Tectonic core of a sedimentary drift: a potential ridge propagation feature beneath the Blake Outer Ridge     

Dayton Dove  Steven C. Jaume  Erin Beutel 《Marine Geophysical Researches》2007,28(1):1-11

The Blake Outer Ridge is a 480–kilometer long linear sedimentary drift ridge striking perpendicular to the North American coastline. By modeling free-air gravity anomalies we tested for the presence of a crustal feature that may control the location and orientation of the Blake Outer Ridge. Most of our crustal density models that match observed gravity anomalies require an increase in oceanic crustal thickness of 1–3 km on the southwest side of the Blake Outer Ridge relative to the northeast side. Most of these models also require 1–4 km of crustal thinning in zone 20–30 km southwest of the crest of the Blake Outer Ridge. Although these features are consistent with the structure of oceanic fracture zones, the Blake Outer Ridge is not parallel to adjacent known fracture zones. Magnetic anomalies suggest that the ocean crust beneath this feature formed during a period of mid-ocean ridge reorganization, and that the Blake Outer Ridge may be built upon the bathymetric expression of an oblique extensional feature associated with ridge propagation. It is likely that the orientation of this trough acted as a catalyst for sediment deposition with the start of the Western Boundary Undercurrent in the mid-Oligocene.  相似文献   

Histopathological biomarkers in estuarine fish species for the assessment of biological effects of contaminants   总被引：1，自引：0，他引：1  

Stentiford GD  Longshaw M  Lyons BP  Jones G  Green M  Feist SW 《Marine environmental research》2003,55(2):137-159

The increasing emphasis on the assessment and monitoring of estuarine ecosystems has highlighted the need to deploy appropriate biological indices for these locations. Fish diseases and histopathology, with a broad range of causes, are increasingly being used as indicators of environmental stress since they provide a definite biological end-point of historical exposure. This study reports on the histopathological alterations observed in selected organs and tissues of three species of estuarine fish (Platichthys flesus, Pomatoschistus minutus and Zoarces viviparus), captured from four British estuaries (the Tyne, Tees, Mersey and Alde), differently impacted by contaminants, including PAHs. A biannual sampling regime was used to identify the important seasonal variations that occur in terms of the observed biological effects. Inflammatory lesions and hepatocellular fibrillar inclusions attained their highest prevalence in P. flesus captured from the Tyne, Tees and Mersey. The presence of pre-neoplastic and neoplastic toxicopathic lesions was highest in P. flesus captured from these sites, when compared to fish from the Aide reference site. In particular, the prevalence of hepatic foci of cellular alteration (up to 43.3%) and hepatocellular adenoma (up to 10%) were highest in P. flesus captured from the Mersey estuary. Intersex (ovotestis) was only recorded in male P.flesus captured from the Mersey estuary (up to 8.3%) and from male Z. viviparous captured from the Tyne estuary (25%). Pathologies associated with the gill and the kidney were also most prevalent in fish captured from the Tyne, Tees and Mersey estuaries. This study has successfully applied histopathology to an estuarine monitoring program, both for the recording of toxicopathic lesions in the liver and other organs, and for the detection of the endpoint of endocrine disruption, intersex. As such, it provides a powerful integrative tool for the assessment of biological effects of contaminants in these environments.  相似文献   

Impacts of stormwater discharges on the nearshore benthic environment of Santa Monica Bay     

