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1.
The Ukrainian Dniepr-Donets Basin (DDB) is a Late Palaeozoic intracratonic rift basin, with sedimentary thicknesses up to 19 km, displaying the effects of salt tectonics during its entire history of formation, from Late Devonian rifting to the Tertiary. Hundreds of concordant and discordant salt structures formed during this time. It is demonstrated in this paper that the variety of styles of salt structure formation in the DDB provide important constraints on understanding the triggering and driving mechanisms of salt kinematics in sedimentary basins in general. Salt movement in the DDB began during the Devonian syn-rift phase of basin development and exerted controls on the later distribution of salt structures though the geometry of basement faults is not directly responsible for the regular spacing of salt structures. Post-rift salt movements in the DDB occurred episodically. Episodes of salt movement were triggered by tectonic events, specifically two extensional events during the Carboniferous, an extensional reactivation at the end of Carboniferous–earliest Permian, and a compressional event at the end of the Cretaceous. Extensional events that induced salt movement were ‘thick-skinned’ (i.e. basement involved in deformation) rather than ‘thin-skinned’. Most overburden deformation related to salt movements is ductile regardless of sedimentary bulk lithology and degree of diagenesis, while the deformation of sedimentary cover in areas where salt is absent is mainly brittle. This implies that the presence of salt changes the predominant mode of deformation of overlying sedimentary rocks. Episodes of salt movement lasted longer than the periods of active tectonics that initiated them. Buoyancy, erosion, and differential loading all played a role in driving halokinesis once tectonic forces had pushed the salt-overburden system into disequilibrium; among these factors, erosion of overburden above growing salt structures acted as a key self-renewing force for development of salt diapirs. Very high sedimentation rates (related to high post-rift tectonic subsidence rates), particularly during the Carboniferous, were able to bury diapirs and to load salt bodies such that buoyancy, erosion, and differential loading forces eventually became insufficient to continue driving diapirism—until the system was perturbed by an ensuing tectonic event. In contrast, some salt anticlines and diapirs developed continuously during the entire Mesozoic because of much-reduced tectonic subsidence rates (and sedimentation supply) during this time. However, a Lower Permian salt series and overhangs of buried diapirs played an important role in preventing overburden piercing (and fracturing) during the Mesozoic and, specifically, during the Late Cretaceous salt diapirism phase.  相似文献   

2.
In this work we attempt to estimate the short- and long-term effects of the Amoco Cadiz oil spill on benthic microalgal populations (cyanophytes and diatoms) which, under natural conditions, live on upper layers of ‘schorres’ soils or of ‘slikke’ muds in the Ile Grande salt marsh system (Côtes du Nord, France). These populations were completely destroyed in 1978 in the oil-affected sites. Ubiquitous species settled fairly rapidly on intertidal polluted muds (tidal flat). The chlorophyll a content values reached 100 μg g−1 dry sediment, i.e. 1000 mg m−2 in 1980. Conversely, the salt marsh soils are still much less densely repopulated 3 years after the Amoco Cadiz grounding—especially when they are infrequently flooded (3 to 40 μg Chl.a g−1, i.e. 40 to 270 mg m−2). Some of these soils remain ten times less populated than reference stations.  相似文献   

3.
Previous laboratory studies1 have shown that physiological and cellular processes of Mytilus edulis are affected by exposure to low and environmentally realistic concentrations of oil. However, there is little information concerning the rate of recovery from oil exposure and the extent to which physiological recovery may be related to the depuration of hydrocarbons from the tissues. The present study has shown a marked reduction in the feeding rate and scope for growth of mussels exposed to two concentrations of diesel oil (30 and 130 μg/litre) for 8 months. During recovery from oil exposure the depuration of hydrocarbons from the tissues was concomitant with the recovery of physiological performance. Mussels exposed to high oil concentrations (‘high-oil’ mussels) were found to recover more rapidly than those exposed to low oil concentrations (‘low-oil’ mussels), both in terms of depuration and scope for growth, and there was evidence of ‘catch-up’ growth. Recovery of both low- and high-oil mussels was complete after approximately 55 days.  相似文献   

