Spatial variability of ¹⁰ Be in deep ice and the influence of the measurement procedure

Abstract. Concentrations of the radionuclide 10Be are often measured in ice cores to reconstruct solar activity and the geomagnetic field, as well as to improve, verify and extend timescales. However, concentration spikes in deep ice, concentrations decreasing faster with age than possible through radioactive decay, and an increasing dust association with depth suggest 10Be is subject to post-depositional processes, which can alter measured 10Be concentrations, that are poorly understood. In ice from EPICA Dome C, we analysed the progression of horizontal 10Be variability with depth, the effect of ion exchange columns and acidic treatment on the measured concentrations and the potential influence of the microstructure. We found that acidic treatment had no effect on the measurement results, while samples treated through ion exchange columns showed a reduction in measured 10Be concentrations of up to 40 %, with the proportion apparently increasing with depth and age. This is the likely cause for the apparent loss of 10Be in deep ice in a previous study. We found that even in samples as small as (10 × 1.5 × 1.5) cm3 (ca. 20 g), the grain boundary content does not vary significantly between samples, while 10Be concentrations differ, so 10Be cannot be homogenously distributed along grain boundaries. However, our data suggest an increase of the horizontal variability with depth, in agreement with a possible local accumulation and depletion of 10Be over time.