Clim. Past, 11, 105–114, 2015 www.clim-past.net/11/105/2015/ doi:10.5194/cp-11-105-2015 © Author(s) 2015. CC Attribution 3.0 License. Tree ring effects and ice core acidities clarify the volcanic record of the first millennium M. G. L. Baillie1 and J. McAneney2 1School of Geography, Archaeology and Palaeoecology, Elmwood Avenue, Queen’s University, Belfast, Belfast BT7 1NN, Northern Ireland, UK 2Independent Researcher, Bangor, Northern Ireland, UK Correspondence to: M. G. L. Baillie ([email protected]) Received: 28 February 2014 – Published in Clim. Past Discuss.: 15 April 2014 Revised: 8 December 2014 – Accepted: 12 December 2014 – Published: 16 January 2015 Abstract. In 2012 Plummer et al., in presenting the volcanic 1 Background chronology of the Antarctic Law Dome ice core, chose to list connections to acid layers in other ice cores and also Large explosive volcanic eruptions can induce hemispheric, possible chronological coincidences between ice acid dates and occasionally global, environmental effects through the and the precise dates of frost damage, and/or reduced growth injection of sulfate aerosols into the stratosphere altering the in North American bristlecone pines. We disagree with the absorption and reflection of solar radiation within the atmo- chronological links indicated by Plummer et al. for the period sphere, producing an overall cooling effect on global climate before AD 700, and in this paper we show that a case can be (Rampino and Self, 1982). Attempts to trace the areal ex- made that better linkages between ice acid and tree ring ef- tent of such environmental effects rely mostly on evidence fects occur for this period if the ice chronologies are system- of tree growth response to climate derived from precisely atically moved forward by around 7 years, consistent with a dated tree ring chronologies. For example, Briffa et al.(1998) hypothesis published by Baillie in 2008. In the paper we seek investigated the relationship between maximum latewood to explore the proposition that frost damage rings in North density (MXD) in high-latitude and high-elevation conifers American bristlecone pines are a very useful indicator of the from around the Northern Hemisphere and historical erup- dates of certain large explosive volcanic eruptions; the dating tions, while Scuderi(1990) assessed growth minima in fox- of major eruptions being critical for any clear understanding tail pines from the Sierra Nevada against volcanic records of volcanic forcing. This paper cannot prove that there is an back to 1000 BC. error in the Greenland Ice Core Chronology 2005 (GICC05), In 1984 LaMarche and Hirschboeck postulated a rela- and in equivalent ice chronologies from the Antarctic, how- tionship between frost rings (damage caused by unseasonal ever, it does provide a coherent argument for an apparent ice frost during the growing season) in high-elevation bristle- dating offset. If the suggested offset were to prove correct it cone pines from the western United States and explosive vol- would be necessary to locate where the error occurs in the ice canism. They suggested that climatic dislocation caused by chronologies and in this regard the dating of the increasingly high-altitude volcanic aerosols could cause unseasonal cold controversial Icelandic Eldgjá eruption in the AD 930s, and air to move down the Rockies freezing still growing trees, the China/Korean Millennium eruption which occurs some 7 leaving visible scarring. Although they were able to show years after Eldgjá, may well be critical. In addition, if the off- reasonable linkages between frost rings and volcanoes in re- set were to be substantiated it would have implications for the cent times (for example they noted frost rings in 1912 the alleged identification of tephra at 429.3 m in the Greenland year of the Katmai eruption in Alaska, and in the years 1884, GRIP core, currently attributed to the Italian volcano Vesu- 1837, 1817, 1680, 1640 and 1601, each within 1 or 2 years vius and used as a critical zero error point in the GICC05 of known eruptions), this relationship tended to break down chronology. further back in time when comparisons were made with vol- canic evidence deduced from ice cores, in the absence of his- Published by Copernicus Publications on behalf of the European Geosciences Union. 