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1.
This work presents a recent grain size study characterizing superficial sediments of the whole sectors of the Gulf of Tunis which extends from Sidi Ali El Mekki to Sidi Daoued. In this study, a total of 112 samples were collected from different depths following 26 profiles perpendicular to the shore and from rivers. The determination of the proportions of coarse and fine fractions and the interpretation of the grain size results lead to dividing the Gulf of Tunis into two principal coasts: (1) the western coast situated between Sidi Ali El Mekki and Borj Cédria, which is characterized by three sedimentary facies: (a) a sandy facies along the coastline, (b) a mixed facies between Ghar El Melh and Raoued, near the Medjerda River, and between La Goulette and Ezzahra, near the Miliane River, and (c) a muddy facies between Ghar El Melh and Kalâat El Andalous and covered by fine to very fine sands, and (2) the eastern coast, which is characterized by a sandy facies and covered by medium to coarse sands. The dominant N–E and N–W waves generate longshore currents that provide sediment transport following the directions N–S, from Sidi Ali El Mekki to Kalâat El Andalous; SE–NW, from Gammarth to Raoued; NE–SW, from Sidi Bou Saïd to La Goulette and from Sidi Daoued to Bir El Jadi; SE–NW, from Hammam-Plage to Ezzahra; and SW–NE, from Port aux Princes to Rtiba.  相似文献   

2.
Analysis of 20-year time series of water levels in the northeastern Gulf of Mexico has revealed that meteotsunamis are ubiquitous in this region. On average, 1–3 meteotsunamis with wave heights >0.5 m occur each year in this area. The probability of meteotsunami occurrence is highest during March–April and June–August. Meteotsunamis in the northeastern Gulf of Mexico can be triggered by winter and summer extra-tropical storms and by tropical cyclones. In northwestern Florida most of the events are triggered by winter storms, while in west and southwest Florida they appear both in winter and summer. Atmospheric pressure and wind anomalies (periods <6 h) associated with the passage of squalls originated the majority of the observed meteotsunami events. The most intense meteotsunamigenic periods took place during El Niño periods (1997–1998, 2009–2010 and 2015–2016). Meteotsunamis were also active in 2005, a year characterized by exceptionally intense tropical cyclone activity. Meteotsunami incidence varied yearly and at periods between 2 and 5 years. Results from cross-wavelet analysis suggested that El Niño and meteotsunami activity are correlated at annual and longer-period bands.  相似文献   

3.
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4.
Molecular geochemical properties of crude oils and surface petroleum seeps from the southern part of the Gulf of Suez were evaluated. The characterizations of individual aliphatic, aromatic, and biomarker compounds were based on gas chromatography (GC) and gas chromatography/mass spectrometry (GC/MS) analyses. The results provided strong evidence for a close genetic association of these samples. The geochemical characteristics suggest an origin from Tertiary source rocks deposited in a normal marine environment that received continental runoff. The molecular signatures of the investigated samples were very similar to those of the Lower Miocene Rudeis Formation source rock in the southern Gulf of Suez. Further, biomarker fingerprints of the investigated oil seeps were compared with those of the Dead Sea asphalt, as well as the bitumen from some Egyptian mummies reported in the literature. The results demonstrate that oil seeps from the southern end of Gebel El Zeit were used by ancient Egyptians for embalming. © 2005 Wiley Periodicals, Inc.  相似文献   

5.
The paper presents the first study of heavy-mineral sand beaches from the Mediterranean coast of Annaba/Algeria. The studied beaches run along the basement outcrops of the Edough massif, which are mainly composed by micaschists, tourmaline-rich quartzo-feldspathic veins, gneisses, skarns and marbles. Sand samples were taken from three localities (Ain Achir, Plage-Militaire and El Nasr). The heavy-mineral fraction comprises between 74 and 91 vol%. The garnets of the beaches are almandine rich and tourmalines vary with respect to their location from schorl to dravite. Tourmaline at Ain Achir and the Plage-Militaire is schorlits, while at El Nasr beach dravite is ubiquitous. The World Shale Average normalised REE of the sands and the basement outcrops reveal: (i) Ain Achir beach: REE pattern of sand and the coastal rocks from the studied beaches reflects a multiple sources; (ii) Plage-Militaire: the sand and the coastal outcrops show similar LREE and a strong enrichment in HREE, suggesting the presence HREE-rich phases found as inclusions in staurolite; (iii) El Nasr: two types of sand patterns are found: one with flat REE pattern similar to the proximal rocks and other one enriched in HREE suggesting a mixed source.  相似文献   

