Mid- and late-Holocene environmental change in western Ireland: New evidence from coastal peats and fossil timbers with particular reference to relative sea-level change

The results of radiocarbon dating and dendrochronological investigations of timbers (mainly pine and oak) preserved in coastal peats on the Atlantic coast of mid-western Ireland are reported. These are complemented by the results of pollen analytical investigations, including a detailed pollen profile from Lough Atalia, a brackish lake located within present-day Galway city and immediately to the east of the medieval town. The results from the fossil timber investigations show that pine stumps exposed on coastal intertidal peats in mid-western Ireland date mainly to ca. 3000 BC, that is, they are coeval with the so-called ‘pine flushes’ on blanket bog in western Ireland. Many of the oak timbers are considerably older while an oak on peat in Turlin Bay, near Silverstrand, persisted until ca. 2100 BC. This fossil timber record, taken in conjunction with the pollen records, suggests conditions very different to those pertaining at present, including absence of direct marine influence because of relative sea levels (RSLs) that were probably at least 2 m, and possibly up to 4 m, lower than at present. Mid-Holocene conditions were less stormy, and lower precipitation and/or higher evapotranspiration facilitated tree colonisation of peat surfaces. Intertidal peat layers at Salthill show that present-day RSL began to be approached at ca. AD 500. This agrees with the evidence from An Loch Mór, Inis Oírr, which indicates that salinity in this brackish lake began to increase noticeably at/immediately prior to ca. AD 1000. A notable feature of the pollen record from L. Atalia is a yew (Taxus)-dominated woodland phase of ca. 600 years duration centred on 2550 BC. A major and widespread expansion of yew at about this time is a distinctive feature of mid-Holocene woodlands in western Ireland.