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Abstract:
The SW Pacific region represents a huge area of the globe that is under-represented in palaeomagnetic secular variation databases and field models. Data from the region is crucial to understanding core processes, since the present-day magnetic pole lies off Antarctica to the south, and several published global models indicate fluctuating flux lobes on the core-mantle boundary beneath the Southwest Pacific. The New Zealand Holocene PSV record presented here includes continuous records of declination and inclination from multiple sediment cores from each of three lakes, each sequence being independently dated by radiocarbon estimates and/or tephrochronology. All records are referenced to 40°S, 175°E. The records differ significantly from predictions of global models that do not incorporate data from the region. They show periods of regular, but aperiodic, moderate amplitude directional swings between 11500 and 8000 BP and between 4000 BP and the present, but lower amplitude variations during the interim 4000 years. In addition, one lake, Mavora, has yielded a relative palaeointensity record that shows similarities with global palaeointensity records with local variability superimposed. Archaeomagnetic results spanning the past 800 years and volcanic data covering the Holocene complement the lake sediment records and suggest some but not a major degree of smoothing of the latter. Archaeomagnetic intensity determinations suggest a 14th – 15th century AD spike-like feature. Finally, we present new directional and intensity data from volcanic rocks dated between 45 and 25 ka, showing evidence of the Laschamp and Mono Lake excursions,with a possible low-intensity period of instability in between.
