Holocene stable-isotope stratigraphy at Lough Gur, County Limerick, Western Ireland

Abstract

After the pronounced fluictuation of 4‰ in δ18O during the Younger Dryas and the 1‰ dip during the Preboreal Oscillation, values for δ18O decreased very steadily from -2.5 to -5.3‰ from 9300 to about 800014C yr BP (uncal.). This early-Holocene decrease of almost3‰is interpreted as a result of a declinle of almost 6°C in the temperature of precipitation. The previous high temperature of much of the Lateglacial and the Preboreal (12000-9300 yr BP uncal.) may reflect warm summers related to greater insolation and warm winters caused by the influence of the Laurentide ice sheet on atmospheric circulation. After 8000 yr BP a disconformity interrupts the sequence, but after about 5000 yr BP the δ18O and δ13C are irregular because of a low lake level, as shown by the occurrence of littoral shells and woody detritus in the littoral core, and because of anthropogenic factors, as inferred from pollen indicators of forest disturbance and farming found in both the littoral and offshore cores.