Petchey, F., Schmid, M.M.E. (2020). Vital evidence: Temporal shifts in the marine ¹⁴C reservoir around New Zealand (Aotearoa) over the last 750 years, and implications for Polynesian settlement. Manuscript submitted for publication.
Permanent Research Commons link: https://hdl.handle.net/10289/13381
Precise and accurate radiocarbon (¹⁴C) chronologies are essential to achieve the tight chronological control needed for the ~750-year period since Polynesian settlement of New Zealand. Robust chronologies enable us to understand the drivers behind rapid archaeological and paleoenvironmental events, such as migration, colonisation(s), human impacts on the environment and climate (and vice versa), as well as changing material culture. For most of the Pacific sites, this goal has been elusive. While 14C datasets in this region typically consist of large numbers of marine and estuarine shell dates, this important set of chronological information is consistently ignored by those interpreting the timing of key events, ostensibly because of unknown regional ¹⁴C reservoir offsets, and/or errors introduced by upwelling, hardwater, intermixing of natural beach deposits and other environmental offsets. Many of these issues have been investigated over the last ten years at locations across the Pacific and can be mitigated, but we still lack a detailed regional calibration methodology for marine shell comparable to the highly precise Southern Hemisphere calibration curve. This gap has occurred because it has been assumed that a region-specific marine offset (DR), applied to the global marine calibration curve, will correct for regional and temporal variation respectively. In this paper, we present a temporal ΔR model for New Zealand based on paired estuarine/marine and terrestrial ¹⁴C dates from 52 archaeological contexts spanning the entire sequence since initial Polynesian settlement. Our dataset indicates that offsets equating to hundreds of years occur between the measured New Zealand data and the modelled global marine radiocarbon curve. These shifts are associated with climatic fluctuations during the late Holocene. Our application of a regional and temporal specific correction to archaeological shell dates will not only improve the accuracy of calibrated ages, but will also help improve the blurred chronology that has plagued archaeological theories about the colonization of New Zealand and other Pacific islands for decades.
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