Abstract
Ice cores are excellent archives for obtaining long and continuous 10Be records. However, traditional ice core 10Be measurements required a lot of ice (0.5–1kg) and often needed to be connected to a large and costly ice core project. These reasons have been the factors limiting the number and variety of 10Be projects and data. In this paper, we show measurements of 10Be on small samples (∼45g) of continuous auger ice chips from a borehole at Little Dome C (LDC), East Antarctica. The sample preparation method for 10Be accelerator mass spectrometry (AMS) was tested and optimized using test samples (∼50g) including well-mixed surface ice chips from the LDC site, snow collected in Lund (Sweden) and frozen Milli-Q water. The results show that our small ice samples should be processed without ion exchange filtration of the melt water and cleaning the subsequent Be(OH)2 precipitate. In addition, co-precipitating Be with Fe led to more reproducible measurement currents and offer the potential for higher efficiency and precision via longer measurement time. We applied the established preparation method to measure 10Be on 76 samples of the auger ice chips. The resulting 10Be concentration record for the period from 1354 to 1950 CE agrees well with the 10Be concentration in a South Pole ice core and the global 14C production rate and thus reflects well the atmospheric production signal of 10Be. We also observed insignificant mixing among the ice chip samples during the process of drilling and retrieving the ice. Therefore, the new ice chip samples are promising for assessing the long-term changes in 10Be deposition at different ice core sites. A wide application of this novel ice chip samples will increase the variety of 10Be records which will help to improve the assessment of long-term solar and geomagnetic shielding of galactic cosmic rays.
Highlights
10Be is a long-lived radionuclide (T1/2=1.387±0.012 Ma, (Korschinek et al, 2010)) produced mainly from cosmic ray-induced spallation of nitrogen and oxygen atoms in the atmosphere. 10Be has a wide range of applications ranging from reconstructing solar activity and the Earth’s magnetic shielding of galactic cosmic rays, to studying atmospheric mixing, hydrological processes and dating of geological archives (Muscheler et al, 2016; Zheng et al, 2021; Mekhaldi et al, 2020; Adolphi and Muscheler, 2016; Alley, 1995)
The British Antarctic Survey has developed a new drilling method, the so called Rapid Access Isotope Drill (RAID), that is based on an auger enclosed in a barrel that collects ice chips instead of recovering a fully intact ice core (Rix et al, 2019)
This opens up the prospect of fast recovery of samples for a continuous 10Be record not necessarily connected to a large and costly ice core project
Summary
For most of these applications, the samples (e.g. from rocks, sediments or ice cores) contain only a tiny amount of 10Be, i.e. in the range of 105 to 108 atoms per sample (Christl and Kubik, 2013). Because of the naturally low concentration of 10Be, a Abbreviation: AMS, Accelerator mass spectrometry; ANOVA, Analysis of variance; EPICA Dome C, EDC; IEC, Ion exchange column; LDC, Little Dome C; RAID, Rapid Access Isotope Drill
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