North African dataset
The North African dataset consists from samples from Tunisia (66), Algeria (3), Morocco (26), and Niger (20). In Tunisia, samples were collected from the Mediterranean northern regions to the margins of the Sahara southwards by L. Ben Khelifa and F. Gasse (1985-1989). In southern Tunisia, samples were taken from small permanent groundwater-fed waterbodies and temporary salt lakes, small artificial ponds developed around boreholes, and in mini reservoir lakes and swamps along Wadi el Akarit. Samples from hydrothermal springs have been collected throughout the country. In northern Tunisia, freshwater samples were also taken from the Mejerda Channel. Waters range from fresh to metasaline. Most samples are of the sodium/chloride or calcium-magnesium/ sulphate type. Diatoms were counted by L. Ben Khelifa. Details of diatom and hydrochemical analyses are given in Ben Khelifa (1989).
Sites from southern Algeria, collected by F. Gasse en 1985, show clear similarities with the waterbodies of southern Tunisia. The 26 samples from Morroco were collected by F. Gasse in 1989 from 17 localities situated between 30°30?-34°30?N and 5°-7°30?E, at altitude ranging from 300 to 2050 m. Sites are distributued in the western plains close to Casablanca, the Middle Atlas mountains, and the more arid southweast margins of the Atlas ranges, from a large variety of waterbodies (permanent and temporary natural lakes, man-made lakes, and wadis. Conductivities range from 195 to 3900 µS cm-1. Freshwaters are of the calcium-sodium/bicarbonate type, while oligosaline waters are of the sodium/chloride type. Diatom samples were counted by F. Gasse.
In southern Niger, samples were collected from the Niger River, the Bara salt pond near Niamey, and from interdunal depressions on the Manga Plateau occupied by permanent or ephemeral waterbodies. A few samples from northern Niger (Aïr) have also been collected from groundwater-supplied ponds. Most waterbodies are of the sodium/carbonate-bicarbonate type. Samples from Niger were collected and analyzed by F. Gasse, except those from the Bara pond (M.-C. Lang). The main characteristics of the water chemistry and diatom communities of the Niger samples are presented in Gasse (1987).
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Summary of environmental data for this dataset:
Publications for this dataset:
Ben Khelifa, L., 1989. Diatomées continentales et paléomilieux du Sud-Tunisien (Palhydaf Site 1) au Quaternaire supérieur. Approche statistique basée sur les diatomées et les milieux naturels. Thesis. Univ. Paris-Sud, 233 pp.
Carvalho, L.R., Cox, E.J., Fritz, S.C., Juggins, S., Sims, PA., Gasse, F., and Battarbee, R.W., 1995, Standardizing the taxonomy of saline lake Cyclotella spp. Diatom Research, 10 (2) 229-240.
El Hamouti, N., Lamb, H., Fontes, J.Ch. et Gasse, F., 1991. Changements hydroclimatiques abrupts dans le Moyen Atlas marocain depuis le dernier maximum glaciaire. C. R. Acad. Sci., Paris. 313 , 259-265.
Fontes, J.Ch., Gasse, F., Callot, Y., Plaziat, J.C., Carbonel, P., Dupeuple, P.A. & Kaczmarska, I., 1985. Freshwater to marine-like environments from holocene lakes in Northern Sahara. Nature, 317, 608-610.
Gasse, F., Fontes, J.Ch., Plaziat, J.C., Carbonel, P., Kaczmarska, I. , De Deckker, P., Soulié-Marsche, I., Callot, Y., & Dupeuple, P.A., 1987. Biological remains, geochemistry and stable isotopes for the reconstruction of environmental and hydrological changes in the Holocene lakes from North Sahara. Paleoecol., Palaeogeogr , Palaeoclimat., 60, 1-46.
Gasse, F., 1987. Diatoms for reconstructing palaeoenvironments and palaeohydrologyn tropical semi-arid zones. Example of some lakes from Niger since 12,000 BP. Hydrobiologia, 154 : 127-163.
Gasse, F., Téhet, R., Durand, A., Gibert, E., Fontes, J.Ch., 1990. The arid-humid transition in the Sahara and the Sahel during the last deglaciation. Nature, vol. 346(6280):141-156.
Gasse, F., Van Campo, E., 1994. Abrupt post-glacial climate events in West Asia and North Africa monsoon domains. EPSL, 126, 435-456.
Lamb, H.F., Gasse, F., Ben Kaddour, A., El Hamouti, N., Van der Kaars, S., Perkins, W.T., Pearce, N.J., Roberts, C.N., 1995. Relation between century-scale Holocene arid intervals in tropical and temperate zones. Nature, 373,134-137.