Research Highlights

The chronology of human settlement, palaeoclimate variability, and marine fisheries in the southern Cook Islands 

Study site of Moturakau Islet, Aitutaki lagoon

As the first island group east of Samoa and Tonga, the southern Cook Islands are a gateway archipelago that stands to inform on the timing and patterning of East Polynesian settlement. Moturakau Rockshelter on Aitutaki Island is one of a few early occupation sites in the Cook Islands, and renowned for its exceptionally large, stratified assemblage of marine archaeofauna and fishing gear. First analysed in the late 1980s, these collections are now the focus of an interdisciplinary study of palaeoclimate effects on marine fisheries and human foragers over the last millennium. High precision dates were required to refine the timing of initial site activities, major marine events (major storms and/or tsunami), and changing patterns of resource use.

The AINSE-funded analysis evaluated an extant radiocarbon chronology defined two decades ago on unidentified bulk charcoal, materials now known to include long-lived trees with the potential for inbuilt age. Archived collections were sampled for short-lived materials (e.g., coconut shell and Pandanus keys) and AMS-dated. Bayesian analysis of the overall date assemblage was used to identify outliers and refine age estimates for the site’s 12 stratigraphic zones, while changing depositional rates were assessed using the Classical Age-Depth Model (CLAM) program.

The resulting geo-chronological model indicates that initial islet use began at a time when human populations were dispersing across East Polynesia in the mid-11th to 13th centuries AD. The 13th to 15th centuries were a period of recurring and significant marine intrusions which disrupted cultural activities. Perhaps related, after the mid-15th century archaeofish remains and fishhooks began to decline. These changes are now being assessed against an emerging carbonate-based (corals, otoliths) palaeoclimate record.

Assoc Prof Melinda Allen (University of Auckland) led the research in collaboration with Prof David Fink and Dr Geraldine Jacobsen (ANSTO). Archaeobotanist Jennifer Huebert (UA) identified the plant samples. Dr Alex Morrison (UA) undertook the Bayesian analysis. The AINSE supported geo-chronological model provides a crucial framework for interpreting prior analyses and supporting our on-going Royal Society of New Zealand–funded palaeoclimate study.