Climate variability and storm impacts as major drivers for human coastal marsh withdrawal over the Neolithic period (Southern Brittany, NW France)

Abstract

Relationships between climate variations, vegetation dynamics, and early human activities during the Neolithic have been reconstructed from high-resolution pollen and foraminiferal records obtained from cores retrieved from coastal wetland located in southern Brittany (Guidel, NW France). Our data show that the area around Guidel corresponded to a dense temperate forest locally replaced by riparian forest in the marsh, without any human disturbance during the early Neolithic. During the mid-Neolithic, between 6500 and 5500 cal years BP, the first episode of probable human settlement is recorded, as suggested by the increase of anthropogenic plants. This early record of human impact is consistent with archeological studies that find a high concentration of funeral monuments around Guidel during this cultural period. This complex first phase is interrupted by the disappearance of anthropogenic influence coinciding with a cold/humid climate period in the region characterized by recurrent major storms. Then, at the transition between the middle to late Neolithic, at 5500 cal years BP, a second phase of human retreat is signaled by both vegetation dynamics and archeological records; this interval also coincides with a climatic deterioration marked by cold/humid conditions recorded in the region (Sorrel et al., 2012). The results of the present study imply that human settlement/departure over the Neolithic was probably influenced by climatic variations. During the Bronze Age, Iron Age, and Middle Ages, a progressive decline of the arboreal forest synchronous with an increase of anthropogenic plants, confirms the high and persistent human activity around the site. Furthermore, our results at Guidel suggest a different anthropogenic trend recorded between north and south Brittany. The human impact is well recorded during the Neolithic at Guidel, while in northern Brittany human settlement is not recorded before the Bronze Age, consistent with existing archeological data.