6.
This study is meant to provide an insight into how discharge playas, which are strongly influenced by a regional salty groundwater flow regime, such as the discharge playa of Sidi El Hani, would respond to the climatic variability and to the materials coming from the subsurface of the Sahel area. In order to choose the appropriate method, a special care was given in this paper to different methods of investigation of the groundwater contribution in water and salt budgets of saline systems. The hydrogeological map of the surrounding aquifers proved their convergence toward Sidi El Hani discharge playa. As consequence of the dominance of a salty groundwater contribution, the climate variability may be considered minor. Accordingly, the model proposed by this study showed the dominance of the salty water coming from the hydrogeology at the expense of the fresh water coming from the climatic contribution. Moreover, according to the adopted model, the effect of the human-induced activity on the hydrogeological contribution such as the installation of dams in the Tunisian center and the overexploitation of the phreatic aquifer of Kairouan was judged increasing the convergence of Kairouan aquifer towards Sidi El Hani discharge playa. On the other hand, the consumption of salt reserves from the discharge playa tends to decrease its salinization.  相似文献   

7.
Using hydrogeochemical analysis of two large boreal rivers (pristine Kalix and hydropower regulated Lule) discharging into the Gulf of Bothnia, the major impacts of regulation on water discharge, element transport and their seasonal redistribution have been assessed. The pre-regulation hydrogeochemical features were assumed to be similar for the two rivers. For the Lule River, the average maximum runoff was almost halved, while the average minimum was tripled as a result of the regulation. The fraction of winter transport of total organic carbon (TOC), Fe, Si, suspended Mn and P in the Lule River was, according to a conservative estimate, two to three times higher than in the pristine river. Longer residence time in the Lule River delayed arrival of the suspended Mn peak and dissolved Si decline to the river mouth. During summer, the suspended C/N ratio in the regulated river was 10–20 compared to <10 for the pristine, suggesting presence of predominantly old organic material. This was supported by a virtually constant suspended P/Fe ratio throughout the year in the Lule River, indicating low abundance of phytoplankton. TOC varied irregularly in the Lule River suggesting temporal disconnection between the river and the upper riparian zone. The disappearance of the spring flow maximum, a shift of element transport from spring to winter and supply of mainly old organic material during the vegetation growth season may have a pronounced impact on the ecosystem of the Gulf of Bothnia and the river itself.  相似文献   

8.
Concentrations of Co, Cu, Fe, Mn, Ni, Pb and Zn in four macroalgae species (Ulva lactuca, Chondracanthus squarrulosus, Sargassum sinicola and Gracilariopsis lemaneiformis) were obtained for the first time from the central part of the west coast of the Gulf of California. Generally, no differences in metal concentrations were found among the different seaweed species, although spatial differences were apparent. Iron, Mn and Cu exhibited higher concentrations at the stations located in front of Angel de la Guarda Island, probably because of high vertical mixing processes present in the zone. The results were compared with dissolved metal concentrations reported for the Gulf of California (Cd, Mn and Fe) and the North Pacific Ocean. The resulting linear regression of the results vs. North Pacific Ocean concentrations indicated that the levels of Cu, Ni and Zn measured in this study were within its 95% confidence level. Furthermore, this comparison was capable of detecting dissolved Fe and Mn enrichments in Gulf of California waters relative to the North Pacific Ocean concentrations. Calculations of total masses of metals associated with algal biomass on the west coast of the Gulf of California indicated that the lowest masses were represented by Cu (108 ± 25 kg) and Ni (184 ± 52 kg), whereas Pb (1.1 ± 0.6 ton) and Fe (10.9 ± 8.5 ton) were the elements with the highest associated masses.  相似文献   

