Wave run-up and overtopping on smooth and rough slopes of coastal structures     

N. J. Shankar  M. P. R. Jayaratne 《Ocean Engineering》2003,30(2):221-238

A series of hydraulic model tests has been carried out in a glass wave flume to investigate the influences of wave height, wave period, wave steepness, surf similarity parameter, roughness, layer thickness and porosity on wave run-up and overtopping of 1:2 sloped impermeable and permeable breakwaters fronted by a 1:10 gentle, smooth beach slope. The analysis of results involves the correlation between the overtopping energy transfer with the relative wall height and the relationship between wave run-up and overtopping rate. Further, measured wave run-up and overtopping rates are compared with the results given in the Shore Protection Manual (1984), Automated Coastal Engineering System (1992)and results of other investigators.  相似文献   

Biogeochemical impacts due to mesoscale eddy activity in the Sargasso Sea as measured at the Bermuda Atlantic Time-series Study (BATS)     

Erin N. Sweeney  Dennis J. McGillicuddy  Jr.  Ken O. Buesseler 《Deep Sea Research Part II: Topical Studies in Oceanography》2003,50(22-26):3017

A comparison of monthly biogeochemical measurements made from 1993 to 1995, combined with hydrography and satellite altimetry, was used to assess the impacts of nine eddy events on primary productivity and particle flux in the Sargasso Sea. Measurements of primary production, thorium-234 flux, nitrate+nitrite, and photosynthetic pigments made at the US JGOFS Bermuda Atlantic Time-series Study (BATS) site were used. During the 3 years of this study, four out of six high thorium-234 flux events occurred during the passage of an eddy. Primary production nearly as high as the spring bloom maximum was observed in two mode-water eddies (May 1993 and July 1995). The 1994 spring bloom at BATS was suppressed by the passage of an anticyclone. Distinct phytoplankton community shifts were observed in mode-water eddies, which had an increased percentage of diatoms and dinoflagellates, and in cyclones, which had an increased percentage of Synechococcus. These variations in species composition within mode-water eddies and cyclones may be associated with the ages of the sampled eddies, and/or differences in physical, chemical, and biological factors in these two distinct eddy types. In general, eddies that were 1–2 months old elicited a large biological response; eddies that were 3 months old may show a biological response and were accompanied by high thorium flux; eddies that were 4 months old or older did not show a biological response or high thorium flux. A conceptual model depicting temporal changes during eddy upwelling, maturation, and decay can explain the observations in all seven upwelling eddies present in the time-series investigated herein.  相似文献   

Imaging of Buried Archaeological Materials: The Reflection Properties of Archaeological Wood   总被引：1，自引：0，他引：1  

Stephanie H.L. Arnott  Justin K. Dix  Angus I. Best  David J. Gregory 《Marine Geophysical Researches》2005,26(2-4):135-144

Effective marine archaeological site management demands detailed information on not only the spatial distribution of artefacts but also the degradation state of the materials present. Although sonar methods have frequently been used in an attempt to detect buried wooden shipwrecks they are currently unable to indicate their degradation state. To assess the sensitivity of acoustic measurements to changes in the degradation state of such material, and hence the potential for sonars to quantify degradation, laboratory measurements of compressional wave velocity, as well as bulk density for oak and pine samples, in varying states of decay, were undertaken. These data enabled the calculation of theoretical reflection coefficients for such materials buried in various marine sediments. As wood degrades, the reflection coefficients become more negative, resulting in the hypothesis that the more degraded wood becomes, the easier it should be to detect. Typical reflection coefficients of the order of −0.43 and −0.52 for the most degraded oak and pine samples in sand are predicted. Conversely, for wood exposed to seawater the predicted reflection coefficients are large and positive for undegraded material (0.35 for oak, 0.18 for pine) and decrease to zero or slightly below for the most degraded samples. This indicates that exposed timbers, when heavily degraded, can be acoustically transparent and so undetectable by acoustic methods. Corroboration of these experimental results was provided through comparison with high resolution seismic reflection data that has been acquired over two shipwrecks.  相似文献   

Management of a shallow temperate estuary to control eutrophication: The effect of hydrodynamics on the system’s nutrient loading   总被引：1，自引：0，他引：1  

A.I. Lilleb  J.M. Neto  I. Martins  T. Verdelhos  S. Leston  P.G. Cardoso  S.M. Ferreira  J.C. Marques  M.A. Pardal 《Estuarine, Coastal and Shelf Science》2005,65(4):697-707

The Mondego estuary, a shallow warm-temperate intertidal system located on the west coast of Portugal, has for some decades been under severe ecological stress, mainly caused by eutrophication. Water circulation in this system was, until 1998, mainly dependent on tides and on the freshwater input of a small tributary artificially controlled by a sluice. After 1998, the sluice opening was effectively minimised to reduce the nutrient loading, and the system hydrodynamics improved due to engineering work in the upstream areas. The objective of the present study was to evaluate the effect of the mitigation measures implemented in 1998. Changes to the hydrodynamics of the system were assessed using precipitation and salinity data in relation to the concentrations of dissolved inorganic nutrients, as well as the linkage between dissolved N:P ratios and the biological parameters (phytoplankton chlorophyll a concentrations, green macroalgal biomass and seagrass biomass). Two distinctive periods were compared, over a ten year period: from January 1993 to January 1997 and from January 1999 until January 2003. The effective reduction in the dissolved N:P atomic ratio from 37.7 to 13.2 after 1998 is a result of lowered ammonia, but not the oxidised forms of nitrogen (nitrate plus nitrite), or increased concentrations of dissolved inorganic phosphorus. Results suggest that the phytoplankton is not nutrient limited, yet maximum and mean biomass of green macroalgae was reduced by one order of magnitude after the mitigation measures. This suggests that besides lowering the water residence time of the system, macroalgal growth became nitrogen limited. In parallel to these changes the seagrass-covered area and biomass of Zostera noltii showed signs of recovery.  相似文献   

