Temperature and heating-induced temperature differences were measured along a chain of thermistors. 2020M26 (a.k.a. Bruncin IMB042) is an autonomous modular instrument that was installed on drifting sea ice in the Arctic Ocean during the 4th leg of MOSAiC in June 2020. The thermistor chain was 5 m long and included 256 sensors. The resulting time series describes the evolution of temperature and temperature differences after three heating cycles of 4, 20 and 24 s as a function of place, depth and time between 26 June 2020 and 19 August 2020 in sample intervals of 1 hour for temperature and 6 hours for temperature differences. In addition, this modular buoy consisted of sensors measuring position (GPS) and barometric pressure at hourly intervals. The buoy was installed on a ridge, called Jaridge that was studied during leg 4, in the MOSAiC Central Observatory. This instrument was deployed as part of the project Ridges - Safe HAVens for ice-associated Flora and Fauna in a Seasonally ice-covered Arctic OCean (HAVOC), funded by the Research Council of Norway (project number 280292).