Temperature and heating-induced temperature differences were measured along a chain of thermistors. SIMBA 2021T86 (a.k.a. AWI_0904) is an autonomous instrument that was installed on landfast sea ice in the Antarctic Atka Bay during the expedition Polarstern PS124 (COSMUS) in 2021. The thermistor chain was 5 m long and included 241 sensors with a regular spacing of 2 cm. The resulting time series describes the evolution of temperature and temperature differences after two heating cycles of 30 and 120 s as a function of location, depth and time between 2021-03-17 and 2021-10-14. Sample intervals are commonly between 1 and 24 hours, but most frequently hit intervals of 6 hours for temperature and 24 hours for temperature differences. In addition to temperature and geographic position, barometric pressure, air temperature measured approximately 1m over the ice level, tilt and compass were measured. The data set has been processed as follows: obvious inconsistencies (missing values) and unrealistic values in position have been removed. This instrument was deployed as part of the project Multidisciplinary Ice-based Distributed Observatory (MIDO), Sea Ice Physics @ AWI (AWI_SeaIce).