Marine magnetic anomalies as recorders of geomagnetic intensity variations

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Abstract

In addition to providing a robust record of past geomagnetic polarity reversals, marine magnetic anomalies often show shorter wavelength variations, which may provide information on geomagnetic intensity variations within intervals of constant polarity. To evaluate this possible geomagnetic signal, we compare sea surface profiles of the Central Anomaly with synthetic profiles based on Brunhes age (0-0.78 Ma) paleointensity records derived from deep sea sediments. The similarity of the synthetic profiles and observed profiles from the ultra-fast spreading southern East Pacific Rise suggests that geomagnetic intensity variations play an important role in the magnetization of the oceanic crust. This interpretation is further supported by systematic variations in the pattern of the Central Anomaly at slower spreading ridges, which are entirely consistent with a progressively smoother record of the sediment-derived paleointensity. If the sedimentary records, as calibrated to available absolute paleointensity data, accurately record variations in dipole intensity over the Brunhes, it follows that much of the Brunhes was characterized by geomagnetic intensities lower than either the mean dipole moment for the past 10 ka or the average for the period from 0.05 to 5.0 Ma. Furthermore, the sediment paleointensity records reflect the significant increase in geomagnetic intensity, from a low of ∼ 2 × 1022 Am2 near 40 ka to a peak value (11 × 1022 Am2) at ∼ 3 ka, that has been well documented from absolute paleointensity determinations. We suggest that geomagnetic intensity variations may be the most important cause of the rapid changes in the source layer magnetization near the ridge crest and the resultant Central Anomaly Magnetic High.

References (39)

  • CandeS.C. et al.

    Behavior of the Earth's palaeomagnetic field from small scale marine magnetic anomalies

    Nature

    (1974)
  • BlakelyR.J.

    Geomagnetic reversals and crustal spreading rates during the Miocene

    J. Geophys. Res.

    (1974)
  • SchoutenH. et al.

    Modeling the oceanic magnetic source layer

  • VogtP.R. et al.

    Magnetic telechemistry of oceanic crust?

    Nature

    (1973)
  • TiveyM.A. et al.

    The central anomaly magnetic high: implications for ocean crust construction and evolution

    J. Geophys. Res.

    (1987)
  • ReaD.K. et al.

    Short-wavelength magnetic anomalies in a region of rapid seafloor spreading

    Nature

    (1975)
  • WilsonD.S. et al.

    The Galapagos axial magnetic anomaly: evidence for the Emperor Event within the Brunhes and for a two-layer magnetic source

    Geophys. Res. Lett.

    (1981)
  • CandeS.C. et al.

    Ultrahigh resolution marine magnetic anomaly profiles: a record of continuous paleointensity variations?

    J. Geophys. Res.

    (1992)
  • KingJ.W. et al.

    A new rock-magnetic approach to selecting sediments for geomagnetic paleointensity studies: application to paleointensity for the last 4000 years

    J. Geophys. Res.

    (1983)
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      The shape of this anomaly displays the characteristic three lobes of the axial anomaly at slow spreading rates (e.g., Gee et al., 1996) in the South Amar segment and the southern part of Amar Minor South segment (south of 36°10′N), as well as in the Amar segment. The central lobe marks the position of the active spreading center, where fresh basalt bears a stronger magnetization (Central Anomaly Magnetic High or CAMH of Klitgord, 1976), and the two secondary lobes correspond to the stronger intensity of the geomagnetic field that prevailed after the Brunhes–Matuyama reversal (Gee et al., 1996). These secondary lobes are not observed in the northern Amar Minor South segment and the whole Amar Minor North segment.

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