The R/V MARIA S. MERIAN cruise MSM21/1b was carried out jointly by GEOMAR Kiel and the Institut für Meereskunde at the Centre for Marine and Atmospheric Sciences of Hamburg University. Scientists and technicians from the Atlantic Branch of the P.P. Shirshov Institute for Oceanology (Kaliningrad, Russia) and the Finnish Meteorological Institute (Helsinki; Finland) also participated in the cruise. The measurements mainly contributed to three projects: 1) "Nordatlantik", funded by the German Ministry of Education and Research (BMBF), 2) "THOR", funded by the European Commission within the framework of FP7, 3) "Valley Mixing", funded by the Deutsche Forschungsgemeinschaft (DFG). The main objectives of the cruise were to characterize the spatio-temporal variability of the Denmark Strait overflow and to identify processes responsible for the exchange of the overflow plume with ambient water downstream of Denmark Strait. A multi-platform approach was taken to achieve the goals, based on moorings, an autonomous underwater vehicle (AUV), as well as lowered and vessel-mounted observations. From these platforms, measurements of temperature, salinity, dissolved oxygen, current velocity, dissipation of turbulent kinetic energy, and bottom pressure were obtained. Altogether, twelve moorings were deployed, one mooring was recovered, data from two PIES were uploaded via acoustic telemetry, turbulence measurements on six extended AUV dives were carried out, and 92 CTD / LADCP casts were taken, 25 of which had additionally been equipped with a profiling turbulence (MSS) probe. Along with this, underway data of surface hydrography and current velocity were collected throughout the cruise. Our research was conducted in the spirit of both the "OSPAR Code of Conduct for Responsible Marine Research" and the "Commitment of responsible marine research" by the DFG Senatskommission
