A PALEOMAGNETIC SECULAR VARIATION RECORD FOR NEW-ZEALAND DURING THE PAST 2500 YEARS

A record of the secular variation of the geomagnetic field over New Zealand for the past 2500 years has been compiled by measuring and averaging logs of the primary magnetization of five cores of lacustrine sediment from Lake Pounui. A time-scale is provided by four radiocarbon age determinations. The record is constrained by historical observations for the last 350 years and is in good agreement with instantaneous palaeomagnetic directions from lava flows. This is the first continuous record of secular variation from New Zealand and one of only a few from the southern hemisphere. Together with existing Australian records, the results show significant evidence of westward drift of the geomagnetic field over the past 2500 years. It contains new information for modelling the geomagnetic secular variation in the southern hemisphere and will also be valuable for dating applications within New Zealand.