Saltmarsh deposition and its relationship to coastal forcing over the last century on the north-west coast of Ireland

Abstract

The mesoscale (time) control of annual storm-surge activity on quasi-annual saltmarsh (tidal marsh) deposition is studied from two estuarine saltmarshes on the high-energy NW coast of Ireland. Both saltmarshes exhibit a cliffed edge where maximum sedimentary variation is expressed in the form of lamination. Sections were logged and characterised by lithofacies based on grain-size determinations. Sections dated using Cs and Pb determinations indicated deposition records of decadal to century scale (c. 0.5 cm a-1). Linear multiple regression explains (p< 0.05) half the variation of the deposition rate by annual coastal forcing (surge frequency and magnitude) and sediment modes (coarse silt to clay). Further variability in deposition rate is partially reflected in the non-linear response between forcing and deposition that is affected by mesoscale (30, 11 and 5-year) periodicities in forcing. Increased annual surge activity appears to be associated with a coarsening of, and reduction in annual deposition. A relationship between annual deposition rate and fractal dimension of surge timing (i.e. the clustering of surge events) is identified.