Cross-shore separation of adult and juvenile euphausiids in a shelf-break alongshore current     

Beiwei Lu  David L. Mackas  Douglas F. Moore 《Progress in Oceanography》2003,57(3-4):381

Euphausiids are an important component of the zooplankton in boundary current upwelling regions, including the Pacific Northwest continental margin. Many aspects of euphausiid distribution and ecology in this region are well known. However, some features of their spatial and temporal distribution are less understood:

• How and why euphausiids aggregate near the shelf-break upwelling center.

• How and why there is (within an alongshore band of high abundance of all stages) spatial segregation of adults and larvae.

• Why, despite spatial association with upwelling, euphausiid abundance off Vancouver Island is weakly or negatively correlated at interannual time scales with upwelling intensity.

To address these, we made km-resolution surveys of adult, juvenile, and larval euphausiid horizontal distributions, water properties, and currents across the Vancouver Island shelf break in mid-to-late spring of two successive years. Survey timing was before (1997) and after (1998) the spring transition to upwelling conditions, and near the annual spring reproductive peak. In both years, early developmental stages occupied an alongshore band that was offset from the late juveniles and adults. The direction of the offset differed between the two surveys. Early life history stages (larvae and early juveniles) were shoreward of adults in April 1997 (downwelling-conditions), but seaward of adults in May 1998 (upwelling-conditions). Separation distance (order 5–10 km) was consistent with expected differences in cumulative wind-driven (and vertically-sheared) cross-shore transport of surface-dwelling larvae and early juveniles vs. transport of diel migratory late juveniles and adults. Separation direction was consistent with recent history of winds and Ekman transport—shoreward during poleward winds, and seaward into blue water (and usually into a strong equatorward current) during equatorward winds.  相似文献   

The regional approach to the ocean, the ocean regions, and ocean regionalisation—a post-modern dilemma     

Adalberto Vallega   《Ocean & Coastal Management》2002,45(11-12)

Essentially, this paper aims at considering how the ocean regionalisation may be implemented focusing on the principle of sustainable development, on the subsequent criteria designed by the inter-governmental organisation framework, and on the approaches from the scientific literature. In this respect, a model is proposed, according to which two main stages are identified: (i) the stage of the modern approach to the ocean, which was operated by the modern society and was supported by the culture of modernity; (ii) the stage of the post-modern approach, which has been triggered by the converging inputs from the changes in society and nature. The watershed between these two stages may be located in the 1970s. The investigation may be carried out considering a triangular relationship between (i) the changing ocean reality (ontological dimension), (ii) the representation of this reality (semiological dimension), and (iii) the building up of signified, consisting in theories, meta-theories and values (epistemological and ethical dimensions). In this framework, special relevance is attributed to the interaction between science and policy.Moving from this basis, how ocean regionalisation had been conceived by oceanography, geography and law is considered focusing on the implications that have arisen in terms of ocean management. Analysis is essentially focused on three questions: (i) how much the conceptual implications of the approach to the ocean regional scale have been underestimated, and how ample the political consequences have been; (ii) why the political designs referring to this spatial scale of the ocean, which have been carrying out since the 1970s, have been marked by a lack of consistency of the legal framework with the prospect of operating sustainable management programmes; (iii) whether, and what kind of, discrepancy has solidified between the legal framework, provided by the 1982 UN Convention on the Law of the Sea (UNCLOS), and the ecosystem-oriented approach to the ocean, designed by the UN Conference on Environment and Development (UNCED).These considerations lead to identify three cardinal needs. First, the need to try lessons from the Regional Seas Programme of the United Nations Environment Programme (UNEP) by carrying out a critical analysis of the conceptual background and methodological endowment which it was based on, and of the subsequent political outcomes. Secondly, an increasing need for scientific approaches supported by the consideration of the ocean as a bi-modular system consisting in ecosystems and organisational patterns, being both modules subject to the impacts from global change and globalisation. Thirdly, a need to design and operate a more effective interaction between science and policy, and, as far as science in itself is concerned, the need to design a more epistemologically-sound interaction between natural and social disciplines.Moving from this discussion, it is proposed to distinguish the mere ocean area, where the organisational patterns have not yet created a real ocean system, from the ocean region, which differently has acquired the features of an ocean system. These two kinds of spaces may be found in the coastal milieu, extending up to the outer edge of the continental margin, in the deep-ocean, extending seawards from the continental margin, or they may extend across the continental margin and the deep-ocean. Where it is agreed that ocean reality may evolve on the basis of these two reference patterns, the following sequence of conceptual mises-au-point and statements may be considered.

