Beryllium-7 concentrations in ice during the MOSAiC expedition

Ice cores were collected using a Kovacs Mark II 9 cm diameter corer (area = 63.62 cm2). We generally took three ice cores (total sample area = 190.85 cm2, 11 samples) from a site and combined them into one sample. Snow was swept away from the ice surface before drilling through the ice column. Once recovered, cores were laid out on a cradle to measure length (ice thickness) and then put in a plastic sleeve before being transported to Polarstern. After placing the cores in buckets, we added the following solutions: 5 ml hydrochloric acid, 2 ml iron chloride solution, and 1 ml of 1000 ppm stable beryllium AA standard (chemical yield tracer). After melting at room temperature, the water volume was measured using a graduated cylinder. Next, the sample was precipitated using ammonium hydroxide. After allowing the precipitate to settle, excess water was removed by decanting and centrifugation. The samples were transferred to petri dishes and placed in an oven for drying, and then analyzed with a high purity germanium (HPGe) gamma detector (Be-7 peak at 478 keV). The detector is calibrated by using a commercially prepared mixed isotope solution added to iron hydroxide powder in a petri dish (same geometry as samples). After gamma counting, samples were brought up to 1 liter in 1% nitric acid solution. The beryllium concentrations (for chemical yield determination) were then obtained using a Perkin Elmer Optima 7300 DV ICP-OES. Our chemical yields averaged over 80%.