Schiff K  Bay S 《Marine environmental research》2003,56(1-2):225-243

Although large loads of potentially toxic constituents are discharged from coastal urban watersheds, very little is known about the fates and eventual impacts of these stormwater inputs once they enter the ocean. The goal of this study was to examine the effects of stormwater discharges on the benthic marine environment of Santa Monica Bay. Sediment samples were collected across a gradient of stormwater impact following significantly sized storm events offshore Ballona Creek (a predominantly developed watershed) and Malibu Creek (a predominantly undeveloped watershed). Sediments offshore Malibu Creek had a greater proportion of fine-grained sediments, organic carbon, and naturally occurring metals (i.e., aluminum and iron), whereas sediments offshore Ballona Creek had higher concentrations of anthropogenic metals (i.e., lead) and organic pollutants (i.e., total DDT, total PCB, total PAH). The accumulation of anthropogenic sediment contaminants offshore Ballona Creek was evident up to 2 km downcoast and 4 km upcoast from the creek mouth and sediment concentrations covaried with distance from the discharge. Although changes in sediment texture, organic content, and an increase in sediment contamination were observed, there was little or no alteration to the benthic communities offshore either Ballona or Malibu Creek. Both sites were characterized as having an abundance, species richness, biodiversity and benthic response index similar to shallow water areas distant from creek mouths throughout the Southern California Bight. There was not a preponderance of pollution tolerant, nor a lack or pollution sensitive, species offshore either creek mouth.  相似文献   

Aquatic surface microlayer contamination in chesapeake bay   总被引：1，自引：0，他引：1  

John T. Hardy  Eric A. Crecelius  Liam D. Antrim  Steven L. Kiesser  Virginia L. Broadhurst 《Marine Chemistry》1990,28(4)

The aquatic surface microlayer (SMIC), 50 μm thick, serves as a concentration point for metal and organic contaminants that have low water solubility or are associated with floatable particles. Also, the eggs and larvae of many fish and shellfish species float on, or come in contact with, the water surface throughout their early development. The objectives of this study were (1) to determine the present degree of aquatic surface microlayer pollution at selected sites in Chesapeake Bay, and (2) to provide a preliminary evaluation of sources contributing to any observed contamination.Twelve stations located in urban bays, major rivers, and the north central bay were sampled three times, each at 5-day intervals during May 1986. Samples of 1.4–4.1 each were collected from the upper 30–60-μm water surface (surface microlayer, SMIC) using a Teflon-coated rotating drum microlayer sampler. One sample of subsurface water was collected in the central bay.At all stations, concentrations of metals, alkanes, and aromatic hydrocarbons in the SMIC were high compared with one bulk-water sample and with typical concentrations in water of Chesapeake Bay and elsewhere. SMIC contamination varied greatly among the three sampling times, but high mean contaminant levels (total polycyclic aromatic hydrocarbons, 1.9–6.2 μg 1⁻¹; Pb, 4.9–24 μg 1⁻¹; Cu, 4–16 μg 1⁻¹; and Zn, 34–59 μg 1⁻¹) were found at the upper Potomac and northern bay sites. Three separate areas were identified on the basis of relative concentrations of different aromatic hydrocarbons in SMIC samples - the northern bay, the Potomac River, and the cleaner southern and eastern portions of the sampling area.Suspected sources of surface contamination include gasoline and diesel fuel combustion, coal combustion, and petroleum product releases. Concentrations of metals and hydrocarbons, at approximately half the stations sampled, are sufficient to pose a threat to the reproductive stages of some fish and shellfish. Sampling and analysis of the surface microlayer provides a sensitive tool for source identification and monitoring of potentially harmful aquatic pollution.  相似文献   

Response of a climate model to tidal mixing parameterization under present day and last glacial maximum conditions     

lvaro Montenegro  Michael Eby  Andrew J. Weaver  Steven R. Jayne 《Ocean Modelling》2007,19(3-4):125-137

Experiments with a climate model were conducted under present day and last glacial maximum conditions in order to examine the model’s response to a vertical mixing scheme based on internal tide energy dissipation. The increase in internal tide energy flux caused by a 120 m reduction in sea level had the expected effect on diffusivity values, which were higher under lower sea level conditions. The impact of this vertical diffusivity change on the Atlantic meridional overturning is not straightforward and no clear relationship between diffusivity and overturning is found. There exists a weak positive correlation between overturning and changes to the power consumed by vertical mixing. Most of the climatic response generated by sea level change was not related to alterations in the internal tide energy flux but rather to the direct change in sea level itself.  相似文献   

