Unlocking the Secrets of the Geodynamo: the Southwest Pacific Key

Abstract:

Three years ago we embarked on a project to boost the coverage of palaeosecular variation data from the Southwest Pacific region, and so to provide the means to enhance global and regional field models, dating tools derived from them, and understanding of features of the geodynamo, particularly beneath this region of the Earth’s surface. Here we present our progress to date, including lake sediment records covering the entire Holocene, archaeomagnetic data from Maori cooking (“hangi”) stones dating back to the earliest occupation of New Zealand, archaeointensities from Lapita pottery from the Pacific Islands (Fiji, Tonga and Papua New Guinea) dating back to ca 3000 BP, and palaeomagnetic directions and intensities from volcanic rocks and lava flows of the North Island of New Zealand. Central to the project is a composite lake sediment record, constrained by a high-resolution radiocarbon-based chronology, which provides a complete record of declination, inclination and relative palaeointensity for New Zealand through the Holocene. This is complemented by directions and absolute intensities from archaeological materials, most of which have associated radiocarbon age control, and lavas with ⁴⁰Ar-³⁹Ar age constraints, the rock magnetism and analytical details of which are discussed in accompanying posters. The overall picture reveals several large amplitude directional swings in the early Holocene magnetic field, followed by relatively low amplitude secular variation for several thousand years leading to the present trend to increasingly easterly declination and steep inclination as the south magnetic pole moves further off the Antarctic continent towards New Zealand.