Item

Abstract

Current millennial-scale time-varying global geomagnetic field models suffer from a lack of intensity data compared to directional data, because only thermoremanently magnetized material can provide absolute information about the past field strength. The number of archeomagnetic artefacts that can provide such data diminishes rapidly prior to 3000 BC. Sediment cores provide time series of declination and inclination and of variations of magnetization: the latter can reflect relative geomagnetic field variations if suitably normalized. We propose a calibration technique based on predictions from global models and use the CALS7K.2 model to alibrate relative paleointensity records from 22 globally distributed locations and assess whether they reflect actual field variations. All except a few contain useful information for 0 to 7 ka and could be used to improve the existing models. Using synthetic data from a numerical dynamo simulation we show that with the existing directional data the distribution of intensity data has an important influence on model quality. Intensity data from a broad range of latitudes seem particularly important. This study opens the possibility of extending global time-varying geomagnetic field models further back in time than the current 7 kyr interval.