9.
Multivariate analysis of contaminant data from a multi-year monitoring program demonstrates alterations in the hepatic chemistry of metals in fish exposed to organic contaminants. Metals (Ag, As, Cd, Cu, Fe, Hg, Mn, Ni, Pb, Se, Sn, Zn) and organic chemicals (PCBs, DDTs, chlordanes, dieldrins, PAHs) were measured in liver and associated sediments for winter flounder (Pleuronectes americanus) from 23 sites along the northeast Atlantic coast and for Atlantic croaker (Micropogonias undulatus) from 30 sites along the southeast Atlantic and Gulf of Mexico coasts of the United States. Concentrations of habitat contaminants varied from nil to levels signifying important anthropogenic inputs and thus provided a range in chronic exposures and related contaminant stress levels with which to investigate the response of hepatic chemistry in fish representative of viable populations. The data, analyzed by principal component, principal component regression, and biplot procedures, demonstrated an opposing relationship between micronutrient elements, principally Zn, and exposure to organic contaminants in winter flounder. This relationship was not present in Atlantic croaker that were resident in less contaminated habitats. Based on median concentrations in sediment, exposure of winter flounder to important organic contaminants (polycyclic aromatic hydrocarbons, polychlorinated biphenyls, DDTs) exceeded that for Atlantic croaker by 7 to 50 times. Coincident with depletion of hepatic Zn and Cd in winter flounder was accumulation of Hg and Ag. My results, in agreement with those of others, implicate the negative effects of hepatic detoxification of organic contaminants on metal binding in liver, which can cause depletion of essential elements while contaminant and potentially toxic elements accumulate.  相似文献   

10.
Boudiaf  Ritz  & Philip 《地学学报》1998,10(5):236-244
Digital elevation models and aerial photographs provide evidence of past drainage diversions associated with known and inferred active faults in Northern Algeria. The El Asnam anticline is a fault-bend fold that is growing in response to displacement on the historically active El Asnam fault. The diversion of the Fodda River and a sequence of uplifted palaeovalleys across the anticline formed in response to the active southwestward propagation of the Sidi Ada–El Ardja segment of the El Asnam anticline. Deformation associated with the 1980 El Asnam earthquake (Ms 7.3) and its effect on drainage demonstrate the occurrence of coseismic uplift of the El Asnam anticline associated with slip on the underlying thrust fault. Similar geomorphic relations are observed between the Isser River and the Thenia fault. Diversions of the Isser River and evidence for Quaternary uplift indicate that the Thenia fault, which is close to Algiers, is tectonically active and should be considered to be a source of potentially damaging earthquakes.  相似文献   

11.
The chemical and mineralogical composition of the Sidi Aïch Formation sandstones in central and southwestern Tunisia has been investigated in order to infer the provenance and tectonic setting, as well as to appraise the influence of weathering. The sixteen studied samples are mainly composed of quartz, feldspar, kaolinite and/or illite. Sidi Aïch sandstones are mainly arkosic, potassic feldspar-rich and immature. Much of the feldspar was transformed to kaolinite. Concerning the relation between sandstone detrital composition and their depositional setting, the Sidi Aïch Formation sandstone in the major studied localities, probably accumulated in relatively proximal small basins within the continental interior. However, for the Khanguet El Ouara study site, sandstones may have been deposited in a foreland basin which received recycled sediments from an adjacent orogenic belt.The source area may have included quartzose sedimentary rocks. The dominance of quartz and enrichment in immobile elements suggest that the depositional basins were associated with a passive margin. The petrography and geochemistry reflect a stable continental margin and sediments were derived from granitic and pegmatitic sources located in the southern parts of the Gafsa basin. High values for the chemical index of alteration (CIA) indicate that recycling processes might have been important. Particularly high CIA values in the Garet Hadid locality indicate more intense chemical alteration, either due to weathering processes or tectonic control.  相似文献   

