New paleointensity results from rapidly cooled Icelandic lavas: Implications for Arctic geomagnetic field strength

Abstract

AbstractThe Earth's magnetic field is assumed to be a geocentric axial dipole (GAD) when averaged over sufficient time (105–106 years). Recent investigations of global paleosecular variation and time‐averaged field behavior on million year timescales generally support a predominantly dipole field in the Northern Hemisphere, but unique field structures at high southern latitudes suggest the presence of a substantial quadrupolar component. Average paleointensity results from Antarctica are approximately half the value predicted by a GAD field; this behavior has not been sufficiently investigated because there is a paucity of absolute paleointensity data from the high latitudes of the Arctic and Antarctic, so no adequate comparisons have been made between the two regions. We collected glassy volcanic material from 129 subaerial and subglacial volcanic units in Iceland in order to provide a suitable intensity data set at high northern latitudes. Forty‐four sites met our very strict specimen and site level selection criteria. Four Holocene sites have a median intensity value of 55.8 ± 15.6μT (virtual axial dipole moment = 78.1 ± 22.0 ZAm2), consistent with the present‐day field. Thirty‐seven sites are between 11 ka and 3.35 Ma with a median intensity of 33.1 ± 8.3 μT (47.0 ± 11.6 ZAm2). This median intensity is indistinguishable from some long‐term global field strength estimates. Reevaluation of existing high‐latitude data suggests a general agreement with our Iceland results, but there are still too few Antarctic sites to adequately compare Arctic and Antarctic field behaviors.