Multidisciplinary investigations, including stable-isotope studies, of thick Late-glacial sediments from Tory Hill, Co. Limerick, western Ireland

Abstract

Multidisciplinary investigations of a 10-m-long, marl-rich, Late-glacial core from Tory Hill, Co. Limerick, have enabled environmental change, including estimates of summer temperature (ST), to be reconstructed for the Late-glacial period. The sequence opens with fine, partially laminated silt/clay that has varve-like microstructure. A cold steppic environment from the final phase of the pleniglacial is represented here. It is estimated to span almost 2000 years (ca. 16.9–15 cal. ka B.P.; ca. 14.6–12.7 ka B.P.). Substantial development of woody vegetation is limited to the early part of the Late-glacial interstadial (cf. Bølling). This consists mainly of juniper and birch, including tree birch ( Betula pubescens), as well as herb-dominated communities. These developments in vegetation and also the evidence from a variety of other proxies, including stable-isotope records (δ 18O and δ 13C), show that the thermal maximum was achieved early in the interstadial but ST probably did not exceeded 14°C. Within this relatively warm period, the various biological, chemical and physical proxies suggest at least one substantial but short-lived climatic oscillation. The later part of the Bølling/Allerød interstadial (after ca. 14 cal. ka B.P.; ca. 12 ka B.P.) began with a considerable and more or less sustained fall in temperature. The low temperature regime was maintained until immediately before the Younger Dryas when a modest but distinct amelioration is recorded by all proxies. This feature, referred to as a `pre-Younger Dryas warming' (pYDw) and which is seen in land, ocean and Greenland ice-core records from the northeast Atlantic region, has not been previously highlighted in the literature. The Younger Dryas stadial, when ST may have fallen to ca. 6°C, has a distinctive pollen assemblage characterised mainly by Gramineae, Thalictrum and Artemisia, but, for reasons not readily explainable, the early part of the stadial is not well defined in the stable-isotope record. As in most records from the northeast Atlantic region, the transition to the Holocene is sharp and clearly recorded. The importance of Juniperus in the Irish Late-glacial record, as an indicator of temperature change, is discussed and also the possible role played by Ephedra and Secale species at Tory Hill. The apparent absence of temperature gradients within Ireland is commented on, and the evidence for much lower ST in Ireland compared with Great Britain is discussed.