Geomagnetic intensity variations over the past 780 kyr obtained from near-seafloor magnetic anomalies

Knowledge of past variations in the intensity of the Earth's magnetic field provides an important constraint on models of the geodynamo. A record of a bsolute palaeointensity for the past 50 kyr has been compiled from archaeom agnetic and volcanic materials, and relative palaeointensities over the pas t 800 kyr have been obtained from sedimentary sequences. But a long-term re cord of geomagnetic intensity should also be carried by the thermoremanence of the oceanic crust. Here we show that near-seafloor magnetic anomalies r ecorded over the southern East Pacific Rise are well correlated with indepe ndent estimates of geomagnetic intensity during the past 780 kyr. Moreover, the pattern of absolute palaeointensity of seafloor glass samples from the same area agrees with the well-documented dipole intensity pattern for the past 50 kyr. A comparison of palaeointensities derived from seafloor glass samples with global intensity variations thus allows us to estimate the ag es of surficial lava flows in this region. The record of geomagnetic intens ity preserved in the oceanic crust should provide a higher-time-resolution record of crustal accretion processes at mid-ocean ridges than has previous ly been obtainable.