|TITLE||HISTORICAL AND PALEO-HYDROLOGICAL CHANGES RECORDED FROM MOROCCAN MIDDLE ATLAS LAKES INFERRED FROM SEDIMENTOLOGICAL AND GEOCHEMICAL APPROACHES|
|AUTHORS||L Vidal (1), G Jouve (1), H Idabdellah (1,2), R Adallal (1,2), K Tachikawa (1), C Sonzogni (1), A Benkaddour (2), A Rhoujjati (2)|
- Aix Marseille University/CEREGE, Aix en Provence, France
- Univ Cadi Ayyad/Géoressources, Marrakech, Morocco
|ABSTRACT||The Moroccan Middle-Atlas is considered as the “Moroccan water tower” and contains several natural lake systems of tectono-karstic origin functioning as “pluviometer”. This region suffers from scarcity of observational hydrological data required for a coherent management of water resources. In this context, the precise study of the lacustrine sedimentary infill can provide some key information about past hydrological changes.
The first study was conducted on well-dated sedimentary deposits of Lake Azigza (32°58’N, 5°26’W, 1550 m a.s.l.) by combining geochemical and mineralogical measurements coupled with microfacies characterization. The detrital component derived from XRF scanning and the microstructures observations of the lake sediments provided proxies of runoff activity and lake-level changes, respectively. These proxies were calibrated with regional hydro-climatic and instrumental measurements available over the last 50 years and used to reconstruct past hydrological changes on inter-annual to decadal time-scales between 1879 and 2013. During this period, lake level and runoff proxies responded to hydro-climate conditions. Following periods of drastic lake-level drop, the runoff proxy is more sensitive to variable precipitation regime.
We also present a study on a 3 m sequence cored at Flower Lake (32° 59’ 04’’N, 5° 27’ 13’’ W, 1554 m asl) a small pond close to lake Azigza. High-resolution geochemistry (XRF) records and sedimentological and isotope analysis of this sequence are supported by five coherent and calibrated radiocarbon dates covering the last ~6 cal kyrs BP. Before 2500 yrs BP, low Ca contents coincided with an important detrital input characterized by high Si, K, Ti and Fe values. This could be related to more humid conditions with higher erosion of the surrounding landscape. The relative high Ca and Sr contents during the last 2500 yrs BP can be connected to drier conditions when carbonate precipitation occurs in shallow waters due to higher evaporation and photosynthetic activity of charophytes algae and other aquatic plants.
These results emphasize the potential of these hydro-climate-sensitive systems and their sedimentary archives to assess the impact of climate change on the southern Mediterranean water cycle.|