12.
The National Oceanic and Atmospheric Administration (NOAA) Status and Trends Mussel Watch Program sampled the largest oysters in nearly every major US coastal lagoon and estuary in the Gulf of Mexico once during the winter from 1986 to 2010. This contribution examines trends in the principal oyster disease in the Gulf of Mexico, Dermo, caused by Perkinsus marinus, and some related population dynamic characteristics for its host, Crassostrea virginica. During the 1986–2000 period, P. marinus prevalence and infection intensity and oyster population dynamics followed the El Niño-Southern Oscillation (ENSO) cycle, responding to variations in salinity caused by variations in rainfall and freshwater inflow. The ENSO signal in the oyster population effectively ceased circa 2002. Beginning around this time, wintertime P. marinus prevalence and weighted prevalence began a decadal decline, as did the length of the largest oysters and the fraction of these largest animals that were female. The trends in Dermo disease, oyster length, and oyster sex ratio are all consistent with the following hypothesis: increasing temperature during the 2000s resulted in an increase in P. marinus infection intensity sufficient to increase the mortality rate in late summer and fall in the larger animals. This simultaneously reduced Dermo prevalence and infection intensity in the winter at the time of sampling and also resulted in the decline in the length of the largest animals targeted by Mussel Watch. Coincident with the decline in length is the expected decline in the fraction female, such that the percent female in the largest animals dropped to ≤50 % throughout much of the Gulf of Mexico. The decline in length leading to fewer large animals reproducing and the loss of females are predicted to have reduced oyster population reproductive capacity substantially during the 2000s. The early 60 % of the Mussel Watch time series took place during a period of negative Atlantic Multidecadal Oscillation (AMO) indices. The AMO moved into positive territory circa 2000. A positive AMO index is consistent with observed warmer water temperatures, and increased water temperature is consistent with an increase in Dermo-induced mortality.  相似文献   

13.
La Goulette, Rades and Sidi Bou Said harbours are considered as the most important commercial and tourist ports in the Gulf of Tunis. They are located on the northeast coast of Tunis and receive industrial and municipal wastewaters from Tunis city. The contamination level of copper, lead, zinc, cadmium, manganese, iron, total nitrogen and total organic carbon in the surface sediments was assessed on the basis of the enrichment index factors and corresponding to sediment quality guidelines. The results revealed moderate to highly elevated concentrations near to the sites of intense industrial, shipping and/or commercial activities suggesting a direct influence of these sources. In winter and summer, concentrations varied for cadmium, 0.28–1.40 mg kg?1; lead, 18–217 mg kg?1; zinc, 87–459 mg kg?1; copper, 8–121 mg kg?1; manganese, 208–254 mg kg?1; and for iron, 24–40 g kg?1. Furthermore, in summer the concentration of the total organic carbon and the total nitrogen contents range between 4.3–6.5 % and 0.06–0.49 % with an average value of 5.9 and 0.15 %, respectively. Whereas, in winter, total organic carbon and the total nitrogen concentrations varied between 2.3–9.6 % and 0.03–0.22 % with an average value of 6.1 and 0.14 %, respectively. The levels of lead, copper, zinc and iron in suspended particulate matter content range between 3.1–27.5 mg kg?1; 0.4–11.7 mg kg?1; 1–1.5 mg kg?1; 1.2–1.7 g kg?1, respectively. This study revealed that heavy metals pollution is mainly localized in the commercial (Rades) and fishing (La Goulette) harbours and not in the yachting (Sidi Bou Said) harbour.  相似文献   

14.
Redox transformations of iron in the surface waters of the Gulf of Aqaba, Red Sea, were studied on recurrent cruises from September 2006 to May 2007. Fe(II) concentrations and oxidation kinetics were measured in situ using luminol chemiluminescence. High Fe(II) concentrations of 200-400 pM were recorded in the autumn, followed by low concentrations of 20-130 pM in the winter-spring. A distinct diurnal pattern in Fe(II) concentrations was observed in the autumn with maximum values coinciding with maximum solar irradiance. In situ and in vitro Fe(II) oxidation rates showed temporal and spatial variability that was accounted for by changes in water temperature and pH. Dissolved oxygen was found to be the dominant oxidant in all but one cruise. In situ photoreduction rates (deduced from oxidation rates) were linearly correlated with solar irradiance during the autumn, suggesting that the reducible iron pool was not exhausted even at the strongest irradiances and that it was kept constant throughout the season. Phytoplankton had no discernible influence on Fe(II) production, consumption, or oxidation kinetics. Given the fast oxidation and photoreduction rates of up to 180 pM min−1, the turn-over rates of iron were estimated at 10-30 per day. Such a dynamic Fe redox cycle probably influences the chemical reactivity and bioavailability of iron and may enhance the solubility of the abundant aerosol dust.  相似文献   

