Southern Hemisphere Radiocarbon Calibration

For example in New Zealand, ¹⁴C dates on wood and peat trace the spread or contraction of forests and glacial advances and retreats in response to global climate change; marine shell dates document the development of beach ridges, estuaries and harbours formed as a result of sea-level rise and fall; charcoal dates measure the timing of volcanic eruptions; and shell, bone and charcoal dates mark the arrival and dispersion of humans and their impact upon the environment.

14C measurements from dendrochronologically-dated New Zealand kauri; overlain by the Northern hemisphere calibration curve (IntCal09).

The atmospheric ¹⁴C concentration has varied through time due to cosmic ray fluctuations. This means that ¹⁴C dates do not equate directly with calendar time and therefore must be corrected using a calibration curve (constructed by ¹⁴C dating of samples of known calendar age). The material of choice for the construction of a calibration curve is wood whose calendar age has been determined precisely by tree ring counting (dendrochronology).

Southern Hemisphere samples have a lower ¹⁴C content than contemporaneous Northern Hemisphere material – referred to as the ¹⁴C interhemispheric offset which varies over time. This obviously has important ramifications for any Southern Hemisphere carbon dating, particularly for studies of climate change, the timing of natural disasters, and anthropogenic effects.

Petchey, F., Dabell K., Clark G., & Parton P, (2023). Evidence of temporal changes in the marine ¹⁴C reservoir in the South Pacific and implications for improved dating resolution across a radiocarbon plateau (2600-2350 cal BP). Journal of Archaeological Science, doi:10.1016/j.jas.2023.105756.

Bunbury, M.M.E., Petchey F., & Bickler S.H., (2022). A new chronology for the Māori settlement of Aotearoa (NZ) and the potential role of climate change in demographic developments. PNAS, 119(46), doi:10.1073/pnas.2207609119.

Allen, M.S., McAlister A., Petchey F., Huebert J., Maeva M., Jones B., (2021). Marquesan Ceramics, Palaeotsunami, and Megalithic Architecture: The Ho‘oumi Beach site (NHo-3) in Regional Perspective, Marquesas Islands (Polynesia). Archaeology in Oceania; doi: 10.1002/arco.5233.

Petchey, F. and Clark, G. (2021).  Clarifying the age of initial settlement horizon in the Mariana Islands and the impact of hard water. A response to Carson 2020. Radiocarbon 63(3):905-913.

Petchey, F., & Schmid, M.M.E. (2020). Vital evidence: Change in the marine ¹⁴C reservoir around New Zealand (Aotearoa) and implications for the timing of Polynesian settlement. Scientific Reports, 10(1):8 pages, doi:10.1038/s41598-020-70227-3.

Petchey, F. (2019). New evidence for a mid - to late-Holocene change in the marine reservoir effect across the South Pacific Gyre. Radiocarbon,  1-13, doi:10.1017/rdc.2019.103.

Petchey, F., & Kirch, P. V. (2019). The importance of shell: Redating of the To’aga site (Ofu Island, Manu'a) and a revised chronology for the Lapita to Polynesian Plainware transition in Tonga and Sāmoa. PLOS ONE, 14(9),  e0211990, doi:10.1371/journal.pone.0211990.