A new continuous 10Be record for the last 5000 years measured on ice chips from a borehole in East Antarctica

Abstract

<p><sup>10</sup>Be concentrations measured from ice cores are key records for the reconstruction of long-term changes in solar activity and geomagnetic field intensity. Furthermore, <sup>10</sup>Be records have additional applications in the dating of ice cores via the global cosmic ray signal, and studies of snow accumulation rates and atmospheric transport and deposition. Here, we present a new long-term <sup>10</sup>Be record from ice chips recovered in austral summer 2017/2018 from Little Dome C, close to Dome Concordia station in East Antarctica and the location of the Beyond-EPICA drilling. The ice chips were drilled by the so-called Rapid Access Isotope Drill method recently developed by the British Antarctic Survey [1]. This new drilling method is based on an auger enclosed in a barrel that quickly collects ice chips instead of recovering a fully intact ice core. The drill design allowed for about 461 m of ice to be drilled in Antarctica in only 104 hours and the chips are suitable for stable water isotope and <sup>10</sup>Be analysis. This opens up the prospect of fast recovery of samples for a continuous <sup>10</sup>Be record not necessarily connected to a large and costly ice core project.</p><p>Our new <sup>10</sup>Be record covers the upper 161 meters of ice chips encompassing the last 5000 years. We prepared and measured the ice chip samples using the optimized method demonstrated in our recent publication [2]. We improved the initial timescale of the ice chips via synchronizing changes in the <sup>10</sup>Be concentration to changes in the atmospheric <sup>14</sup>C concentration inferred from IntCal20. We then reconstruct solar activity and geomagnetic field intensity from the <sup>10</sup>Be record using a newly developed Bayesian model aiming at separating the influence of the two processes. The reconstructed solar activity is compared to similar reconstructions based on other ice core <sup>10</sup>Be records and the atmospheric <sup>14</sup>C record. Similarly, the reconstructed geomagnetic field intensity is compared to the results of global geomagnetic field models that combine paleomagnetic data from archaeological artefacts, igneous rocks and sediments. We highlight the advantages of the new Bayesian model to separate and reconstruct the solar and geomagnetic field signals compared to the conventional methods where an independent geomagnetic field reconstruction is in fact required to reconstruct the solar signal.</p><p> </p><p>[1]      J. Rix, R. Mulvaney, J. Hong, D.A.N. Ashurst, Development of the British Antarctic Survey Rapid Access Isotope Drill, J. Glaciol. 65 (2019) 288–298. https://doi.org/10.1017/jog.2019.9.</p><p>[2]      L. Nguyen, C.I. Paleari, S. Müller, M. Christl, F. Mekhaldi, P. Gautschi, R. Mulvaney, J. Rix, R. Muscheler, The potential for a continuous 10Be record measured on ice chips from a borehole, Results in Geochemistry. 5 (2021) 100012. https://doi.org/10.1016/j.ringeo.2021.100012.</p><p> </p>