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 EM122, a deep-water multibeam echosounder operating at 11.5–12.25 kHz, was used in working areas A and I. It provided seafloor coverage of up to six times the water depth, with 864 beams per ping, a beam width of 2° × 2° (TX × RX), and a maximum ping rate of 5 Hz. Angular coverage was set manually to 65° per side, with HD equidistant beam spacing and automatic ping mode. EM122 operation was largely unaffected by simultaneous use of the PARASOUND PS70 and ADCP systems. 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