The potential for a continuous 10Be record measured on ice chips from a borehole

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.