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 20:00:00 and 2015-01-16 11:56:00. 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 and contains quality flags for different kinds for erroneous data. Flag values are the sum of individual error codes. The value of 0 refers to no error. Quality flag, position: The geographic position is flagged +1 if the drift velocity, as derived from the GPS longitude and latitude, exceeds a threshold of 10 deg latitude or 50 deg longitude per time step; +2 if the position exceeds extreme values, such as longitude > 360 deg; +4 if the position is exactly 0.0. This instrument was deployed as part of the project FMI.