• The ocean area—This kind of ocean space may solidify in those areas where the ocean is frequented and used in the traditional ways without benefiting from a well-designed organisational pattern. Human presence and resource uses have brought about spatial differentiation but not such a real cohesion which may be only achieved by adopting an organisational plan.

• The ocean region—This occurs only where an ocean area is endowed with such an organisational framework that allows the pursuit of clearly pre-determined objectives in terms of environmental, resource management, and economic development. This is the product of an extensive human interaction with the ocean ecosystem, and of a substantial political approach to the ocean milieu.

Where it is agreed that ocean reality may evolve on the basis of these two reference patterns, the following sequence of conceptual mises-au-point and statements may be considered:

• The ocean region and regional strategy—At the present time, ocean regions may be found only in quite limited parts of the ocean world.

• The final objective—Where the decision-making centres conform their programmes and actions to the principles and guidelines from UNCED, the objective of each ocean region should be the pursuit of sustainable development on the regional scale.

• Sustainable region—This occurs where the regional organisation is primarily based on the protection of the ecosystem integrity, where economic development operates through the optimisation of resource usage, and where social equity, including the access to the natural and cultural heritage of the ocean environment, is guaranteed.

• Ocean regionalisation—When an individual ocean is subject to the organisational forces that lead to the creation of regions, it can be stated that an ocean regionalisation has occurred.

• Global change—Ocean regionalisation should be viewed as one of the most important consequences of the global, environmental and social change that characterises the present phase of society.

• Globalisation—The setting up of a transport and communication global network, together with the associated establishment of global production and consume patterns, of market strategies and social behaviour, may be regarded as the cardinal set of socio-economic factors, which ocean regionalisation is going to increasingly depend on.

• Enlargement of the geographical approach—The development of ocean regions encourages to set up effective inter-disciplinary approaches, that primarily should focus on: (i) the consistency of the regional organisation with the regional objectives; (ii) the consistency of the ocean resource use with the protection of the ecosystem, primarily the safeguard of its biodiversity, productivity and resilience; and (iii) the configuration and functions of the decision-making system in guiding regional organisation.

• Ocean region and ecosystem—The most desirable conditions in terms of optimal ocean organisation on the regional scale occur where the spatial extent of the ocean, which is encompassed by an individual regional management programme, fully coincides with the spatial extent of an ocean ecosystem, or with a set of contiguous ecosystems.

• Decision-making systems—The more the co-operative process between decision-making systems operating in contiguous ocean regions develops, the greater the potential for a holistic political approach to the oceans becomes. The spatial consequences deriving from the interaction between the decision-making centres are of peculiar interest.

The response of a hydrofoil to wave orbital velocity fields     

Peter R. Payne 《Ocean Engineering》1997,24(3):235-263

For study purposes, a simplified model of a hydrofoil craft is constructed with the assumption that it has:

• heave only motion;

• no surface proximity effect on the foil;

• no foil broaching.

