This dataset provides snow depth and sea ice thickness derived from temperature and heating measurements obtained from SIMBA (Snow and Ice Mass Balance Array; Jackson et al., 2013, doi:10.1175/JTECH-D-13-00058.1) buoy 2025T143 deployed on Arctic sea ice during the CONTRASTS expedition in 2025. Processed data from buoy 2025T143 span 12 July to 21 August 2025 and cover approximately 82.4–83.9° N and 25.6–38.2° E based on quality-controlled geolocation. The buoy was installed on a small ridge on an ice floe associated with regime 1. The thermistor string consisted of 240 sensors with 2 cm vertical spacing, providing a 4.8 m vertical temperature profile through the snow and sea ice column. The initial ice thickness at the deployment site was 2.85 m. The dataset contains time-resolved vertical temperature profiles and active heating-cycle responses with 30 s and 120 s heating intervals on a fixed vertical grid referenced to the water level. Geographic position is provided for each timestamp, including both raw GPS positions and quality-controlled geolocation. Quality-controlled positions were derived using outlier detection, speed filtering, and interpolation. Heating-cycle geolocation was obtained by interpolating the quality-controlled temperature-axis positions onto the heating time axes. Raw GPS data contain significant errors and are therefore supplemented by corrected coordinates and associated quality flags. Temperature profiles were quality-controlled to remove physically unreasonable values and sensor artefacts prior to interface detection. Heating-cycle data were additionally filtered to remove records with insufficient bottom-sensor response. Gaps in geolocation were filled by interpolation and, where necessary, constrained extrapolation based on buoy drift continuity. Temperature and heating data were processed using a manual classification approach to derive snow depth, sea ice thickness, and the vertical positions of the air–snow, snow–ice, and ice–water interfaces relative to the initial water level. The processing workflow and analysis scripts are available at Salganik et al. (2026, doi:10.5281/zenodo.20274777). Derived variables include the air–snow, snow–ice, and ice–water interface depths obtained from temperature profiles and supplemented by manual observations. Snow depth and sea ice thickness were calculated from these interfaces. 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. The dataset includes temperature and heating-cycle measurements, interface depths, snow depth, sea ice thickness, manual interface observations, and geographic position data. Locations of the buoy deployment sites overlaid on optical imagery 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).

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).