Relative microbial activity and mineralization associated with water masses in the lower Cook Inlet,Alaska     

R. P. Griffiths  T. M. McNamara  S. E. Steven  R. Y. Morita 《Journal of Oceanography》1981,37(5):227-233

A study of the microbial uptake and respiration (mineralization) of radioactive glutamic acid was made in 141 surface water samples in the Cook Inlet, Alaska during three sampling periods (October, 1976; April, 1977; and November, 1977). The rate at which the test substrate was incorporated into cell material plus that respired as CO₂ was used to calculate the relative microbial activity. A northern water mass with salinities less than 31 showed high rates of relative microbial activity but low mineralization rates as indicated by respiration of¹⁴CO₂. The reverse pattern was seen in the water mass (salinity higher than 31) to the south which was more typical of coastal water. These data suggest that the organic nutrients in these two water masses are quite different either qualitatively or quantitatively. This study illustrates how the observed measurement of relative microbial activity might be helpful in defining specific water masses.(The publication of this article was unintentionally delayed owing to a fault in secretarial routine.)Published as Technical Paper No. 6009, Oregon Agricultural Experiment Station.  相似文献   

The sea as a source of atmospheric phosphorus   总被引：1，自引：0，他引：1  

William F. Graham  Steven R. Piotrowicz  Robert A. Duce 《Marine Chemistry》1979,7(4):325-342

The geochemical fractionation of phosphorus on the drop produced by bubbles bursting in seawater has been studied using a field sampling system called the Bubble Interfacial Microlayer Sampler (BIMS). The droplets from bursting bubbles were collected on filter samples in Narragansett Bay, Rhode Island during the summer of 1975. Phosphorus was found to be fractionated by the bubble-bursting process. The enrichment factor ranged from 4 to 170. Enrichment was found to increase with decreasing phosphorus concentration at 20 cm depth while it decreases with increasing wind velocity. Enrichment was independent of bubbling depth. Together these facts suggest that the sea-surface microlayer is the source of the phosphorus on the ejected drops. Organic phosphorus on the filter samples was found to be enriched relative to surface-water phosphorus by factors of 100–200, while reactive phosphorus was enriched by factors of only 6–8. This suggests that surface-active organic phosphorus compounds are the source phosphorus in the microlayer.The organic phosphorus content of samples of atmospheric particulates collected over the phosphate-rich upwelling waters near the Peru coast was found to correlate significantly with sea-salt sodium. Enrichments calculated using the average phosphorus concentration of the surface water in this area agree well with the results of the BIMS study. Thus it appears that phosphorus fractionation does occur in nature and may be important in supplying this nutrient to some coastal regions of the world.  相似文献   

Effects of the water-soluble fraction of microbiologically or physically altered crude petroleum on the heterotrophic activity of marine bacteria     

J.Michael Henson  Steven S. Hayasaka 《Marine environmental research》1982,6(3):205-214

Crude petroleum was emulsified or degraded by marine microorganisms and physically altered by an artificial weathering process. Only the water-soluble fraction from emulsified crude petroleum inhibited glutamate uptake by marine microorganisms from South Carolina and Georgia coastal waters. Chloroform extraction recovered almost equal amounts of total hydrocarbon from each water-soluble fraction. Chromatographic data indicated that the composition of microbially emulsified petroleum was similar to that of microbially degraded petroleum. Emulsification of crude petroleum was only observed in summer water samples and did not consistently occur at a given location. Results of this study indicate that the process by which crude petroleum is altered will influence its toxicity to microbial heterotrophic activity.  相似文献   

Seasonal variations of alkenones and U₃₇ in the Chesapeake Bay water column     

Jennifer L. Mercer  Meixun Zhao  Steven M. Colman   《Estuarine, Coastal and Shelf Science》2005,63(4):675-682

