Holocene climatic change and past Irish societal response Chris S.M. Turney a, * , Mike Baillie b , Jonathan Palmer b , David Brown b a GeoQuEST Research Centre, School of Earth and Environmental Sciences, University of Wollongong, Wollongong NSW 2522, Australia b Palaeoecology Centre, School of Archaeology & Palaeoecology, Queen’s University, Belfast BT7 1NN, UK Accepted 19 May 2005 Abstract The extent to which North Atlantic Holocene climatic perturbations influenced past human societies is an area of considerable uncertainty and fierce debate. Ireland is ideally placed to help resolve this issue, being occupied for over 9000 yr and located on the eastern Atlantic seaboard, a region dominated by westerly airflow. Irish bog and lake tree populations provide unambiguous evidence of major shifts in surface moisture through the Holocene similar to cycles recorded in the marine realm of the North Atlantic, indicating significant changes in the latitude and intensity of zonal atmospheric circulation across the region. To test for human response to these cycles we summed the probabilities of 465 radiocarbon ages obtained from Irish archaeological contexts and observe enhanced archaeological visibility during periods of sustained wet conditions. These results suggest either increasing density of human populations in key, often defensive locations, and/or the development of subsistence strategies to overcome changing conditions, the latter recently proposed as a significant factor in avoiding societal collapse. Regardless, we demonstrate environmental change is a significantly more important factor in influencing human activity in the landscape than has hitherto been acknowledged. Ó 2005 Elsevier Ltd. All rights reserved. Keywords: Archaeological visibility; Bog oaks and pines; Dendrochronology; Human response; North Atlantic; Millennial climatic and environmental change; Tree populations 1. Introduction The present interglacial was until recently considered to be a period of exceptional climatic stability [8]. Changes in the concentration of lithic grains through Holocene North Atlantic sediments, however, have now been shown to represent a pervasive quasi-cyclicity close to 1500 yr (‘Bond’ cycles), recording the southward advection of cold, ice-bearing waters from the Labrador and Nordic Seas [4]. These quasi-cycles have now been identified within numerous North Atlantic marine records [3,13,17,24], suggesting a regional signal. The representation of Holocene climatic changes on land and their impact on human populations, however, remain unclear [7,18,22,30,33,11,10] largely due to the selection of palaeoclimate proxies and ‘smearing’ of archaeological chronologies. Ireland’s maritime climate is dominated by a pre- vailing westerly airflow and is effectively free of any influence of major ice masses and continents, making it extremely sensitive to past fluctuations in the strength of thermohaline circulation in the North Atlantic [20,34]. We have developed Irish tree-ring chronologies using bog grown oaks (Quercus spp.) and pines (Pinus sylvestris L.). The marginal environments of these species growing on bogs coupled with the effectively random nature of the sampling has allowed us to generate an absolute-dated Holocene record of tree populations in Ireland which appear to have changed in response to varying hydrological conditions associated with North Atlantic millennial-scale cycles [34]. Ireland * Corresponding author. Fax: C61 2 42214250. E-mail address: turney@uow.edu.au (C.S.M. Turney). 0305-4403/$ - see front matter Ó 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.jas.2005.05.014 Journal of Archaeological Science 33 (2006) 34e38 http://www.elsevier.com/locate/jas