Rapid climate changes and human dynamics during the Holocene in the Eastern Mediterranean (Lower Strymon Valley, northern Greece)

International audienceThe study was conducted in the southern part of the lower Strymon valley, in northern Greece, and revealed up to 25 m of fluvio-lacustrine sediments deposited over the last seven millennia. This sedimentary record represents a significant opportunity for high-resolution palaeoenvironmental studies of the period from 6 to 3 ka cal BP linked to land use and climate change. The results of geophysical investigations, multi-proxy sedimentological (grain size, magnetic susceptibility, loss-on-ignition), pollen and NPP analyses, based on high-precision radiocarbon dating enabled reconstruction of past landscapes as well as a comprehensive discussion of anthropogenic responses and their impact on the vegetation cover, especially during periods with well-known Holocene Rapid Climate Change events (5.6, 4.2 and 3.2 ka cal BP). During the 7-5.7 ka cal BP corresponding to the Late and Final Neolithic, wet conditions created an extended lake surrounded by the densely wooded Strymon watershed, followed by a shift to a shallower lake environment that lasted until ca. 4.5 ka cal BP. The continuous presence of anthropogenic taxa suggests the persistence of human activities even in the absence of formally recognized sites, suggesting the relocation of settlements. The first signs of human disturbance of the landscape at regional scale occurred toward 5.2 ka cal BP (onset of the Early Bronze Age). The so-called « 4.2 ka BP event », which coincided with the end of the Early Bronze Age and the transition to the Middle Bronze Age, is divided into three distinct periods (4.35-4.1, 4.1-3.95 and 3.95-3.75 ka cal BP). The first corresponds to gradual aridification before a period with severe dry conditions that marks a tipping point toward wetland contraction. From this period on, diversification, and multiplication of anthropogenic species including Olea, Juglans and Castanea reflect a global trend toward cultural landscapes. The later periods are characterized by dramatic climatic change around 3.2-3 ka cal BP, at the end of Late Bronze Age, and increasing impacts of agro-pastoral activities and forest clearing starting at the beginning of Antiquity, around 2.8 ka cal BP (Thracian period). After the 4.2 ka cal BP event and we suggest that climatic adversity may have acted as a stimulus to innovation and relocation rather than retarding societal development in the region. To conclude, environmental factors in the lower Strymon valley were not sufficient on their own to trigger a social crisis similar to that mentioned in the Middle East