Holocene paleoenvironmental reconstructions in western Brittany (Bay of Brest): Part II – A 7 kyr human-environment story with a focus on the Neolithic-Bronze Age transition

Abstract

The Bay of Brest (BB, NW France) is a semi-enclosed basin of 180 km² subject to macro-tidal dynamics and to the fluvial influences of the rivers Aulne and Elorn, which combined drain watersheds of 2600 km². This coastal environment is subject to natural climate oscillations overlaid on the long-term landscape transformations inherited from the post-glacial sea level rise and increasing anthropogenic forcing since the Neolithic (6.9 ka BP), and especially from the Bronze Age (4.2 ka BP) onwards. The BB therefore appears suitable for the reconstruction of the interactions between climate, environment and human dynamics across the Holocene. In this study, a palynological stack was created based on five cores (including two new cores PALM-KS05 and PALM-KS06 from the Brest harbour), allowing us to discuss vegetation dynamics over the last 7 kyrs. Since the Neolithic period, the forest cover has decreased in favour of open and agro-pastoral landscapes. This trend is not uniform, however: forest cover first declined slowly around 4 ka BP, then strongly decreased at the end of the Iron Age, before experiencing a revival of about five centuries at the end of the Roman period (1.7–1.2 ka BP). Finally, a drastic fall of tree pollen taxa is recorded at the start of the Middle Ages. This study is the first on long-term Holocene trends that allows discussion of both climatic and anthropogenic forcing at an unprecedent average study resolution of 35 years. We also place this local evolution in a wider context to detail interactions between natural and anthropic forcings over the last 7 kyrs BP at a regional-scale and we discuss paleoenvironments and human dynamics thanks to the incorporation of an up-to-date corpus of archaeological data.