ALBERT

Description: Multibeam echosounder (MBES) data recorded during RV MARIA S. MERIAN cruise MSM20-2 between 17.01.2012 and 15.02.2012 around Tristan da Cunha. The Tristan da Cunha hotspot is thought to have played a major role in the rifting of the South Atlantic margins and the creation of the aseismic Walvis Ridge by impinging at the base of the continental lithosphere shortly before or during the breakup of the South Atlantic margins. MSM20-2 staged therefore a multi-disciplinary geophysical study of the Tristan da Cunha hotspot by acquiring passive marine electromagnetic and seismic data, bathymetric data as well as gravity data from which we will derive an electrical resistivity, velocity and density model down to a depth of several hundred kilometers. CI Citation: Paul Wintersteller (seafloor-imaging@marum.de) as responsible party for bathymetry raw data ingest and approval. Description of the data source: During the RV MARIA S. MERIAN cruise, MSM20-2 the Kongsberg EM120 multi-beam echo sounder was used. The echosounder uses a nominal sounding frequency of 12 kHz. 191 beams with a 2°/2° footprint are formed for each ping while the seafloor is detected using amplitude and phase information for each beam sounding. For further information, consult https://epic.awi.de/26725/1/Kon2007a.pdf. The EM120 was operated continuously during the cruise including transit routes in a 24-hour schedule. The angular coverage sector and beam pointing angles were set to vary automatically with depth according to achievable coverage. The beam spacing was set to equidistant. The ship's speed varied from 13 kn during the transits and during the deployments to 8 kn during the surveys around Tristan da Cunha, the Tristan da Cunha Fracture Zone and the Mid-Atlantic Ridge. The quality of the data varied considerably during the cruise, being extremely noisy during the fast speed lines (see section Data Quality Evaluation). The maximum opening angle for the swath also varied during the cruise, being set to 56-56 for the fast speed lines and up to 64-64 (port-starboard) for the slow speed survey lines, since most of the external beams were lost at fast speeds. This resulted in an extremely variable ratio width/depth for the swath. Responsible person during this cruise / PI: Marcia Mia (marcia.maia univ-brest.fr). Chief scientist: Marion Jegen-Kulcsar (mjegen@geomar.de) CR: https://www.tib.eu/de/suchen/id/awi%3Adoi~10.2312%252Fcr_msm20_2/ CSR: https://www2.bsh.de/aktdat/dod/fahrtergebnis/2012/20120063.htm ADCP: https://doi.pangaea.de/10.1594/PANGAEA.823159