Importance of coarse sedimentation events in the resilience of microtidal back-barrier saltmarshes to sea-level rise

Type Article
Date 2022-05
Language English
Author(s) Goslin JeromeORCID1, 2, Bernatchez P.2, Barnett R.L.2, 3, Ghaleb B.4, Béland C.2, Didier D.2, Garneau M.4
Affiliation(s) 1 : Geo-ocean, IFREMER, 29880 Plouzané, France
2 : Chaire de recherche en géoscience côtière, Université du Québec à Rimouski, Québec-Océan et Centre d'études nordiques, Rimouski, Québec G5L 3A1, Canada
3 : Geography, College of Life and EnvironmeFntal Sciences, University of Exeter, Amory Building, Rennes Drive EX4 4RJ, UK
4 : Chaire de recherche sur la Dynamique des Ecosystèmes Tourbeux et Changements Climatiques, Université du Québec à Montréal, Centre GEOTOP, Montréal, Québec H3C 3P8, Canada
Source Marine Geology (0025-3227) (Elsevier BV), 2022-05 , Vol. 447 , P. 106793 (25p.)
DOI 10.1016/j.margeo.2022.106793
Keyword(s) Sandy barrier, Saltmarshes, Sea-level, Accretion rates, Resilience, Washover, Storminess

An improved understanding of the resilience capacity of salt-marsh environments, which are recognized as one of the most vulnerable yet valuable coastal morpho-sedimentary systems is important for enhancing resilience to future sea-level rise. The aim of this study is to provide a long-term (multi-centennial) context to the capacity of response of saltmarsh environments to relative sea-level rise by reconstructing the accretion histories of two microtidal back-barrier (one aggradational and one transgressive) saltmarshes in the Bay of Gaspé (Québec, Eastern Canada) over the last centuries. Particular emphasis is put on coarse minerogenic sedimentation and the role it played in the response of the two marshes to relative sea-level changes. To do so, lithostratigraphic, geochronological, and geochemical analyses are carried out on sedimentary cores taken in the back-barrier marsh areas. The accretion histories and the chronology of coarse deposition upon the marshes are reconstructed and yield the following two main results: (1) Coherent yet contrasting records of coarse sedimentation histories are obtained for the two sites, which relate to the distinct configurations and functioning of the fronting barrier systems. The coarse sedimentation time-series of both marshes carry pluri-decadal periodicities typical of atmospheric and intra-oceanic modes of variability, as well as periodicities of 18.0 to 18.5 years, which are interpreted as the expressions of the influence of the 18.6-year nodal tidal cycle. (2) We observe intra- and inter-site variations in the accretionary behavior of the two systems as well as in their respective histories of coarse minerogenic deposition. We show that coarse sedimentation at the surface of the two marshes has been crucial for maintaining accretion rates both in minerogenic and organogenic environments, and thus for allowing saltmarshes to build a resilience capacity in a regime of relative sea-level rise.

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