The 5.2 ka climate event: Evidence from stable isotope and multi-proxy palaeoecological peatland records in Ireland

T.P Roland,T.J Daley,C.J Caseldine,D.J Charman,C.S.M Turney,M.J Amesbury,G.J Thompson,E.J Woodley

doi:10.1016/j.quascirev.2015.07.026

Abstract

Evidence for a major climate event at 5.2 ka has been reported globally and is associated with considerable societal disruption, but is poorly characterised in northwest Europe. This event forms part of a broader period of re-organisation in the Earth's ocean-atmosphere circulation system between 6 and 5 ka. This study tests the nature and timing of the event in northwest Europe, a region highly sensitive to change in meridional overturning circulation and mid-latitude westerly airflow. Here we report three high-resolution Irish multi-proxy records obtained from ombrotrophic peatlands that have robust chronological frameworks. We identify the 5.2 ka event by a sustained decrease in δ18Ocellulose at all three sites, with additional and parallel changes in δ13Ccellulose and palaeoecological (testate amoebae, plant macrofossil and humification) data from two sites in northern Ireland. Data from Sluggan Moss demonstrate a particularly coherent shift towards wetter conditions. These data support the hypothesis that the event was caused by a prolonged period of positive North Atlantic Oscillation conditions, resulting in pervasive cyclonic weather patterns across northwest Europe, increasing precipitation over Ireland.

Highlights

Forcing of the Holocene thermal maximum (HTM) is commonly attributed to the orbitally-driven summer insolation maximum in the Northern Hemisphere (NH) (Wanner et al, 2008; Bartlein et al, 2011), with its complex spatio-temporal structure explained by the influence of additional forcing mechanisms and feedbacks, including the decay of the remnant
During the 5.2 ka event, widespread cooling was accompanied by drier conditions in central and eastern Asia, Africa, the Mediterranean and parts of North America, with wetter conditions in northern Europe and southern South America (Magny et al, 2006), demonstrating that the dynamic processes associated with the event extend beyond the influence of the North Atlantic Oscillation (NAO)
The climatic sensitivity and chronological potential possessed by these archives creates considerable potential for the reconstruction of past climate change through multi-proxy palaeoecological and novel stable isotopic analyses (δ18O and δ13C)

Summary

Introduction

1.1 A mid-Holocene climatic transitionThe occurrence of a substantial transition in the global climate system during the period 6 – 5 ka Whilst NH summer insolation decreased gradually from the early Holocene onwards, the steepestAn extensive review of potentially correlative short-lived, multi-centennial climatic event signalsThe abrupt termination of the African humid period c. 5.5 ka, following a weakening of the is widely acknowledged (Steig, 1999; Mayewski et al, 2004; Wanner et al, 2008; Brooks, 2012).This transition marked the termination of the Holocene thermal maximum (HTM), a relatively warm period with temperatures markedly higher than those of the pre-industrial era, as recorded in a range of palaeoclimate archives (e.g. Davis et al, 2003; Kaufman et al, 2004; Jansen et al, 2009; Seppä et al, 2009; Bartlein et al, 2011). 5.5 ka, following a weakening of the is widely acknowledged (Steig, 1999; Mayewski et al, 2004; Wanner et al, 2008; Brooks, 2012) This transition marked the termination of the Holocene thermal maximum (HTM), a relatively warm period with temperatures markedly higher than those of the pre-industrial era, as recorded in a range of palaeoclimate archives Thirty-four of the records examined by Magny et al (2006) have ages defining the onset of the event, of which the average was 5.23 ka and so the event will be referred as the ‘5.2 ka event’ Many of these signals are consistent with the ‘cool poles, dry tropics’ pattern typical of a number of climate episodes which punctuate the mid- to late-Holocene, including the 4.2 ka, 2.8 ka and Little Ice Age events (Mayewski et al., 2004). During the 5.2 ka event, widespread cooling was accompanied by drier conditions in central and eastern Asia, Africa, the Mediterranean and parts of North America, with wetter conditions in northern Europe and southern South America (Magny et al, 2006), demonstrating that the dynamic processes associated with the event extend beyond the influence of the NAO

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