Temperature and heating-induced temperature were measured along a chain of thermistors. Digital Thermistor Chain DTC51 is an autonomous instrument that was installed on drifting sea ice in the Arctic Ocean during the MOSAiC expedition on 23 August 2020. The thermistor chain was 4.16 m long and included sensors with a regular spacing of 2 cm. The initial ice thickness was 1.52 m, the snow thickness was 0.02 m, and the freeboard was 0.16 m. The resulting time series describes the evolution of temperature during the heating cycle of 20 s and after the heating cycle during the following 40 s as a function of geographic position (GPS), depth, and time between 23 August 2020 and 17 September 2020 in sample intervals of 6 hours. It also contains manually estimated positions of air-snow, snow-ice, and ice-water interfaces. The DTC was installed in the undeformed second/multiyear ice next to ice mass balance buoys 2020T78: doi:10.1594/PANGAEA.958438.

Temperature after the cooling cycle and temperature before the heating cycle both represent in situ temperature. The temperature before the heating cycle may contain errors in measurements and is provided for reference. It is recommended to use temperature after the cooling cycle and temperature difference after the heating cycle for further analysis.