Authigenic ¹⁰Be/⁹Be ratio signatures of the cosmogenic nuclide production linked to geomagnetic dipole moment variation since the Brunhes/Matuyama boundary

Abstract

Geomagnetic dipole moment variations associated with polarity reversals and excursions are expressed by large changes of the cosmogenic nuclide beryllium‐10 (10Be) production rates. Authigenic 10Be/9Be ratios (proxy of atmospheric 10Be production) from oceanic cores therefore complete the classical information derived from relative paleointensity (RPI) records. This study presents new authigenic 10Be/9Be ratio results obtained from cores MD05‐2920 and MD05‐2930 collected in the west equatorial Pacific Ocean. Be ratios from cores MD05‐2920, MD05‐2930 and MD90‐0961 have been stacked and averaged. Variations of the authigenic 10Be/9Be ratio are analyzed and compared with the geomagnetic dipole low series reported from global RPI stacks. The largest 10Be overproduction episodes are related to dipole field collapses (below a threshold of 2 × 1022 Am2) associated with the Brunhes/Matuyama reversal, the Laschamp (41 ka) excursion, and the Iceland Basin event (190 ka). Other significant 10Be production peaks are correlated to geomagnetic excursions reported in literature. The record was then calibrated by using absolute dipole moment values drawn from the Geomagia and Pint paleointensity value databases. The 10Be‐derived geomagnetic dipole moment record, independent from sedimentary paleomagnetic data, covers the Brunhes‐Matuyama transition and the whole Brunhes Chron. It provides new and complementary data on the amplitude and timing of millennial‐scale geomagnetic dipole moment variations and particularly on dipole moment collapses triggering polarity instabilities.

The Role of Geomagnetic Field Intensity in Late Quaternary Evolution of Humans and Large Mammals

“…There is substantial agreement among Late Quaternary stacks of global sedimentary RPI data (Channell et al, ; Valet et al, ; Xuan et al, ; Ziegler et al, ) that are independently supported by 10 Be/ 9 Be data from marine sediments (e.g., Simon et al, ) due to the role of the geomagnetic field in modulating cosmogenic isotope ( 10 Be) production. Agreement is, however, poor among stacks of sedimentary RPI data and 10 Be/ 9 Be data in the 0‐40 ka interval (see Figure of Channell et al, ) that is attributed to subtle and often unrecognized drilling disturbance in poorly consolidated uppermost sediments recovered from the ocean floor.…”

Mid‐Brunhes magnetic excursions in marine isotope stages 9, 13, 14, and 15 (286, 495, 540, and 590 ka) at North Atlantic IODP Sites U1302/3, U1305, and U1306

“…[] deduced minima in axial dipole field intensity at 285, 493, 540, and 588 ka, and Simon et al . [] noted episodes of 10 Be overproduction, corresponding to paleointensity minima, at 284–288, 534–540, and 585–586 ka. In addition, there is a prominent peak in 10 Be/ 9 Be at ∼290 ka in sediments from the Portuguese Margin coincident with the Portuguese Margin excursion [ Carcaillet et al ., ; Thouveny et al ., ].…”

“…It has long been known that magnetic excursions and long‐lived reversals correspond to RPI minima [e.g., Valet and Meynadier , ] although not all RPI minima are apparently associated with magnetic excursions. All four excursions recorded at Sites U1302/3, U1306, and U1305 correlate with minima in the PISO RPI stack (Figures and ), and episodes of 10 Be overproduction in sediments from the equatorial western Pacific [ Ménabréaz et al ., ; Simon et al ., ].…”

The competition between coastal trace metal fluxes and oceanic mixing from the 10Be/9Be ratio: Implications for sedimentary records

“…In seawater the 10 Be/ 9 Be ratio thus provides important information on, e.g., mixing of reactive trace metals. The 10 Be/ 9 Be ratio in authigenic phases is also used to constrain chronologies of marine sediments, of 10 Be deposition rates, and variations of Earth's magnetic field [e.g., Kusakabe and Ku, 1984;Segl et al, 1984;Bourlès et al, 1989a;Christl et al, 2003;Carcaillet et al, 2004;Knudsen et al, 2008;Ménabréaz et al, 2014;Simon et al, 2016aSimon et al, , 2017. The 10 Be/ 9 Be ratio in authigenic phases is also used to constrain chronologies of marine sediments, of 10 Be deposition rates, and variations of Earth's magnetic field [e.g., Kusakabe and Ku, 1984;Segl et al, 1984;Bourlès et al, 1989a;Christl et al, 2003;Carcaillet et al, 2004;Knudsen et al, 2008;Ménabréaz et al, 2014;Simon et al, 2016aSimon et al, , 2017.…”

“…Locating the sites of exchange in turn is required to identify the oceanic environment in which authigenic 10 Be/ 9 Be ratios can be used to faithfully reconstruct continental weathering [von Blanckenburg and Bouchez, 2014] or the cosmic ray variations resulting from changes Earth's magnetic field strength [Simon et al, 2016a]. Locating the sites of exchange in turn is required to identify the oceanic environment in which authigenic 10 Be/ 9 Be ratios can be used to faithfully reconstruct continental weathering [von Blanckenburg and Bouchez, 2014] or the cosmic ray variations resulting from changes Earth's magnetic field strength [Simon et al, 2016a].…”