Raw data acquired by two thermosalinographs (SBE21, SeaBird GmbH) on board RV Polarstern were processed to yield a calibrated and validated data set of temperature, conductivity and salinity during expedition PS121. Both sensors were equipped with a more accurate external temperature sensor (SBE38, Sea-Bird GmbH). Data were downloaded from the DAVIS SHIP data base (https://dship.awi.de) with a resolution of 1 sec. The raw hex data were converted to temperature and conductivity while a sensor drift correction was applied using calibration coefficients from before and after the expedition. Salinity was calculated according to the instructions from the Practical Salinity Scale PSS-78, using the obtained (internal) temperature and conductivity data and a pressure of 11 dbar which represents the water depth of the inlet of the TSG system on Polarstern. A speed filter of 0.5 knots minimum speed was applied. Processed data are provided as 10min means of seawater salinity, conductivity and temperature, aligned with position data taken from the master track of PS121 (doi:10.1594/PANGAEA.908157). Further details and evaluation of the data is outlined in the data processing report found at the EPIC repository under URL (https://hdl.handle.net/10013/epic.7fffb528-06bd-48ae-8489-cea0444c4eab).

We thank Franziska Nehring (Fielax) for the processing of the data. We acknowledge the support of Winfried Markert and Olaf Hüttebräucker (Laeisz) for maintenance of the instruments on board. We appreciate the help of the PANGAEA team for their help in archiving the dataset.