing for potential sources of sediment trap biases, we found little significant or consistent difference in rate estimates between short-term drifting traps and long-term moored traps, between preserved and unpreserved traps in short-term experiments, between different preservatives (mercury or formalin) in long-term experiments, between different designs of small cylindrical traps, and between deep-moored cylindrical traps and large conical traps. We did, however, find that sediment trap samples collected and analyzed on 0.45 μm silver filters gave estimates of carbon and nitrogen fluxes about 25% higher than samples collected on GF/F glass-fiber filters. Concurrent trap deployments at two stations 18km apart revealed low mesoscale variability in flux estimates. Seasonal patterns in carbon and nitrogen flux were not evident in our data, but strong seasonality, with spring maxima and summer minima, were observed for fluxes of phaeopigments and biogenic silica out of the euphotic zone.Time-averaged rates of particulate flux for long-term trap deployments from January to August 1990, were 121, 18.8, 1.5, 67 and 633mg m⁻²d⁻¹ at 110–135m for carbon, nitrogen, phaeopigment, biogenic silica and mass, respectively. Flux estimates to the basin floor (835–860m) were 50, 6.5, 0.64, 41.6 and 575mg m⁻²d⁻¹ for the same parameters. The former estimates are constrained by and in good agreement with independent assessments of new production from nitrate uptake in the euphotic zone. The latter agree with rates previously inferred from the sedimentary record using ²¹⁰Pb as a tracer. In addition, the difference in carbon estimates in the water column between the euphotic zone and the basin floor is consistent with the requirements for bacterial growth and metabolism at intermediate depths as measured by the thymidine method.  相似文献   

Threshold of motion of coarse-grained sediment under waves in shallow water   总被引：1，自引：0，他引：1  

John C. Morfett   《Coastal Engineering》1992,18(3-4)

This paper considers the threshold of motion of sediment in shallow coastal waters under breaking and non-breaking waves. A simple model, representing conditions at the fluid/sediment interface, is developed. The representation of a breaking wave is based on bore theory, and the shear stress at the bed is based on the friction formula of O'Connor and Yoo. A threshold formula is presented based on the use of energy dissipation. The threshold data is also related to the Shields threshold criterion.  相似文献