Amplitude and timing of the Laschamp geomagnetic dipole low from the global atmospheric ¹⁰Be overproduction: Contribution of authigenic ¹⁰Be/⁹Be ratios in west equatorial Pacific sediments

Abstract

Authigenic 10Be/9Be ratios were measured along a sediment core collected in the west equatorial Pacific in order to reconstruct cosmogenic 10Be production variations near the equator, where the geomagnetic modulation is maximum. From 60 to 20 ka, the single significant 10Be production impulse recorded at 41 ka results from the geomagnetic dipole low that triggered the Laschamp excursion. No significant 10Be overproduction signature is recorded at the age of the Mono Lake excursion (∼34 ka). A compilation of authigenic 10Be/9Be records obtained from sediments was averaged over a 1 kyr window and compared with the 1 kyr averaged 10Be flux record of Greenland ice cores. Their remarkable similarity demonstrates that 10Be production is globally modulated by geomagnetic dipole variations and redistributed by atmosphere dynamics. After calibration using absolute values of the virtual dipole moment drawn from paleomagnetic database, the authigenic 10Be/9Be stack allows reconstructing the geomagnetic dipole moment variations over the 20–50 ka time interval. Between 48 and 41 ka, the dipole moment collapsed at a rate of −1.5 × 1022 A m2 kyr−1, which will be an interesting criterion for the assessment of the loss rate of the historical field and the comparison of dipole moment loss prior to excursions and reversals. After a 2 kyr duration of the minimum dipole moment (∼1 × 1022 A m2), a slow increase started at 39 ka, progressively reaching 5 × 1022 A m2 at 20 ka. The absence of a significant dipole moment drop at 34 ka, the age of the Mono lake excursion, suggests that the duration and amplitude of the dipole weakening cannot be compared with that of the Laschamp. This study provides a reliable basis to model the production of radiocarbon and in situ cosmogenic nuclides and to improve the calibration of these dating methods.

Beryllium isotopes as tracers of Lake Lisan (last Glacial Dead Sea) hydrology and the Laschamp geomagnetic excursion

“…the 10 Be concentration in the closest samples that fit the 10 Be-Al + Fe correlation). These values are similar to the expected ∼2 fold increase in the 10 Be signal during geomagnetic excursions (Elsasser et al, 1956;Wagner et al, 2000;Carcaillet et al, 2004;Masarik and Beer, 2009;Ménabréaz et al, 2011Ménabréaz et al, , 2012 indicating that although the Lisan Formation cannot be used to monitor moderate variations in the 10 Be production induced by solar variability, production rate variations caused by strong variations in the geomagnetic field are detectable. This demonstrates the applicability of using 10 Be as a chronostratigraphic horizon of continental archives (Nilsson et al, 2011) and the global occurrence of the 10 Be peak caused by the Laschamp excursion (Ménabréaz et al, 2012).…”

“…4, Section 3.3). Six of these samples form a positive 10 Be peak across the interval of the Laschamp paleomagnetic excursion at ∼41 ka cal BP (Guillou et al, 2004;Singer et al, 2009;Ménabréaz et al, 2011Ménabréaz et al, , 2012Nilsson et al, 2011). The conclusion that the outlier samples relate to geomag- 10 Be/(Al + Fe) vs. age (B), 10 Be vs. age (C) and 10 Be vs. sample elevation in the sampled M1 section (D).…”

“…Usoskin, 2008;Beer et al, 2012;Ménabréaz et al, 2012). Generally, high-temporal-resolution reconstructions cannot be obtained from marine sediments due to effective bioturbation.…”

Extensive wet episodes in Late Glacial Australia resulting from high-latitude forcings

“…16). Overall, the observed ε Nd trend between about 90 and 20 ka correlates well with palaeoprecipitation records for the tropical western Pacific region5171819 (Fig. 3a,b,c).…”

Recent progress on rock and paleomagnetism by means of deepsea drilling

“…1 10 nm , , e.g., Kopp andKirschvink, 2008 TEM 2000 first-order reversal curve FORC e.g., Roberts et al, 2000ARM IRM e.g., Egli, 2004Yamazaki, 2008Egli et al, 2010;Li et al, 2012;Chang et al, 2014Roberts et al, 2011, 2012Yamazaki, 2012;Yamazaki and Ikehara, 2012 e.g., Yamamoto et al, 2003;Paterson et al, 2014;Cromwell et al, 2015 ARM, IRM 1990 e.g., Tauxe, 1993 90 / 80 Sint-800; Guyodo and Valet, 1999 IODP e.g., Karlin, 1990; Ohno et al, 2012) and Site U1308 (gray, Channell et al, 2016) in the North Atlantic, and (lower) the EPAPIS-3000 stack from equatorial Pacific piston cores (Yamazaki and Oda, 2005 Suganuma et al, 2010;Ménabréaz et al, 2012;Horiuchi et al, 2016 10 Be Granot et al, 2012 e.g., Channell et al, 1998;Yamazaki, 1999;Thouveny et al, 2004Xuan et al, 2008Valet et al, 2011Kitaba et al, 2013 Kono, 1980;Tarduno et al, 2003 Expedition 330 Koppers et al, 2012aKoppers et al, 2012bSteinberger et al, 2004Hassan et al, 2016 anisotropy of magnetic susceptibility, AMS AMS AMS AMS AMS …”