Relative geomagnetic intensity of the field during the last 140 ka

Relative magnetic field palaeointensities have been obtained from three marine cores in the Somali basin (western Indian Ocean). The correlation between the records based on changes in the low-field susceptibility and the inclination is extremely detailed. A time versus depth correlation has been established from the δ 18O record. The remanence intensity was normalized with respect to the anhysteretic remanent magnetization with special attention to changes in grain sizes, coercivities and mineralogy. The synthetic record of relative palaeointensity has been extended to cover the last 140 ka. The quasi-cyclic pattern observed during the last 80 ka confirms the results previously obtained in the Mediterranean sea and thereby establishes its dominantly dipolar character. Between 140 and 80 ka the field intensity exhibits a much longer cycle. Spectral analysis of the intensity records shows the presence of two dominant periodicities, but the length of the signal is too short to document the presence of a stationary process.