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.2019 Aug 7;5(8):eaaw4621.
doi: 10.1126/sciadv.aaw4621. eCollection 2019 Aug.

Synchronizing volcanic, sedimentary, and ice core records of Earth's last magnetic polarity reversal

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Synchronizing volcanic, sedimentary, and ice core records of Earth's last magnetic polarity reversal

Brad S Singer et al. Sci Adv..

Abstract

Reversal of Earth's magnetic field polarity every 105 to 106 years is among the most far-reaching, yet enigmatic, geophysical phenomena. The short duration of reversals make precise temporal records of past magnetic field behavior paramount to understanding the processes that produce them. We correlate new40Ar/39Ar dates from transitionally magnetized lava flows to astronomically dated sediment and ice records to map the evolution of Earth's last reversal. The final 180° polarity reversal at ~773 ka culminates a complex process beginning at ~795 ka with weakening of the field, succeeded by increased field intensity manifested in sediments and ice, and then by an excursion and weakening of intensity at ~784 ka that heralds a >10 ka period wherein sediments record highly variable directions. The 22 ka evolution of this reversal suggested by our findings is mirrored by a numerical geodynamo simulation that may capture much of the naturally observed reversal process.

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Figures

Fig. 1
Fig. 1. Lava flow sequences that record transitional geomagnetic field behavior associated with the Matuyama-Brunhes reversal.
Vertical axes are the lava flow site numbers from the original studies arranged in order of eruption from oldest at the bottom to youngest on top. VGP lat., virtual geomagnetic pole latitude in degrees.40Ar/39Ar ages (in thousand years) for dated flows are shown with ±2σ analytical uncertainties. The paleomagnetic directional data are from Punaruu South, Tahiti (29); Quebrada Turbia West-10 and West-11, Chile (30); Los Tilos, La Palma (31); Punaruu North, Tahiti (see the Supplementary Materials) (16); Guadeloupe (17); and Haleakala (14). The red open circles are determinations of the virtual dipole moment (VDM) for samples measured in this study from Haleakala (see the Supplementary Materials), Punaruu North [data from (16)], and Chile [data from (27)].
Fig. 2
Fig. 2. Age spectra and isochrons from four representative M-B lava samples in Table 1.
Samples from bottom to top are from Punaruu North, Chile, La Palma, and Haleakala, respectively.
Fig. 3
Fig. 3. Correlation of volcanic, sedimentary, and ice core records of geomagnetic field behavior associated with the Matuyama-Brunhes reversal.
(A) VGPs from dated lavas in each of the seven sections of Fig. 1 are shown with 2σ age uncertainties. The VGPs of undated flows that crop out between dated flows are plotted using the weighted mean age calculated for transitional lavas in each section and are shown without age uncertainty. The purple, blue, and pink vertical bands are the weighted mean ages of lavas in Punaruu North, Chile, and Guadeloupe combined, and Punaruu South, La Palma, and Haleakala combined, respectively, as discussed in the text. (B) High–deposition rate marine sediment records of VGP evolution, each placed on its independent astronomical age model (data sources in Table 2) that is not tied to an M-B reversal age. (C) Paleointensity proxy records spanning the M-B reversal. Plotted are relative paleointensity (RPI) records (×20) for ODP 984, ODP 1308, and MD90-961 sediment cores; the virtual axial dipole moment (VADM; units of 1022 Am2) for the PISO 1500 stack of 13 marine records; and10Be flux records [104 atoms/g/cm2 for the Epica Dome (EDC) Antarctic ice core; authigenic decay-corrected10Be × 108 atoms/g for the MD98-2183 marine sediment core; data sources in Table 2)]. Lava VDMs are from this study (table S2) and (16,27). Note that for gauging paleointensity only, the unfilled stars for normally and reversely magnetized lavas are shown at the same age as the weighted mean age of the associated transitional lavas; see Fig. 1 for ages of these flows.
Fig. 4
Fig. 4. VGPs from seven lava flow sequences (located at the “×” symbols) that record the M-B reversal process.
The historic NAD antipodes (i.e., the average position and antipode of the maximum vertical field of the Australian NAD flux patch between 1590 and 1995 AD) are from (28).
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References

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