Human History

Radiocarbon dating of ancient Polynesian canoe

Isotopic studies help to trace the origin of precious Maori feather cloaks

Radiocarbon dating of ancient Polynesian canoe

Dating a piece from an ancient canoe discovered in New Zealand provides insights into a remarkable episode in the history of human migration and seafaring. 

The radioactive carbon isotope 14C, also called radiocarbon, is a rare and naturally occurring isotope of the element carbon. While plants and animals are alive, the proportion of the three isotopes of carbon (12C, 13C and 14C) inside them remains constant. When a living thing dies, the amount of radiocarbon slowly decreases relative to the two other stable isotopes of carbon in the material. Analysing the proportion of remaining radiocarbon in the sample provides an objective method of determining the time ranges within which an object may be placed.

One example of radiocarbon dating of archaeological samples by GNS Science’s Rafter Radiocarbon Laboratory was to determine the age of a piece from an ancient waka (canoe) that was dug up at a remote site in the South Island of New Zealand. By initial visual assessment of its structure, archaeologists could tell it was very old; they even suspected it was pre-European (pre-1800s). Radiocarbon dating showed that the piece was approximately 600 years old. The canoe is the older of the only two pre-European Polynesian canoes ever identified. Until now, reconstructions of the canoes used by Polynesians have been based mainly on observations from European explorers, instead of direct evidence. The discovery provides new information about early Polynesian canoe technology and insights into a remarkable episode in the history of human migration and seafaring.

Sample preparation in the Radiocarbon Dating laboratory, GNS Science

Sample preparation in the Radiocarbon Dating laboratory, GNS Science.

Since the radiocarbon dating method was invented in 1949, it has revolutionised archaeology, permitting more accurate dating than did previous methods. Today it remains the most accurate and widely-applicable method, allowing the dating of samples world-wide and back 50,000 years.  

GNS Science Radiocarbon Laboratory is the world’s longest continuously running radiocarbon lab. In just the past ten years over 25,000 samples have been measured from clients in New Zealand and throughout the world. With our state-of-the-art Accelerator Mass Spectrometry facility, we are able to directly count the relative numbers of the atoms of the different carbon isotopes present in the materials. This enables us to date extremely small samples between a few milligrams and a few grams, once considered too small for radiocarbon dating analysis.    

Isotopic studies help to trace the origin of precious Maori feather cloaks

Historical Māori cloaks and other artefacts made of bird feathers are intricate art forms widely sought by collectors and museums through trading and gifting. However, their origins are often lost in the passage of time. In a pilot study which shows that New Zealand's unique geographical shape in the South Pacific Ocean can be used to determine multiple bird habitat regions based on stable-hydrogen isotope signals, scientists are helping to trace the geographical origin of precious Māori feather cloaks.

Analyses of stable-hydrogen isotope 2H of feathers and tissues are a powerful tracer to assess the geographical origins of many bird species, as feathers and tissues retain the isotopic “fingerprint” of the geographical location where that tissue was grown. This provides a potential new option as a forensic or historical research tool to establish the connection of feather-based indigenous artefacts to an iwi/tribe of origin.

Feathers retain the isotopic “fingerprint” of their geographical origin

Feathers retain the isotopic “fingerprint” of their geographical origin

In a collaborative study led by GNS Science scientist Karyne Rogers, feathers of tui, an extant native bird species, along with feathers from an introduced species, California Quail, were sampled from museum collections. The samples were then analysed to investigate the use of the stable hydrogen isotope 2H as a geographical tracer of New Zealand faunal landscape origin. The findings suggest that archived tui and quail feathers retained their isotopic record over time, and stable hydrogen isotope analysis of these samples can be used with some degree of confidence as a geographical indicator of location of origin. The results can be further improved with the additional use of other stable isotopes or geochemical tracers. This study was the first to show that New Zealand's unique geographical shape in the South Pacific Ocean can be used to determine multiple bird habitat regions based on stable-hydrogen isotope signals.

Compared to another method that has shown promise using mitochondrial DNA to distinguish kiwi feathers from different localities, stable isotope analysis offers significant advantages, such as the ability to screen and analyse a large number of samples in a quick and cost efficient manner in order to construct multiple species-specific isomaps. Isotope analysis is also more specific to locality, rather than relying on identifiable groups of individuals as for DNA analyses.

For more information, please contact:

Mike Sim, Head of Department, Isotope Biogeoscience, GNS Science