4.
Halokinesis causes a dynamic structural evolution with the development of faults and fractures, which can act as either preferential fluid pathways or barriers. Reconstructing reactive fluid flow in salt dome settings remains a challenge. This contribution presents for the first time a spatial distribution map of diagenetic phases in a salt dome in northern Oman. Our study establishes a clear link between structural evolution and fluid flow leading to the formation of diagenetic products (barite and calcite) in the salt dome roof strata. Extensive formation of diagenetic products occurs along NNE-SSW to NE-SW faults and fractures, which initiated during the Santonian (Late Cretaceous) and were reactivated in the Miocene, but not along the E-W fault, which was generated during Early Paleocene time. We propose that the diagenetic products formed by mixing of a warm (100 °C) saline (17 wt% NaCl eq.) 87Sr enriched (87Sr/86Sr: 0.71023) fluid with colder (35 °C) meteoric fluid during Miocene to Pleistocene. The stable sulphur and strontium isotope composition and fluid inclusion data indicate that a saline fluid, with sulphate source derived from the Ara Group evaporite and Haima Supergroup layers, is the source for barite formation at about 100 °C, predominantly at fault conjunctions and minor faults away from the main graben structure in the dome. In the Miocene, the saline fluid probably ascended along a halokinesis-related fault due to fluid overpressure (due to the rising salt and impermeable layers in the overlying stratigraphic sequence), and triggered the formation of barite due to mixing with barium-rich fluids, accompanied by a drop in temperature. Subsequently, evolving salt doming with associated fault activity and erosion of the Jebel allows progressively more input of colder meteoric fluids, which mix with the saline warmer fluid, as derived from stable isotope data measured in the progressively younger barite-associated calcite, fault zone calcite and macro-columnar calcite. The reconstructed mixing model indicates a 50/50 to 90/10 meteoric/saline fluid mixing ratio for the formation of fault zone calcite, and a 10 times higher concentration of carbon in the saline fluid end member compared to the meteoric fluid end member. The presented mixing model of salt-derived fluids with meteoric fluids is suggested to be a general model applicable to structural diagenetic evolution of salt domes world wide.  相似文献   

5.
Major sequence boundaries associated with eustatic sea level changes are correlated to the general stratigraphy of the north-eastern Gulf of Mexico. The details of a Middle Cretaceous Flooding Surface, marking a major break in sedimentation, are documented. The sequence stratigraphic work provides an example of the ‘stratigraphic signature of the Neogene’. Three major episodes of sediment accumulation are represented by: (1) Late Jurassic (150.5 Ma) to Middle Cretaceous (94 Ma) aggradation and progradation of sediments with significant sediment accumulation in the present shelf and slope areas; (2) an extended period of starved sedimentation during 94-30 Ma corresponding to Middle Cretaceous flooding events (93.5 and 91.5 Ma) and the lack of sediment supply; and (3) since Late Oligocene time, unusually rapid sedimentation rates that characterize the deep water study area. These patterns of sediment accumulation directly affect the formation of allochthonous salt in the study area.  相似文献   

6.
High sedimentation rates (as much as 2500 m/Ma) during Pliocene-Pleistocene, with a resultant undercompacted section as thick as 10,000 m, and lower than normal geothermal gradients are the main characteristics which have created all the means for generation and preservation of oil at deep layers in the Lower Kura Depression.Oils collected from eight different oil fields for analyses seem to have originated from a common source rock which probably is clastic, deposited in relatively subanoxic to suboxic transitional marine environment receiving low to moderate input of terrestrial organic matter.Oils from shallow (< 3000 m) and cold (< 70–80°C) reservoirs have been altered to various extent by bacterial activity.A computer-aided basin modeling study has been carried out to outline the spatial variation of the oil window and thus help in further identification of possible source rocks for the reservoired oil in the Lower Kura Depression. Results suggest that the potential hydrocarbon source horizons of the Miocene and Pliocene Red Bed Series of the so called Productive Succession are, even at depocenter areas, immature with respect to oil generation, and thus, are very unlikely to have been source rocks for the reservoired oils. However, the Oligocene-Lower Miocene Maykop rocks are marginally mature to mature depending on locality and the Eocene and older rocks are mature with respect to oil generation at all representative field locations. Oil generation commenced at the end of Pliocene and continues at present at depths between 6000 and 12,000 m.An unusually deep (> 10,000 m) oil window in the depocenter areas has been caused by the depressed isotherms due to extremely high sedimentation rates (up to 3000 m/Ma) for the last two million years. The main phase of oil generation is taking place at depths greater than what most of the wells in the study are have reached.  相似文献   

