An analysis of paleomagnetic secular variation in the Holocene

Abstract

Time series records of Holocene paleomagnetic secular variation (PSV) contain large-amplitude oscillations in both inclination and declination with periods on the order of 10 3 yr. This oscillatory character, along with the phase relationship between records from nearby sites, suggests that the source of PSV consists of propagating wave-like disturbances originating in the outer core. An analysis has been made of PSV records from nine sites located on four continents: North America, South America, Eurasia, and Australia. Both single site modelling and multiple site cross-correlation analyses have been made. Sites on the same continent exhibit a high degree of correlation, whereas the correlation between sites on different continents is generally much lower. Models consisting of two plane waves, one having a period ranging from 2400 to 3200 yr and the second with a period of about half that of the first, have been fitted to the data at eight of the nine sites. The propagation directions derived from the best-fitting wave models and from phase delays resolved from cross-correlation analyses have strong poleward components in both hemispheres. There is evidence of both eastward and westward components of motion, but these are smaller than the poleward components. In both hemispheres all propagation directions are within ±40° of the pole. This indicates that Holocene PSV may consist of a superposition of propagating wave-like disturbances with either eastward or westward components, but also with strong poleward components of motion. Two interpretations are possible: these represent either non-dipole fields advected poleward by a meridional circulation pattern in the outer core which is antisymmetric about the equator, or alternatively, propagating αω-dynamo wave instabilities generated just beneath the core-mantle boundary.