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The atmospheric general circulation models ARPEGE-climate and LMDz are used in an aquaplanet configuration to study the response of a zonally symmetric atmosphere to a range of sea surface temperature (SST) forcing. We impose zonally-symmetric SST distributions that are also symmetric about the equator, with varying off-equatorial SST gradients. In both models, we obtain the characteristic inter-tropical convergence zone (ITCZ) splitting that separates two regimes of equilibrium (in terms of precipitations): one with one ITCZ over the equator for large SST gradients in the tropics, and one with a double ITCZ for small tropical SST gradients. Transition between these regimes is mainly driven by changes in the low-level convergence that are forced by the SST gradients. Model-dependent, dry and moist feedbacks intervene to reinforce or weaken the effect of the SST forcing. In ARPEGE, dry advective processes reinforce the SST forcing, while a competition between sensible heat flux and convective cooling provides a complex feedback on the SST forcing in the LMDz. It is suggested that these feedbacks influence the location of the transition in the parameter range. 相似文献
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Boutheina Farhat Abdallah Ben Mammou Lamia Kouzana Ismail Chenini Francesca Podda Giovanni De Giudici 《Resource Geology》2010,60(4):377-388
The present paper investigates hydrochemical processes and water quality in the Mornag aquifer in NE Tunisia. Groundwater samples were collected during a field campaign, and were analysed for major and trace elements. The collected waters have a chemical facies rich in Ca2+, Na+ and Cl-. Piper diagram shows a progressive increase in chloride ions along with increasing salinity. Saturation indexes calculated by using PHREEQC (USGS) show that the Mornag waters are slightly saturated with respect to carbonates (calcite and dolomite), while undersaturated with respect to gypsum, halite and other evaporitic minerals. The current composition of waters takes place via dissolution of halite and Ca-sulfates, where the increase in calcium is partially balanced by possible calcite precipitation. The relevant recorded pollutant is nitrate, which was likely dispersed from agricultural soils, while heavy metals were generally far below values of pollution thresholds, indicating no influence by mining activity. 相似文献
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Hajer Ferchichi Boutheina Farhat Mohamed F. Ben-Hamouda Abdallah Ben-Mammou 《Arabian Journal of Geosciences》2017,10(23):530
The rapid urbanization and industrialization of the Manouba plain (Northeastern Tunisia), the extensive agricultural expansion and the succession of dry years during recent decades have exerted greatly load on the water needs and lead to groundwater quality degradation. The aim of this study is to evaluate the processes controlling the groundwater mineralization of the shallow aquifer for determining its suitability for drinking and agricultural purposes. For establishing that, we combine several geological, hydrological and hydrochemical data with geostatistical techniques. The samples were collected at 17 sites covering 230 km2 of the study area and analyzed for major and trace components. The total dissolved solid (TDS) content ranges from 1372 to 3999 mg/l. The results of Piper diagram indicate that Na+/Cl? and Ca2+?>?Na+/SO4 2? were the main dominant water types localized in the sloping sides of the watershed and near the saline depression; the suitability for irrigation use was also evaluated. The high concentrations of nitrates and chlorides are indicators of anthropogenic pollution, like the agricultural over application of nitrogen fertilizers and the discharge of domestic and industrial wastewater. Saturation indexes calculated by using PHREEQC (USGS) program show that groundwaters are undersaturated with evaporitic minerals (halite, gypsum) and saturated with carbonates (calcite, aragonite). The use of principal component analysis and hierarchical cluster analysis has shown that two main factors accounting 67.13% of the information of variability within the dataset confirm the existence of dissolution of evaporitic minerals and the mechanisms of nitrate increasing the salinity of the Manouba groundwater. 相似文献
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Amel Dhib Mounir Ben Brahim Boutheina Ziadi Fourat Akrout Souad Turki Lotfi Aleya 《Marine pollution bulletin》2013
We studied the distribution of planktonic and epiphytic ciliates coupled with environmental factors and microalgae abundance at five stations in Ghar El Melh Lagoon (Tunisia). Planktonic ciliates were monitored for a year and epiphytic ciliates were sampled during summer 2011 in concordance with the proliferation of the seagrass Ruppia cirrhosa. Ciliate assemblage was largely dominated by Spirotrichea followed respectively by Tintinnida of and Strombidiida. No significant difference was found in the distribution of ciliate species among the stations. Redundancy analysis indicates that abiotic factors (temperature and nutriments) have a significant effect on the dynamics of certain ciliates. For epiphytic ciliates, 4 species were identified: Tintinnopsis campanula, Aspidisca sp., Strombidium acutum and Amphorides amphora. Based on PERMANOVA analyses, ciliates exhibit significant correlations among months and stations. According to ACP, epiphyte distribution follows roughly those of R. cirrhosa and pH. Significant correlations were found between harmful dinoflagellates and both planktonic and epiphytic ciliates. 相似文献
