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

Abstract

International audienceRelationships 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. (C) 2015 Elsevier B.V. All rights reserved

Oceanic versus continental influences over the last 7 kyrs from a mid-shelf record in the northern Bay of Biscay (NE Atlantic)

“…As a first general observation, the first clear retreat of mixed temperate forest was recorded between 4.5 and 4 ka BP, indicating the beginning of the landscape opening and onset of inland agro-pastoral practices (as shown by the presence of ruderal plants such as Rumex and P. lanceolata accompanied by first low Cerealia occurrences, Figure 10). This is consistent with other pollinic studies carried out in north-western France (e.g., Gaudin, 2004;David, 2014;Fernane et al, 2014Fernane et al, , 2015, i.e., with the transition from the Neolithic to the Bronze Age cultural periods (Figure 10). The next major step in landscape opening dynamics occurred at the Bronze to Iron Age transition, shown well by the increase of ruderal and cultivated plants, as well as by a higher "dinocyst (without L. machaerophorum) to pollen" ratio (Figure 10).…”

Palaeoenvironmental reconstructions during the Meso- to Neolithic transition (9.2–5.3 cal. ka BP) in Northwestern France: Palynological evidences

“…On a regional scale, recent studies reconstructed and quantified the post-glacial sea-level rise on Brittany's coasts (Goslin et al, 2013(Goslin et al, , 2015Stéphan et al, 2015;García-Artola et al, 2018), estimated from about 10 to 15 mm/year between the end of the last glacial period and 9,000 years cal BP to around 4.6 mm/year between 7,500 and 6,500 years cal BP, and less than 1 mm/year after 6,000 years cal BP. Moreover, palaeoecological data recently acquired on Holocene Brittany's coastal sequences discussed past environmental variations (vegetation changes, palaeo-storm dynamics, precipitation regimes) and linked these rapid coastal changes with climate dynamics as well as human occupation on watersheds (Fernane et al, 2014(Fernane et al, , 2015. These studies especially focused on the Neolithic, a period when the development of agro-pastoral societies became more and more pronounced (Visset and Bernard, 2006;Pailler et al, 2011).…”

“…yr BP. Moreover, palaeoecological data recently acquired on Holocene Brittany's coastal sequences discussed past environmental variations (vegetation changes, palaeo-storm dynamics, precipitation regimes) and linked these rapid coastal changes with climate dynamics as well as human occupation on watersheds (Fernane et al, 2014(Fernane et al, , 2015. These studies especially focused on the Neolithic, a period when the development of agro-pastoral societies became more and more pronounced (Pailler et al, 2011;Visset and Bernard, 2006).…”

Sedimentological and palynological records since 10 ka BP along a proximal-distal gradient on the Armorican shelf (NW France)

“…Superimposed on these natural forcings, Holocene paleoenvironments are impacted by the evolution of human societies (i.e., cultural and technical changes), especially since the start of the Neolithic (i.e., ~7 ka BP in Brittany; Pailler et al, 2008). The related landscape changes are mainly recorded thanks to palynological data highlighting the progressive deforestation and the introduction and intensification of the agro-pastoral activities thanks to Anthropogenic Pollen Indicators (API) (e.g., Marguerie, 1992;Visset et al, 1995Visset et al, , 1996Gaudin, 2004;Visset and Bernard, 2006;Naughton et al, 2007;Fernane et al, 2014Fernane et al, , 2015Penaud et al, 2020). In parallel with terrestrial bio-indicators (pollen grains), aquatic bio-indicators (dinoflagellate cysts or dinocyts) allow discussing surface water evolution through time linked with sea level variations or leaching of nutrients from soils to coastal waters (e.g., Lambert et al, 2018;Penaud et al, 2020).…”

“…Secondly, this study aims at understanding palynological signatures along a proximal-distal gradient from coastal (Lambert et al, 2019; this study), mid-shelf (Naughton et al, 2007) to deep marine environments (Zumaque et al, 2017;Fersi et al, in prep) on the 8.5-8.3 ka BP interval. Finally, the API detection is discussed from continental (South Brittany maritime marsh; Fernane et al, 2015) to Armorican shelf environments (Penaud et al, 2020; this study) over the last 7 kyrs BP taking into account anthropogenic and natural forcing.…”