A new high-resolution record of Holocene geomagnetic secular variation from New Zealand

Abstract

We present the first full Holocene palaeomagnetic secular variation record from New Zealand. The 11 500 year-long record, from the sediments of Mavora Lakes, comprises composite declination, inclination and relative palaeointensity logs, compiled from two six-metre long cores and the uppermost 1.5 m of another. An age model has been developed from 28 AMS radiocarbon age determinations on fragments of southern beech (Lophozonia menziesii and Fuscospora cliffortioides) leaves. The excellent between-core correlation in all three components of the field results in a high-resolution palaeosecular variation record, with precise and accurate age control. The variations change in character from high amplitude in-phase declination and inclination swings in the earliest part of the record to low amplitude variations in the middle part and declination and inclination swings that are 90° out of phase, leading to broad looping of the vector in the upper part of the record, that is consistent with westward drifting sources in the outer core. The present-day field at the site (Dec = 24.2°E, Inc=−70.7°, F=59 μT) represents a rare steep and easterly extreme direction, but close to average intensity. The palaeointensity is inferred to have varied between about 40 and 90 μT, with variations that, to some extent, mirror variations in the virtual axial geomagnetic dipole moment seen from global data, but also show some notable differences, particularly in the past few thousand years.