It is then shown that a fully submerged hydrofoil, mounted at the bottom of rigid struts, can transmit large vertical force fluctuations to the hull, even in an idealized sinusoidal seaway because of the orbital velocity field in the water. But if the foil support struts are hinged, inclined aft and resiliently supported, so that the hydrofoil can swing about the strut's pivot in response to the changes in local water velocity, then the vertical accelerations transmitted to the hull are reduced. The more the strut is inclined to the vertical, the smaller are the accelerations transmitted to the hull. A hinged strut whose equilibrium angle (for 1 g) is 60° to the vertical can reduce the vertical accelerations by an order of magnitude. It also has two other practical advantages. The strut(s) and foil will ride up towards horizontal during the rare but inevitable impacts with large marine objects (such as whales or flotsam) and during groundings. And when they encounter a region of water moving rapidly downward (which can cause a conventional fully submerged hydrofoil to experience a violent hull impact on the water) they move in such a way as to maintain a roughly constant lift force on the hull, so that there is negligible hull motion in heave.  相似文献   

Mooring optimization of floating platforms using a genetic algorithm   总被引：1，自引：0，他引：1  

Mehdi Shafieefar  Aidin Rezvani 《Ocean Engineering》2007,34(10):1413-1421

This paper presents a new procedure for the optimization of the mooring design of floating platforms, in which an automatic design sequence is also established. Regarding the optimization philosophy, the following aspects are dealt with:

• The optimization of the platform heading and its mooring pattern, taking into account the environmental force spreading;

• optimum line length or line tension for each mooring line, associated to the optimization of the mooring line materials and sizes.

Basically, the main goal of this paper is to introduce a new method, which will provide the quickest way to find the best mooring system, defined here as that which minimizes platform responses.A genetic algorithm (GA) is applied in this contribution, and this paper describes exactly the procedure of developing a GA code directed toward the solution of mooring design optimization problems. In order to prove the efficiency and the vast potential of the proposed algorithm as a design tool, sample moorings are analyzed for different environmental conditions and the final results, including the time required to run them, are presented.  相似文献   

Polyester mooring for the Mad Dog spar—design issues and other considerations     

David Petruska  Jeff Geyer  Rick Macon  Michael Craig  Alex Ran  Neil Schulz 《Ocean Engineering》2005,32(7):767-782

The Mad dog project will use a polyester mooring system on the drilling and production truss spar. This will be the first use of a permanent polyester mooring system on a Floating Production System (FPS) outside of Brazil and the first time polyester has been used on a spar. As such, there were many challenges, which include:

• Regulatory approval.

• Designing a mooring system which is dominated by current loadings.

• Largest polyester rope break load ever required.

• Rope design qualification and testing.

• Quality control and assurance.

• Inspection, Maintenance, Repair and Retirement (IMRR) of such a mooring system.

This paper will focus on the design issues, rope design, manufacturing, qualification and testing, and the IMRR plan that was developed to provide the assurance that the polyester mooring system could be safely operated over the 20-year field life.  相似文献   

A prediction technique for the transverse vortex-induced oscillations of tensioned risers   总被引：1，自引：0，他引：1  

G. Benassai  A. Campanile 《Ocean Engineering》2002,29(14):1805-1825

In this paper, a model for the prediction of the vortex-induced transverse oscillations of tensioned risers is proposed.The model, based on the peak amplitudes of the oscillations recorded for cylindrical bodies in a uniform current, has been extended to multimodal oscillations in a sheared flow condition through a modal priority technique. The difference between this model and other similar ones lies in the following features:

the hydrodynamic damping, which has been introduced in a more general form without ‘a priori’ approximations;

the modal priority, which is based on the local amplitudes of the active vibration modes, rather than on their frequencies.

Some comparisons with experimental and numerical results available in the literature are presented and discussed.  相似文献   

Altimeter-derived surface circulation in the large–scale NE Pacific Gyres. : Part 1. seasonal variability     

P Ted Strub  Corinne James 《Progress in Oceanography》2002,53(2-4)

The seasonal variability of sea surface height (SSH) and currents are defined by analysis of altimeter data in the NE Pacific Ocean over the region from Central America to the Alaska Gyre. The results help to clarify questions about the timing of seasonal maxima in the boundary currents. As explained below, the long-term temporal mean of the SSH values must be removed at each spatial point to remove the temporally invariant (and large) signal caused by the marine geoid. We refer to the resulting SSH values, which contain all of the temporal variations, as the ‘residual’ SSH. Our main findings are:

1. The maximum surface velocities around the boundaries of the cyclonic Alaska Gyre (the Alaska Current and the Alaska Stream) occur in winter, at the same time that the equatorward California Current is weakest or reversed (forming the poleward Davidson Current); the maximum surface velocities in the California Current occur in summer. These seasonal maxima are coincident with the large-scale atmospheric wind forcing over each region.

