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Long-term seafloor geomagnetic station in the northwest Pacific: A possible candidate for a seafloor geomagnetic observatory


For two years, geomagnetic variations have been measured at the seafloor in the northwest Pacific. The seafloor data consist of the geomagnetic vector field measured by a three-component fluxgate magnetometer and the absolute scalar total force measured by an Overhauser (1953) magnetometer with attitude measurements for both orientation and tilt. Using the attitude data, the geomagnetic data at a site in the northwest Pacific (41o06′08″N, 159°57′47″E, -5580 m), hereafter referred to as NWP, were converted into the same reference frame as land and satellite measurements. Short-period variations of the converted vector data were examined by Hamano’s (2002) global time domain analysis method, which showed compatibility of the seafloor geomagnetic observatory data with the existing land observatory network. The smooth and gradual change of the Earth’s main field (i.e., the geomagnetic secular variation) was also found consistent with those predicted by the latest International Geomagnetic Reference Field (IGRF-10; IAGA, 2005) and by Ørsted Satellite (Olsen, 2002) for not only the scalar field but also the vector field. This means that observation of the geomagnetic vector secular variation is now feasible on the seafloor.


  1. Barker, F. S. and D. R. Barraclough, The effects of the non-uniform distribution of magnetic observatory data on secular variation models, Phys. Earth Planet. Inter., 37, 65–73, 1985.

  2. Beranzoli, L., T. Braun, M. Calcara, P. Casale, A. De Santis, G. D’Anna, D. Di Mauro, G. Etiope, P. Favali, F. Frugoni, J.-L. Fuda, F. Gamberi, M. Marani, C. Millot, C. Montuori, and G. Smriglio, Mission results from the first GEOSTAR observatory (Adriatic Sea, 1998), Earth Planets Space, 55, 361–373, 2003.

  3. Chave, A. D., D. J. Thompson, and M. E. Ander, On the robust estimation of power spectra, coherences, and transfer functions, J. Geophys. Res., 92, 633–648, 1987.

  4. Copley, J., All wired up, Nature, 427, 10, 2004.

  5. Hamano, Y., A new time-domain approach for the electromagnetic induction problem in a three-dimensional heterogeneous Earth, Geophys. J. Int., 150, 753–769, 2002.

  6. International Association of Geomagnetism and Aeronomy (IAGA), Division V, Working Group VMOD: Geomagnetic Field Modeling, The 10th generation of International Geomagnetic Reference Field, Geophys. J. Int., 161, 561–565, 2005.

  7. Jackson, A. and J. Bloxham, Mapping the fluid flow and shear near the core surface using the radial and horizontal components of the magnetic field, Geophys. J. Int., 132, 199–212, 1991.

  8. Kerridge, D., INTERMAGNET: Worldwide near-real-time geomagnetic observatory data, Proc. Workshop on Space Weather, ESTEC, 2001.

  9. Langel, R. A., R. H. Estes, G. D. Mead, E. B. Fabiano, and E. R. Lancaster, Initial geomagnetic field model from Magsat vector data, Geophys. Res. Lett., 7, 793–796, 1980.

  10. Langel, R. A., R. T. Baldwin, and A. W. Green, Toward an improved distribution of magnetic observatories for modeling of the main geomagnetic field and its temporal change, J. Geomag. Geoelectr., 47, 475–508, 1995.

  11. LeMouel, J. L., Outer core geostrophic flow and secular variation of Earth’s magnetic field, Nature, 311, 734–735, 1984.

  12. Macmillan, S., S. Maus, T. Bondar, A. Chambodut, V. Golovkov, R. Holme, B. Langlais, V. Lesur, F. Lowes, H. Lühr, W. Mai, M. Mandea, N. Olsen, M. Rother, T. Sabaka, A. Thomson, and I. Wardinski, The 9th generation international geomagnetic reference field, Phys. Earth Planet. Inter., 140, 253–254, 2003.

  13. Mandea, M. and S. Macmillan, International Geomagnetic Reference Field—the eighth generation, Earth Planets Space, 52, 1119–1124, 2000.

  14. Nakanishi, M. and E. L. Winterer, Tectonic history of the Pacific-Farallon-Phoenix triple junction from Late Jurassic to Early Cretaceous: An abandoned Mesozoic spreading system in the Central Pacific Basin, J. Geohpys. Res., 103, 12453–12468, 1998.

  15. Neubert, T., M. Mandea, G. Hulot, von R. Frese, F. Primdahl, J. L. Jørgensen, E. Friis-Christensen, P. Stauning, N. Olsen, and T. Risbo, Ørsted satellite captures high-precision geomagnetic field data, Eos, Trans. Amer. Geophys. Union, 82, 81–88, 2001.

  16. Olsen, N., A model of the geomagnetic field and its secular variation for epoch 2000 estimated from Ørsted data, Geophys. J. Int., 149, 454–462, 2002.

  17. Overhauser, A. W., Polarization of nuclei in metals, Phys. Rev., 92, 411–415, 1953.

  18. Reigber, C., H. Luhr, and P. Schwintzer, CHAMP mission status, Adv. Space Res., 30, 129–134, 2002.

  19. Roberts, P. and S. Scott, On the analysis of the secular variation I. A hydrodynamic constraint: theory, J. Geomag. Geoelectr., 17, 137–151, 1965.

  20. Toh, H. and Y. Hamano, The first realtime measurement of seafloor geomagnetic total force—Ocean Hemisphere Project Network, J. Japan Soc. Mar. Surv. Tech., 9, 1–23, 1997.

  21. Toh, H., T. Goto, and Y. Hamano, A new seafloor electromagnetic station with an Overhauser magnetometer, a magnetotelluric variograph and an acoustic telemetry modem, Earth Planets Space, 50, 895–903, 1998.

  22. Toh, H., Y. Hamano, M. Ichiki, and H. Utada, Geomagnetic observatory operates at the seafloor in the Northwest Pacific Ocean, Eos, Trans. Amer. Geophys. Union, 85, 467–473, 2004.

  23. Voorhies, C. V. and G. E. Backus, Steady flows at the top of the core from geomagnetic field models: The steady motions theorem, Geophys. Astrophys. Fluid Dyn., 32, 163–173, 1985.

  24. Whaler, K., Does the whole of the Earth’s core convect?, Nature, 287, 528–530, 1980.

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Correspondence to H. Toh.

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Toh, H., Hamano, Y. & Ichiki, M. Long-term seafloor geomagnetic station in the northwest Pacific: A possible candidate for a seafloor geomagnetic observatory. Earth Planet Sp 58, 697–705 (2006).

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Key words

  • Long-term seafloor geomagnetic observation
  • secular variation
  • IGRF
  • satellite measurements
  • the Earth’s main field
  • attitude data
  • scalar and vector geomagnetic fields