Contemporary process controls on the evolution of sedimentary coasts underlow to high energy regimes: western Ireland

Sedimentary environments, representative of the Irish west coast, have been studied to examine their responses at the microscale (10(-1)-10(0) yr). Th is was achieved using a variety of techniques, including grain-size analysi s, measurement of accretionary responses and radiometric dating. Monthly el evation monitoring of silt-dominated marshes shows an annual pattern in sed iment accumulation. This reflects two processes: a) winter accretion attrib utable to storm events, and b) summer consolidation and contraction of the marsh sediments. Together, the results suggest that intertidal sedimentatio n is likely to be dominated by episodic processes, primarily storms. Examin ation of the tidal regime shows a weaker than expected influence of hydrope riodicity on intertidal accretion, although this influence remains distinct ive, as expressed by a landward textural fining. Storms were also identifie d as of major importance in the functioning of higher-energy sandy coastal systems, again having a largely accretional influence, primarily through ae olian transport. Erosion at such study sites is probably controlled by the attainment of a critical threshold surface elevation, or by exceptional sto rm action, or a combination of both. The linking of microscale sedimentatio n rates with those at the meso- to macroscale, and assessment of their impo rtance for coastal functioning, is difficult due to the geological averagin g effect of the sedimentary record. Human impacts on this coast in historic al times are large but difficult to quantify.