Circulation over the continental shelf in the northern Gulf of Mexico   总被引：1，自引：0，他引：1  

J. Carter Ohlmann  P. Peter Niiler 《Progress in Oceanography》2005,64(1):45-81

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Development of two novel CYP-antibodies and their use in a PCB exposure experiment with Mytilus edulis     

H. Jonsson  K. Viken Sandnes  D. Schiedek  R. Schneider  B. E. Grsvik  A. Goksyr 《Marine environmental research》2004,58(2-5):655

In an attempt to learn more about the cytochrome P450 (CYP) system of mussels, we used protein databases and alignment software to extract highly conserved CYP sequences. From these alignments synthetic peptides were produced and used for rabbit immunisation, which yielded polyclonal antibodies against the CYP families 2 and 4. The antibodies were evaluated with Western Blot and ELISA assays, using digestive gland microsomal samples from the mussel Mytilus edulis. Western Blots revealed immunoreactions for both antibodies. The anti-CYP2 sequence rendered one major immunopositive protein of ≈49 kDa size, and weak signals for proteins of ≈41 and 56 kDa size. The anti-CYP4 sequence rendered two major bands of ≈56 and 59 kDa size, and also a weak immunoreaction with a protein of ≈43 kDa size. ELISA rendered only weak signals even with a 1:50 dilution of IgG-purified serum. A 10-day exposure to Aroclor 1254 did not appear to affect any of the immunopositive proteins, while total PCBs in soft bodies increased from 14–40 ng/g DW in controls to 373–638 ng/g DW in exposed mussels.  相似文献   

Simulating a heavy metal spill under estuarine conditions: Effects on the clam Scrobicularia plana     

E. García-Luque  T. A. DelValls  C. Casado-Martínez  J. M. Forja  A. Gmez-Parra 《Marine environmental research》2004,58(2-5):671

We describe the effect of heavy metals Zn, Cd, Pb and Cu on the induction of methallothioneins on the clam Scrobicularia plana along a salinity gradient simulated under laboratory conditions. The clams were exposed to constant heavy metal concentrations in a dynamic estuary simulator during a 15-day assay to investigate possible induction of metal-binding proteins in them. The concentration of heavy metals in water was analysed. Clams were analysed for methallothionein concentrations. The speciation of Zn, Cd, Pb and Cu along the salinity gradient was modelled. Zn showed the highest concentrations and its prevalent species was the free ion. Intersite differences have been observed in methallothionein concentration and related to the salinity gradient. It seems that synthesis of methallothioneins is the result of physiological forces acting in concert with the changes in the chemical speciation of metals, owing to the trace metals uptake is controlled by means of an interaction of physiology and physicochemistry.  相似文献   

Calibration of JASON-1 Altimeter over Lake Erie     

C. Shum  Y. Yi  K. Cheng  C. Kuo  A. Braun  S. Calmant  D. Chambers 《Marine Geodesy》2003,26(3):335-354

This article describes absolute calibration results for both JASON-1 and TOPEX Side B (TSB) altimeters obtained at the Lake Erie calibration site, Marblehead, Ohio, USA. Using 15 overflights, the estimated JASON altimeter bias at Marblehead is 58 ± 38 mm, with an uncertainty of 19 mm based on detailed error analysis. Assuming that the TSB bias is negligible, relative bias estimates using both data from the TSB-JASON formation flight period and data from 48 water level gauges around the entire Great Lakes confirmed the Marblehead results. Global analyses using both the formation flight data and dual-satellite (TSB and JASON) crossovers yield a similar relative bias estimate of 146 ± 59 mm, which agrees well with open ocean absolute calibration results obtained at Harvest, Corsica, and Bass Strait (e.g., Watson et al. 2003). We find that there is a strong dependence of bias estimates on the choice of sea state bias (SSB) models. Results indicate that the invariant JASON instrument bias estimated oceanwide is 71 mm, with additional biases of 76 mm or 28 mm contributed by the choice of Collecte Localisation Satellites (CLS) SSB or Center for Space Research (CSR) SSB model, respectively. Similar analysis in the Great Lakes yields the invariant JASON instrument bias at 19 mm, with the SSB contributed biases at 58 mm or 13 mm, respectively. The reason for the discrepancy is currently unknown and warrants further investigation. Finally, comparison of the TOPEX/POSEIDON mission (1992-2002) data with the Great Lakes water level gauge measurements yields a negligible TOPEX altimeter drift of 0.1 mm/yr.  相似文献   

Weighting of acoustic- and trawl-survey indices for the assessment of North Sea herring   总被引：1，自引：2，他引：1  

Simmonds  E.J 《ICES Journal of Marine Science》2003,60(3):463-471

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Synthetic echograms generated from the relative frequency response   总被引：1，自引：3，他引：1  

Korneliussen  Rolf J; Ona  Egil 《ICES Journal of Marine Science》2003,60(3):636-640

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