Temperature and heating-induced temperature differences were measured along a chain of thermistors. SIMBA 2015T18 (a.k.a. FMI_16) is an autonomous instrument that was installed on drifting sea ice in the Antarctic Ocean during the expedition Polarstern PS89 (ANT30/2) in 2014/15. The thermistor chain was 5 m long and included 240 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 2015-01-03 and 2015-01-16. 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. 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 FMI.