Ayre o Swinister

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This spectacular double bar and lagoon complex comprises the North Ayre, the South Ayre and the intertidal area of the Houb. Small marsh remnants line the interior face of the South Ayre, passing inwards into a small area of inter-tidal flat. An originally more extensive marsh has virtually disappeared, exposing a peat substrate which extends between and perhaps underneath the double South Ayre. The intertidal area is better classed as an intertidal peat flat, on which cracks readily develop as drying out proceeds during the lower tidal cycles. On the eastern shore of the Houb, peat overlies glacial tills and extends below the high water mark. The peat contains tree boles with trunks and bases at least 30 centimetres in diameter. These trees stumps are clearly in their original growth position. The whole feature displays the result of shoreline regularisation by bars which have enabled sedimentation, but which in turn are washed over and the materials driven inwards as submergence proceeds (Smith in Birnie et al., 1996).

Coring by Jackie Birnie of one of the uncut peat areas in the lagoon showed approximately three metres of organic material overlying grey, gritty clay. The sediment had accumulated under fen or bog conditions. Birch pollen reached 48 per cent of the total 2.3 metres from the surface, followed by a peak in willow and then the dominance by Calluna from 1.75 metres. A radiocarbon date of cellulose from birch fragments at 1.6 metres below the surface gave an age of 4586±40 BP. Ayre of Swinister provides an important record of local environmental change, principally dominated by changes in the water table controlled by the formation of the complex coastal features.