Temperature, salinity, and isotopic values data from sea ice samples taken during MOSAiC leg 4 (PS122/4). Sea ice samples were taken from Jaridge, Alli's Ridge, and the Remote Sensing site. The ice cores were extracted either with a 9-cm (Mark II) or 7.25-cm (Mark III) internal diameter ice corers (Kovacs Enterprise, US). During each coring event, ice temperature was measured in situ from a separate temperature core, using Testo 720 thermometers in drill holes with a length of half-core-diameter at 5–20 cm vertical resolution. Salinity ice cores were stored in sterile U-Lines bags and transported back to the ship within 2 hours of sampling. Ice bulk practical salinity was measured from melted core sections at 5 cm resolution using a YSI 30 conductivity meter (practical salinity scale, unitless). The relative volume of brine was estimated from ice salinity and temperature using Cox and Weeks (1983) for cold ice and Leppäranta and Manninen (1988) for ice warmer than –2°C. The data contains the event label (1), time (2), and global coordinates (3,4) of each coring measurement. The location (5) refers to the ridge name with other installations and measurements (Jaridge, Alli's Ridge, and Remote Sensing site). Each separate core has its local coordinates X (5) and Y (6) in meters. Each salinity core has its manually measured ice thickness (8), ice draft (9), and mean snow height (10). Each core section has the total length of its middle (11) measured in situ, as well as the estimated depth of the section middle (12). Each core section has the value of its temperature (14), as well as sea ice practical salinity (15) and isotopic values (16, 17) (doi:10.1594/PANGAEA.943746), co-located to the depth of temperature measurements. Brine volume (14) fraction estimates are presented only for fraction values from 0 to 30%. Each core section also has material (23) describing if the sample is from ice, ridge void, snow, or air. For Jaridge, a drill hole with local coordinates of (0,0) coincides with the ice mass balance buoy 2020M26 installation described in doi:10.1594/PANGAEA.938354. For Alli's ridge, a drill hole with local coordinates of (7.5,0) coincides with the ice mass balance buoy SIMBA 2020T61 installation described in doi:10.1594/PANGAEA.926580. The Remote Sensing site was close to the Infrared camera installation described in doi:10.1594/PANGAEA.940717.