1 - High and low frequency climate variability impact on ecosystems over the past 430,000 years

In the long pollen sequences of the Massif Central, five interglacials have been evidenced. They are marked by forest successions that differ from one interglacial to another. A particular floristic specificity correspond to each interglacial : e.g., the presence of forests with Pterocarya, a wet plains tree now extinct in Europe, in the Holsteinian (OIS 11, around 410 ka), or the absence of forests of Fagus throughout the Eemian (OIS 5 : 115 - 127 ka).
The long sequence of Les Echets (region of Lyon, SE France), 140 000 years old, was analysed in high resolution. This allowed us to reconstruct « instantaneously » the response of ecosystems to rapid climate changes (100 years of less than 100 years) whose origin is still debated. This is the case of the cold period of Montaigu, lasting 1075 years at Les Echets and occuring between 102 and 101 ka BP. It is characterized by the sudden disappearance of the Quercus and Carpinus deciduous forest and its replacement by an arctic grassland with Poaceae and Artemisia. When the mixed deciduous forest comes back 1000 years later, its structure is changed. This non-return to the initial state is probably the consequence of the long duration and the intensity of cooling of the Montaigu event. During the warmest period of the last glaciation (OIS 3), alternately warm and cold phases are recorded. The cold events (Heinrich events) are characterized by an expansion phase of an arctic grassland. The temperated phases (Dansgaard-Oeschger cycles) are characterized by a return of a boreal forest. At Les Echets, the duration of Heinrich’s events varies from 475 and 1150 years, that of the Dansgaard-Oeschger cycles varies from 123 and 583 years. The multi-method climatic reconstructions undertaken on the OIS3 des Echets have just shown that the coldest temperatures of the year controled whether the forest ecosystems survived in situ or not (unpublished). The classical methods of climatic reconstruction used at Les Echets, and the more innovative method based on Archaea showed that, during OIS3, the TMA (Annual Average Temperatures) were high (between 7 ° and 11 ° C) during temperate OIS3 episodes, and low during cold Heinrich (0 ° to 2 ° C). This work was undertaken as part of an international consortium, the Echets Working Group, in which several expertise in biology, geology and statistics are involved.

2 - The effects of man-made disturbances on natural environments during temperate periods.

I work on the relationships between biological events revealed by sedimentary records and the history of human populations that can impact the natural environment (forest expansion during periods of war or social instability ; decline of the forest during phases of social stability and demographic optimum ; introduction of foreign plants during commercial exchanges). Thanks to the cross-study of several markers, we have obtained interesting results. 1) we evidenced, between the 5th and the 19th century AD, a phase of hemp cultivation in the paleolacustrine archives of Aydat (Massif Central, France), resulting in an hyper-eutrophication of the lacustrine waters in which retting of this plant was carried out (Lavrieux et al., 2013) ; 2) we discovered fossil Cannabidiol, a molecule of hemp, in this same serie of Aydat (Lavrieux et al., 2013) ; 3) we identified and dated the cultivation of teasel in the Lower Rhone Valley (SE of France, Andrieu-Ponel et al., 2000). It started during Middle Ages, between 1 035 and 1 206 AD and stopped in the 1950 AD ; 4) the ancient practice of cereal farming in Provence was identified at Courthézon (SE France), and dated to ca 5000 uncal BP. Cereal cultivation was without dramatic consequences on the Mediterranean forest ecosystems that healed after each episode of clearing ; 5) we worked in the Tiber delta (region of Roma) and we identified the dramatic impact of upstream deforestation on the functioning of the ancient port of Rome (thesis of C. Pepe) ; 6) we identified the poorly diversified forest ecosystems that develops in Malta from 7000 BP and the early impact of agro-pastoral activities on vegetation (B. Gambin’s thesis) ; 7) In Persia, we observed that agricultural practices (pastoralism, fruticulture) differ from one civilization to another during the last 5000 years (thesis and post-doctorate of Mr. Djamali) ; 8) In Crete, we highlighed a freshwater lake (not salt water) in the downstream part of the alluvial plain of Messara (Crete), near the Minoan town of Phaistos, which may explain the duration of occupation of the site and the prosperity of the inhabitants who lived there between 3200 to 2600 cal BP (end of the Minoan period to the Geometric period) (Ghilardi et al., 2018) ; 9) In Uzbekistan, we identified paleo-vegetations (riparian forest with willows and poplars) and farming systems (cereal crops including rye and grapevine, breeding of herbivores with spores of coprophilous fungi) in the Bukhara oasis (Fouache et al., 2016 and in press). Datings are in progress. I am also working on other sites in Asia, Iran (Persepolis region) and Nakhchivan (Eastern Caucasus) (Marro et al., in progress), research is ongoing.

3 - The landscapes of the oldest hominins in the eastern Mediterranean : the sources of the Neolithic Revolution

In SW Turkey, the oldest Homo erectus is dated to 1.6 - 1.2 Ma (Lebatard et al., 2014), documenting the migratory axis of Hominin populations from Africa to Europe. In the same area, we have access to an exceptional lacustrine archive (more than 1000 m of sedimentary cores dated 2.5-Ma), and palaeontological sites rich in megafauna. Never, on the continent, an old archive has been preserved in such a context that allows us to study the biological, geological and palaeoanthropological components in order to reconstruct in a systemic and interdisciplinary approach : 1) the interrelations and feedbacks between the different actors responsible for the functioning of environments in a geological context dynamic (tectonics, volcanism) ; 2) the main quaternary climate cycles to be situated within regional and global climate records and models ; and 3) the dynamics of ecosystems (vegetation, fauna, hominins), as well as the climate of this key region of the Eastern Mediterranean. We will extend this approach, to other sites in Europe (France, Italy, Spain) that were frequented by Hominins and herds of large mammals from 2 Ma. We will use an interdisciplinary approach combining concepts and techniques of life sciences (biology, ecology, paleogenetics), earth sciences (geology, geophysics, isotope geochemistry) and human sciences (paleontology, archeology, ethnology). The consortium ACIGOL that we have built is up to the ambition of the project and brings together internationally recognized specialists from the universities of Leipzig and Freiburg (Germany), Pamukkale and Izmir (Turkey), Aix-Marseille, Montpellier and Perpignan, the National Museum Natural History of Parisand various CNRS or CEA laboratories (IMBE, ISEM, LSCE).