Importance of coarse sedimentation events for maintaining back-barrier salt-marshes resilience to sea-level rise
|Author(s)||Goslin Jerome1, 2, Bernatchez Pascal2, Barnett Robert3, Ghaleb Bassam4, Beland Charles2, Didier David2, Garneau Michelle4|
|Affiliation(s)||1 : Ifremer - Geosciences Marines
2 : Université du Québéc à Rimouski - LDGIZC
3 : University of Exeter
4 : Université du Québec à Montreal - Geotop
|Keyword(s)||saltmarshes, sea level, storminess, washover, accretion, resilience|
The aim of this study is to provide a long-term (multi-centennial) context to the resilience capacity of salt-marsh environments by reconstructing submersion event histories at two back-barrier (one aggradational and one transgressive) salt marshes in the Bay of Gaspé (Eastern Canada). Lithostratigraphic, geochronological and geochemical analyses were carried out for both sites to identify coarse sedimentation events and derive salt-marsh accretion rates. Coherent yet contrasting records of sedimentation histories were derived for the sites, which relate to the distinct configurations and functioning of the two barrier-system types. A periodicity of 18 to 18.5 years is identified in the frequency of coarse sedimentation events within both sedimentary archives, which is interpreted to be an expression of the influence of the 18.6 year nodal tidal cycle on tidal amplitude. We further observe variations in the accretionary behaviour of the two systems, which we identify as differences in sedimentary response pathways to sea-level rise and storm events, as a function of site morphology. Coarse sedimentation events associated with washover deposits are crucial for maintaining long-term accretion at the transgressive barrier site, whereas such events are part of the modal accretionary behaviour at the aggradational barrier site. We identify the clear importance of coarse sedimentation events for maintaining accretion rates, particularly in mature marsh environments, and for building resilience capacity against sea-level rise.
1) First worksheet of the .xls file is entitled "Grain-size and Age data". It presents the age and grain size data obtained along the two cores that served for the study : core PEN ST 3-1 retrieved from Penouille marsh and core SB-ST-M1 retrieved from Sandy Beach marsh (see fig.1 of the publication for core locations).
The data for each core are presented one below the other and are displayed in the following order. Column A is the depth of the analyzed sample in core in cm. Cores were sampled at 1-cm steps so a depth of e.g. 0.5cm means that the sample contains the 0-1cm depth interval. Column B contains the modelled age data, as derived from the mixed 210Pb and 14C age models obtained for the cores, descride in the figures 6 and 10 of the article, respectively. Colum C and D are the grain-size data that served at reconstructing the coarse sedimentation events.
2) Second worksheet of the .xls file is entitled "accretion data". It displays accretion data for the Penouille and Sandy Beach marshes as derived from the analysis of the PEN-ST 3-1 and SB-ST M1 cores, respectively.
Data for each core are again shown one below the other. Column A is the depth in core in cm, column B is the age of teh deposit in years C.E., column C shows the evolution of the elevation of the marsh surface (in m NAD 83), column D is the grain size in µm, column E the Loss-on-Ignition (4.5H at 550°C), column F & G show the accretion rates (in mm.yr) and the deposition rates (kg m-2 yr-1), respectively. Last column (column H) show the sea-level data for each core level, as originally published by Barnett et al. (2019).