106 M. G. L. Baillie and J. McAneney: Tree rings and ice cores clarify the volcanic record torically dated volcanoes. This early attempt at linking tree bristlecone pines (LaMarche and Hirschboeck, 1984; Salzer ring effects and ice core acidities was elaborated further by and Hughes, 2007) while only 1838 is singled out as a nar- Salzer and Hughes(2007) who provided lists of frost ring row ring event (Salzer and Hughes, 2007). Unfortunately by and narrow ring dates back to 5000 years ago, while high- raising the issue of narrow rings Salzer and Hughes allowed lighting tree effects that occurred within 5 years of ice core researchers to pick tree ring phenomena – either frost rings or acidity dates. narrow rings – that occurred proximate to volcanic acid sig- From such work certain dates for explosive volcanism nals dated within the ice core chronologies, these links sug- stand out, for example, AD 1640, AD 1601 and AD 1257 gesting support for the dating of the ice cores (Plummer et al., are represented as acid layers in the Greenland Crête and the 2012). Before analysing the deficiencies in this approach it is Greenland Ice Core Project (GRIP) ice cores (Hammer et al., necessary to provide background on the issue of the ice core 1980; Clausen et al., 1997), they show up in the Greenland chronologies. Ice Sheet project (GISP2) core at 1603 ± 2, 1642 ± 2 and Long ice cores mostly exhibit clear annual layering. Vi- 1259 ± 2 (Zielinski, 1995), in the North Greenland Eemian sual inspection is supplemented by study of annually fluc- Ice Drilling “NEEM-2011-S1” (hereafter NEEM S1) and tuating chemical and isotopic signals that allow unequivo- West Antarctic Ice Sheet Divide (WDC06A) cores (Sigl cal identification of most annual layers. However, ice cores et al., 2013) and in the Antarctic Law Dome (Plummer et al., do suffer from periodic “problem layers” where uncertainty 2012), Dronning Maud Land (DML) (Traufetter et al., 2004), creeps into the layer counting. This is handled by adding and South Pole (Ferris et al., 2011) cores. This implies that 0.5 ± 0.5 years for each problem layer (Vinther et al., 2006) these eruptions were equatorial. However, while trees regis- and by accumulating these problem layers an error figure is ter the effects of the 1640 and 1601 eruptions widely (Briffa obtained for ancient dates. This procedure is short-circuited et al., 1998; Scuderi, 1990; Salzer and Hughes, 2007), the by attempts to identify traces of known volcanoes such massive eruption, now believed to have taken place in AD as Öraefajökull (1362), Hekla 1 (1104) and Vesuvius (AD 1257 and attributed to the Salamas volcano in Indonesia 79) in the ice. Indeed it is claimed that acid and tephra at (Lavigne et al., 2013), shows up patchily in trees (Jones et al., 429:1=429:3 m in the GRIP ice core derived specifically from 2013; D’Arrigo et al., 2013) with perhaps the clearest evi- Vesuvius and provide a zero-error point in the ice chronolo- dence for upset being provided by bristlecone pine frost rings gies (Barbante et al., 2013). While this sounds coherent, one in 1257 and 1259 (Salzer and Hughes, 2007). key issue relates to independent replication of the ice acid- What emerges from this background is that bristlecone ity dates in Dye3, GRIP and NGRIP. Vinther et al.(2006) pine frost rings in high-elevation bristlecone pines from the state that “The three ice core records have been synchronized western United States can be, as originally postulated by using volcanic reference horizons”. This involved identify- LaMarche and Hirschboeck(1984), used as sensitive indi- ing significant ECM signals and then independently count- cators of explosive volcanism. Obviously the relationship is ing the layers between the ECM signals. In our view this not one-to-one; not every volcano automatically produces was a flawed procedure. True dating replication could only frost damage in bristlecone pines, while some frost rings ap- be achieved by counting the whole of each core indepen- pear not to be related to volcanism. However, a case exists dently. For comparison, in dendrochronology replication is that numbers of key large volcanic events are associated with often provided by comparing chronologies produced by in- bristlecone pine frost rings (see Supplement). When these oc- dependent workers in independent laboratories. This appar- cur, the precise dating provided by dendrochronology makes ent lack of completely independent replication of the Dye3, frost ring dates important in any attempts to link to histor- GRIP and NGRIP cores makes the identification of Vesuvius ical records of how human populations were affected. Un- tephra in the ice absolutely critical for the chronology of the fortunately, the introduction of narrow ring dates by Salzer European ice cores. That overall chronology, the Greenland and Hughes(2007) served to complicate the relationship be- Ice Core Chronology 2005 (GICC05), has been regarded as tween volcanoes and tree ring effects. Narrow ring occur- definitive since 2006 (Vinther et al., 2006). rences have the disadvantage that they can have a number The reason for rehearsing this history lies in the conclusion of possible causes, in contrast to frost rings which appear un- of the Vesuvius dating paper by Barbante et al.(2013). They equivocally to be caused by anomalous, unseasonal extreme state: “We identified volcanic glass fragments at 429.3 m cold. depth where the elemental analysis strongly suggests that For example, if we look at a recent paper by Jones et al.