7.
Thirty-six Silurian core and cuttings samples and 10 crude oil samples from Ordovician reservoirs in the NC115 Concession, Murzuq Basin, southwest Libya were studied by organic geochemical methods to determine source rock organic facies, conditions of deposition, thermal maturity and genetic relationships. The Lower Silurian Hot Shale at the base of the Tanezzuft Formation is a high-quality oil/gas-prone source rock that is currently within the early oil maturity window. The overall average TOC content of the Hot Shale is 7.2 wt% with a maximum recorded value of 20.9 wt%. By contrast, the overlying deposits of the Tanezzuft Formation have an average TOC of 0.6 wt% and a maximum value of 1.1 wt%. The organic matter in the Hot Shale consists predominantly of mixed algal and terrigenous Type-II/III kerogen, whereas the rest of the formation is dominated by terrigenous Type-III organic matter with some Type II/III kerogen. Oils from the A-, B- and H-oil fields in the NC115 Concession were almost certainly derived from marine shale source rocks that contained mixed algal and terrigenous organic input reflecting deposition under suboxic to anoxic conditions. The oils are light and sweet, and despite being similar, were almost certainly derived from different facies and maturation levels within mature source rocks. The B-oils were generated from slightly less mature source rocks than the others. Based on hierarchical cluster analysis (HCA), principal component analysis (PCA), selected source-related biomarkers and stable carbon isotope ratios, the NC115 oils can be divided into two genetic families: Family-I oils from Ordovician Mamuniyat reservoirs were probably derived from older Palaeozoic source rocks, whereas Family-II oils from Ordovician Mamuniyat–Hawaz reservoirs were probably charged from a younger Palaeozoic source of relatively high maturity. A third family appears to be a mixture of the two, but is most similar to Family-II oils. These oil families were derived from one proven mature source rock, the Early Silurian, Rhuddanian Hot Shale. There is a good correlation between the Family-II and -III oils and the Hot Shale based on carbon isotope compositions. Saturated and aromatic maturity parameters indicate that these oils were generated from a source rock of considerably higher maturity than the examined rock samples. The results imply that the oils originated from more mature source rocks outside the NC115 Concession and migrated to their current positions after generation.  相似文献   

