ANALYSIS OF 11 MYR OF GEOMAGNETIC INTENSITY VARIATION

We have conducted a detailed exploratory analysis of an II million yea r long almost continuous record of relative geomagnetic paleointensity from a sediment core acquired on Deep Sea Drilling Project Leg 73, at Site 522 in the South Atlantic. We assess the quality of the paleoint ensity record using spectral methods and conclude that the relative in tensity record is minimally influenced by climate variations. Isotherm al remanence is shown to be the most effective normalizer for these da ta, although both susceptibility and anhysteretic remanence are also a dequate. Statistical analysis shows that the paleointensity variations follow a gamma distribution, and are compatible with predictions from modified paleosecular variation models and global absolute paleointen sity data. When subdivided by polarity interval, the variability in pa leointensity is proportional to the average, and further, the average is weakly correlated with interval length. Spectral estimates for time s from 28.77 until 22.74 Ma, when the reversal rate is about 4 Myr(-1) , are compatible with a Poisson model in which the spectrum of intensi ty variations is dominated by the reversal process in the frequency ra nge 1-50 Mgr(-1) In contrast, between 34.7 and 29.4 Ma, when the rever sal rate is about 1.6 Myr(-1), the spectra indicate a different secula r variation regime. The magnetic field is stronger, and more variable, and a strong peak in the spectrum occurs at about 8 Myr(-1). This pea k magi be a reflection of the same signal as recorded by the small var iations known as tiny wiggles seen in marine magnetic anomaly profiles .