Correspondence

IntCal13 calibrated ages of the Vedde andSaksunarvatn ashes and the Younger Dryas boundariesfrom Krakenes, western Norway

ØYSTEIN S. LOHNE,1 JAN MANGERUD1* and HILARY H. BIRKS21Department of Earth Science and Bjerknes Centre for Climate Research, University of Bergen, Allegaten 41 N-5007, Bergen,Norway

2Department of Biology and Bjerknes Centre for Climate Research, University of Bergen, Post Box 7803 N-5020, Bergen, Norway

Received 21 February 2013; Revised 15 May 2014; Accepted 18 May 2014

ABSTRACT: From Krakenes Lake in western Norway there exist 118 accelerator mass spectrometry 14C dates forthe time interval 12 000–8000 14C a BP that we earlier calibrated using the IntCal09 data set. These yielded themost accurate and precise ages available for the Younger Dryas boundaries and the Vedde and Saksunarvatn ashes.Here we present a new calibration using the recently published IntCal13 data set. All differences between the twosets of calibrated ages are within the�1s error of the original IntCal09 results. The most significant differences arethat the error for the Allerød/Younger Dryas boundary decreased, that this boundary became slightly older and thatthe length of the Younger Dryas increased slightly. Copyright # 2014 John Wiley & Sons, Ltd.

KEYWORDS: Allerød; Bayesian age–depth modelling; Saksunarvatn Ash; Vedde Ash; Younger Dryas.

Introduction

We recently published new ages for the start and end of theYounger Dryas and for the Vedde and Saksunarvatn ashesbased on 118 accelerator mass spectrometry (AMS) 14C datesfrom the Krakenes Lake in western Norway (Lohneet al., 2013). However, when calibrating to ‘calendar’ yearswe used the IntCal09 database (Reimer et al., 2009). Subse-quently the new IntCal13 calibration program has beenreleased (Reimer et al., 2013). Because we consider that ourages presently represent the most accurate and precise 14Cages available for all four mentioned levels it is of majorinterest to have available calibrated ages based on the mostupdated calibration program and data set.

Methods

We originally (Lohne et al., 2013) performed an age–depthmodelling using the P_Sequence function in OxCal (Bronk

Ramsey, 2008, 2010) after calibration of the radiocarbon ageswith the IntCal09 data set. Here we present a repeated agemodel where we have recalibrated the 14C ages with theIntCal13 calibrated dataset, without doing any other modifi-cations or changes of the numbers or methods. The uncor-rected 14C ages are given in the online supporting material toLohne et al. (2013).

Results and discussion

The results are given in Table 1. The most striking result isthat all IntCal13 ages are within the�1s error limits of theIntCal09 ages. We therefore consider the discussion andconclusions in Lohne et al. (2013) to be valid also for thenew results and will only make some short additionalcomments. A major interest for many readers is the compari-son with Greenland ice core time scales and we havetherefore included GICC05 ages in Table 1 (Rasmussen

�Correspondence: J. Mangerud, as above.E-mail: jan.mangerud@geo.uib.no

Table 1. Calibrated ages (yr BP¼B1950) for the Younger Dryas (YD) boundaries and the Vedde and Saksunarvatn ashes obtained with theIntCal13 data set compared with ages obtained with IntCal09 (Lohne et al., 2013) and with Greenland ice core ages (also given as B1950) fromTable 4 in Rasmussen et al. (2006).

Median Age interval (95.4%) Mean�1sGreenland ice core ages�1s

Intcal09 Intcal13 Intcal09 Intcal13 Intcal09 Intcal13 GICC05�

YD/Holocene boundary 11 542 11532 11674–11431 11655–11419 11546�59 11535�58 11653�50†

Allerød/YD boundary 12 705 12733 12825–12615 12809–12680 12711�52 12737�31 12846�69†

Vedde Ash 12 067 12065 12151–11981 12163–11965 12066�42 12064�48 12121�57Saksunarvatn Ash 12 210 12211 10282–10137 10284–10135 10210�35 10210�35 10297�45Duration of the YD 1165�79 1202�66 1193�20†

�To compare with calibrated 14C years we have subtracted 50 years from all GICC05 ages, which originally were given as ‘before 2000’ (B2k).We used 0.5 MCE as 1s (Andersen et al., 2006).†These are the boundaries for Greenland Stadial 1 (GS1), which are not identical to the YD boundaries (Lohne et al., 2013).

Copyright # 2014 John Wiley & Sons, Ltd.

JOURNAL OF QUATERNARY SCIENCE (2014) 29(5) 506–507 ISSN 0267-8179. DOI: 10.1002/jqs.2722

et al., 2006). Note that to facilitate comparison with calibrat-ed 14C years (given as BP¼B1950), we have subtracted50 years from the GICC05 ages that were originally given as‘before 2000’ (B2k).The largest improvements in precision are related to the

Allerød/Younger Dryas boundary. This is expected becausewithin the time interval discussed here, it is there that thereare most new data in IntCal13 compared with IntCal09. The1s error decreased from 52 to 31 years and the 95.4%significance interval decreased from 215 to 119 years for thisboundary. The mean IntCal13 age for this boundary alsoincreased 26� 61 years. Because the Younger Dryas/Holo-cene boundary moved the other way, the (mean) duration ofthe Younger Dryas became 37 years longer and thus moresimilar to the estimated duration of Greenland Stadial 1 inice-core years (Table 1).We note that several ashes with a main element composi-

tion similar to the Saksunarvatn Ash have been found inmarine cores near Greenland (Jennings et al., 2014), makingcorrelation of the Saksunarvatn Ash at the type localitywith the assumed Saksunarvatn Ash in ice cores moreuncertain. Nevertheless, the IntCal13 calibrated age for theSaksunarvatn Ash at Krakenes is the same as the IntCal09age.

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Copyright # 2014 John Wiley & Sons, Ltd. J. Quaternary Sci., Vol. 29(5) 506–507 (2014)

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