2. Most of the seasonal variability occurs as strong residuals in alongshore surface currents around the boundaries of the NE Pacific basin, directly connecting the boundaries of the subpolar gyre, the subtropical gyre and the Equatorial Current System.

3. Seasonal variability in the surface velocities of the eastward North Pacific Current (West Wind Drift) is weak in comparison to seasonal changes in the surface currents along the boundaries.

4. There is an initial appearance next to the coast and offshore migration of seasonal highs and lows in SSH, alongshore velocity and eddy kinetic energy (EKE) in the Alaska Gyre, similar to the previously-described seasonal offshore migration in the California Current.

5. The seasonal development of high SSH and poleward current residuals next to the coast appear first off Central America and mainland Mexico in May–June, prior to their appearance in the southern part of the California Current in July–August and their eventual spread around the entire basin in November–December. Similarly, low SSH and equatorward transport residuals appear first off Central America and Mexico in January–February before spreading farther north in spring and summer.

6. The maximum values of EKE occur when each of the boundary currents are maximum.

Continuous Plankton Recorder sampling off the east coast of North America: history and status     

J. W. Jossi  A. W. G. John  D. Sameoto 《Progress in Oceanography》2003,58(2-4):313

The Continuous Plankton Recorder (CPR) survey has sampled plankton on 14 routes off the coasts of the northeast United States and Canada between 1959 and 2000. Six of these routes are still operating and are sampled on a monthly basis. Some 2047 CPR tows have been made to the end of 2000 and the resulting database represents the most extensive time series of marine plankton available anywhere in the northwest Atlantic. The location and time span of coverage of each route is presented. In addition selected information is presented on:

1. zooplankton abundance as departures from baselines for the northeast US continental shelf;

2. interannual variation in seasonality of Gulf of Maine phytoplankton;

3. zooplankton relationships to local hydrography of the Gulf of Maine and to the North Atlantic Oscillation;

4. time-space matrices of zooplankton abundance and anomalies southeast of New York City;

5. time series of phyto- and zooplankton on the Scotian Shelf;

6. seasonal cycles of Phytoplankton Colour and of zooplankton on the Scotian Shelf and Georges Bank, and in the Gulf of Maine; and

7. monthly abundance of zooplankton in Narragansett Bay, Rhode Island.

  相似文献   

Impact of El Niño events and climate regime shift on living resources in the western North Pacific     

Takashige Sugimoto  Shingo Kimura  Kazuaki Tadokoro 《Progress in Oceanography》2001,49(1-4)

Features of El Niño events and their biological impacts in the western North Pacific are reviewed, focusing on interactions between ENSO and the East Asian monsoon. Impacts of El Niño on the climate in the Far East become evident as ‘cool summers and warm winters’. Effects of climate regime shift on ENSO activities, western boundary currents and upper-ocean stratification, as well as their biological consequences are summarized. These have been:

1. In the western equatorial Pacific, an eastward extension of the warm pool associated with El Niño events induces an eastward shift of main fishing grounds of skip jack and big eye tunas.

2. The surface salinity front in the North Equatorial Current region retreats southward, associated with El Niño events. This leads to a southward shift of the spawning ground of Japanese eel, which is responsible for a reduction in the transport of the larval eels to the Kuroshio and Japanese coastal region, causing poor recruitment.

3. Intensification of winter cooling and vertical mixing associated with La Niña (El Niño) events in the northern subtropical region of the western (central) North Pacific reduces surface chlorophyll concentration levels and larval feeding condition for both Japanese sardines and the autumn cohort of Neon squid during winter–early spring. The semi-decadal scale calm winter that occurred during the early 1970s triggered the first sharp increase of sardine stock around Japan.