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Asma Sakka Hlaili Boutheina Grami Nathalie Niquil Michel Gosselin Dominique Hamel Marc Troussellier Hassine Hadj Mabrouk 《Estuarine, Coastal and Shelf Science》2008
The structure and the trophic interactions of the planktonic food web were investigated during summer 2004 in a coastal lagoon of south-western Mediterranean Sea. Biomasses of planktonic components as well as bacterial and phytoplankton production and grazing by microzooplankton were quantified at four stations (MA, MB, MJ and R) inside the lagoon. Station MA was impacted by urban discharge, station MB was influenced by industrial activity, station MJ was located in a shellfish farming sector, while station R represented the lagoon central area. Biomasses and production rates of bacteria (7–33 mg C m−3; 17.5–35 mg C m−3 d−1) and phytoplankton (80–299 mg C m−3; 34–210 mg C m−3 d−1) showed high values at station MJ, where substantial concentrations of nutrients (NO3− and Si(OH)4) were found. Microphytoplankton, which dominated the total algal biomass and production (>82%), were characterized by the proliferation of several chain-forming diatoms. Microzooplankton was mainly composed of dinoflagellates (Torodinium, Protoperidinium and Dinophysis) and aloricate (Lohmaniellea and Strombidium) and tintinnid (Tintinnopsis, Tintinnus, Favella and Eutintinnus) ciliates. Higher biomass of these protozoa (359 mg C m−3) was observed at station MB, where large tintinnids were encountered. Mesozooplankton mainly represented by Calanoida (Acartia, Temora, Calanus, Eucalanus, Paracalanus and Centropages) and Cyclopoida (Oithona) copepods, exhibited higher and lower biomasses at stations MA/MJ and MB, respectively. Bacterivory represented only 35% of bacterial production at stations MB and R, but higher fractions (65–70%) were observed at stations MA and MJ. Small heterotrophic flagellates and aloricate ciliates seemed to be the main controllers of bacteria. Pico- and nanophytoplankton represented a significant alternative carbon pool for micrograzers, which grazing represented 67–90% of pico- and nano-algal production in all stations. Microzooplankton has, however, a relatively low impact on microphytoplankton, as ≤45% of microalgal production was consumed in all stations. This implies that an important fraction of diatom production would be channelled by herbivorous meso-grazers to higher consumers at stations MA and MJ where copepods were numerous. Most of the microalgal production would, however, sink particularly at station MB where copepods were scare. These different trophic interactions suggest different food web structures between stations. A multivorous food web seemed to prevail in stations MJ and MA, whereas microbial web was dominant in the other stations. 相似文献
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Lluís Casas Boutheina Fouzai Marta Prevosti Nejia Laridhi‐Ouazaa Ramon Jrrega Siwar Baklouti 《Geoarchaeology》2016,31(6):564-576
Two isolated kilns of unknown age and three well‐dated artifacts from Tunisia have been investigated using archaeomagnetic techniques. Dating has been attempted for the kilns and archaeomagnetic intensities have been obtained for the artifacts. The kilns lack datable artifacts although one of them (Sidi Zahruni) could be related to a nearby late Roman site. Comparison with the SCHA.DIF.3K regional geomagnetic model suggests for both kilns two possible periods of last use, either Roman or Medieval. Three archaeomagnetic intensities were obtained for the well‐dated ceramic artifacts adding to scarce archaeomagnetic data from Africa. The new data along with recently published archaeointensities from other Tunisian sites have been compared with the regional model SCHA.DIF.3K, its updated version, and the global ARCH3k.1 geomagnetic model. The models show relatively good agreement with the new archaeointensities and with previously published intensities. The uncertainty of the experimental data tends to increase for older artifacts, and their agreement with the geomagnetic models diminishes. The observed trend of the intensity models to underestimate values in the Tunisian area for the Roman period could be overcome by adding new data from well‐dated artifacts from North African, particularly from pre‐Roman and Roman sites. 相似文献
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Résumé Cette étude est basée sur l'analyse des données gravimétriques; elle a pour but d'améliorer la connaissance de la structure de la plaine de Mornag. La carte de l'anomalie résiduelle a d'abord été calculée à partir de la carte de l'anomalie de Bouguer en enlevant un gradient régional. La résiduelle calculée fournit des informations sur la variation de la densité dans le bassin de Mornag. Afin de mettre en évidence les différentes structures dans le bassin, nous avons calculé la magnitude du gradient horizontal (MGH). Cette technique a permis de déterminer des linéaments gravimétriques représentant l'emplacement des contrastes de densité, et de déduire une carte structurale de la zone d'étude. Cette carte constitue un document très utile pour orienter l'exploration des ressources en eau dans la plaine de Mornag. Citation Farhat, B., Benassi, R., Jallouli, C. & Ben Mammou, A. (2010) Contribution de la gravimétrie à l'étude de la structure de la plaine de Mornag (nord est de la Tunisie): implications hydrogéologiques. Hydrol. Sci. J. 55(8), 1396–1404. 相似文献
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