HOLOCENE CLIMATE CHANGE IN WESTERN IRELAND: EVIDENCE FROM THE OSTRACOD POPULATIONS OF LOCH INCHIQUIN

Holocene climate has varied over decadal to millennial time scales and has included many significant fluctuations. The most notable of these fluctuations is the Younger Dryas event (~10 to 11ka), which approximately marks the boundary between the Pleistocene and Holocene epochs. In an 8 m core from Loch Inchiquin in western Ireland, a 0.2 m thick grey clay that interrupts a period of marl deposition marks the Younger Dryas Event. In the 5.4 m thick marl deposited following the Younger Dryas event, there are a few organic-rich intervals before a 1.2 m thick peat occurs at the top of the succession. The upper third of the peat is marked by a relative increase in carbonate followed by a thin layer of organic material in the 0.1 m below the surface of the present day lake shoreline.

Four ostracod genera are present in the Loch Inchiquin sediment: Limnocythere, Candona, Heterocypris?, and Metacypris. Limnocythere occurs in relative abundance with shallow infaunal bivalves in the clay-rich marl directly preceding and following the Younger Dryas event and in the carbonate-rich layer in the upper part of the peat. Limnocythere is rare or absent throughout much of the remaining marl deposits where total ostracod population counts increase dramatically and Heterocypris? and Candona dominate. A relative abundance of Limnocythere is interpreted to reflect a combination of changes in lake depth, temperature, and climate, and may specifically represent a shift to deeper, cooler, and/or more arid conditions.