4. A remarkable weakening of southward intrusion of the Oyashio off the east coast of Japan during 1988–91, resulted in a decrease in chlorophyll concentrations and mesozooplankton biomass in late spring–early summer of the Kuroshio-Oyashio transition region. Changes occurred in the dominant species of small pelagic fish, through successive recruitment failures of Japanese sardine.

The upwelling area off Northwest Africa—A description of phenomena related to coastal upwelling     

Ekkehard Mittelstaedt 《Progress in Oceanography》1983,12(3):307-331

  相似文献   

Off-shelf fluxes of labile materials by an upwelling filament in the NW Iberian Upwelling System     

X. A. lvarez-Salgado  M. D. Doval  A. V. Borges  I. Joint  M. Frankignoulle  E. M. S. Woodward  F. G. Figueiras 《Progress in Oceanography》2001,51(2-4)

Daily changes in the concentrations of carbon and nitrogen species were monitored during the course of a Lagrangian drifter experiment in a recurrent upwelling filament south of Cape Finisterre (NW Iberian Upwelling System). A drifting buoy released at the southern edge of the upwelling centre generated by the Cape moved 60km southwestwards from 3 to 7 August 1998. Organic matter in the 50m deep study water mass (average 77±2 μM C) consisted of: 57μM C of dissolved organic matter (DOM) with a C/N molar ratio of 19±2; 6μM C of DOM with a C/N ratio of 9±2, and 14μM C of 50% DOM and 50% suspended organic matter (POM_susp) with a C/N ratio of 6.0±0.4.Net conversion of consumed inorganic salts into accumulated TOM=POM_susp+DOM was 40% for nitrogen and 30% for carbon. Since the parcel of water crossed the shelf-edge, these conversion efficiencies are equivalent to net horizontal export-ratio of 0.4 and 0.3 respectively. A second drifter was deployed in the offshore-end of the filament, and was displaced 20km west between 14 and 17 August 1998. Nitrate was exhausted in the surface water and no significant changes were observed in the variables measured during the course of the second experiment. Low C/N ratios (6.5±0.4) and rapid POM_susp/DOM inter-conversion in the 20 μM C excess observed in the study volume points to the persistence of the labile materials formed on the shelf during transport to the ocean. Our data demonstrate

a) the key role of upwelling filaments in off-shelf export of organic materials and

b) the major contribution of DOM to this horizontal export, a previously unaccounted amount.

The high nitrogen content of the materials exported make them attractive organic substrates for use by microbial populations in the adjacent oligotrophic ocean.  相似文献   

Sediment—sea interaction     

R Pelet 《Marine Chemistry》1977,5(4-6)

1. (1) The nature of sediment—sea interactions depends on the time scale considered. At a time scale commensurate with human life, one can define a water—sediment interface, and the main exchanges are solutes exchanges through this interface by concentration diffusion. This condition will be termed as “Short time-scale equilibrium interaction”.

On the other hand, at a geological time scale, there is a continuous accretion to the “sediment” of suspended particulate matter, bottom-current borne materials and sometimes precipitates of previously dissolved salts; to this sediment build-up corresponds a flux of water of reverse sense, from the sediment to the water column, due to the compaction of muds and oozes which reduce their porosity (their water content) under their own load. The concept of interface is then of limited utility, since physically it is constantly changing, and since the material balance of the exchanges does not depend on its characteristics at a first order of approximation. This condition will be termed “long time-scale geological interaction”.

These situations are extreme ones. In areas of present important detrital sedimentation, even for short time spans it is doubtful if the definition of an interface has some utility: we are in a situation close to “geological time scale”. On the contrary, in abyssal zones remote from continents, the rate of sedimentation is so low that even for eons an interface separating two environments in physico-chemical equilibrium exists.

