HIGH-RESOLUTION HOLOCENE CLIMATE VARIABILITY AT LOUGH INCHIQUIN, WESTERN IRELAND: EVIDENCE FROM STABLE CARBON AND OXYGEN ISOTOPE VALUES OF LACUSTRINE SEDIMENT

A 7.5m square piston core was retrieved and analyzed for lithological characteristics, loss on ignition, and subsampled for radiometric dating as well as stable carbon and oxygen isotopes. Loss on ignition reveals that calcite content is ~75%, except during the early Holocene and ~1.5m of peat at the uppermost portion of the core. Stable isotope analyses were conducted at 1 cm intervals (~15 year resolution) throughout the core while areas that display rapid or large isotopic change are sampled at a 2mm resolution (~3 year resolution). Because calcite is biologically mediated during summer months, carbonate isotope values represent a summer climate signal. d¹⁸O values that vary by up to 5‰ are interpreted to predominantly reflect changes in the isotope value of lake water as this variation is too large to represent changes in temperature alone. We suggest that d¹⁸O values of lake water are controlled by changes in the circumpolar vortex that alter the source of moisture and therefore precipitation d¹⁸O values. Significant negative shifts in d¹⁸O values occur during periods of known rapid climate change such as the Younger Dryas, 8.2 ka Cold Event, and the Piora Oscillation most likely as a response to expanding circumpolar vortex. d¹³C values display a very large range (~10‰), following the end of the Late Glacial and the Younger Dryas periods. This is likely a result of changes in the d¹³C value of lake water DIC related to an influx of carbon from surrounding bedrock of Visean Carboniferous limestone (d¹³C=+3.2‰VPDB). Above ~10 ka, DIC d¹³C values appear to be controlled by terrestrial and lacustrine vegetation. d¹⁸O values of sediment organic matter are used to generate an independent record of lake water d¹⁸O that coupled with d¹⁸O values of carbonate provides a summer-temperature time-series through the Holocene.