Early Holocene vegetation and climate dynamics with particular reference to the 8.2 ka event: pollen and macrofossil evidence from a small lake in western Ireland

Abstract

A detailed, AMS 14C-dated, pollen record from Cooney Lough, a small lake in Co. Sligo, western Ireland, is presented. Fluctuations in the pollen curves, indicative of changes in pollen productivity and shifts in woodland composition, suggest that the period spanned by the record (9.4–6 ka) was characterised by considerable climate instability. In all, five climate anomalies are recognised (CA-1 to CA-5). The most pronounced anomaly, CA-3, is dated to 8.45–8.2 ka, with the high point of that anomaly (CA-3b) centred on 8.2 ka and lasting about a century. On the basis of age, and also intensity and structure, CA-3b is equated with the 8.2 ka event as recorded in many proxies and especially the Greenland ice-core δ18O records. Key features of the event as recorded in the lake sediments include increased representation of Betula and Pinus (birch and pine; both widely recognised as cold tolerant trees) and a decline in Corylus and also Quercus (hazel and oak; both thermophilous). The anomalies CA-1 and CA-2 precede the 8.2 ka event, the former corresponding probably to the 9.2 ka event and the latter more pronounced, centred on ca. 8.8 ka and with a duration of approximately 100 years. The CA-4 event, at ca. 7.5 ka, is relatively minor as regards intensity while CA-5, which began at ca. 7.1 ka, initiated what seems to be a more long-lasting shift towards cooler conditions. The relationship of these developments to the arrival and expansion of alder (Alnus), a key feature of the Boreal/Atlantic transition in European, including Irish pollen records is also discussed.