During cruise MSM120, high-resolution bathymetric data were acquired using the hull-mounted Kongsberg EM122 and EM712 multibeam echosounders (MBES) on RV MARIA S. MERIAN. Beam positions and depths were calculated from two-way travel time and beam angle, with real-time motion, heading, and position provided by a Kongsberg Seapath 320 system. Surface sound velocity was measured using an AML C-keel probe, and raw data including backscatter were stored in *.all format. The EM712, optimized for shallow to medium water depths (40–100 kHz), was deployed in working areas B, C, D, E, and F. It achieved seafloor coverage of approximately seven times the water depth, with 800 beams per ping, 0.5° × 0.5° beam width, and a ping rate up to 40 Hz. Angular coverage was set between 55° and 65° per side depending on conditions, and acquisition was synchronized with the PS70 using the K-Sync trigger box at a 2:1 ping ratio. ADCPs were turned off during EM712 operation to avoid interference. Sound velocity profiles from CTD casts were applied during post-processing for beamforming corrections. Surveys were conducted at 8–10 kn, with transit profiles recorded at 12 kn. In total, 2,623 nautical miles of track were covered, mapping 2,855 km² of seafloor. Both MBES systems performed reliably, providing high-quality bathymetric and backscatter datasets for detailed seafloor morphology studies.

These data should not be used for navigational purposes.Data publishing was realized by Henriette Kolling, Kiel University, Germany