Ridge snow oxygen and hydrogen isotope data MOSAiC Leg 4 (PS122/4)

Oxygen (dO18) and hydrogen (dH) isotope ratio data from snow samples taken during MOSAiC leg 4 (PS122.4). Snow samples were taken from several locations around the central observatory (main ice floe. They were collected using a metal density cutter, placed in plastic cups with lids and melted at room temperature. Once completely melted, ~20 ml sub-samples were poured into 20 ml glass or plastic vials with lids and sealed with parafilm tape for isotope analyses. These samples were stored at +4°C. After the sub-samples were taken, bulk salinity was measured on the remaining water sample using a calibrated YSI 30 conductivity meter (practical salinity scale, unitless). The stable oxygen isotopic compositions of the melted snow samples (δ18O) were determined in the central laboratory of the Swiss Federal Institute for Forest, Snow and Landscape, Birmensdorf, Switzerland with an Isotopic Water Analyzer IWA-45-ER (ABB - Los Gatos Research Inc., US). Measurement uncertainty for δ18O is ±1‰, the precision ± 0.5‰. All samples were measured in duplicate and averaged. 169 The quality control was conducted with three standards for δ18O at 0.00‰, -12.34‰ and -55.50‰ and are presented as per mil difference relative to VSMOW (‰, Vienna Standard Mean Ocean Water)