The Equatorial Atlantic Mid-Ocean Channel: An Ultra High-Resolution Image of Its Burial History Based on TOPAS Profiles     

Baraza  J.  Ercilla  G.  Farrán  M.  Casamor  J. L.  Sorribas  J.  Flores  J. A.  Sierro  F.  Wersteeg  W. 《Marine Geophysical Researches》1997,19(2):115-135

Multibeam bathymetric and ultra high-resolution seismic data reveal that the distal course of the Equatorial Atlantic Mid-Ocean Channel (EAMOC) extends further east and south than was previously known, and is controlled by the presence of morphologic highs related to the Fernando de Noronha Fracture Zone. Distal course of the EAMOC is buried by sediments, and does not have bathymetric expression on the seafloor. The channel fill consists of three seismic sequences, suggesting that the recent geological evolution of the channel is composed of successive phases of decreasing sedimentary activity that finally resulted in its complete burial. Tectonic and volcanic activity related to the Fernando de Noronha Fracture Zone and Ridge, together with the effect of strong pulses of the Antarctic bottom water current during the upper Pliocene are suggested to have contributed to the progressive burial and the final abandonment of the EAMOC.  相似文献   

Microbial Biomass Dynamics Along a Trophic Gradient at the Atlantic Barrier Reef off Belize (Central America)   总被引：2，自引：0，他引：2  

Gerhard J.  Herndl 《Marine Ecology》1991,12(1):41-51

Abstract. Recent findings indicate that heterotrophic bacteria and not phytoplankton are the most numerous biomass components even in the euphotic zone of oligotrophic, open oceans. In this study it was hypothesized that the microbial biomass components change within a few hundred meters as oligotrophic water flows across the reef and becomes enriched with nutrients. Along a trophic gradient, four stations at the Atlantic Barrier Reef off Belize (Central America) were sampled for microbial biomass components. Phytoplankton biomass (measured as chlorophyll a) ranged from the most oligotrophic station (St. 1) to the most eutrophic station (St. 4) from 6.9–415.5 μg CI"' (assuming a C:chl a ratio of 30): heterotrophic bacterial biomass increased 4-fold (from 10.1–46.4μg C 1^-1), heterotrophic nanoflagellate (HNAN) biomass increased from 4.6-19ug C 1^-1, and cyanobacteria from 0.9-4.5 μg C-1^-1. Production estimates derived from seawater cultures revealed a 5-fold increase in bacterial production from the oligotrophic station (3.7 ug C 1^-1 d^-1) to the eutrophic St. 4 (17.8ug C-1-d1^-1)- Cyanobacterial production rose from 1.1–3.5ug C-1–d^-1 and HNAN production from 0.65-1.13 μg C-1^-1 -d^-1. While cyanobacteria contributed between 13 and 20% to the autotrophic plankton component in the oligotrophic waters, their contribution dropped to about 1 % at the eutrophic stations.  相似文献   

Stratal patterns in the southwestern margin of the Ulleung Basin off southeast Korea: sequence architecture controlled by back-arc tectonism     

S. K. Chough  S. H. Yoon  S. J. Park 《Geo-Marine Letters》1997,17(3):207-212

 Major variations in type and rate of tectonic movement in the southwestern margin of the Ulleung Basin coincide in time with changes in stratal patterns at succession boundaries, suggesting that the effect of tectonism was dominant for the development of sequence architecture. During the back-arc opening (16–12 Ma), the rise of relative sea level and the high rate of sediment supply gave rise to sequences with sigmoid progradational patterns. During the back-arc closing (12–6.5 Ma), fall- and rise-dominated relative sea-level fluctuations resulted in sequences with varying stratal patterns depending upon changes in deposition rate. The rise-dominated relative sea level has been prevalent during the later stage (6.5 Ma–Present) with low sedimentation rate. Received: 16 January 1996 / Revision received: 7 February 1997  相似文献   

Complexation of mercury by dissolved organic matter in surface waters of Galveston Bay, Texas   总被引：3，自引：0，他引：3  

Seunghee Han  Gary A. Gill  Ronald D. Lehman  Key-Young Choe 《Marine Chemistry》2006,98(2-4):156-166

The chemical speciation of dissolved mercury in surface waters of Galveston Bay was determined using the concentrations of mercury-complexing ligands and conditional stability constants of mercury-ligand complexes. Two classes of natural ligands associated with dissolved organic matter were determined by a competitive ligand exchange-solvent solvent extraction (CLE-SSE) method: a strong class (L_s), ranging from 19 to 93 pM with an average conditional stability constant (K_HgLs) of 10²⁸, and a weak class (L_w) ranging from 1.4 to 9.8 nM with an average K_HgLs of 10²³. The range of conditional stability constants between mercury and natural ligands suggested that sulfides and thiolates are important binding sites for dissolved mercury in estuarine waters. A positive correlation between the estuarine distribution of dissolved glutathione and that of mercury-complexing ligands supported this suggestion. Thermodynamic equilibrium modeling using stability constants for HgL, HgCl_x, Hg(OH)_x, and HgCl(OH) and concentrations of each ligand demonstrated that almost all of the dissolved mercury (> 99%) in Galveston Bay was complexed by natural ligands associated with dissolved organic matter. The importance of low concentrations of high-affinity ligands that may originate in the biological system (i.e., glutathione and phytochelatin) suggests that the greater portion of bulk dissolved organic matter may not be important for mercury complexation in estuarine surface waters.  相似文献   

