Sea-ice thickness, salinity, temperature, density, and stable water isotope composition were measured during surveys at the Ridgey McRidgeFace (RMRF) coring site during the MOSAiC expedition (leg 3). RMRF was a first-year ice ridge formed in March 2020. 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). This data set includes data from coring site visits performed on 22 April 2020 and 05 May 2020 at RMRF in the MOSAiC Central Observatory (Kanzow and Damm, 2023). 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-cm vertical resolution. Ice bulk practical salinity was measured from melted core sections at 5-cm resolution using a YSI 30 conductivity meter. Ice density was measured using the hydrostatic weighing method (Pustogvar and Kulyakhtin, 2016) from a density core in the freezer laboratory onboard Polarstern at the temperature of -(16–18)°C. Relative volumes of brine and gas were estimated from ice salinity, temperature, and density using Cox and Weeks (1983) for ice colder than -2°C 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, coring site (5), and core type (6). Each core has its manually measured ice thickness (7), ice core length (8), and mean snow height (9). Each core section has the total length of its middle (10), top (11), and bottom (12) measured in situ. Each core section has the value of its practical salinity (13), as well as sea ice temperature (14), laboratory temperature (15), and ice density at the laboratory (16) and in situ (17) temperatures, brine volume fraction estimates (18), and gas volume fraction estimates at the laboratory (19) and in situ (20) temperatures. Some core sections have stable water isotopic values (21, 22). The location of ice sections relative to the nearby ridge void is described in comment (23). The locations of the coring sites are shown on the digital elevation map (Hutter et al., 2023).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. 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).