Hydrological variability (modern and past) in Morocco since the Holocene

Hydrological variability (modern and past) in Morocco since the Holocene in relation with this project one Labex OT-Med thesis started in January 2014 (PHYMOR)

PHYMOR is an integrated multidisciplinary climate research project that intend to challenge the present knowledge of North African hydrological and paleohydrological variability and its relationships with temperate as well as sub-tropical climate forcing factors during the Holocene (climate variability during the last millenium, the timing and abruptness of the aridification at the end of the African Humid period, the 8,200 yrs cold event, the sapropel event…). PHYMOR will focus on Moroccan Middle Atlas lake systems and will combine modern lake hydrological cycle study using water isotopes, proxy calibration for isotopic-paleoprecipitations reconstructions, and accurately dated sediments to reconstruct continental hydrological variability (for the last millennium) based on a variety of environmental proxies.

The modern hydrological cycle will be investigated by estimating hydro/isotopic balance from lakes located in the Middle Atlas which will provide key information for interpreting paleorecords from the same sites. Preliminary results on several karstic lakes from the Middle Atlas (Tiguelmamine and Azigza at ca. 1500 m absl) (Figure 1) have shown that they are very sensitive to climatic conditions. Moreover the study of the processes controlling the lake hydrological balance will potentially give important information about the hydrological variability of one of the main fluvial system from the Oum R’bia catchment (Figure 1). The goal is to establish through monthly instrumental monitoring and modelling -i) the influence of local precipitation/temperature at seasonal and interannual scales on the lake physical, chemical parameters and isotope composition and -ii) the origin of air masses reaching site location.

The other important aspect of the project is to develop a proxy calibration for paleoprecipitation reconstructions. We intend to establish the relation between precipitation water isotope, lake water isotopic composition and oxygen isotope measured on biogenic fossil samples. These karstic lakes offer the possibility to validate our calibration on biogenic carbonate and silicate samples. Oxygen isotope on ostracods and diatoms will be measured from surface and subsurface sediment samples and directly compared with the instrumental data obtained from the lake monitoring. This is one challenging part of the project since most of the paleohydrological reconstructions are based on qualitative interpretation (rather than quantitative) of lacustrine sedimentary isotope data with only sparse information about the modern lake system.

The recovery of sedimentary sequences will give access to temporal reconstructions of past variations of climatic, environmental and anthropogenic changes. The short sedimentary sequences retrieved from Tiguelmamine and Azigza lakes provide records of the last 5 centuries (as demonstrated from preliminary geochronological data) and we expect high resolution sediment sequences covering the last 2,000 years. High resolution studies of sedimentological and biogenic parameters will provide information about the imprint of human activities and climatic factors at centennial scale. It will be the first time that hydrological signatures of isotopic versus non-isotopic proxies will be compared for the same record.

Finally, the strength of the project is based on the integration of modern lake system knowledge (through monthly monitoring and isotopic hydrological lake balance estimates within the frame of a PhD Thesis in progress) with lacustrine sedimentary climate records in order to gain quantitative information of North African hydrological changes during the last millennia.

PHYMOR involves 5 French laboratories (CEREGE, ISEM, GEODE, GEOSCIENCES, CEFREM) and the Laboratory Géoressources (Univ. Cadi Ayyad, FST, Marrakech).

Figure 1 : a)-Precipitation (MAP) distribution in Morocco; b)-Map of the Oum R’Bia fluvial system (one of the most important in Morocco) and its watershed (R. Adallal, thesis). Red star indicates the study area.

date mise a jour 15 September 2014