Holocene salt‐marsh sedimentary infilling and relative sea‐level changes in West Brittany (France) using foraminifera‐based transfer functions

Abstract

International audienceIn order to reconstruct the former sea-levels and to better characterize the history of Holocene salt-marsh sedimentary infillings in West Brittany (western France), local foraminifera-based transfer functions were developed using Weighted-Average-Partial-Least-Squares (WA-PLS) regression, based on a modern dataset of 26 and 51 surface samples obtained from salt-marshes in both the bay of Tressseny and the bay of Brest. Fifty cores were retrieved from Tresseny, Porzguen, Troaon and Arun salt-marshes, which were litho- and biostratigraphicaly analyzed in order to reconstruct palaeoenvironmental changes. A total of 26 AMS 14C age determinations were performed within the sediment successions. The Holocene evolution of salt-marsh environments can be subdivided into four stages: (1) a development of brackish to freshwater marshes (from c. 6400 to 4500 cal. a BP); (2) salt-marsh formation behind gravel barriers in the bay of Brest (from 4500 to 2900 cal. a BP); (3) salt-marsh erosion and rapid changes of infilling dynamics due to the destruction of coastal barriers by storm events (c. 2900-2700 cal. a BP); (4) renewed salt-marsh deposition and small environmental changes (from 2700 cal. a BP to present). From the application of transfer functions to fossil assemblages, 14 new sea-level index points were obtained indicating a mean relative sea-level rise around 0.90±0.12 mm a-1 since 6300 cal. a BP

Multiple Stable States and Catastrophic Shifts in Coastal Wetlands: Progress, Challenges, and Opportunities in Validating Theory Using Remote Sensing and Other Methods

“…Much of this coastal population is directly or indirectly affected by coastal flood risks, even as such risks might be mitigated by forward-thinking coastal wetland management and preservation [7]. Stratigraphic and paleoecological evidence documents that coastal wetlands have adapted to marine transgressions and regressions throughout the Holocene [8][9][10][11][12][13]. Hence, coastal wetlands appear to be self-sustaining ecosystems despite human, climate, and sea level impacts.…”

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

“…The first recorded assemblage is characterized by high percentages of non-calcareous taxa (Trochammina inflata and Jadammina macrescens), while the second type of foraminiferal assemblage is characterized by the dominance of calcareous taxa (Astergerinata mamilla, Haynesina germanica, Elphidium williamsoni, and Lobatula lobatula). From an ecological point of view, it has already been shown that non-calcareous species dominate in the upper part of the salt marsh in Brittany (Rossi et al, 2011;Stéphan et al, 2015) while calcareous foraminifera dominate in sub-tidal, tidal, and marine environments (Liu and Fearn, 1993;Collins et al, 1999;Scott et al, 2001;Murray, 2006). Even if the stratigraphy of GL1 is not robust enough, this sediment sequence is evidence that the downstream part of the Guidel marsh was submitted to continuous marine influences over the last 7000 cal BP (Fernane, 2014) with a high tide level close to −7 m NGF (Goslin et al, 2013;Goslin, 2014).…”

Coastal barrier stratigraphy for Holocene high-resolution sea-level reconstruction

“…1 mm/yr after the inflection at ca. 6 ka6364 while reconstructions from the western Netherlands document greater rates (8 m of sea-level rise after 7 ka) without a clear inflection point but a continuous attenuation rate. Goslin et al 65.…”