This dataset provides snow depth and sea ice thickness derived from temperature and heating measurements obtained from five SIMBA (Snow and Ice Mass Balance Array; Jackson et al., 2013, doi:10.1175/JTECH-D-13-00058.1) buoys deployed on Arctic sea ice during the CONTRASTS expedition in 2025. Each buoy was equipped with a thermistor string consisting of 240 sensors with 2 cm vertical spacing, providing a 4.8 m vertical temperature profile. The dataset comprises observations from buoys 2025T143, 2025T144, 2025T145, 2025T135, and 2025T136, with processed data spanning 12 July to 15 November 2025. The buoy drift covered the Arctic Ocean north of Svalbard and extended into the Fram Strait region (approximately 77.7–84.8° N and 17.7° W–38.2° E) based on quality-controlled geolocation. The buoys recorded vertical temperature profiles within the snow and sea ice column, as well as temperature responses during active heating cycles (30 s and 120 s). The dataset provides time-resolved measurements on a fixed vertical grid referenced to the water level, together with geolocation at each timestamp. For heating-cycle data, both raw GPS positions from the heating files and quality-controlled positions are provided; the latter are derived by interpolating the quality-controlled temperature-axis geolocation onto the corresponding heating time axes. Raw GPS data contain significant errors. Therefore, both raw and quality-controlled latitude and longitude are provided. Quality-controlled positions on the temperature time axis are derived using outlier detection, speed filtering, and interpolation, and serve as the basis for geolocation on the heating time axes. Temperature profiles were quality-controlled to remove physically unreasonable values and sensor artefacts prior to interface detection. Profiles with extreme temperatures or inconsistent mid- and deep-column temperature ranges were excluded. Heating-cycle data were additionally filtered to remove records with insufficient bottom-sensor response. For buoy 2025T135, measurements below the identified sensor-failure level were replaced by the nearest reliable sensor value after the failure time. Gaps in geolocation are filled using interpolation and, where necessary, extrapolation constrained by the temporal continuity of buoy drift. Derived variables include the positions of the air–snow, snow–ice, and ice–water interfaces, obtained from temperature profiles and supplemented by manual observations. The accuracy of the detected air–snow and ice–water interfaces, evaluated against manual measurements, is ±0.04 m and ±0.06 m (RMSE), respectively. Snow depth and sea ice thickness are calculated from these interfaces. The dataset includes time and depth coordinates; geographic position (raw and quality-controlled) with associated flags; temperature and heating-cycle responses; interface depths; derived snow depth and sea ice thickness; and manual interface measurements. Buoys 2025T143, 2025T144, and 2025T145 were deployed on small ridges on ice floes with different regimes (1, 2, and 3), respectively, while buoys 2025T135 and 2025T136 were deployed on level ice with regimes 2 and 3. The initial ice thickness at the deployment sites was 2.85 m, 3.40 m, 3.23 m, 1.97 m, and 2.09 m, respectively. The locations of the buoy sites, overlaid on optical images for each ice floe and visit, are provided in Linck Rosenhaim et al. (2026, doi:10.1594/PANGAEA.992627). SIMBA buoy data were primarily obtained from the Meereisportal database (data.meereisportal.de/relaunch/buoy.php). For buoy 2025T135, data from 31 July to 7 August 2025 were manually incorporated from direct downloads from the buoy, while the remaining data were obtained from Meereisportal.

Acknowledgements: The data collection is part of the expedition of the Research Vessel Polarstern (Knust, 2017, doi:10.17815/jlsrf-3-163) during the expedition CONTRASTS (PS149, grant: AWI_PS149_00). ES and MAG were supported through the European Union's Horizon 2020 research and innovation programme under grant agreement No. 101003472 - Arctic PASSION. DD's participation in the CONTRASTs cruise was supported by internal funding from the Norwegian Polar Institute. ES and RT were supported by the Helmholtz Distinguished Professorship awarded to Julienne Stroeve (W3 program for the recruitment of leading international female scientists).