8.
The North Inlet marsh-estuarine system encompasses the spectrum of interaction between the ocean and the uplands typical of the southeastern United States. The system is an ebb-dominated, bar-built estuary with good flow connection to the sea and some freshwater input.The North Inlet basin has evolved from a forested, relic, beach-ridge terrain under a regime of slowly rising sea level (2 mm year−1). This mode of development is supported by historic tide gage data. 210Pb dating of sediment cores, the presence of spodic soil horizons and tree roots at shallow depths beneath the marsh surface, and the presence of relic ‘cat eye’ ponds at the edge of the salt marsh. As sea level rises, the boundary between forest and salt marsh recedes upslope and forest spodosols are gradually transformed into marsh soils by salinization, the deposition and mixing of marine mud into the upper horizons of the forest soil and the accumulation of reduced sulfur via sulfate reduction. As a forest watershed is transformed into a salt-marsh basin, the hydraulic geometry of the original, black-water (fresh) stream increases to accommodate the increasing volumes of tidal discharge. Forest sands move seaward while marine muds are transported into the basin.As water moves between the forest and the sea, it passes through creeks in different developmental stages. Large mature creeks interact with the ocean while young, ephemeral creeks drain the uplands and intertidal marsh zones. Intermediate stage creeks connect these two and are characterized by the presence of oyster reefs. Net nutrient fluxes appear to be different in each developmental stage.The ‘Bly Creek’ study of Dame and coworkers addressed the flux of materials between a creek at the intermediate stage of development and the adjacent mature system. Material fluxes from a freshwater stream draining into Bly Creek from the adjacent uplands were also observed. The role of the salt marsh and the oyster reefs in determining material fluxes was examined. The Bly Creek basin imports particulate nutrients and exports dissolved forms.The ‘Outwelling’ study of Dame and coworkers at North Inlet focused on the flux of materials between the mature creeks and the Atlantic Ocean. All constituents were exported seasonally and annually from the estuary, except total sediments (imported during fall and winter) and chlorophyll a (imported in the summer and fall). The export of carbon, nitrogen and phosphorus was high compared with other estuarine systems.On a unit area basis, primary productivity is higher and nutrient fluxes are lower in Bly Creek (intermediate stage of development) as compared with the mature North Inlet system. These observations support the general ecosystem development hypothesis that nutrient storage and retention are higher in younger systems than more mature systems where growth is lower and fewer nutrients are needed.  相似文献   

9.
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10.
Interactions between ‘oxygen concentration’ (normoxia: >80% oxygen saturation, and hypoxia: 18% oxygen saturation) and ‘water flow velocity’ (low: 0.1 cm s−1, and moderate: 0.5 cm s−1) were studied on growth rates in the brittle star Amphiura filiformis in a flow-through aquaria system. Effects of ‘sublethal predation’ on growth rates were investigated as ‘number of amputated arms’ (1 and 3 arms) and ‘amputation of the disk’. A significant interaction between oxygen concentration and water flow velocity was observed in mean arm regeneration rate, but in both flow velocities higher mean arm regeneration rates were observed in normoxia compared to hypoxia. In hypoxia a positive response in arm regeneration rate was observed in moderate flow compared to low flow velocity. In normoxia, however, no response to flow velocity was observed. The latter observation indicates that Amphiura filiformis is able to maintain the ventilation of the burrow at low flow velocities, but in low oxygen concentrations hydrodynamic forces seem to affect growth. A significant interaction between oxygen concentration and disk amputation was observed in both arm and disk regeneration rates, indicating that the disk is the major organ for gas exchange in this species. The number of arms amputated, however, did not affect mean arm regeneration rate. The results obtained in this study suggest that the secondary production in subtidal infaunal populations could be negatively affected by low oxygen concentrations and that this response is even more negative in combination with low flow velocities in the near-bottom water.  相似文献   

11.
A set of hydrographic surveys were carried out in the Ría of Vigo (NW Spain) at 2–4 d intervals during four 2–3 week periods in 1997, covering contrasting seasons. Residual exchange fluxes with the adjacent shelf were estimated with a 2-D, non-steady-state, salinity–temperature weighted box model. Exchange fluxes consist of a steady-state term (dependent on the variability of continental runoff) and a non-steady-state term (dependent on the time changes of density gradients in the embayment). More than 95% of the short-time-scale variability of the exchange fluxes in the middle and outer ría can be explained by the non-steady-state term that, in turns, is correlated (R2>75%) with the offshore Ekman transport. Conversely, 96% of the variability of exchange fluxes in the inner ría rely on the steady-state term. The outer and middle ría are under the direct influence of coastal upwelling, which enhances the positive residual circulation pattern by an order of magnitude: from 102to 103 m3s−1. On the contrary, downwelling provokes a reversal of the circulation in the outer ría. The position of the downwelling front along the embayment depends on the relative importance of Ekman transport (Qx, m3s−1km−1) and continental runoff (R, m3s−1). When Qx/ R>7±2 the reversal of the circulation affects the middle ría. Our results are representative for the ‘Rías Baixas’, four large coastal indentations in NW Spain. During the upwelling season (spring and summer), 60% of shelf surface waters off the ‘Rías Baixas’ consist of fresh Eastern North Atlantic Central Water (ENACW) upwelled in situ. The remaining 40% consists of upwelled ENACW that previously enters the rías and it is subsequently outwelled after thermohaline modification. During the downwelling season (autumn and winter), 40% of the warm and salty oceanic subtropic surface water, which piled on the shelf by the predominant southerly winds, enters the rías.  相似文献   

