Long-term trends in paleointensity: The contribution of DSDP/ODP submarine basaltic glass collections

Abstract The Deep Sea Drilling Project and the Ocean Drilling Program have been collecting fresh appearing submarine basaltic glass from the world’s oceans for over three decades. This glass has proved nearly ideal for estimating paleointensity variations of the Earth’s magnetic field. We compile here data for 726 paleointensity experiments from six publications on paleointensity using DSDP/ODP glass. We also include new data for an additional 225 specimens. These were obtained through the so-called “IZZI” paleointensity experiment of [Tauxe, L., Staudigel, H., 2004. Strength of the geomagnetic field in the cretaceous normal superchron: new data from submarine basaltic glass of the troodos ophiolite. Geochem. Geophys. Geosyst. 5 (2), Q02H06, doi:10.1029/2003GC000635 ] whereby infield-zerofield steps are alternated with the zerofield-infield steps to enhance quality assessment of the resulting data. The entire collection of data from 951 experiments was prepared for uploading to the MagIC data base ( http://earthref.org ), including original measurements, interpretations, and useful metadata. Excellent results were obtained throughout the depth ( > 1400  mbsf) and age (0–160 Ma) range sampled. DSDP/ODP glass data are compared with published paleointensity data meeting minimal acceptance criteria from the time interval 1–160 Ma. Paleolatitudes were estimated for all cooling units in a self-consistent manner for use in calculating virtual axial dipole moments. We conclude: (1) There is about a 20% difference in mean values between the SBG and the lava flow data ( 48 ± 36 and 57 ± 29  ZAm2 respectively). The difference is caused by the fact that there are more higher values in the lava flow data than in the SBG data set rather than a difference in the minimum values. Lava flows cooling over a periods of days to months can account for the discrepancy. (2) The positive relationship between polarity interval length and average paleofield intensity first hypothesized by [Cox, A.V., 1968. Lengths of geomagnetic polarity intervals. J. Geophys. Res. 73, 3247–3260] is supported by data compiled here. The Brunhes data (for which we have only a minimum estimate for polarity interval length) are consistent with a long polarity interval, suggesting that instead of racing toward reversal [Hulot, G., Eymin, C., Langlais, B., Mandea, M., Olsen, N., 2002. Small-scale structure of the geodynamo inferred from oersted and magsat satellite data. Nature 416, 620–623], we could instead be in the midst of a long stable polarity interval. (3) Because the average value appears to be a function of polarity interval length, it is probably not useful to calculate a mean value. Nonetheless, it appears that most of the time (apart from the Brunhes and the longest polarity intervals), the average dipole moment is substantially less than the present day value as suggested by [Juarez, T., Tauxe, L., Gee, J.S., Pick, T., 1998. The intensity of the earth’s magnetic field over the past 160 million years. Nature 394, 878–881].

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