The CTD data on cruise MSM121 contain oceanic measurements of temperature, salinity, oxygen and pressure at 60 stations. The data were collected with the research vessel Maria S. Merian. Region: subpolar North Atlantic, 9°W-43°W, 41°N-50°N; Ports: Nuuk - Ponta Delgada; Date: September 22 - October 16, 2023. The data where collected by a CTD device of type SBE 9. The CTD was mounted to a metal frame with 22 water sample bottles, which was lowered from the sea surface down to 10 m above the seafloor. The sampling frequency was 24 Hz, the raw data were then interpolated on 1 dbar intervals. The CTD system was comprised of two sensor sets for temperature, conductivity, and oxygen. For every profile, the data given here are based on that set of sensors which were estimated to be of better quality. Salinity and oxygen data from the CTD were calibrated by comparison with samples from the water bottles. The bottle salinity was analysed by a salinometer of type Guildline Autosal 8400A, bottle oxygen samples by Winkler titration. The accuracy of the calibrated CTD measurements is: 1 dbar for pressure, 0.002 °C for temperature, 0.003 for salinity, 1.4% (about 3.5 µmol/kg) for oxygen. Detailed information can be found in the cruise report: https://doi.org/10.48433/cr_msm121.