Coastal palaeoenvironmental record of the last 7 kyr BP in NW France: Sub-millennial climatic and anthropic Holocene signals

To date, Holocene palaeoecological signatures on the Northwestern coast of France have not been thoroughly investigated. In this study, environmental changes related to both climate processes and human disturbances were reconstructed over the last 7000 cal. yr BP, based on pollen and chironomid assemblages from four coastal cores retrieved in Western Brittany (Porsmilin beach, NW France). Pollen and chironomid records show an environmental response to both millennial- and centennial-scale climate changes. During the mid-Holocene (until around 4200 cal. yr BP), when human impact was low, Porsmilin’s landscape was characterized by a mixed oak forest dominated by Corylus trees. Comparison of our data with other palynological data from the NW French Atlantic coast shows that this dominance may be related to more humid conditions prevailing at Porsmilin. Furthermore, over the mid- Holocene, Corylus and Quercus patterns appear anti-correlated, with Quercus declines appearing synchronous with major storms revealed by data recently compiled for the Holocene in Brittany, suggesting that cold conditions probably caused the Quercus contractions, which in turn favoured the rise of the heliophile taxon Corylus . Regarding chironomids over this period, our results show variations in lotic–lentic taxa related to hydrological conditions, more specifically changes in river run off strength. Over the Late Holocene, the Porsmilin palynological record shows progressive vegetation changes mainly related to human settlement and development of agricultural activities.