Nutrient dynamics and seasonal succession of phytoplankton assemblages in a Southern European Estuary: Ria de Aveiro, Portugal   总被引：2，自引：1，他引：2  

C.B. Lopes  A.I. Lilleb  J.M. Dias  E. Pereira  C. Vale  A.C. Duarte 《Estuarine, Coastal and Shelf Science》2007,71(3-4):480-490

The spatial and temporal dynamics of dissolved inorganic nitrogen, dissolved phosphate, dissolved silica and chlorophyll a were measured seasonally at eight stations in the Ria de Aveiro. Between December 2000 and September 2001, the seasonal succession of phytoplankton assemblages, inferred after the spatial and seasonal variation of silica and of chlorophyll a concentrations, showed that diatoms (μmol Si L⁻¹) dominated from late autumn until early spring, while chlorophytes (μg Chl a L⁻¹) bloomed during late spring and summer. The Si:N:P ratios and Si concentrations indicated no seasonal depletion in dissolved silica, as in other temperate systems, possibly because of abnormal precipitation and flood events prolonging the supply of dissolved Si to the system. The Si:N:P ratios suggested P limitation at the system level. Despite the relative proportions of available nutrients, the mean phosphorus concentration (5.3 μmol L⁻¹) was above the reported half-saturation constants for P uptake by phytoplankton. Thus, in Ria de Aveiro, the seasonal succession of phytoplankton assemblages may also be dependent on the grazing capacity of the pelagic community through top-down regulation.  相似文献   

A time-varying parameter model of a body oscillating in pitch     

A.P. McCabe  G.A. Aggidis  T.J. Stallard   《Applied Ocean Research》2006,28(6):359-370

Among the assumptions upon which linear time-invariant models of floating bodies are based is that the body motions are so small that any change in the body’s angular position can be disregarded. However, it is often a major design requirement of a wave energy conversion device that the response amplitude is large, thereby invalidating one of the assumptions of the linear model. In particular, the immersed geometry of a body undergoes considerable variation when it is moved in pitch. With regard to this we investigate the difference in performance between a quasi-linear model in which the change of immersed surface is modelled by time-varying parameters and a basic linear model in which the immersed surface is time-invariant. The time-varying parameter model is realized by interpolation between the appropriate parameter values of a set of linear time-invariant (LTI) models derived for the different immersed surfaces that occur at discrete body displacements. It is shown that the responses predicted using the time-varying parameter model are closer to those measured experimentally than those of a standard frequency-domain model. Particular improvement occurs when the responses are large, such as at or near the resonance frequency. A problem which may limit the general use of the model is also discussed.  相似文献   

Isotopic and Elemental Variations of Carbon and Nitrogen in a Mangrove Estuary   总被引：6，自引：0，他引：6  

L.A. Cifuentes  R.B. Coffin  L. Solorzano  W. Cardenas  J. Espinoza  R.R. Twilley 《Estuarine, Coastal and Shelf Science》1996,43(6):781-800

Variations in elemental and isotopic ratios of suspended particulate matter (SPM) were investigated in the Guayas River Estuary Ecosystem (GREE) that empties into the Gulf of Guayaquil, Ecuador. Detritus in the system was identified on the basis of extremely high carbon:chlorophyll aratios (>1000). This material had mean δ¹³C of −26·4±0·3, δ¹⁵N of +4·8±0·2, and (C:N)_atomicof 14·1±0·9. The isotopic data were comparable to measurements reported for fresh and degrading mangrove leaves, whereas the elemental ratio was comparatively enriched in nitrogen. Isotope measurements of SPM throughout the GREE were more similar to values for riverine material and detritus compared with that for the coastal end-member. Values indicative ofin situproduced algae, sewage and shrimp pond effluent were only found at selected sites. Bacterial bioassays, which were used to document potential sources of dissolved organic matter in the GREE, were isotopically similar to SPM. This correspondence coupled with the relatively low (C:N)_aof SPM could be explained by bacterial immobolization of nitrogen onto detritus. Finally, tidal variations of (C:N)_aand δ¹³C at a brackish mangrove site were similar in magnitude to spatial variations encountered throughout the GREE. Based on these results, the authors caution that care must be taken when samples are taken for food-web studies in these systems.  相似文献   

Population dynamics of two marine polychaetes: the relative role of density dependence, predation, and winter conditions     

van der Meer  Jaap; Beukema  Jan J; Dekker  Rob 《ICES Journal of Marine Science》2000,57(5):1488-1494

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Atlantic mackerel (Scomber scombrus L.) stocks and genes: A review     

Jamieson  Alan; Smith  Peter J. 《ICES Journal of Marine Science》1987,44(1):66-72

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Launching and joining of a product carrier of 30,500 DWT built in two sections     

S. B. Dharmadhikari  E. Garcia  S. Espinoza  J. Dominguez  J. M. Goris 《Ocean Engineering》1978,5(3):165-180

This paper describes the process of launching and joining of two sections of a product carrier of 30,500 DWT built at Dianca shipyard at Puerto Cabello, Venezuela. The specifications and characteristics of this ship are in line with the market requirements. This paper deals with the problems encountered during the decision of dividing the ship in two halves, use of syncrolift for launching and subsequent joining of two halves in the dry dock.  相似文献