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Weaker axially dipolar time-averaged paleomagnetic field based on multidomain-corrected paleointensities from Galapagos lavas

  1. Pierre Rochettec
  1. aEarth and Planetary Sciences, Rutgers University, Piscataway, NJ 08854;
  2. bLamont–Doherty Earth Observatory, Columbia University, Palisades, NY 10964;
  3. cAix-Marseille Université, CNRS, IRD, CEREGE UM34, 13545 Aix en Provence, France

  1. Edited by Norman H. Sleep, Stanford University, Stanford, CA, and approved October 19, 2015 (received for review March 18, 2015)

Significance

Our multidomain-corrected paleointensity results from near-equatorial lavas from the Galapagos give a mean intensity only about one-half of that obtained from the only robust published result from near-polar lavas from Antarctica. This new evidence is consistent with the factor-of-2 equator-to-pole paleointensity signature of a geocentric axial dipole field and also indicates that the time-averaged field is considerably weaker than the present-day field. The resulting dipole moment provides a new calibration standard for cosmogenic isotope production rates and suggests that the present decrease in geomagnetic field intensity may simply be a return to a more average magnitude rather than a harbinger of a polarity reversal.

Abstract

The geomagnetic field is predominantly dipolar today, and high-fidelity paleomagnetic mean directions from all over the globe strongly support the geocentric axial dipole (GAD) hypothesis for the past few million years. However, the bulk of paleointensity data fails to coincide with the axial dipole prediction of a factor-of-2 equator-to-pole increase in mean field strength, leaving the core dynamo process an enigma. Here, we obtain a multidomain-corrected Pliocene–Pleistocene average paleointensity of 21.6 ± 11.0 µT recorded by 27 lava flows from the Galapagos Archipelago near the Equator. Our new result in conjunction with a published comprehensive study of single-domain–behaved paleointensities from Antarctica (33.4 ± 13.9 µT) that also correspond to GAD directions suggests that the overall average paleomagnetic field over the past few million years has indeed been dominantly dipolar in intensity yet only ∼60% of the present-day field strength, with a long-term average virtual axial dipole magnetic moment of the Earth of only 4.9 ± 2.4 × 1022 A⋅m2.

Footnotes

  • ↵1Present address: Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139.

  • ↵2To whom correspondence should be addressed. Email: dvk{at}rutgers.edu.

  • Author contributions: H.W. and D.V.K. designed research; H.W. performed research; P.R. provided samples and preliminary data; H.W. and D.V.K. analyzed data; and H.W., D.V.K., and P.R. wrote the paper.

  • The authors declare no conflict of interest.

  • This article is a PNAS Direct Submission.

  • This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10.1073/pnas.1505450112/-/DCSupplemental.

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