2. (2) If there were no internal sources of dissolved species in the sediment, the only concentration changes to occur would be due to the decrease in porosity (in water content) following gravitational compaction of sediments. But this phenomenon is the same as sedimentation, thus transfer of matter would be unappreciable within short time spans. The fact that this transfer can be measured at human time scale shows therefore that dissolved species are actually produced in the sediment. Some of these can originate from possible inorganic chemical reactions, but all the organic molecules, and an important part of the inorganic (such as phosphates, nitrates, NH₄⁺, S^2-) require processing of organic matter for their production. Whether or not this reworking is of biological origin remains controversial. On the whole, the quantities of matter thus transferred are very minute compared to the quantities present in oceanic waters. They cannot be considered in general as a significant input. But they may be important locally (nearshore restricted water bodies, or manganese nodules formation).

3. (3) At geological time scale, sedimentation, which adds solid material to the preexisting sediment, results also in the compaction of this sediment. At every depth in the sediment there exists an equilibrium value of the porosity, i.e. the fluids content, of the sediment; it tends to this value by expelling the corresponding quantity of fluids, with a rate determined by its permeability. This input may be important, but it is mainly water, and water formerly oceanic: therefore it is not a true input, but simply a delayed return. The transfer of other fluids (mainly oil and gas) is unsignificant generally speaking. Once more, it may be locally important (submarine seepages).

4. (4) On the whole, the processes of water—sediment interaction appear not to add any new matter into the oceanic pool, but rather to regulate the restitution by the sediment to the water of substances which were already present in ocean, in particulate or dissolved form, either free or combined. One can trace out two main processes, which differ in their rates and yields:

4.1. (a) the short time scale diffusion—high rate low yield restitution of organics and inorganics in dissolved state:

4.2. (b) the long time scale compaction: low rate high yield restitution of entrapped fluids, essentially water (devoid of dissolved species).

Not only do these processes not bring any new matter to the ocean, but even the absolute quantities involved are modest compared either to the quantities present in the ocean or to the quantities generated by the photosynthetic primary production or brought by the rivers.In contrast to the insignificance of the water—sediment interaction in the oceanic material balance, this same interaction is one of the main sources for the material sedimented and especially the organic one, and therefore it is a fundamental key for all the subsequent sedimentary history.The significant inputs at the limit “bottom”-water come from the regions of deep tectonic activity, volcanism, creation of new oceanic crust etc… There tremendous amounts of substances can be brought into solution, changing at least locally the concentration equilibrium values of seawater. They are of course inorganic ions, but they can have important biological consequences. The buffering capacity of the world ocean is so high that only cosmic events can influence its composition.  相似文献   

Adriatic seiche decay and energy loss to the Mediterranean     

Ivana Cerove?ki  Mirko Orli?  Myrl C. Hendershott 《Deep Sea Research Part I: Oceanographic Research Papers》1997,44(12):2007-2029

A salient feature of sea level records from the Adriatic Sea is the frequent occurrence of energetic seiches of period about 21 h. Once excited by a sudden wind event, such seiches often persist for days. They lose energy either to friction within the Adriatic, or by radiation through Otranto Strait into the Mediterranean.The free decay time of the dominant (lowest mode) seiche was determined from envelopes of handpassed sea level residuals from three locations (Bakar, Split and Dubrovnik) along the Croatian coast during twelve seiche episodes between 1963 and 1986 by taking into consideration only time intervals when the envelopes decreased exponentially in time, when the modelled effects of along-basin winds were smaller than the error of estimation of decay time from the envelopes and when across-basin winds were small. The free decay time thus obtained was 3.2±0.5 d. This value is consonant with the observed width of the spectral peak.The decay caused by both bottom friction and radiation was included in a one dimensional variable cross section shallow water model of the Adriatic. Bottom friction is parameterized by the coefficient k appearing in the linearized bottom stress term _ρ0u (where u is the along-basin velocity and ρ₀ the fluid density). The coefficient k is constrained by values obtained from linearization of the quadratic bottom stress law using estimates of near bottom currents associated with the seiche, with wind driven currents, with tides and with wind waves. Radiation is parameterized by the coefficient f appearing in the open strait boundary condition ζ =auh/c (where ζ is sea level, h is depth and c is phase speed). This parameterization of radiation provides results comparable to allowing the Adriatic to radiate into an unbounded half plane ocean. Repeated runs of the model delineate the dependence of model free seiche decay time on k and a, and these plus the estimates of k allow estimation of a.The principle conclusions of this work are as follows.

