[FRANCH]

Climate changes reconstitution from hydrologic cycle fluctuations in North Africa

Collaboration:

 DAYACLIM has been formally endorsed by  Centre for Scientific and Technical Research on Arid Zones (CRSTRA,Biskra ),

in collaboration with :

- University of  Ouargla- Algeria. (Saharan Bio-Resources & Arid Environment Laboratory)

-Houari Boumedien's Sciences and Technologies University - Algéria.(Physical planning &Image Processing Laboratories- USTHB) 

-Centre for Nuclear Researches  of Algiers  (Department of Dosimetry CRNA).

-National Institute of Agronomy ( Soil-Water&Ecosystem Laboratory  - SWEL INA Algiers ).

-Agronomic National Institute , Paris-Grignon (INA P-G),  UER Dynamique des Milieux et

 Organisations Spatiales, Equipe micromorphologie des sols (France).

Project Group :

Scientists working within the project deal with several   fields: climatology,  hydrology, meteorology, nuclear physics, pedology, geology, sedimentology, prehistory, ecology -   .

Objectives :

-  Formulating and coordinating an integrated multidisciplinary approach by  observing, modelling and investigating global change phenomena and processes in NASD regions, including impacts on ecosystems and socio-economic environments.

- Analysis of interacting groundwater and hydrological process ( watershed hydrology,  paleo-drainage, paleo-lake …etc)

-Reconstituting past climatic changes and  variations in order to forecast future changes.

-Providing useful information in order to identify climate changes and variability origin and causes in North Africa .

-Constituting a scientific and technical paleo-environment database on Arid Regions.

-Identifying climate evolution at local and global scales,and also energetic needs,water and food supply.

Strategy :

The paleoclimatogists have two major concerns:

 (i) selecting  investigated sites with a high signals of climate changes and variability.

 (ii) making sure that these investigated sites offers a continuous signals of past climate oscillations.

However, in the NASD regions at interglacial phases, flooded base-level plains and endoreïc depressions (i.e. playa “sabkha” and Dayas) where water is periodically stored at the surface could function as paleoclimate geo-archives (Rognon, 1980, Lézine, 1993, Messen et al., 2004(a & b)).

Sediments in depressions are temporary dried under effect of drought, they are covered with a sand layer and aeolan sand deposition, thereafter the fluvial and detritic sediments drained by water during pluvial phase are interstratified with sandy accumulations (i.e. aeolian and hydric accretion).

The climatic theory  on  terraces construction is currently discussed, Paleoclimatogists and paleopedologists proposed  it as past climate signal in mid-latitude regions.In arid and semi-arid regions some alluvial terraces are encased within aeolian sands dunes, they are closely related to climatic fluctuations events.

analyses must pointed out of  of water slope system:

-Heavy minerals analysis

-Clays  analysis

-Morpho radioscopy

-Gramulometric analysis

-Geochemical analysis

Our approach supports the theory of bio-rhexistasy which involves a complex succession of sedimentation/pedological phases alternating with erosional episodes, both being controlled by climate forcing (Fedoroff et Courty, 1999).

However, the concept of hierarchy of soil attributes (i.e. paleosol) in terms of a chronology of events and their paleoclimatic significance (Fedoroff et Courty, 1999, Hamdi-Aïssa, 2002) is adopted in the DAYACLIM project.

it is understandable that the DAYACLIM project in NASD region is closely linked to planetary climate change.For dating the pedo-sediment layers we will have recourse to absolute dating (i.e. radiochronology) and relative dating (biostragraphy, geostratigraphy, micromorphology). 

For the application of this theory, constraints specific to studied sites must be considered:

-The system must remain closed (i.e. free from any additional contribution "black box" which recorded phenomena climatic by an irreversible process.

-The use of two chronometers to ensure the correct dating.

According to the sampling interval and the nature of pedo-sediment material of DAYACLIM selected sites, chronometers choice is limited to :

1- U/Th disequilibrium dating .

2- Electron Spin Resonance dating (ESR) or Electron Paramagnetic Resonance (EPR).

3- Luminescence dating (thermal or optical stimulated luminescence).

Luminescence techniques are the most appropriate methods for dating sediments, particularly when the samples contain small quantities of organic constituents where ¹⁴C dating is not adequate in this project.

Satement of the alluvials levels and examination of the various layers cut  on the ground .

 Presentation of a cut with alternance of the wind deposits and fluvials. (Dry episodes and wet episodes)