15.
The fossil clam shrimp genus Cratostracus was first described from the Turonian–Coniacian (Upper Cretaceous) Qingshankou Formation in the Jilin and Heilongjiang provinces of China, and it has been found to range down into the Aptian Guantou Formation in Zhejiang Province of southeastern China. Recently, species tentatively attributable to it (Cratostracus? cheni) has been recorded in the well-known Jehol Biota bearing Barremian–lower Aptian (Lower Cretaceous) Yixian Formation in western Liaoning Province of northeastern China. The species described in this paper as Cratostracus? tunisiaensis sp. nov. was recovered from the Sidi Aïch Formation in the Chotts area of southern Tunisia. Although only tentatively attributed to Cratostracus, its occurrence is consistent with a Barremian (Early Cretaceous) age for the formation. This first direct dating of the Sidi Aïch Formation gives a valuable insight for the stratigraphy of the region and will make it possible to more precisely correlate the different outcrops of the Sidi Aïch Formation. Moreover, the new fossil discovery allows a reconstruction of the paralic ecosystem that characterized the study area during the Barremian.  相似文献   

16.
To constrain seasonal changes in the long-range atmospheric transport of land-derived lipid biomarker compounds, we investigated the compound-specific stable isotopic composition of marine aerosol n-alkanes collected from 1990 to 1993 at a remote island, Chichi-Jima (27°04′N, 142°13′E), in the western North Pacific. Compound-specific isotope analysis revealed, in particular, strong seasonal changes in the δ13C values of the C29 and C31n-alkanes (biomarkers for higher plants). Lighter δ13C values were observed in winter (typically −32 to −34‰), with a transition to heavier values in summer (typically −28 to −31‰). Using a mixing equation and typical end members for C3 and C4 plants, we found that this is due to relative increases in the contributions from C4 plants in the summer season. Using backward air-mass trajectory analyses, it was shown that the Asian continent was the major source region for C3 plant material during winter/spring, whereas Indonesia/Australia and possibly the Americas were the major source regions for C4 material during the summer/autumn. Also observed was an enhanced atmospheric transport of n-alkanes from C4 plants in 1991 summer/autumn during a strong El Nino event, which was associated with forest and bushfires in Indonesia and Australia. In addition to providing information on contemporary processes, this study also provides a base for future paleoclimatological work in ocean sediments.  相似文献   

17.
In order to assess pollutants and impact of environmental changes along the Egyptian Red Sea coast, seven recent and Pleistocene coral species have been analyzed for Zn, Pb, Mn, Fe, Cr, Co, Ni, and Cu. Results show that the concentration of trace elements in recent coral skeletons is higher than those of Pleistocene counterpart except for Mn and Ni. In comparison with recent worldwide reefs, the present values are less than those of Central America coast (iron), Gulf of Aqaba, Jordan (lead, copper), Gulf of Mannar, India (chromium, zinc, manganese), Costa Rica, Panama (chromium, nickel), North-west coast of Venezuela and Saudi Arabia (copper). The present values are higher than those of Gulf of Aqaba, Jordan (iron, zinc, manganese), Gulf of Mannar, India (lead, cobalt, nickel), North-west coast of Venezuela (lead, zinc, chromium, manganese), Australia (copper, nickel, zinc, manganese). The highest values were recorded in Stylophora pistillata (iron, lead and copper), Acropora cytherea (cobalt), Pocillopora verrucosa (zinc) and the lowest concentrations were recorded in Goniastrea pectinata (iron, chromium, copper and nickel), Favites pentagona (lead, zinc and manganese), and Porites lutea (cobalt). The differences in metals content among the studied species are attributed to differences in microstructure and microarchitecture.  相似文献   

