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

Oxygen (dO18) and hydrogen (dH) isotope ratio data from sea ice samples taken during MOSAiC leg 4 (PS122/4). Sea ice samples were taken from Jaride and Alli's Ridge. Sea ice cores were extracted f 139 rom the ridges using a 9 cm inner diameter ice corer (Kovacs Enterprise Mark II coring system) powered by a cordless electric drill. Salinity/isotope ice cores were stored in sterile U-Lines bags (sections < 1 m), immediately placed in Styrofoam boxes and transported back to the ship within 2 hours of sampling. Ice cores were stored in a -20°C walk-in freezer until processing. The ice cores were cut into ~5 cm sections using a stainless steel, electric butcher band saw. To ensure we captured potential transition zones within the sea ice (i.e., rapid transitions in salinity), we only cut to the top or bottom of natural breaks in the ice cores (i.e., some sections were thicker or thinner than 5 cm but all in the range of 2-7 cm). The samples were 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 ice 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).