A set of 1 m firn profiles was sampled in December 2018 across a traverse of ~ 100 km near Kohnen Station to quantify stratigraphic noise in high resolution isotope records. At each of six different locations (D2, C4, C5, D7, D24, D38), 5 profiles were extracted on one line, perpendicularly to the overall large scale wind direction and with an interprofile spacing of 10 m. Each firn profile was vertically extracted from the snow surface by inserting a 1 m pipe of carbon fiber at the sidewall of a snow-pit. Vertical target resolution was 1.1 cm in the upper 16.5 cm and 3.3 cm in the lower part. Due compression and expanding while handling, transportation and cutting at site, we assume a maximum depth uncertainty from these steps of 2 cm. All samples (N = 1249) were packed in plastic bags and transported to Germany in a constantly frozen state. Measurements of the stable water isotopic composition (δ¹⁸O, δD) of the firn samples were done using a Cavity Ring-Down Spectroscopy instrument (CRDS) of PICARRO Inc (model L2140-i) in the Stable Isotope Facility at the Alfred Wegener Institute in Potsdam, Germany. Post-run correction was done as described in Münch et al., (2016 - doi:10.5194/cp-12-1565-2016). Scaling to the VSMOW/SLAP (Vienna Standard Mean Ocean Water/StandardLight Antarctic Precipitation) scale results in the δ-notation, describing the ratio of heavy to light isotopes in ‰. In-house standards were used for quality control. The mean combined measurement uncertainty is 0.07‰ for δ¹⁸O and 0.5‰ for δD (root mean square deviation, RMSD).

The ISOLAB Facility metadata is part of the sensor web: Sensor (2022): Metadata for laboratory ISOLAB Facility – Stable Isotope Laboratory Potsdam at Current Version. hdl:10013/sensor.ddc92f54-4c63-492d-81c7-696260694001Sensor (2022): Metadata for Isotopic Water Liquid Analyzer for the online determination of the hydrogen and oxygen isotopic composition using Cavity Ring-Down Spectroscopy (CRDS) L2140-i: hdl:10013/sensor.33733b4e-78bc-4524-ae27-9d92a1542ae9