18.
Cedar Bayou, a natural tidal inlet, was recently dredged to allow for direct water exchange between the Gulf of Mexico and Mesquite Bay, TX, USA. We quantified changes in densities of juvenile nekton (fish, shrimps, and crabs) and community structure in Mesquite Bay after Cedar Bayou was reopened by collecting samples at both control and impact sites using an epibenthic sled 1 year before (October 2013–April 2014) and after (October 2014–April 2015) opening. Significantly higher densities of total nekton were observed at the impact sites after opening using a before-after control-impact design. Red Drum (Sciaenops ocellatus), Atlantic Croaker (Micropogonias undulatus), post-larval penaeid shrimps (Farfantepenaeus aztecus, F. duorarum, and Litopenaeus setiferus), and Blue Crabs (Callinectes sapidus) were significantly more abundant at impact sites after Cedar Bayou was opened. Multivariate analysis showed a significant change in impact site communities after opening and was driven by an increased presence of estuarine-dependent species. Overall, this study demonstrates that opening tidal inlets, such as Cedar Bayou, and reconnecting Mesquite Bay to the Gulf of Mexico increased the presence of numerous estuarine-dependent species, many of which were not present or occurred at very low densities prior to reopening. Thus, reestablishing the historical connectivity between a productive estuary and the open Gulf of Mexico via Cedar Bayou should reinstitute natural nekton recruitment processes important to the Aransas, Mesquite, and San Antonio Bay regions.  相似文献   

19.
This research is conducted as part of a Spanish International Cooperation Agency project with the aim to investigate the sustainable protection of Tunisian coastal zones, as in the case of Beni Khiar and Dar Chaabane coasts (Hammamet Gulf) separated by Oued El Kebir river. The sedimentary dynamic of these beaches is studied in order to identify the main causes responsible for their erosion by the use of different approaches of in situ measurements and numerical methods. Geophysical surveys and sedimentary analyses have demonstrated that sediments are finer and less carbonated from Beni Khiar to Dar Chaabane. Then, the shoreline mapping of several missions of aerial photos has illustrated a mean shoreline retreat between 3 and 4 m/year. In terms of sand volume, a sediment loss more than 30,000 m3/year at Dar Chaabane has been observed since the hill lake structures were built within Oued El Kebir river in 1996. Finally, modelled hydrodynamic and sedimentary patterns have illustrated the refraction of waves in deep water close to shoals and a high-energy concentration along Dar Chaabane coast. The sediment transport direction is mainly of NE-SW induced by ESE-SE wave-driven alongshore current. Results provided by these approaches have shown the importance of Oued El Kebir sediment yield in supplying the neighbouring beaches. Changes in sedimentary dynamics are affected by the modification of hydrodynamic patters caused by the presence of hydrological dams and the implementations of hotels close to the shoreline. This finding underlines the key role of Oued El Kebir fluvial activity in controlling the equilibrium of beaches and their sensitivity to coastal managements induced by man activities, as in the case of the most Mediterranean beaches.  相似文献   

20.
Monthly field sampling of active animals in a Louisiana coastal salt marsh monitored changes in size class frequency distributions, ovarian development of females, and rates of egg extrusion for two species ofUca endemic to the Gulf of Mexico. Ovigerous females occurred no earlier than February forUca spinicarpa and April forUca longisignalis. Peak percentages of ovigerous females were observed in June 1992 forUca longisignalis (67%) and in March 1993 forUca spinicarpa (85%). Peaks in ash-free dry weight (AFDW, in g) of females coincide with peak periods of ovarian development and subsequent ovigery. Mean biomass as AFDW of males and females combined forUca longisignalis was 0.26 g individual?1 and forUca spinicarpa was 0.17 g individual?1. A significant correlation existed between AFDW and carapace width in both species, males and females.U. longisignalis appears to be of warm-temperate lineage, and its reproductive activity is the more seasonally restricted, with later ovarian development, earliest egg laying delayed to late spring, and peak ovigery in summer. In keeping with putative tropical affinities ofUca spinicarpa, ovarian development is episodic over a longer-period from late winter to summer, and eggs are produced earlier in the year. The more striking seasonality in reproductive activity and biomass peaks forUca longisignalis may also reflect some nutritional dependency on temperate, annual marsh plants that characterize its preferred habitats.  相似文献   

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