1. (1) Exponential decay of seiche amplitude with time does not necessarily guarantee that the observed decay is free of wind influence.

2. (2) Winds blowing across the Adriatic may be of comparable importance to winds blowing along the Adriatic in influencing apparent decay of seiches; across-basin winds are probably coupled to the longitudinal seiche on account of the strong along-basin variability of across-basin winds forced by Croatian coastal orography.

3. (3) The free decay time of the 21.2 h Adriatic seiche is 3.2±0.5 d.

4. (4) A one dimensional shallow water model of the seiche damped by bottom stress represented by Godin's (1988) approximation to the quadratic bottom friction law ρ₀C_Du|u| using the commonly accepted drag coefficient C_D = 0.0015 and quantitative estimates of bottom currents associated with wind driven currents, tides and wind waves, as well as with the seiche itself with no radiation gives a damping time of 9.46 d; radiation sufficient to give the observed damping time must then account for 66% of the energy loss per period. But independent estimates of bottom friction for Adriatic wind driven currents and inertial oscillations, as well as comparisons between quadratic law bottom stress and directly measured bottom stress, all suggest that the quadratic law with C_D=0.0015 substantially underestimates the bottom stress. Based on these studies, a more appropriate value of the drag coefficient is at least C_D=0. In this case, bottom friction with no radiation leads to a damping time of 4.73 d, radiation sufficient to give the observed damping time then accounts for 32% of the energy loss per period.

  相似文献   

The Portugal coastal counter current off NW Spain: new insights on its biogeochemical variability   总被引：1，自引：0，他引：1  

X.A Álvarez-Salgado  F.G FigueirasF.F Pérez  S GroomE Nogueira  A.V BorgesL Chou  C.G CastroG Moncoiffé  A.F RíosA.E.J Miller  M FrankignoulleG Savidge  R Wollast 《Progress in Oceanography》2003,56(2):281-321

Time series of wind-stress data, AVHRR and SeaWiFS satellite images, and in situ data from seven cruises are used to assemble a coherent picture of the hydrographic variability of the seas off the Northwest Iberian Peninsula from the onset (September-October) to the cessation (February-May) of the Portugal coastal counter current (PCCC). During this period the chemistry and the biology of the shelf, slope and ocean waters between 40° and 43°N have previously been undersampled. Novel information extracted from these observations relate to:

1.

The most frequent modes of variability of the alongshore coastal winds, covering event, seasonal and long-term scales;

2.

The conspicuous cycling between stratification and homogenisation observed in PCCC waters, which has key implications for the chemistry and biology of these waters;

3.

The seasonal evolution of nitrite profiles in PCCC waters in relation to the stratification cycle;

4.

The Redfield stoichiometry of the remineralisation of organic matter in Eastern North Atlantic Central Water (ENACW)—the water mass being transported by the PCCC;

5.

The separation of coastal (mesotrophic) from PCCC (oligotrophic) planktonic populations by a downwelling front along the shelf, which oscillates to and fro across the shelf as a function of coastal wind intensity and continental runoff; and

6.

The photosynthetic responses of the PCCC and coastal plankton populations to the changing stratification and light conditions from the onset to the cessation of the PCCC.

