In January 2018, RV Polarstern crossed the Maud Rise region during the transit from Capetown, South Africa to the Neumayer III research station as part of the PS111-expedition. A few months before the expedition, the region featured the strongest occurrence of the "Maud Rise polynya" in four decades. During the crossing toward Neumayer III, CTD measurements were carried out by use of an underwayCTD system, which allows hydrographic sampling while the ship is in transit. A total of 23 stations between 60°S and 69°S were occupied to a depth of ~600 m.

The underway CTD is a self-contained free-falling probe measuring temperature, conductivity, depth while the ship is transiting. The conductivity sensor is unpumped, and has a response time that is different from that of the temperature sensor. Therefore, converting conductivity into salinity is not straightforward. We followed the recommendation of the manufacturer and computed salinity by use of the Seabird processing software as outlined in the document “UCTD salinity”.The processed data file includes temperature, pressure, and salinity. Please note that the upper 20 m were removed because the quality of the measurements cannot be guaranteed due to the 11m draft of the vessel and the associated turbulent overturning behind the ship.Additional information about the underway CTD can be found in Rudnick, D. L., and J. Klinke, 2007.The raw data are also included and can be used to reprocess the salinity data if desired.