Ice cores were collected using a Kovacs Mark II 9 cm diameter corer (area = 63.62 cm2). 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 where they were placed in buckets for melting.

We generally took three ice cores (total sample area = 190.85 cm2, 11 samples) from a site and combined them into one sample, but for some samples we took 4 cores (area = 254.5 cm2, 5 samples) or 6 cores (area = 381.7 cm2, 3 samples).

For two samples (Core11 and Core13), cores were cut into segments before melting. For example, Core11 consists of 6 cores, each of which was cut into three segments (Core11a = 0-40cm, Core11b = 40-80cm, and Core11c = 80-123cm, where depth = 0cm at the snow-ice surface). For all other samples, the full length of each core was melted without segmenting.

Shipboard Laboratory Procedure: 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. Finally, the samples were transferred to petri dishes and placed in an oven for drying.

Gamma Analysis: Dried samples in petri dishes were counted by gamma spectroscopy. Be-7 has a readily identifiable gamma peak at 478 keV. The counting system was calibrated for all samples by preparing a commercial standard in a geometry identical to the samples.

Chemical Yield Determination: After gamma counting, samples were brought up to 1 liter in 1% nitric acid solution. The beryllium concentrations were then determined using a Perkin Elmer Optima 7300 DV ICP-OES. Our chemical yields averaged over 80% (Kadko et al., 2019).