A 44-year high-resolution ocean and atmospheric hindcast for the Mediterranean Basin developed within the HIPOCAS Project

A set of 44-year (1958–2001) homogeneous and high-resolution hindcasts of atmospheric, sea level residuals, and wave states was performed for the Mediterranean Basin within the framework of the HIPOCAS European Project. To this aim, different numerical models were used. As a first step, a Mediterranean high-resolution atmospheric database, suitable to provide realistic and homogeneous forcing for ocean hindcast runs was generated. The HIPOCAS atmospheric database was created by means of dynamical downscaling from the global reanalysis NCEP, using for that the limited area model SN-REMO along with a spectral nudging technique. In a second stage, different Mediterranean oceanic hindcasts were performed. On one hand a long-term database of sea state over the western Mediterranean was generated by means of the wave model WAM and on the other hand a sea level residual database containing storm surge events was obtained from a long-term integration of the HAMSOM model over the entire basin. The three different hindcast runs have been exhaustively validated. On that score, various simulated parameters have been compared to both satellite and in situ measurements. Such comparisons provide a measure of the skills of the different simulated fields to realistically reproduce the observed features. Once these skills are evaluated, a study of the ocean and atmospheric climate trends as well as the interannual variability for the whole 44-year period was carried out with the hindcasted data. The reliability of the data as shown by its comparison to measurements and a proven temporal homogeneity over the 44 years of simulation make the Mediterranean HIPOCAS ocean–atmosphere hindcasted database a useful tool for studies focused on regional climatic variability, as well as for further applications in coastal and environmental decision processes in the Mediterranean area.     

Implementation and evaluation of multivariate analysis for groundwater hydrochemistry assessment in arid environments: a case study of Hajeb Elyoun–Jelma, Central Tunisia

In most arid zones, groundwater (GW) is the major source of domestic, agriculture, drinking, and industrial water. Accordingly, the monitoring of its quality by different techniques and tools is a vital issue. The purpose of this paper is the evaluation of the combination of principal components analysis (PCA) and geostatistics as a technique for (1) identifying the processes affecting the groundwater chemistry of the detrital unconfined Middle Miocene Aquifer (MMA) of the Hajeb elyoun Jelma (HJ) aquifer (Tunisia) and (2) mapping the controlling variables for groundwater quality. This work is based on a limited database recorded in 22 wells tapping the aquifer and unequally distributed in the field. The proposed approach is carried out in two steps. In the first step, the application of PCA revealed that rock–water interaction, agriculture irrigation and domestic effluents could explain 85 % of the observed variability of the chemical GW quality of the MMA. As a result, two new variables are defined: V1 (rock–water interaction influence) and V2 (irrigation and domestic effluent influence). In the second step, the spatial variability of these variables over the extent of the MMA is mapped by applying a kriging interpolation technique. The results of this study suggest that, while both natural and anthropogenic processes contribute to the GW quality of the MMA, natural impacts can be considered as the most important.     

Manifestations tectono-diapiriques synsédimentaires et polyphasées d'âge Crétacé supérieur–Quaternaire dans la région de Zag Et Tir (Tunisie centre-nord)

The geodynamic evolution of the diapir of Zag Et Tir is the result of the coexistence of the diapiric and tectonic activity from the Upper Cretaceous until the Quaternary. The interference of the tectonic and diapiric phenomena is at the origin of the basin individualization with differential sedimentation during the Miocene. This explains the current distribution of the Neogene deposits on both sides of Zag Et Tir Triassic structure. The submeridian faults that subdivide our sector played a significant role during the Atlasic compression, inducing an unequal distribution of the folds on both sides of these accidents, as well in kind as in number, showing the anteriority of the faults compared to the folds. To cite this article: R.A. Gharbi et al., C. R. Geoscience 337 (2005).     

Neotectonic and seismotectonic investigation of seismically active regions in Tunisia: a multidisciplinary approach

Due to its key position within the Africa–Europe convergence zone, Tunisia is marked by thrusting, folding, and faulting and has a major rupture zones associated with active faults. Consequently, most of Tunisian land is seismically active with significant active deformations, showing recent seismic events and their relative surface effects. This paper reports on several aspects of the seismotectonics, historical, and present-day seismicity and places them in the general tectonic and geodynamic framework of Tunisia. Field investigations, based on an integrated multidisciplinary approach, included (1) the identification of active faults, their motion and displacement, geomorphic aspects, and scarps and their relation with the general structural map of Tunisia and (2) an extensive analysis of brittle tectonic deformation affecting Quaternary deposits in several sites throughout Tunisia. The integration of field data within the existing data related to the seismic events that took place during the last decades allowed the establishment of an earthquake distribution map, as well as major seismic zones for better understanding of the seismicity database of Tunisia. To establish microzonation maps in seismic regions such as Gafsa and its surroundings, we have analyzed surface effects and secondary structures associated with active faults and correlated them with deformation rates, reconstructed for significant seismic events. Most faults exhibited typical left-stepping en-echelon with strike-slip component pattern suggesting that Tunisia is presently subjected to NNW–SSE compression. The focal mechanism of most Tunisia earthquakes combined with the existing tectonic and structural information and reconstruction of the Quaternary stress tensor allowed (a) better understanding of seismic zoning, (b) provided better assessment of the seismic hazard, and (c) facilitated the interpretation of the relationship between seismic zones and the geodynamic African–Eurasian plate boundary.     

Mg/Ca-paleothermometry in the western Mediterranean Sea on planktonic foraminifer species Globigerina bulloides: Constraints and implications

We generated a high-resolution SST_Mg/Ca record for the surface-dwelling planktonic foraminifera Globigerina bulloides from the core MD99-2346 collected in the Gulf of Lion, and compared it to that obtained using modern analogue techniques applied to fossil foraminiferal assemblages (SST_MAT). The two temperature records display similar patterns during the last 28,000 years but the SST_Mg/Ca estimates are several degrees warmer (∼ +4 °C) than SST_MAT. The temperature shift between SST_Mg/Ca and SST_MAT remained relatively constant over time. This seems to exclude a bias on the Mg/Ca record associated with salinity or secondary Mg-rich calcite encrustation on the foraminiferal tests during early diagenesis. Therefore, anomalously high Mg/Ca suggests either: (1) the empirical equation for G. bulloides of Elderfield and Ganssen (2000) is incorrect; or (2) there is a specific Mediterranean genotypes of G. bulloides for which a specific Mg/Ca-temperature calibration is needed.