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

The mesoscale (time) control of annual storm-surge activity on quasi-annual saltmarsh (tidal marsh) deposition is studied from two estuarine saltmarsh es on the high-energy NW coast of Ireland. Both saltmarshes exhibit a cliff ed edge where maximum sedimentary variation is expressed in the form of lam ination. Sections were logged and characterised by lithofacies based on gra in-size determinations. Sections dated using Cs and Pb determinations indic ated deposition records of decadal to century scale (c. 0.5 cm a(-1)). Line ar multiple regression explains (p < 0.05) half the variation of the deposi tion rate by annual coastal forcing (surge frequency and magnitude) and sed iment modes (coarse silt to clay). Further variability in deposition rate i s partially reflected in the non-linear response between forcing and deposi tion that is affected by mesoscale (30, 11 and 5-year) periodicities in for cing. Increased annual surge activity appears to be associated with a coars ening 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.