12.
As part of the ‘National Hydrographic and Oceanographic Research Plan for the Spanish Exclusive Economic Zone’, multibeam bathymetry and seismic reflection profiles were obtained in the Canary Islands aboard the R/V Hespérides. The submarine flanks of the Anaga offshore extension of Tenerife Island are here studied to analyze its geomorphology. In the north sector of the Anaga submarine massif, the extension of the Anaga Debris Avalanche has been mapped for the first time, and a volume of 36 km3 was calculated. The relationship between the Anaga and Orotava Debris Avalanches is also described. Faulting has been recognized as a key process for the occurrence of debris avalanches and the growth of volcanic lineaments. Moreover, faulting affects previous structures and the channelling of debris flows. Structural analysis shows the typical radial pattern of an oceanic island. In addition, a NE-SW dominant direction of faulting was obtained, consistent with the Tenerife Island structural trend seen in the Anaga Massif and Cordillera Dorsal. NW-SE and E-W are two other main trends seen in the area. Special interest is manifest in two long faults: ‘Santa Cruz Fault’ bounds the southern edge of Anaga offshore Massif with a length of 50 km and a direction that changes from NE-SW to almost E-W. The Güimar Debris Avalanche was probably channeled by this fault. The ‘Guayotá Fault’ was recognized in several seismic profiles with a N-S direction that changes towards NW-SE at its southern end. This fault affects the more recent sediments with a vertical offset of 25–30 m, along 60~km. It has been interpreted as a transpressive strike-slip fault.ZEE Working Group**F. Carrilloa, C. Matéa, M. Ballesterosb, M. Vaquerob, J. Martín-Dávillac and J.A. MaríncaInstituto Hidrográfico de la Marina. CádizbInstituto Español de Oceanografía. Madrid.cReal Observatorio de la Armada. S. Fernando, Cádiz.  相似文献   

13.
The processes which produce bottom water in the Mediterranean are studied. Observations show three phases. The first, called ‘preconditioning’, is not studied. The second ‘violent mixing’ phase occurs when the cold Mistral begins. Cooling at the surface leads to intense vertical mixing in a narrow chimney-like region. When the wind stops, the ‘sinking and spreading’ phase begins. Interleaving of water masses occurs; horizontal eddying on scales of 15 km is observed; and 600 m columns of water can be lifted up to 500 m.A two-dimensional model is used to explain the mixing phase. Non-penetrative vertical convection explains the observations well. Advection of water from outside the column is small, and slows down the descent of the outer parts of the column as observed. The column does not break up even when it reaches the bottom, or if the strong winds cease.The most efficient mechanism for the spreading phase is baroclinic instability. In conditions of vertical overturning there is a large amount of potential energy available to drive the instability. For an eddy viscosity of 50 m2 s−1, after 10 days sinking the growth time is 3–4 days and the eddies are mainly concentrated at the surface with a major axis length of about 15 km. These tend to stabilize the top few hundred meters of the column. Later, finite amplitude effects will produce slower perturbations in the rest of the column.  相似文献   

