The bulk of multibeam bathymetric data were acquired during RV Maria S. Merian cruises MSM11/2 (Bickert et al., 2009), MSM82/2 (Krastel et al., 2019a) and MSM87 (Krastel et al., 2019b) with hull-mounted Kongsberg Simrad systems EM120 (MSM11/2) and EM122 (MSM82/2 and MSM87). The nominal sonar frequency is 12 kHz. The angular coverage is up to 150°, and each angular beam accuracy was 2° by 2°. Kongsberg Seapath system provides the combined motion, position and time data, which are transmitted to the Processing Unit (PU) of the multibeam echosounder to achieve real-time motion compensation in pitch, roll and yaw. All raw data were processed with MB-System software (Caress and Chayes, 2017: https://www.mbari.org/products/research-software/mb-system/). Sound velocities were measured with a Conductivity, Temperature, Depth (CTD) probe during MSM 82/2 and an expendable sound velocimeter during MSM87. The multibeam data in cruise MSM82/2 were collected from the 11th to 13th of May in 2019 in the headwall area of the Sahara Slide Complex. Only two sound velocities were measured on the 11th and 12th of May, and we applied the measured sound velocities to data from these two days. In the mean time, the measured sound velocity on 12th of May was also applied to data collected on 13th of May. For MSM11/2, sound velocities were adjusted using the mbvelocity tool implemented in the MB-System software. The multibeam bathymetric data were gridded by using the splines with tension algorithm to a final grid with 150 m cell spacing in lateral direction. Echosounder data were acquired during several cruises with RV Maria S. Merian (MSM11/2, MSM82/2, MSM87). The high-resolution parametric ATLAS Parasound System DS3 (Atlas Hydrographic®) is a hull-mounted parametric echo sounder; the secondary low frequency (SLF) was set to 4 kHz through our cruises. The opening angle of the system is 4.5°. The system allows imaging of the uppermost 50-100 m of sediment at a sub-meter vertical resolution. The echogram sections were filtered with a wide band pass filter to improve the signal-to-noise ratio. The data were analyzed and interpreted in IHS Kingdom®. Gravity cores were acquired with a 5 m-long standard gravity corer during RV Maria S. Merian Cruise MSM82/2 (cores MSM82/2-34, MSM82/2-35 and MSM82/2-36). They were studied by color analysis, photography and sedimentological description. Accelerated Mass Spectrometry 14C-age dating of the planktonic foraminifera Globigerinoides ruber (Bonfardeci et al., 2018) was performed at the Leibniz Laboratory for Radiometric Dating and Stable Isotope Research at Kiel University. The Calib 704 and the Marine 13 calibration curve were applied to calibrate 14C age to calendar years (Reimer et al., 2013); the reservoir age was set to ±500 years (Mangerud and Gulliksen, 1975).
