The CLIMAG team is interested in the reconstruction of modern and past environments in relation to climatic variations, based on the analysis of the magnetic, sedimentological and elemental properties of marine and continental sediments. This may involve, for example, tracing past variations in the intensity of deep ocean circulation or identifying the continental sources of marine sediments. Our team is also studying past variations in the Earth’s magnetic field on archaeological and sedimentary or igneous products. By constructing robust reference curves with high temporal resolution, these analyses provide a powerful geochronological tool (for dating blast furnaces, for example) and enable long-distance, multi-archive stratigraphic correlations.
Reconstruction of modern and past environments
The CliMag team investigates past variations of two main environmental processes:
- The intensity of the deep ocean circulation;
- The provenance of continental sources, as indicators of past changes in continental erosion and precipitation regimes on land (e.g. monsoons)
These environments are reconstructed on several time scales: glacial-interglacial changes over several climate cycles, rapid variability, sub-millennial to centennial.
For this purpose, we analyse the magnetic, sedimentological and elemental properties of marine sediment cores collected from several oceanographic basins (e.g. Atlantic, Southern). The study of the magnetic properties allows to identify the nature, size and concentration of ferromagnetic grains, as well as their preferential orientation in the sediment possibly related to the action of bottom currents. Grain-size and elemental X-ray Fluorescence analyses, also performed within the group, provide additional environmental information.
Finally, the analysis of recent samples from river suspended sediments, riverbeds or soils provides a more thorough characterization of the modern continental source of terrigenous material that deposits offshore at the coring locations.
High-resolution studies of past geomagnetic field variations
In order to investigate the dynamics and the morphology of the geomagnetic field generated by dynamo effect in the Earth’s outer core, the CliMag group studies its full-vector variation (direction and intensity) at different timescales:
- The secular variation during the Holocene is reconstructed from the study of the thermoremanent magnetization of archaeological baked clays (kilns, fireplaces, potteries…) and volcanic lava flows. Our main study areas are Western Europe and Sub-Saharan Africa.
- The group also focuses on the variability over the last million years, especially during periods characterized by reversals or excursions of the geomagnetic field. These variations are reconstructed both from lava flows and marine sedimentary cores.
Once well established, the models of variations in the geomagnetic field can be used as a geochronological tool in archaeomagnetic dating and in chronostratigraphy. For example, in sediments, the variation of the geomagnetic field, independent from climatic variables, allows to evaluate inter-hemispheric and inter-basin climatic phase shifts, which is essential to understand climatic mechanisms at the global scale.
To carry out these research activities, the group leads sampling fieldwork on land and oceanographic cruises, and has a fully-equipped laboratory. Our projects are funded by national (e.g. CNRS-INSU, ANR, Region Ile-de-France, IPSL) and international (e.g. European projects, International Research Project with Brazil, projects of the French Ministry of Europe and Foreign Affairs in Africa) research programs.