Alkenone unsaturation indices (U^K₃₇ and U^K′₃₇) have long been used as proxies for surface water temperature in the open ocean. Recent studies have suggested that in other marine environments, variables other than temperature may affect both the production of alkenones and the values of the indices. Here, we present the results of a reconnaissance field study in which alkenones were extracted from particulate matter filtered from the water column in Chesapeake Bay during 2000 and 2001. A multivariate analysis shows a strong positive correlation between U^K₃₇ (and U^K′₃₇) values and temperature, and a significant negative correlation between U^K₃₇ (and U^K′₃₇) values and nitrate concentrations. However, temperature and nitrate concentrations also co-vary significantly. The temperature vs. U^K₃₇ relationships (U^K₃₇=0.018 (T)−0.162, R²=0.84, U^K′₃₇=0.013 (T)−0.04, R²=0.80) have lower slopes than the open-ocean equations of Prahl et al. [1988. Further evaluation of long-chain alkenones as indicators of paleoceanographic conditions. Geochimica et Cosmochimica Acta 52, 2303–2310] and Müller et al. [1998. Calibration of the alkenone paleotemperature index U^K′₃₇ based on core-tops from the eastern South Atlantic and the global ocean (60°N–60°S). Geochimica et Cosmochimica Acta 62, 1757–1772], but are similar to the relationships found in controlled studies with elevated nutrient levels and higher nitrate:phosphate (N:P) ratios. This implies that high nutrient levels in Chesapeake Bay have either lowered the U^K₃₇ vs. temperature slope, or nutrient levels are the main controller of the U^K₃₇ index. In addition, particularly high abundances (>5% of total C₃₇ alkenones) of the tetra-unsaturated ketone, C_37:4, were found when water temperatures reached 25 °C or higher, thus posing further questions about the controls on alkenone production as well as the biochemical roles of alkenones.  相似文献   

The sea-surface microlayer of puget sound: Part I. Toxic effects on fish eggs and larvae     

John Hardy  Steven Kiesser  Liam Antrim  Alan Stubin  Richard Kocan  John Strand 《Marine environmental research》1987,23(4)

The sea surface is an important habitat for the developmental stages (eggs and larvae) of many fish and invertebrates; it is also a concentration point for anthropogenic contaminants entering the sea. Studies were conducted to determine the extent to which the sea surface of Puget Sound was toxic to the early life history stages of fish. Three urban bays with suspected contamination, a rural reference bay, and a Central Sound site were compared. Surface-dwelling eggs and organisms (zooneuston) were collected with a surface-skimming neuston net and their densities enumerated. Sand sole (Psettichthys melanostictus) embryos were exposed in the field and laboratory to the sea-surface microlayer. To develop a useful year-round approach to monitoring sea-surface toxicity, larval development of anchovies, kelp bass, and sea urchins was also evaluated as an indication of sea-surface microlayer toxicity.During the spawning season (February and March), urban boys in Puget Sound had lower concentrations of sand sole eggs and neustonic organisms on the sea surface than did the rural bayor Central Sound reference sites. Compared to the reference sites, laboratory exposure to surface microlayer samples collected from urban bay sites generally resulted in more chromsomal aberrations in developing sole embryos, reduced hatching success of sole larvae, and reduced growth in trout cell cultures. In situ hatching success of sole eggs was reduced by half or more in urban bays compared to reference sites.Toxicity was associated with visible surface slicks and, in urban bays, increased with increasing surface pressure (dynes cm⁻¹). Results to be reported separately (Part II) indicate that toxicity is strongly correlated with the presence of high concentrations of polycyclic aromatic hydrocarbons and metals in the sea-surface microlayer. The toxicity of SMIC samples was similar when evaluated by sole, anchovy, kelp bass, or sea urchin tests. A sea-surface monitoring program could use sea urchin embryos to evaluate site-specific sea-surface toxicity throughout the year.  相似文献