Ages of 24 widespread tephras erupted since 30,000 years ago in New Zealand, with re-evaluation of the timing and palaeoclimatic implications of the Lateglacial cool episode recorded at Kaipo bog

Tephras are important for the NZ-INTIMATE project because they link all three records comprising the composite inter-regional stratotype developed for the New Zealand climate event stratigraphy (NZ-CES). Here we firstly report new calendar ages for 24 widespread marker tephras erupted since 30,000 calendar (cal.) years ago in New Zealand to help facilitate their use as chronostratigraphic dating tools for the NZ-CES and for other palaeoenvironmental and geological applications. The selected tephras comprise 12 rhyolitic tephras from Taupo, nine rhyolitic tephras from Okataina, one peralkaline rhyolitic tephra from Tuhua, and one andesitic tephra each from Tongariro and Egmont/Taranaki volcanic centres. Age models for the tephras were obtained using three methods: (i) C-14-based wiggle-match dating of wood from trees killed by volcanic eruptions (these dates published previously); (ii) flexible depositional modelling of a high-resolution C-14-dated age depth sequence at Kaipo bog using two Bayesian-based modelling programs, Bacon and OxCal's P_Sequence function, and the IntCal09 data set (with SH offset correction -44 +/- 17 yr); and (iii) calibration of C-14 ages using OxCal's Tau_Boundary function and the SHCal04 and IntCal09 data sets. Our preferred dates or calibrated ages for the 24 tephras are as follows (youngest to oldest, all mid-point or mean ages of 95% probability ranges): Kaharoa AD 1314 +/- 12; Taupo (Unit Y) AD 232 +/- 10; Mapara (Unit X) 2059 +/- 118 cal. yr BP; Whakaipo (Unit V) 2800 +/- 60 cal. yr BP; Waimihia (Unit S) 3401 +/- 108 cal. yr BP; Stent (Unit Q) 4322 +/- 112 cal. yr BP; Unit K 5111 +/- 210 cal. yr BP; Whakatane 5526 +/- 145 cal. yr BP; Tuhua 6577 +/- 547 cal. yr BP; Mamaku 7940 +/- 257 cal. yr BP; Rotoma 9423 +/- 120 cal. yr BP; Opepe (Unit E) 9991 +/- 160 cal. yr BP; Poronui (Unit C) 11,170 +/- 115 cal. yr BP; Karapiti (Unit B) 11,460 172 cal. yr BP; Okupata 11,767 192 cal. yr BP; Konini (bed b) 11,880 +/- 183 cal. yr BP; Waiohau 14,009 +/- 155 cal. yr BP; Rotorua 15,635 +/- 412 cal. yr BP; Rerewhakaaitu 17,496 +/- 462 cal. yr BP; Okareka 21,858 +/- 290 cal. yr BP; Te Rere 25,171 +/- 964 cal. yr BP; Kawakawa/Oruanui 25,358 +/- 162 cal. yr BP; Poihipi 28,446 +/- 670 cal. yr BP; and Okaia 28,621 +/- 1428 cal. yr BP. Secondly, we have re-dated the start and end of the Lateglacial cool episode (climate event NZce-3 in the NZ-CES), previously referred to as the Lateglacial climate reversal, as defined at Kaipo bog in eastern North Island, New Zealand, using both Bacon and OxCal P Sequence modelling with the IntCal09 data set. The ca 1200-yr-long cool episode, indicated by a lithostratigraphic change in the Kaipo peat sequence to grey mud with lowered carbon content, and a high-resolution pollen-derived cooling signal, began 13,739 +/- 125 cal. yr BP and ended 12,550 +/- 140 cal. yr BP (mid-point ages of the 95% highest posterior density regions, Bacon modelling). The OxCal modelling, generating almost identical ages, confirmed these ages. The Lateglacial cool episode (ca 13.8-12.6 cal. ka BP) thus overlaps a large part of the entire Antarctic Cold Reversal chronozone (ca 14.1-12.4 cal. lea BP or ca 14.6-12.8 cal. lea BP), and an early part of the Greenland Stadial-1 (Younger Dryas) chronozone (ca 12.9-11.7 cal. ka BP). The timing of the Lateglacial cool episode at Kaipo is broadly consistent with the latitudinal patterns in the Antarctic Cold Reversal signal suggested for the New Zealand archipelago from marine and terrestrial records, and with records from southern South America. (C) 2012 Elsevier Ltd. All rights reserved.