  相似文献   

Trace metal adsorption on inorganic solid phases under estuarine conditions     

《Marine Chemistry》1991,32(2-4)

The adsorption of trace metals (Pb, Zn, Cu, Cd and Hg) on calcite, kaolinite and bentonite has been studied in Krka river water of various salinities (S = 3, 20 and 38‰).Model experiments were performed at pH 8 in natural water and in UV-irradiated water samples to determine the importance of natural soluble organic matter. Cold vapour atomic absorption spectrometry was used for the Hg determination, and a differential pulse anodic stripping voltammetry (DPASV) method for determination of other trace metals, using either a hanging mercury drop electrode or a mercury-coated glassy carbon working electrode. The following results have been obtained on calcite:

1. (1) a powerful absorption of Pb and Zn was observed for both natural and UV-irradiated waters at S=20‰;

2. (2) a strong adsorption of Hg was observed in natural water, and significantly lower adsorption in UV-irradiated water at all three salinities, particularly at low salinity;

3. (3) Cd adsorption was of medium intensity in both waters at S=20‰;

4. (4) Cu was practically not adsorbable in both waters at S=20‰ if the total Cu ion concentration was lower than the copper complexing capacity value;

5. (5) Cu adsorption was of a medium intensity at S=38‰. It has not influenced by the EDTA model ligand.

Trace metals Pb, Zn and Cu are adsorbable on kaolinite and bentonite at S=38‰, whereas Cd is practically not adsorbed. The Krka River is a calcareous river, which supplies the sea with calcite and aluminosilicates. In the light of our model experiments, we suggest that the self-purification of the Krka River is remarkable in respect to Pb, Zn and Hg; this occurs to a lesser extent for Cu, and is negligible in the case of Cd.  相似文献   

Dissolved silica concentrations and reactions in pore waters from continental slope sediments offshore from Cape Hatteras, North Carolina, USA     

Joan D. Willey  Arthur J. Spivack 《Marine Chemistry》1997,56(3-4)

The pore water concentrations of dissolved silica in sediment cores from the continental slope offshore from Cape Hatteras, North Carolina, varied from 150 to almost 700 μ,M with depth in the top 40 cm of sediment. Sediment cores from 630 to 2010 m depth had very similar profiles of dissolved silica in their pore waters, even though these cores came from regions greatly different in slope, topography, sedimentation rate, and abundance of benthic macrofauna. Cores from 474 to 525 m were more variable, both with respect to pore water dissolved silica profiles, and with respect to sediment texture. Experiments indicate that both the rate of dissolution of silica and the saturation concentration decrease as sediment depth below the sediment-seawater interface increases. These data are consistent with depletion of a reactive silica phase in surface sediment, which may be radiolarian tests, or the alteration of biogenic silica to a less reactive form over time. Experimental results suggest that the pore water dissolved silica concentration in sediments below the top few centimeters may be higher than the sediments could now achieve. The flux of dissolved silica out of these sediments is estimated to be 15 μmoles cm⁻² yr⁻¹.  相似文献   

Facies analysis by “correspondence analysis”: Numerous advantages of this new statistical technique     

Marthe Melguen 《Marine Geology》1974,17(3):165-182

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Borehole image-based evaluation of coral reef porosity distribution characteristics     

Jin-chao Wang  Chang-qi Zhu  Sheng Hu 《Marine Georesources & Geotechnology》2017,35(7):1008-1017

In this study, we used digital borehole image camera to obtain images of porosity distribution in coral reefs in South China Sea, and developed an effective evaluation system for such distributions. First, the original images are preprocessed, allowing the pore regions to be automatically detected. The depth and sectional functions are established to measure five parameters: pore count, pore radius, radius concentration rate, total pore area ratio, and fractal dimension count. These are used to calculate the characteristic values of porosity distributions, and their fuzzy relationships are used to build the evaluation model, determine the Hamming distances between distributions, and establish the relationships between the characteristics and coral rock classifications. Test results from applying the method on a deep borehole image segment show the results to be consistent with other methods, and the following conclusions can be reached: (1) the porosity evaluation model is a viable way to analyze porosity distribution characteristics; (2) the resulting classification method is viable; and (3) porosity distribution analysis on coral reefs has important implications.  相似文献   

Experiments with Littorina species to determine the relevancy of oil spill data from Southern California to the gulf of Alaska     

Dale Straughan  Diane Hadley 《Marine environmental research》1978,1(2):135-163

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Geology of the Strait of Juan de Fuca     

Ian R. Mayers  Lee C. Bennett 《Marine Geology》1973,15(2):89-117

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