1988 Articles

Inclination anomalies from Indian Ocean sediments and the possibility of a standing non-dipole field

Schneider, David A.; Kent, Dennis V.

We report magnetic inclinations measured in deep-sea sediments of the equatorial Indian Ocean which record the behavior of a nondipole component of the timeaveraged geomagnetic field during the Plio-Pleistocene (0-5 Ma). The magnitude of the nondipole effect recorded in these sediments appears to depend on polarity state, with inclinations showing departures from geocentric axial dipole directions which are small (2°) during normal polarity and larger (5°) during reverse polarity times. The overall nondipole effect observed here is consistent with prior spherical harmonic estimates of the paleomagnetic field; the polarity bias found agrees, in both sense and magnitude, with earlier reports of polarity asymmetry in the low-degree zonal harmonic fields. The presence of this asymmetry supports previous suggestions of the existence of a standing component of the nondipole field which does not invert during reversals of the main field. We explore whether the standing field so indicated may have influenced paleomagnetic directions recorded during polarity transitions at other equatorial sites.