The intensity of the time-averaged geomagnetic field: the last 5 Myr

Abstract

The existing database for paleointensity estimates of the ancient geomagnetic field contains more than 1500 data points collected through decades of effort. Despite the huge amount of work put into obtaining these data, there remains a strong bias in the age and global distribution of the data toward very young results from a few locations. Also, few of the data meet strict criteria for reliability and most are of unknown quality. In order to improve the age and spatial distribution of the paleointensity database, we have carried out paleointensity experiments on submarine basaltic glasses from a number of DSDP sites. Of particular interest are the sites that provide paleointensity data spanning the time period 0.3-5 Ma, a time of relatively few high quality published data points. Our new data are concordant with contemporaneous data from the published literature that meet minimum acceptance criteria, and the combined data set yields an average dipole moment of 5.49 +/- 2.36*10^22 Am². This average value is comparable to the average paleofield for the period 5-160 Ma (4.2 +/- 2.3*10^22 Am²) [T. Juarez, L. Tauxe, J.S. Gee and T. Pick (1998) Nature 394, 878-881] and is substantially less than the value of approximately 8U1022 Am2 often quoted for the last 5 Myr (e.g. [McFadden and McElhinny (1982) J. Geomagn. Geoelectr. 34, 163-189; A.T. Goguitchaichvili, M. Preévot and P. Camps (1999) Earth Planet. Sci. Lett. 167, 15-34]).