Intrinsic bias in averaging paleomagnetic data

The transformation of isotropically distributed geomagnetic poles to local site directions introduces slight apparent inclination shallowing if the directional average is compared to the geocentric axial dipole direction. This effect depends on site latitude and pole dispersions. For typical dispersions of poles, theta(63) between 10 degrees and 20 degrees, the average inclination will appear too shallow by about 1 degrees to 2 degrees for site latitudes of 10 degrees to 60 degrees North or South. On the other hand, when some of the scatter might be due to isotropic scatter in directions, averaging all the data in polar space, will introduce a steepening effect. For most paleomagnetic studies this intrinsic inclination bias will be small in comparison with other uncertainties, typically of the order of 5 degrees to 10 degrees. However, for integrated high resolution studies of specific aspects of the geomagnetic field this methodological ambiguity might bias the results, and we caution against averaging paleomagnetic data only in directional space.