Holocene Palaeosecular Variation in New Zealand and the South West Pacific: Records and Models

Abstract

We develop a palaeomagnetic secular variation (PSV) record from a Holocene sediment sequence of Lake Pupuke, containing declination and inclination logs for the period 1150-9600 yr BP. Magnetic measurements from three cores showed excellent between-core correlation and were compiled in a high-resolution palaeosecular variation record. An age model has been developed from three previously published AMS radiocarbon age determinations on wood fragments and bulk sediments and six identified tephra layers. The PSV from Pupuke is comparable with PSV results from two other New Zealand lakes, Mavora and Pounui, during the Holocene. A New Zealand Master Curve is constructed from these three PSV results. An age correction was applied to the Pounui record by correlation with the Mavora record before being included in the master curve. The record shows in-phase declination and inclination swings prior to 8000 yr BP, consistent with westward drift of sources of the non-dipole field. There is little variation in the middle section of the record, and from ~4000 yr BP to the present day the record shows declination and inclination swings which are approximately 90◦ out of phase. The present-day field at the site (Dec. = 19.6◦, Inc. =−62.7◦), is unusually steep and easterly in direction. The PSV curve is reasonably coherent with pfm9k.1b modelled values, especially for the period before 2000 BP. There is no data from NZ in the model for this time period, so the general correlation appears to imply regional coherence to the field. The master curve can potentially be used as a dating tool in archaeomagnetic and geological studies. A database of fifteen PSV records from the South West Pacific is compiled for use in spherical cap harmonic analysis (SCHA) models. Preliminary SCH analyses have been made for the period 2000-1000 BP, and suggestions made for continuation of modelling studies.