16 Cruise Report, RV ATAIR, Cruise 067I033-1, Bremerhaven – Thybor?n – Aberdeen, 23 Jul – 15 Aug 2024 Overall, the performance of the CTD sensor unit during the cruise was good. Several profiles showed larger spikes most times within the gradients or layers of high biological activity, which might have let to clogging of one or both sensor packs. The supplementary SBE 35 temperature sensor was read out after every station and compared to CTD-derived temperature recorded at the time of closing the Niskin bottles during the up- cast. Data was downloaded directly from the sensor using the software SeaTerm, version 1.59. 5.6 Post-Cruise Processing of CTD Data Post-cruise comparisons were made between CTD sensor packs TC1 and TC2 and between CTD temperatures and a supplementary temperature sensor of type SBE35 installed at the height of the Niskin bottles. Furthermore, a comparison between CTD salinities and AU- TOSAL-derived salinities was performed (compare Tables 5.3 and 5.4 and Figures 5.5 and 5.6). The following correction procedure is applied to temperatue and conductivity/salinity measure- ments as well as oxygen data: ? Assumed measurement accuracy: T-CTD: ± 0.002, C-CTD: ± 0.003, S: estimated: ± 0.004 ? A temperature correction will be applied in case the temperature difference (CTD vs. SBE35) exceeds 2x 0.002 and/or the difference between temperature sensors T1 and T2 exceeds 2x 0.002. ? A conductivity correction will be applied in case the salinity difference (AUTOSAL vs. CTD) exceeds 0.003 and/or the difference between conductivity sensors C1 and C2 exceeds 2x 0.003. ? The random error of oxygen samples obtained from titration is approximately 1%. Corrections are made if the oxygen difference (bottle vs. CTD oxygen) exceeds 1%. Post-cruise quality control showed that the CTD data of cruise 067I033-1 were of high quality, and differences between TC sensor pairs were consistently small. When considering all data, all differences (at the latest after exclusion of outliers) are well within the error bounds. How- ever, there are characteristic patterns in the sensor differences for conductivity and, even more clearly, for salinity when passing through a profile, especially at the deep profiles. Profiles that exceeded 200 dbar reveal a slight pressure dependence of the two sensors. All comparisons revealed small differences, which were within the error bounds and were slightly smaller for temperature, conductivity and salinity from the secondary sensors. Temperature differences between the T-sensors of the CTD-unit and the attached and external SBE35 sensor were within 0.0009 for 92% of the measurements when using temperature data from the primary sensor T1, and within -0.0001 for the secondary sensor T2. This is well within the uncertainty range of ± 0.004°C, see above.