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

Abstract

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 absolute palaeointensity for the past 50 kyr has been compiled from archaeomagnetic and volcanic materials, and relative palaeointensities over the past 800 kyr have been obtained from sedimentary sequences. But a long-term record of geomagnetic intensity should also be carried by the thermoremanence of the oceanic crust. Here we show that near-seafloor magnetic anomalies recorded over the southern East Pacific Rise are well correlated with independent 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 ages of surficial lava flows in this region. The record of geomagnetic intensity preserved in the oceanic crust should provide a higher-time-resolution record of crustal accretion processes at mid-ocean ridges than has previously been obtainable.

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Figure 1: Location of survey and comparison of geomagnetic intensity variations in Brunhes from sedimentary records and near-bottom magnetic anomalies.
Figure 2: Comparison of absolute palaeointensities from seafloor glass samples with independent estimates of geomagnetic field intensity.
Figure 3: Representative absolute palaeointensity results.
Figure 4: Similarity of glass palaeointensities and inversion solution magnetization for profile at 19.75° S.
Figure 5: Lava emplacement models and associated magnetic anomaly profiles for profiles at 19.75° S and 17.38° S on the East Pacific Rise.

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Acknowledgements

We thank D.V. Kent and S. Carbotte for helpful comments on the manuscript. H. Schouten provided an exhaustive review. This work was supported by funding from the National Science Foundation.

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Correspondence to Jeffrey S. Gee.

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Gee, J., Cande, S., Hildebrand, J. et al. Geomagnetic intensity variations over the past 780 kyr obtained from near-seafloor magnetic anomalies. Nature 408, 827–832 (2000). https://doi.org/10.1038/35048513

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