14.
Physical forcing plays a major role in determining biological processes in the ocean across the full spectrum of spatial and temporal scales. Variability of biological production in the Bay of Bengal (BoB) based on basin-scale and mesoscale physical processes is presented using hydrographic data collected during the peak summer monsoon in July–August, 2003. Three different and spatially varying physical processes were identified in the upper 300 m: (I) anticyclonic warm gyre offshore in the southern Bay; (II) a cyclonic eddy in the northern Bay; and (III) an upwelling region adjacent to the southern coast. In the warm gyre (>28.8 °C), the low salinity (33.5) surface waters contained low concentrations of nutrients. These warm surface waters extended below the euphotic zone, which resulted in an oligotrophic environment with low surface chlorophyll a (0.12 mg m−3), low surface primary production (2.55 mg C m−3 day−1) and low zooplankton biovolume (0.14 ml m−3). In the cyclonic eddy, the elevated isopycnals raised the nutricline upto the surface (NO3–N > 8.2 μM, PO4–P > 0.8 μM, SiO4–Si > 3.5 μM). Despite the system being highly eutrophic, response in the biological activity was low. In the upwelling zone, although the nutrient concentrations were lower compared to the cyclonic eddy, the surface phytoplankton biomass and production were high (Chl a – 0.25 mg m−3, PP – 9.23 mg C m−3 day−1), and mesozooplankton biovolume (1.12 ml m−3) was rich. Normally in oligotrophic, open ocean ecosystems, primary production is based on ‘regenerated’ nutrients, but during episodic events like eddies the ‘production’ switches over to ‘new production’. The switching over from ‘regenerated production’ to ‘new production’ in the open ocean (cyclonic eddy) and establishment of a new phytoplankton community will take longer than in the coastal system (upwelling). Despite the functioning of a cyclonic eddy and upwelling being divergent (transporting of nutrients from deeper waters to surface), the utilization of nutrients leading to enhanced biological production and its transfer to upper trophic levels in the upwelling region imply that the energy transfer from primary production to secondary production (mesozooplankton) is more efficient than in the cyclonic eddy of the open ocean. The results suggest that basin-scale and mesoscale processes influence the abundance and spatial heterogeneity of plankton populations across a wide spatial scale in the BoB. The multifaceted effects of these physical processes on primary productivity thus play a prominent role in structuring of zooplankton communities and could consecutively affect the recruitment of pelagic fisheries.  相似文献   

15.
New England salt marshes are dominated by the supratidal high marsh grass, Spartina patens. This grass forms a nearly planar surface, which makes it highly vulnerable to the predicted regime of accelerated sea-level rise (SLR). If the high marsh cannot keep pace with rising sea level it will be transformed to intertidal environments, leading to unusually rapid coastal evolution. Winter processes such as ice-loading of surface peat may degrade the marsh surface. Large volumes of snow and ice compress peat, resulting in shallow compaction and a net loss of elevation in some areas.On the Webhannet marsh in Maine, a simulated ice compaction experiment indicates that thick ice can compress marsh peat (46 cm simulated ‘ice’ produced 6.9 ± 0.3 mm of compaction; 24 cm ‘ice’ produced 3.0 ± 0.8 mm). Experimental data suggest that ice thicknesses greater than 10 cm depress the marsh surface by 2 mm for each cm of total ice thickness. However, surface elevations rebounded to near-control levels within 2 weeks of the removal of simulated ‘ice’ from the surface of the marsh. Normal winter ice accumulations on New England marshes, therefore, do not appear to be sufficient to permanently compact marsh surface peat and lead to loss in marsh surface elevation.  相似文献   

16.
The performance of extractants commonly used in the determination of acid volatile sulfide minerals (e.g., ‘amorphous-FeS’, mackinawite and greigite) and pyrite has been evaluated using pure mineral phases and anoxic sediments. ‘Amorphous-FeS’ and mackinawite are quantitatively recovered by most cold acid extractions, but greigite recovery is incomplete. Harsher extractants with reducing agents are necessary for the complete recovery of greigite, but dissolution of fine-grained synthetic pyrite occurs under such conditions. A quantitative separation between greigite and pyrite is not possible using these techniques, but the use of ‘acid volatile sulfide’ and ‘pyrite’ as operational categories is adequate for most field studies.  相似文献   

