Archaeomagnetism in New Zealand - Recent Advances

Over the past four years systematic archaeomagnetic studies in New Zealand have provided important data for regional and global geomagnetic field models, and, as well, have equipped local archaeologists with a new dating tool. The primary target material has been Maori hangi (earth oven) stones and, so far, we have studied 19 archaeological sites (over 25 hangi pits) around New Zealand, recovering reliable directional data from twelve sites and intensities from thirteen. Radiocarbon dating of charcoal fragments of short lived species, found amongst the stones at some sites, indicates an age range from 1400 AD to the present-day. Comparison of the directional data with the recently developed New Zealand palaeosecular variation curve, NZPSV1k, yields archaeomagnetic dates that, in some cases resolve ambiguities in the calibration of radiocarbon dates, and in others provide the only available age control. Recently we have extended the target material to bricks, from the European era, and baked soils such as the floors of hangi-pits and soils that have been heated during de-forestation and burning. These extremely fragile samples require consolidation before they can be subjected to thermal demagnetization or palaeointensity experimentation. Thellier palaeointensity determinations on hangi stones yield intensities ranging from 55 to 76 µT. We will present the first New Zealand archaeointensity record. This, together with data from Australia and Southwest Pacific islands, is consistent with predictions of the gufm1 global model back to 1838 AD, and its extension to 1590 AD. Prior to this date however, the data suggests more rapid variations and some unusually high palaeointensities. We will discuss these in comparison with coeval archaeointensity records from other regions of the world and global estimates of the dipole moment.