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Investigating the Interhemispheric 14C Offset in the 1st Millennium AD and Assessment of Laboratory Bias and Calibration Errors

Published online by Cambridge University Press:  18 July 2016

Alan Hogg*
Radiocarbon Laboratory, University of Waikato, PB 3105, Hamilton 3240, New Zealand.
Jonathan Palmer
Gondwana Tree-Ring Laboratory, P.O. Box 14, Little River, Canterbury 7546, New Zealand.
Gretel Boswijk
School of Environment, University of Auckland, PB 92019, Auckland, New Zealand.
Paula Reimer
Centre for Climate, the Environment & Chronology (14CHRONO), School of Geography, Archaeology and Palaeoecology, Queen's University Belfast, Belfast, BT7 1NN, United Kingdom.
David Brown
Centre for Climate, the Environment & Chronology (14CHRONO), School of Geography, Archaeology and Palaeoecology, Queen's University Belfast, Belfast, BT7 1NN, United Kingdom.
Corresponding author. Email:
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Past measurements of the radiocarbon interhemispheric offset have been restricted to relatively young samples because of a lack of older dendrochronologically secure Southern Hemisphere tree-ring chronologies. The Southern Hemisphere calibration data set SHCal04 earlier than AD 950 utilizes a variable interhemispheric offset derived from measured 2nd millennium AD Southern Hemisphere/Northern Hemisphere sample pairs with the assumption of stable Holocene ocean/atmosphere interactions. This study extends the range of measured interhemispheric offset values with 20 decadal New Zealand kauri and Irish oak sample pairs from 3 selected time intervals in the 1st millennium AD and is part of a larger program to obtain high-precision Southern Hemisphere 14C data continuously back to 200 BC. We found an average interhemispheric offset of 35 ± 6 yr, which although consistent with previously published 2nd millennium AD measurements, is lower than the offset of 55–58 yr utilized in SHCal04. We concur with McCormac et al. (2008) that the IntCal04 measurement for AD 775 may indeed be slightly too old but also suggest the McCormac results appear excessively young for the interval AD 755–785. In addition, we raise the issue of laboratory bias and calibration errors, and encourage all laboratories to check their consistency with appropriate calibration curves and invest more effort into improving the accuracy of those curves.

Copyright © The Arizona Board of Regents on behalf of the University of Arizona 


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