17.
Exposure to a mercury-equilibrated algal suspension containing 0·25, 0·42 and 1 μg Hg litre−1 as mercuric chloride in solution reduced the growth and condition of pairs of adults of the slipper limpet Crepidula fornicata in a 16-week period. Reproduction rates and larval survival to settlement were also reduced over the first three spawnings when the exposed pairs reached sexual maturity. The adult and larval 96-h LC50s were 330 and 60 μg Hg litre−1, respectively, as mercuric chloride in solution, indicating that a ‘safety factor’ of 10−1 needs to be applied to adult data to protect the most sensitive stage in the life cycle. However, the chronic exposure of the maturing adults showed that levels of inorganic mercury below the ‘safe’ concentration derived from the adult 96 h LC50 affected growth and reproductive success.  相似文献   

18.
The speciation of dissolved iodine and the distributions of the iodine species in the deep Chesapeake Bay underwent seasonal variations in response to changes in the prevailing redox condition. In the deep water, the ratios of iodate to iodide and iodate to inorganic iodine decreased progressively from the Winter through the Summer as the deep water became more poorly oxygenated before they rebounded in the Fall when the deep water became re-oxygenated again. The composition of the surface water followed the same trend. However, in this case, the higher biological activities in the Spring and the Summer could also have enhanced the biologically mediated reduction of iodate to iodide by phytoplankton and contributed to the lower ratios found during those seasons. Superimposed on this redox cycle was a cycle of input and removal of dissolved iodine probably as a result of the interactions between the water column and the underlying sediments. Iodine was added to the Bay during the Summer when the deep water was more reducing and removed from the Bay in the Fall when the deep water became re-oxygenated. A third cycle was the inter-conversion between inorganic iodine and ‘dissolved organic iodine’, or ‘‘DOI’’. The conversion of inorganic iodine to ‘DOI’ was more prevalent in the Spring. As a result of these biogeochemical reactions in the Bay, during exchanges between the Bay and the North Atlantic, iodate-rich and ‘DOI’-poor water was imported into the Bay while iodide- and ‘DOI’-rich water was exported to the Atlantic. The export of iodide from these geochemically reactive systems along the land margins contributes to the enrichment of iodide in the surface open oceans.  相似文献   

19.
Photogrammetric measurements of dye dispersion in a high-energy surf zone provided semi-quantitative measurements of the pattern and flux of water exchange between the surf zone and nearshore. The intensity of current flow, the rip morphology and its position within the surf zone have important ecological implications for the surf zone and nearshore biota. A variety of water-movement patterns was found, ranging from currents which remained confined to the beach terrace to those which involved substantial exchange across the breaker line. In considering rips as exchange mechanisms, two rip types are recognized. Depending on the exchange of water across the breaker line, a rip may be classified as ‘exchange’ or ‘non-exchange’. The ecological significance of these current types is discussed and a classification scheme for rip currents is proposed. Offshore fluxes across the breaker line by rip currents ranged from negligible to 80 m3s−1 rip−1. The estimated maximum flux per running meter of the Sundays River Beach was calculated as 0·0.32m 3 s−1. The half-residence period of surf-zone water ranged from as little as 22 min t0 5 days, averaging 3·6 h.A dichotomy of current patterns found between the water column and surface layers is used to explain the build up of a concentration gradient in cell numbers of the surf diatom Anaulus birostratus within the surf zone despite extensive flushing by surf circulation.  相似文献   

20.
The globalisation of the economy and the need for sustainable growth are having a strong influence on international sea freight transport and its infrastructures. Commercial sea ports, faced with the loss in ‘loyalty’ of their traffic and the appearance of ‘new rules in the game’, are developing new strategies in order to achieve the loyalty of their clients. The present paper is a reflection on the findings generated in recent years in the area of competitive port policies. The main focus is on the formulation of commercial and technological strategies, the new legislative framework and its consequences for the European Union in the context of the future ‘Common Ports Policy’.  相似文献   

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