HOLOCENE CLIMATE CHANGE IN WESTERN IRELAND: A PALEONTOLOGICAL AND GEOCHEMICAL PERSPECTIVE

A comprehensive study of the freshwater mollusks and ostracodes contained in the sediment of Lough Carra, in County Mayo, western Ireland provides information regarding regional climate change as well as information pertaining to the North Atlantic Oscillation (NAO) over the last 2 ka. An examination of the various species present in sediment cores from the lake and their relative abundances throughout the cores, combined with the isotopic data obtained from the mollusk shells, provides an opportunity to record changes in climate. Lough Carra, a temperate, 14 km.², freshwater lake, with an average depth of 1.75 m lies in close proximity to the Atlantic coast of Ireland. High precipitation amounts, trivial rain fractionation, and limited ground water input cause the lake to reflect the existing d¹⁸O values of the North Atlantic, thus rendering it an advantageous location to study climate change. Carboniferous limestone composes the bed rock of the 104 km.² catchment area, providing little to no siliciclastic material to the lake. Four cores with lengths ranging from 82 cm to 218 cm were taken from the lake marl with a push core device. The mollusks present, as well as their corresponding geochemical data, have been analyzed for all four cores. The ostracode assemblages have been examined in the most biologically diverse core. All mollusks and ostracodes were counted and classified for every fifth centimeter. The d¹⁸O and d¹³C values, and Ca:Mg and Ca:Sr ratios have been determined in the same intervals. The elemental ratios and stable isotope data have been analyzed from the gastropod genus Bulimus, and the bivalve genus Pisidium. Geochemical data, coupled with environmental interpretation of the lake’s fauna, provides corroborative accounts of lake temperature, salinity, and nutrient characteristics over a period of approximately 2 ka. Comparison with faunal assemblages and temperature proxies of similar climates in North America yields valuable information regarding recent changes in the NAO and the ensuing effects on global climate variability.